At Jordan University of Science and Technology

Determination of Temperature Distributions and Thermal Stresses for RCC Dams Using Two Different

Finite Element Codes (Comparative Study)

By

Ehab Salem Shatnawi

At Jordan University of Science and Technology

January 2004

Determination of Temperature Distributions and Thermal Stresses for RCC Dams Using Two Different Finite

Element Codes (A Comparative Study)

By

Ehab Salem Shatnawi

A thesis submitted in partial fulfillment of the requirements of the degree of M.Sc. in Civil Engineering

At

The Faculty of Graduate Studies

Jordan University of Science and Technology

January 2004

Signature of Author ..................................................................., January 2004 Committee Members Date and Signature Prof. Abdallah I. Husein Malkawi, Advisor ...................................... Dr. Mousa Attum ......................................

Dr. Nezar A. Hammouri (Cognate, Hashemite University) ......................................

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II

Dedication

To My Family

And

Friends

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III

Table of Contents

ACKNOWLEDGEMENTS ............................................................................................... I

DEDICATION .................................................................................................................III

TABLE OF CONTENTS ................................................................................................ IV

LIST OF TABLES......................................................................................................... VII

LIST OF FIGURES......................................................................................................VIII

CHAPTER ONE................................................................................................................ 1

INTRODUCTION ............................................................................................................. 1

1.1 INTRODUCTION .................................................................................................... 1

1.2 CASE STUDY AL-WEHDAH RCC DAM ........................................................... 3

1.2.1 DESCRIPTION OF THE DAM ............................................................................... 3

1.2 LITERATURE REVIEW ........................................................................................ 6

1.4 OBJECTIVES........................................................................................................... 8

1.5 THESIS OUTLINE .................................................................................................. 9

CHAPTER TWO............................................................................................................. 10

BACKGROUND.............................................................................................................. 10

2.1 OVERVIEW ........................................................................................................... 10

2.2 ROLLER COMPACTED CONCRETE .............................................................. 10

2.2.1 PLACING AND COMPACTING RCC ................................................................. 10 ٢٫٢٫٢ RCC PROPORTIONS .................................................................................. 11

2.2.2.1 Portland Cement .................................................................................... 11 ٢٫٢٫٢٫٢ Pozzolanic Materials ...................................................................... 11 2.2.2.3 Flyash Materials .................................................................................... 12

2.2.3 STRUCTURAL RCC PROPERTIES .................................................................... 13 2.2.3.1 Density (ρ ). ............................................................................................ 13 2.2.3.2 Compressive and Tensile Strength (Fc, Ft). .......................................... 13 2.2.3.3 Modulus of Elasticity (E c)..................................................................... 14 2.2.3.4 Poisson's Ratio (υ) ................................................................................. 15

2.2.4 THERMAL RCC PROPERTIES ......................................................................... 15 2.2.4.1 Thermal Conductivity (k). ..................................................................... 15 2.2.4.2 Coefficient of Thermal Expansion (Cth) . ............................................. 16 2.2.4.3 Specific Heat (C).................................................................................... 16 2.2.4.4 Adiabatic Temperature Rise (Tab) ......................................................... 16 2.2.4.5 Heat of Hydration. ................................................................................. 17 2.2.4.6 Tensile Strain Capacity (ε tc ). ................................................................ 17

2.3 THE FINITE ELEMENT METHOD................................................................... 18

2.4 THERMAL ANALYSIS ........................................................................................ 18

IV

2.4.1 THERMAL ANALYSIS CONCEPT ....................................................................... 18 2.4.2 THERMAL ANALYSIS OBJECTIVES .................................................................. 20

2.5 TEMPERATURE CONTROL REQUIREMENTS............................................ 20

CHAPTER THREE......................................................................................................... 22

MODELING..................................................................................................................... 22

3.1 OVERVIEW ........................................................................................................... 22

3.2 MODELING METHODOLOGY ......................................................................... 22

3.3 PRINCIPAL ASSUMPTIONS .............................................................................. 23

3.4 MODEL PROPERTIES AND PARAMETERS.................................................. 24

3.4.1 CEMENTITIOUS MATERIALS........................................................................... 24 3.4.2 CONCRETE PLACEMENT TEMPERATURE ....................................................... 26 3.4.3 INITIAL TEMPERATURE OF ROCK FOUNDATION ........................................... 27 3.4.4 MATERIEL PROPERTIES AND ENVIRONMENTAL CONDITIONS ...................... 27 3.4.5 HEAT OF HYDRATION...................................................................................... 29

3.5 BOUNDARY AND INITIAL CONDITIONS...................................................... 32

CHAPTER FOUR ........................................................................................................... 34

COMPARATIVE STUDY BETWEEN COSMOS & ANSYS .................................... 34

4.1 OVERVIEW ........................................................................................................... 34

4.2 COSMOS/M SOFTWARE .................................................................................... 34

4.3 ANSYS SOFTWARE ............................................................................................. 37

4.4 MODEL ANALYSIS.............................................................................................. 39

4.4.1 TWO-DIMENSIONS MODEL ANALYSIS USING COSMOS............................... 39 4.4.2 THREE-DIMENSIONS MODEL ANALYSES USING COSMOS .......................... 39 4.4.3 TWO-DIMENSIONS MODEL ANALYSIS USING ANSYS................................... 40 4.4.4 THREE-DIMENSIONS MODEL ANALYSES USING ANSYS............................... 41

4.5 FINITE ELEMENT RESULTS ............................................................................ 45

4.5.1 FINITE ELEMENT RESULTS OF COSMOS ..................................................... 45 4.5.2 FINITE ELEMENT RESULTS OF ANSYS.......................................................... 50

4.6 SUMMARY AND DISCUSSION.......................................................................... 55

THERMAL AND STRESS ANALYSIS........................................................................ 60

5.1 OVERVIEW ........................................................................................................... 60

5.2 THERMAL ANALYSIS FOR RCC DAM........................................................... 61

5.2.1 EFFECT OF CONVECTION COEFFICIENTS....................................................... 61 5.2.2 EFFECT OF HEAT OF HYDRATION AND PLACEMENT TEMPERATURE............ 61 5.2.3 RESULTS AND DISCUSSION OF THERMAL ANALYSIS ...................................... 61

5.3 THERMAL STRESSES IN RCC DAM ............................................................... 80

5.3.1 THERMAL STRESS DUE TO TEMPERATURE DROP NEAR THE FOUNDATION. 80 5.3.2 THERMAL STRESSES DUE TO TEMPERATURE DEFERENCE BETWEEN THE SURFACE AND INTERIOR OF DAM. ................ 81

V

5.3.3 THERMAL STRESSES DUE TO RESTRAINT OF FOUNDATION.......................... 81 5.3.4 THERMAL STRESSES DUE TO VERTICAL TEMPERATURE DIFFERENCE........ 81 5.3.5 INFLUENCE OF GALLERY IN THE DAM BODY................................................. 82 5.3.6 RESULTS AND DISCUSSION OF STRUCTURAL ANALYSIS ................................ 82

5.4 CRACKING ANALYSIS....................................................................................... 95

5.4.1 INTRODUCTION................................................................................................ 95 5.4.2 TRANSVERSE CONTRACTION JOINTS. ............................................................ 96 5.4.3 CONSTRUCTION JOINT SPACING ASSESSMENT .............................................. 96

CHAPTER SIX.............................................................................................................. 100

CONCLUSIONS AND RECOMMENDATIONS ...................................................... 100

6.1 CONCLUSIONS................................................................................................... 100

6.2 RECOMMENDATIONS ..................................................................................... 102

REFERENCES .............................................................................................................. 103

APPENDIX A................................................................................................................. 105

VI

List of Tables

Table

Description Page

3.1 Predicted RCC Placement Temperatures …………………………… 27 3.2 Properties Adopted for Thermal Analysis …………………………... 28 4.1 Summary Results for COSMOS and ANSYS. ……………………… 57 5.1 Peak Temperature in the dam core at the end of heat of hydration. … 67 5.2 Maximum temperatures occurred during the construction process…. 68 5.3 Crack Analysis in Al Wehdah Dam for Different RCC Mix and

Placement Temperatures. …………………………………………… 99

VII

List of Figures

Figure

Description Page

1.1 Location of Al Wehdah Dam Site. …………………………………… 41.2 Longitudinal section of Al Wehdah Dam …………………………... 5 1.3 Typical Cross Section for Al Wehdah Dam ………………………... 51.4 Imaginary Overview for AL-Wehda Dam ………………………….. 62.1 Compressive strength test results for different pozzolanic materials

uses ………………………………………………………………….. 143.1 The Accumulative Heat of Hydration after 7 days for different

Percent of Different Pozzolanic Material …………………………… 253.2 The Percent of the Heat of Equivalent Cement calculated from

different Percent of Different Pozzolanic Material …………………. 253.3 The accumulative heat of hydration of the cement (OPC) …………. 293.4 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3

South Africa fly ash), for Finite Element Analysis …………………. 303.5 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3

Turkey fly ash), for Finite Element Analysis ……………………….. 303.6 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3

Jordanian Pozzolan), for Finite Element Analysis ………………….. 313.7 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3

Rock Flour), for Finite Element Analysis …………………………... 313.8 Thermal Boundary Conditions for Thermal Analysis ……………… 334.1 Time Curves Used in COSMOS/M for the 1st three layers ………… 364.2 Births and Death of Elements ………………………………………. 384.3 Element Types Used in COSMOS …………………………………… 424.4 Element Types Used in ANSYS ……………………………………... 424.5 Two Dimension Model Mesh in COSMOS ………………………… 434.6 Three Dimension Model Mesh in COSMOS ……………………….. 434.7 Two Dimension Model Mesh in ANSYS …………………………... 444.8 Three Dimension Model Mesh in ANSYS …………………………. 444.9 Temperature Contour after 100 days for (28°C) Placement

Temperature using COSMOS ………………………………………. 464.10 Temperature Contour at the End of Heat of Hydration, 410 days for

(28°c) Placement Temperature using COSMOS …….……………… 474.11 Predicted temperature history in the dam center at different heights .. 48

4.12

Predicted Temperature History at Different Nodal Point at 12m from the Base of the Dam …………………………………………………

494.13 Temperature Contour after 100 days using ANSYS ………………... 514.14 Temperature Contour at the End of Heat of Hydration, 410 days for

(28°c) Placement Temperature using ANSYS ……………………… 52

VIII

4.15 Predicted Temperature History in the Dam Center at Different Heights using ANSYS for 2D & 3D Analysis Respectively ……….. 53

4.16 Predicted Temperature History at Different Nodal Point at 12m from the Dam Base using ANSYS for 2D & 3D Analysis Respectively … 54

4.17 Comparative Predicted Temperature History using ANSYS and COSMOS at the Dam Center and 12 m from the Dam Base using 3D Analysis ……………………………………………………………... 58

4.18 Comparative Predicted Temperature History using ANSYS and COSMOS at 3m from Upstream and 12 m from the Dam Base using 2D Analysis …………………………………………………………. 58

4.19 Cross Section Temperature Distribution at 22 m from the Dam Base using ANSYS and COSMOS ……………………………………….. 59

4.20 Vertical Temperature Distribution at the Dam Center using ANSYS and COSMOS ………………………………………………………. 59

5.1 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28°C) for RCC mix of South Africa Fly ash ………………………………………………… 63

5.2 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24 and 28 °C) for RCC mix of Turkey Flyash ……………………………………………………….. 64

5.3 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28 and 32 °C) For RCC mix of Jordanian Pozzolan ………………………………………….. 65

5.4 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28 and 32 °C) For RCC mix of Rock Flour …………………………………………………... 66

5.5 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for Different Placement Temperatures for RCC Mix of South Africa Flyash …………………………………………………. 68

5.6 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for Different Placement Temperatures for RCC Mix of Turkey Flyash ……………………………………………………….. 69

5.7 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for Different Placement Temperatures for RCC Mix of Jordanian Pozzolan ………………………………………………….. 69

5.8 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for Different Placement Temperatures for RCC Mix of Rock Flour …………………………………………………………...

70

5.9 Comparison 2D & 3D Analysis for Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of South Africa Flyash …………………. 71

5.10 Comparison 2D & 3D Analysis for Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C

IX

Place_Temp for RCC Mix of Turkey Flyash ……………………….. 725.11 Comparison 2D & 3D Analysis of Predicted Temperature History at

Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of Jordanian Pozzolan ………………………………...

735.12 Comparison 2D & 3D Analysis for Predicted Temperature History

at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of Rock Flour …………………………... 73

5.13 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of South Africa Flyash ……………………………………………………………….. 75

5.14 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of Turkey Flyash ……………………………………………………………….. 75

5.15 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of Jordanian Pozzolan …………………………………………………………… 76

5.16 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of Rock Flour .. 76

5.17 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of South Africa Flyash ……. 77

5.18 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of Turkey Flyash ………….. 78

5.19 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of Jordanian Pozzolan …….. 78

5.20 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of Rock Flour ……………... 79

5.21 Summary for the Maximum Temperature Occurred in the Dam during the Construction Process …………………………………….. 80

5.22 Different Stress Contour (σx, σz, N/m2) at the End of Heat of Hydration using 2D Analysis ……………………………………….. 84

5.23 3D Stress Contour (X-direction, N/m2) at the End of Heat of Hydration ……………………………………………………………. 85

5.24 3D Principal Stress Contour (S1, N/m2) at the End of Heat of Hydration ……………………………………………………………. 85

5.25 3D Stress Contour (Z-direction, N/m2) at the End of Heat of Hydration …………………………………………………………….

86

5.26

Principal Stresses History at Different Nodal Points at 9m from the Dam Base Using 2D Analysis ……………………………………….

88

5.27 Cross Valley Stresses ( z-direction ) History at Different Nodal Points at 9m from the Dam Base Using 2D Analysis ………………. 88

5.28 Principal Stresses History at Different Nodal Points at 6m from the Dam Base Using 3D Analysis ………………………………………. 89

X

5.29 Cross Valley Stresses ( z-direction ) History at Different Nodal Points at 6m from the Dam Base Using 3D Analysis ………………. 89

5.30 Comparison Cross Valley Stresses ( z-direction ) History for 2D & 3D Analysis at 1.5 m from base of dam and 2.5 m from upstream ... 90

5.31 Principal stresses across dam section at different time period (9 m from the dam base) Using 2D Analysis …………………………….. 91

5.32 Comparison Principal stresses across dam section using 2D and 3D (9 m from the dam base) ……………………………………………. 91

5.33 Principal and Cross Valley Stresses Distribution at Vertical Section at the Dam Centre Using 2D Analysis ……………………………… 93

5.34 Principal and Cross Valley Stresses Distribution at Vertical Section at the Dam Centre Using 2D Analysis ……………………………… 93

5.35 Comparison between temperature and stresses in z-direction at 1.5 m from base of dam and 2.5 m from upstream Using 2D Analysis ... 94

5.36 Comparison between temperature and stresses in z-direction at 1.5 m from base of dam and 2.5 m from upstream using 3D Analysis …. 95

XI

Determination of Temperature Distributions and Thermal Stresses for RCC Dams Using Two Different Finite Element

Codes (Comparative Study)

By: Ehab Shatnawi Supervisor: Prof. Abdallah I. Husein Malkawi

Abstract

In this thesis, thermal and structural analyses are performed for Al-

Wehdah RCC dam in Jordan, using different finite element codes namely

ANSYS and COSMOS. Two and three-dimensional finite element methods

have been carried out in order to understand the thermal influence of several

elements and constituent materials of the dam. The effect of RCC heat of

hydration and placement conditions on the resulting temperature and stress

distribution has been studied.

ANSYS program was chosen to carry out parametric study to find the

placement temperature at which the block length between contraction joints

not to exceed 20 m. Different cementitious material (i.e. South Africa flyash,

Turkey flyash, Jordanian pozzolan, and rock flour) with different placement

temperatures (i.e. 20, 24, 28, and 32 °C) were used in this study. A design

chart to determine the RCC placement temperature was developed from this

parametric study.

A comparative study between the two finite element programs was done

using Jordanian pozzolan RCC mix with 28°C placement temperature. The

study demonstrated that the results of temperature computed using ANSYS

numerical model analysis is higher and more conservative than the COSMOS

results.

The same cementitious material (Jordanian pozzolan) with the same

placement temperature (28°C) was used to perform a structural analysis. The

locations of tensile cracks were determined as a result of this analysis.

XII

CHAPTER ONE

INTRODUCTION

1.1 Introduction

Roller-compacted concrete (RCC) is defined as "concrete compacted

by rolling compaction which, in its unhardened state, will support a roller

while being compacted" (American Concrete Institute ACI).

RCC dams consist of concrete placed at a lower water-to-cement ratio as

compared to conventional concrete with the aid of compaction equipment and

methodologies normally employed for earthfill placement. RCC has gained

worldwide acceptance as an alternative to conventional concrete in dam

construction due to the construction advantages and proved performance

(Luna, et al, 2000). When RCC was first introduced in dam construction, for

a time it was thought that there was no problem in the temperature control of

RCC because the amount of cement in RCC is much less than that in the

conventional concrete. But some time later, it was discovered after RCC still

has the problem of temperature control when it is used in dam construction

(Zhu, et al, 1999). Since less cement is used, the hydration heat produced by

RCC is much less than that produced by conventional concrete. Therefore,

the rate of hydration process is slower in RCC.

1

Mass concrete placement requires precautions to minimize cracking.

During the hydration process, cement liberates a substantial amount of heat

with a resulting rise of the concrete temperature. It is often reaches about 40-

70 °C (Ishikawa M, 1991), after the maximum temperature is reached inside

the RCC dam, the latter cools down slowly to a constant temperature. This

temperature variation can induce two kinds of problems. First, the heat

generated creates temperature gradients between the surface and the RCC

core. The resulting nonuniform temperature distribution generates undesired

stresses. Second, the reduction of the global concrete temperature to the final

equilibrium temperature induces volumetric changes that lead to additional

stresses if the mass concrete is externally restrained (Ayotte, et al., 1997).

These temperature gradients induce cracks in the structures, which harm their

integrity, permeability, and durability.

Crack control is achieved by constructing the concrete gravity dam in a

series of individually stable monoliths separated by transverse construction

joints filled with sand-blasting or polystyrene (Forbes and Williams, 1998).

The significance of obtaining an accurate computer model is to provide

the engineer with means of predicting excessive tensile stresses and strains,

which could indicate possible cracking, therefore, allowing the designer to

take appropriate measures to limit or control such potential cracks (Truman,

et al., 1991).

2

To find the optimum construction method to avoid thermal cracks

before the structure construction, numerical simulations with Finite Element

Method (i.e. FEM) can be carried out and it can be checked for cracking. In a

simulation, some parameters can be assumed, such as kind of cement, mixed

design of concrete, casting schedule, and curing method, etc (Ishikawa M,

1991). Many finite element software packages can be used to predict the heat

generated by the concrete, Such as ANSYS, COSMOS/M, ABAQUS and

ADINA.

The finite element methods are becoming an increasingly popular and

powerful tool for civil engineers to analyze practical problems. With rapid

developments in the fields of computational methods, software design and

high speed and low cost hardware, up to date commercial finite elements

codes are capable of dealing with highly complex problems involving staged

construction, complex geometries and material properties.

1.2 Case Study AL-Wehdah RCC Dam

AL-Wehdah dam, located at latitude 32.714 N Longitude 35.822 E, is

situated about 26 km east of the Jordan Rift Valley (see Figure 2.2).

The upstream face of the dam is vertical with a batter at 1:0.6 from El 65

to foundation level, the stepped downstream slope is at 0.8:1 (Figure 2.3).

1.2.1 Description of the Dam

AL-Wehdah dam will be built on the Yarmouk River near the Maqarin

Railroad Station. The dam will regulate the stream flow of the Yarmouk

3

River to provide enough water for irrigation in the Jordan Valley and for

municipal and industrial supplies to the Amman/Zarqa area. Al-Wehdah dam

will be built as a Roller Compacted Concrete (RCC) gravity dam of about

96m high with crest at elevation 110 m ASL. The total storage capacity is

about 110 MCM at elevation 110 m ASL, the normal maximum reservoir

level (see Figure 2.4 and 2.5).

Fig. 1.1 Location of Al Wehdah Dam Site.

4

Fig. 1.2 Typical Cross Section for Al Wehdah Dam

Fig. 1.3 Longitudinal section of Al Wehdah Dam

5

Fig. 1.4 Imaginary View for AL-Wehdah Dam

1.2 Literature Review

In the recent years many researchers conducted studies to determine the

RCC thermal properties.

Truman, et al. (1991) used the finite element program, ABAQUS, along

with user – developed subroutines and experimentally derived material

constants to analyze a pile – founded mass concrete lock and dam structure,

which is performed by an incremental construction analysis including

thermal load.

Ayotte, et al. (1997) presented details of an experimental and

numerical study of thermal strains and induced stresses in large – scale mass

6

concrete. Three large scale monoliths were built on a dam construction site in

the James Bay Territory to monitor the thermal behavior of mass concrete

subjected first to heat of hydration development and subsequent freeze and

thaw cycles. The modeling of one monolith was carried out with computer

program ADINA. Excellent agreement between measured and computed

temperature and stresses was obtained.

Malkawi, et al. (2002) determined the thermal and structural stresses and

temperature control requirements for the 60m high Tannur RCC dam in

Jordan. Also they study temperature distribution with time, concrete

placement temperature limits, and joint spacing requirements to minimize

cracking in the Tannur dam. The computer program ANSYS was used to

simulates the construction process of the Tannur dam. The actual temperature

distribution in the body of the dam also was measured by thermocouples and

was compared with that obtained by ANSYS, and generally a good

agreement was obtained.

Forbes and Williams (1998) discussed the thermal stress modeling,

using of high sand RCC mixes and in-situ modification for RCC construction

of the Candiangullong dam. They concluded that finite element thermal and

stress analysis using ANSYS provide a good understanding of the thermal

condition.

Crichton, et al. (1999) presented a thermal structural analysis using the

ANSYS computer program to assess the effect of heat of hydration in RCC

7

structural stresses. The effect of using simple linear elastic material

properties on the calculated stresses has been compared to a more complex

time variant material modulus and creep analysis. They concluded that the

simple models overestimate the initial stresses and underestimate or cannot

predict the long-term tensile stresses.

Nollet, et al. (1994) described the general aspect of design of the Lac

Robertson dam, its thermal characteristics, methodology and results of the

thermal analysis carried out. The analysis was performed using COSMOS/M

program and consisted of a series of consecutive analysis using the previous

temperature results as initial conditions.

The U.S. Army Corps of Engineers, Engineer Technical Letter (ETL)

1110-2-542(1997) provides guidance for performing thermal studies of mass

concrete structures (MCS) and provide methodology for the first two levels

of thermal studies. Background and examples for several levels of less

complex analysis are presented in this (ETL).

1.4 Objectives

The purpose of this work is to study the temperature distributions and

thermal stresses for RCC dams using two and three – dimensional unsteady

thermo – mechanical analysis. AL-Wehdah dam is presented and analyzed as

case study.

8

A parametric study to find the placement temperature at which the block

length between contraction joints not to exceed 20 m was done for different

cementitious material the have different heat of hydration.

The commercially available software ANSYS and COSMOS/M were

chosen to perform this analysis on a PC work station to model a 2D and 3D

section of the dam, these software are based on the Finite Elements Method

(FEM). Also, comparing the predicted temperatures resulted using ANSYS

program versus the temperature obtained from COSMOS/M program.

1.5 Thesis Outline

In this thesis, Chapter two presents a background about the roller

compacted concrete and its properties, and about the finite element method,

also, it contains a background about thermal analysis. The case study for this

work is described also in this chapter.

Chapter three describes the model characteristics that will be used to

perform the thermal and stress analysis of AL-Wehdah dam.

In Chapter four, a comparison and discussion of the results obtained

from both ANSYS and COSMOS.

A parametric study considering different RCC mixes and different

placement temperatures was presented in Chapter five; analysis and

discussion of the obtained results are also presented in this chapter.

Conclusions and recommendation for this study will be presented in

chapter six

9

CHAPTER TWO

BACKGROUND

2.1 Overview

Three major subjects can be seen from the title of this thesis; thermal

analysis; roller compacted concrete; and finite element method. In this

chapter these subjects will be discussed widely.

2.2 Roller Compacted Concrete

RCC is a concrete that differs from conventional concrete principally in

that it has a consistency that will support a vibratory roller and an aggregate

grading and fines content suitable for compaction by the roller. RCC offers

some substantial benefits over conventional materials for the construction of

major engineered structures such as dams and roads. The significant

advantages of RCC over conventional earth and rock fill construction

including time of construction and hence cost, as well as the lower cost of

materials.

2.2.1 Placing and Compacting RCC

RCC dams are built with a construction technology that uses a concrete

of no-slump consistency. This material is transported, placed and compacted

10

using earth and rockfill construction equipment with the same design

philosophy of conventional gravity dams (Andriolo, 1998).

2.2.2 RCC Proportions

The objective of RCC proportioning is to provide a dense and stable mass

that meets the strength, durability, and permeability requirements for its

application. Materials used for RCC include cementitious materials (Portland

cement and pozzolans such as fly ash), aggregates, water, and admixtures. A

wide range of materials has been used successfully to produce RCC mixtures.

RCC can be made with any of the basic types of cement or combination

of cement and pozzolanic material. Selection of cementitious materials to

resist to chemical attack of sulfate and potential alkali reactivity with certain

aggregates should follow the same standard procedures adopted for CVC.

2.2.2.1 Portland Cement

RCC can be made from any of the basic types of Portland cement. For

mass applications, cements with lower heat of generation are beneficial. They

include Type II (low heat), Type IP (Portland Pozzolanic cement), and Type

IS (Portland Blast Furnace slag cement). The blended cement can be

beneficial also. Pozzolanic Portland cement manufactured by the Jordan

Cement Factory was used in the mixes.

2.2.2.2 Pozzolanic Materials

The selection of pozzolanic material suitable for RCC should be based on

its conformance with applicable standards (ASTM C-618). This standard

11

defines pozzolan as “siliceous or siliceous and aluminous materials which in

themselves posses little or no cementitious value but will, in finely divided

from in the presence of moisture, chemically react with calcium hydroxide at

ordinary temperatures to form compounds possessing cementitious

properties”.

The type of pozzolanic material can include natural pozzolans;

diatomaceous earth; Industrial waste material as fly ash or silica fume.

The use of a pozzolanic material in RCC serves some purposes:

As a partial replacement for cement to reduce heat generation

To increase compressive strength at great ages, if the material

has high pozzolanic activity with cement.

To increase durability

To reduce cost.

As a mineral addition to the mixture to provide fines to improve

workability.

2.2.2.3 Flyash Materials

Flyash is residue of the combustion of the finely ground coal used in the

generation of electric power. The use of fly ash in a properly designed mix

should also help to produce a more homogenous and densely with better

surface finish and all these will tend to reduce the permeability.

The influence of flyash on fresh concrete, ordinary Portland cement

grains are prone to exhibit some coagulation or flocculation in fresh concrete,

12

which tends to produce an inhomogeneous and non-uniform hydrate structure.

The addition of flyash, or any ultra-fine powder, can physically disperse these

cement flows, thus freeing more paste to lubricate the aggregates and

improving workability.

2.2.3 Structural RCC Properties

The strength and elastic properties of RCC vary depending on the mix

components and mix proportions in much the same manner as that for

conventional mass concrete. Aggregate quality and water-cement ratio are the

principal factors affecting strength and elastic properties.

2.2.3.1 Density (ρ ).

Density is defined as mass per unit volume, typical values of density

for mass concrete range from 2240 to 2560 kg /m3 (U.S. Army Corps of

Engineers, 1997).

2.2.3.2 Compressive and Tensile Strength (Fc, Ft).

RCC strength depends upon the quality and grading of the aggregate,

mixture proportions, as well as degree of compaction. The significant

properties of conventionally placed concrete are also significant in Roller

Compacted Concrete. These are compressive strength, tensile strength, and

modulus of elasticity.

Compressive strength test results that shown in Figure 2.1 which done by

(Malkawi, et al. 2003) show that the average compressive strength for RCC is

a bout 10 MPa. The ratio of tensile strength to compressive strength for RCC

13

0

2

4

6

8

10

12

14

16

18

0 50 100 150 200 250 300

Age (day)

Com

pres

sive

Stre

ngth

, MP

a

FlyAsh

Pozzolan

60 kg cement

75 kg cement

100 kg cement

mixtures has typically varied depending on aggregate quality, age, cement

content and strength. Tensile strength of RCC can be determined by tests

either by measuring direct tension or splitting (indirect) tension. The splitting

tension test is also known as the Brazilian test. Data from 22 dams or testing

programs indicates that the average tensile strength of RCC is 10% to 15% of

its compressive strength (Andriolo, et al, 2002).

Figure 2.1 Compressive strength test results for different pozzolanic materials uses

2.2.3.3 Modulus of Elasticity (E c)

Principal factors affect the RCC modulus of elasticity are.

Age of test: the modulus increase with age up to maximum value.

Aggregate type: At large ages the RCC modulus could be similar to

that of the aggregate.

14

Water to cement ratio

2.2.3.4 Poisson's Ratio (υ)

It appears that values for RCC are similar to values reported for CVC

mixtures. A range from about 0.17-0.22 has occurred (U.S. Army Corps of

Engineers, 1997).

2.2.4 Thermal RCC Properties

The important properties for a thermal analysis of a mass-concrete

structure are: convection coefficients, ambient temperature of the air, lift

placement rate, adiabatic temperature rise, specific heat, and coefficient of

thermal expansion.

2.2.4.1 Thermal Conductivity (k).

The thermal conductivity of a material is the rate at which it transmits

heat and is defined as the ratio of the flux of heat to the temperature gradient.

Water content, density, and temperature significantly influence the thermal

conductivity of a specific concrete.

Typical values for thermal conductivity of mass concrete range from

1.73 to 3.46 W/m-k, while for foundation material may ranges from 4.15

W/m-k for clay, to 4.85 W/m-k for sand, to 5.19 W/m-k for gravels, and can

range from 1.73 to 6.23 W/m-k for rock (U.S. Army Corps of Engineers,

1997).

15

2.2.4.2 Coefficient of Thermal Expansion (Cth) .

The coefficient of thermal expansion can be defined as the change in

linear dimension per unit length divided by the temperature change. It is

usually considered constant for temperature varying between 0°C and 65° C

(Ayotte, et al. 1997).

2.2.4.3 Specific Heat (C).

Specific heat is the amount of heat required per unit mass to cause a unit

rise of temperature. It is affected by temperature changes but should be

assumed to be constant for the range of temperature in mass concrete

structure (MCS). For mass concrete mixtures, specific heat is not

substantially affected by age. Typical values for specific heat of mass

concrete range from 0.75 to 1.17 kJ/kg-k, while for soil foundation ranges

from 0.8 kJ/kg–k for sand, to 0.92 kJ/kg–k for clay. Specific heat for

foundation rock generally ranges from 0.8 to 1.0 kJ/kg–k (U.S. Army Corps

of Engineers, 1997).

2.2.4.4 Adiabatic Temperature Rise (Tab)

An adiabatic system is a system in which heat is neither allowed to enter

nor leave. Therefore, adiabatic temperature rise is the change in the

temperature of the concrete due to heat of hydration of the cement under

adiabatic conditions. It is the measure of the heat evolution of the concrete

mixture in a thermal analysis. In a very large mass of concrete, temperatures

near the center of the mass will be approximately equal to the sum of the

16

placement and adiabatic temperatures. However, near the surfaces, the

temperature will be close to the ambient air temperature. The magnitude of

the adiabatic temperature rise and the shape of the curve can vary

significantly for different concrete mixtures. Typical values for the adiabatic

temperature rise of the mass of concrete range from 11–19°C at five days to

17–25°C at 28 days.

2.2.4.5 Heat of Hydration.

The reaction of water with cement is exothermic and generates a

considerable amount of heat over an extended period of time. Heats of

hydration for various cements vary from 300 to 400 J/g at 28 days. The

higher the concrete temperature, the faster the rate of hydration and the more

rapid heat is generated in the concrete member, the higher the cement

content, the greater the potential temperature rises in the concrete.

2.2.4.6 Tensile Strain Capacity (ε ). tc

The strain capacity is considered as the ultimate deformation under

tension before the rupture. Strain is induced in concrete when a change in its

volume is restrained. When the volume change results in tensile strains that

exceed the capability of the material to absorb the strain, a crack occurs.

Design is based on maximum tensile strain. The modulus of rupture test

(CRD-C 16) is done on concrete beams tested to failure under third-point

loading. Tensile strain capacity is determined by dividing the modulus of

rupture by the modulus of elasticity. Typical values range from 50 to 200

17

millions depending on loading rate and type of concrete. Tensile strain

capacity of the RCC is 80µm (Dunstan, 1981)

2.3 The Finite Element Method

Early thermal analysis of mass concrete made use of very simple

concepts and various stepwise, hand calculation methods of determining

temperature changes. Later development of Finite Element (FE) techniques

made possible more accurate and realistic thermal analysis.

The finite element method is a numerical analysis technique for solving

differential equations or boundary value problems in science and engineering.

The differential equations, which govern the physical problem to be solved,

are assumed to exist in a certain domain. The domain then is divided into

smaller parts, which are termed finite elements, and the connected set of

finite elements is called a finite element mesh. The behavior of each element

is described by geometry, kinematics and proper constitutive relationships.

Finally, the elements are linked together to represent the whole domain, and

boundary conditions are applied.

2.4 Thermal analysis

2.4.1 Thermal analysis concept

Mass concrete is defined by ACI code as "any volume of concrete with

dimension large enough to require that measures be taken to cope with

generation of heat of hydration of the cement and attendant volume change to

minimize cracking." When Portland cement combines with water, the

18

ensuring exothermic (i.e. heat-releasing) chemical reaction causes a

temperature rise in concrete mass. The actual temperature rise in a mass

concrete structure (MCS) depends upon the heat generating characteristics of

the mass concrete mixture, the thermal properties, environment conditions,

geometry of MCS, and construction conditions. Usually, the peak

temperature is reached in a few days to weeks after placement, followed by a

slow reduction in temperature. Over period of several months to several

years, the mass eventually cools to some stable temperature, or a stable

temperature cycle for thinner structures. A change in volume occurs in the

MCS proportional to the temperature change and the coefficient of thermal

expansion of the concrete. If volume change is restrained during cooling of

the mass, by either the foundation, the previously placed concrete, of the

exterior surfaces, sufficient tensile strain can develop to cause cracking.

Cracking generally occur in main body or at the surface of the MCS. These

two cracking phenomenon are termed mass gradient and surface gradient

cracking, respectively. ACI 207.1R contains detailed in formation on heat

generation, volume change, restraint, and cracking in mass concrete.

The objectives of the thermal analysis were to define a procedure of

analysis that could be used in larger RCC projects. The intentions were not to

use the results of the analysis in the design process, but to take advantage of

the available information during the construction. The thermal characteristics

of the material, the thermal conditions and the modeling assumptions have

19

been studied to obtain a model giving a temperature distribution as close as

possible to the temperatures measured in the dam. The working model allows

predicting the temperature distribution in the dam at different time.

2.4.2 Thermal analysis Objectives

Thermal analysis is one of the most important analyses that must be

done for the design purposes; it provides a guide for formulation

advantageous design features, optimizing concrete mixture proportions, and

implementing necessary construction requirements. Also it provides cost

savings by revising the structural configuration, constriction sequence,

construction requirements for concrete placement temperature, mixture

proportions, placement rates, and insulation requirements. Cost savings may

be achieved through items such as eliminating unnecessary joints, allowing

increased placing temperatures, increased lift heights, and reduced insulation

requirements. In addition it is necessary to more accurately predict behavior

of unprecedented structures for which limited experience is available, such as

structure with unusual structural configuration, extreme loading, unusual

construction constraints, or severe operational requirements.

2.5 Temperature Control Requirements

Significant thermal induced stresses are developed as a result of the heat

of hydration of the cementitious materials in RCC dams. The temperature

distribution through the dam and its evolution with time depend on the

following:

20

RCC concrete properties,

Climatic factors,

Construction procedure,

lifts Thickness, and

Initial temperature of the lifts, and the Interval between their

placements.

These thermally induced stresses can be significant enough to induce

cracks in the RCC. Recent developments in sophisticated software based on

advanced numerical methods, together with the continually increasing power

of computers allow complex analyses for such thermal-structural problems.

The ANSYS and COSMOS/M computer programs based on the finite

element method were used to analyze the thermal behavior of AL-Wehdah

Dam. The desired outcome of the numerical analysis was

To determine the spatial distribution of temperature and its evolution

with time,

To determine the stress distribution during and following the dam

construction and at the time of reservoir filling,

To identify the appropriate joint spacing to minimize the development

of transverse cracking, and

To determine the concrete placement temperature limits.

21

CHAPTER THREE

MODELING

3.1 Overview

The numeric modeling of the 96 meter high AL Wehdah dam is based

on the information obtained from the literature and the field, that includes:

the daily ambient temperature, the temperature of the RCC in unsettled initial

stage, the adiabatic increment curve of temperature, thermal conductivity,

specific heat, density of the RCC, the bedding mix., and the placement

temperature of the concrete.

3.2 Modeling Methodology

Modeling thermal processes is essential for the analysis of many

structural problems. Obtaining good thermal and stress results is a complex

problem due to the uncertainties related to the prediction of spatial and

temporal variations of material properties and applied loading.

The thermo-mechanical analysis was modeled using an un-coupled

approach. The thermal behavior of the dam was firstly simulated using

incremental construction of the finite element mesh. The results of the

thermal model were then applied using direct super positioning to a structural

model, which also included the step-by-step construction process. The

22

analysis was time marching to closely model the construction of 3m RCC

"lifts" in 10 day intervals over the 320 day construction period.

3.3 Principal Assumptions

The analysis considered some simplifying assumptions related to factors

that should affect thermal variations and the stress distribution.

The first calibration of the thermal characteristics of the material as well

as the modeling assumptions were done on small models of the test section

and the spillway.

The model divided the RCC dam in to 32 layers, each layer was 3 m

high and constructed in 10 days, while according to the actual method of

construction, the layer is 30 cm high constructed each day. Placing lifts every

ten days results in higher temperatures since the new lift adds heat to the

previous lift before a significant amount of cooling can occur. The

temperature of the convective medium, the air, is the mean daily ambient

temperature that is a function of time and represents the project site

conditions. A mean daily temperature is used because of the difficulty in

predicting changes in the temperature variations throughout the day and to

alleviate the need for an excessive number of time steps.

The analysis was carried out considering plain strain linear elastic

behavior, simplified soil-structure interaction entailing elastic foundation and

a uniform, homogeneous foundation, a uniform placement temperature, and a

uniform convection coefficient to all layers.

23

Linear stress analysis was assumed in this study, that is; the relationship

between loads and the induced response is linear. If you double the

magnitude of loads, for example, the response of the model (displacements,

strains, and stresses), will also double. All real structures behave nonlinearly

in one way or another at some level of loading. In some cases, linear analysis

may be adequate. In many other cases, the linear solution can produce

erroneous results. In such cases, nonlinear analysis must be used.

3.4 Model Properties and Parameters

3.4.1 Cementitious Materials

The analysis is based on an RCC mixture containing 60 kg/m3 of

Portland cement and 30 kg/m3 of different pozzolanic material. As shown in

Figure 3.1 theses materials have different heat of hydration. They assumed to

produce different percent of the heat of equivalent cement shown in Figure

3.2, the percent of the heat of equivalent cement that calculated from the

average of (25,40%) was used in this model.

24

100

150

200

250

300

350

400

0% 10% 20% 30% 40% 50%

Pozzolanic Material %

Hea

t of h

ydra

tion

kJ/k

g

Flyash South Africa

Flyash Turkey

Pozzolan Jordan

Rock Flour

Fig. 3.1 The Accumulative Heat of Hydration after 7 days for different Percent of Different Pozzolanic Material

0

10

20

30

40

50

60

70

South Africa Turkey Pozzolana Rock Flour

Type of Pozzolanic Material

perc

ent o

f the

hea

t of e

quiv

alen

t cem

ent ,

% Avg(10,25,40%)

Avg(25,40%)

40%

Fig. 3.2 The Percent of the Heat of Equivalent Cement calculated from different Percent

of Different Pozzolanic Material

25

3.4.2 Concrete Placement Temperature

The temperature of concrete aggregate has the greatest influence on the

initial temperature of the fresh RCC. Due to the low volume of mix water and

the minor temperature difference of the water compared to the aggregate, the

water temperature has a much less significant effect on the overall

temperature. Table 3.1 provides the basis for estimating aggregate

temperature and approximating the RCC placing temperature used in the

analysis. Since aggregate production will be done concurrently with the RCC

placement, stockpile temperatures should closely parallel the average

monthly ambient temperatures. Some heat is added because of screening,

crushing, and transportation activities. In practice, that temperature may vary

from one layer to the other because of exposition to the sun (Nollet, 1994).

The average monthly ambient air temperature is shown in Table 3.1

RCC placement was assumed to take place in the cooler months of the year

i.e., from November to the end of April. Based on the average ambient air

temperature from November to April of 19.7o C, an average RCC placement

temperature of 20.o C was adopted., also the analysis was carried out for an

average RCC placement temperature of 24oC considering placing RCC all

over the year and limiting the RCC placement temperature to (28,32)oC

during the hot months .

26

3.4.3 Initial Temperature of Rock Foundation

Before calculating the temperature we must know the temperature

distribution in the rock ground just before the starting of the casting of the

concrete. It may be difficult to measure the temperature within the rock

foundation directly. Usually the temperature distribution within rock

foundation is obtained from calculation. As a method to calculate it, it is

assumed that the initial temperature for all nodes corresponding to the rock

foundation are the same changing in atmospheric temperature for two or

three years according to the observed data (Ishikawa, M., 1991).

Table 3.1 Predicted RCC Placement Temperatures Month Mean

Monthly Temp (oC)

Mean Annual

(oC)

Diff (oC)

2/3 Diff (oC)

Sub Total (oC)

Aggregate Crushing

Add (oC)

Aggregate Stocking

Temp (oC)

Mixing Add (oC)

Trans. Add (oC)

Final Temp (oC)

Jan. 12.3 21.2 -8.9 -5.93 15.27 1.2 16.47 1.2 -0.6 17.07 Feb. 12.8 21.2 -8.4 -5.60 15.60 1.2 16.80 1.2 0 18.00 Mar. 15.6 21.2 -5.6 -3.73 17.47 1.2 18.67 1.2 0.6 20.47 Apr. 20.6 21.2 -0.6 -0.40 20.80 1.2 22.00 1.2 0.6 23.80 May 24 21.2 2.8 1.87 23.07 1.2 24.27 1.2 1.1 26.57 Jun. 26.7 21.2 5.5 3.67 24.87 1.2 26.07 1.2 1.1 28.37 Jul. 28.4 21.2 7.2 4.80 26.00 1.2 27.20 1.2 1.7 30.10

Aug. 30.1 21.2 8.9 5.93 27.13 1.2 28.33 1.2 1.7 31.23 Sep. 27.8 21.2 6.6 4.40 25.60 1.2 26.80 1.2 1.1 29.10 Oct. 24.5 21.2 3.3 2.20 23.40 1.2 24.60 1.2 0.6 26.40 Nov. 19 21.2 -2.2 -1.47 19.73 1.2 20.93 1.2 0 22.13 Dec. 14 21.2 -7.2 -4.80 16.40 1.2 17.60 1.2 -0.6 18.20

Average 24.4

3.4.4 Materiel Properties and Environmental Conditions

The model properties used were assessed from available data and

typical RCC properties. The density, modulus, Poisson ratio, specific heat

27

and thermal conductivity are given in Table 3.2. A convection coefficient for

air was used, which is consistent with moderate wind speed.

The thermal behavior of the RCC dam was modeled by considering the

heat generated by the exothermic reaction of the cement paste during the

cure. The heat transfers by conduction in the concrete mass and the rock, as

well as the convection on the faces exposed to ambient temperature were

considered. The thermal expansion coefficient is another properties used in

analysis on thermal stress in concrete.

Table 3.2 Properties Adopted for Thermal Analysis

Roller Compacted Concrete Density 2450 kg/m3

Coeff. of Thermal Expansion 8.6 E-6 /deg C Specific Heat 920 J/kg deg C Thermal Conductivity 2.15 J/s m deg C Film (convection) Coefficient (air) 15 J/s m2

Heat Generation of RCC 405 J/g at 28 days Placement Temperature 20o, 24o, 28o and 32o C Modulus of Elasticity 10.0 GPa

Rock Foundation Density 2600 kg/m3

Coeff. of Thermal Expansion 6.0 E-6 /deg C Specific Heat 900 J/kg deg C Thermal Conductivity 2.15 J/s m deg C Foundation Rock Temperature 21.3o Modulus of Elasticity 4.9 GPa

28

0

50

100

150

200

250

300

350

400

450

500

0 50 100 150 200 250 300 350 400

Time (day)

H.H

. (J/

g)

3.4.5 Heat of hydration

During the hydration of cementations materials, numerous factors and

interaction are involved, some of which are currently not fully understood.

As part of this study, a different cementations materials and mixture

proportions that give a different heat of hydration are used.

Heat generation rates adopted for the 60 kg/m3 cement plus 30 kg/m3

pozzolanic material were based on the heat of hydration of the Jordanian

Ordinary Portland Cement (OPC) plus that of pozzolanic material as shown

in Figure 3.1. A heat of hydration of 405 J/g at 28 days was adopted and used

in the thermal analysis (Figure 3.3). Figures 3.4, 3.5, 3.6, and 3.7 show the

simulated heat of hydration for finite element analysis for the four pozzolanic

material.

Fig. 3.3 The accumulative heat of hydration of the cement (OPC)

29

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90 100

Time (day)

Rat

e of

H.H

. (J/

m3.

s)

Fig 3.4 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3 South Africa

flyash), for Finite Element Analysis

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Time (day)

Rat

e of

H.H

. (J/

m3.

s)

Fig 3.5 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3 Turkey flyash),

for Finite Element Analysis

30

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Time (day)

Rat

e of

H.H

. (J/

m3.

s)

Fig 3.6 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3 Jordanian

pozzolan), for Finite Element Analysis

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Time (day)

Rat

e of

H.H

. (J/

m3.

s)

Fig 3.7 Heat of Hydration for RCC mix (60 kg/m3 cement, and 30 kg/m3 rock flour), for Finite Element Analysis

31

3.5 Boundary and Initial Conditions

Figure 3.8 shows the boundary and initial conditions for thermal and

structural analysis, which are:

1. All boundaries around the foundation rock satisfy the adiabatic

condition: 0.0=∂∂ nT (i.e., no change in temperature in the direction

normal to the planes. The dam and foundation that are exposed to the

atmosphere satisfy the following condition (as defined previously).

( ) ( )Bf TThnTK −−=∂∂ 3.1

Where T is the transient temperature, n the outer unit normal, K is the

thermal conductivity, hf is the film coefficient and TB is ambient temperature.

2. Initial condition. The initial temperature for all nodes of foundation is

assigned from rock temperature. The initial temperature of each layer of

the dam is set to be equal to the placement temperature.

3. Structural boundary conditions. The foundation rock is infinite, and no

horizontal movement is allowed; thus the foundation rock is restricted

in all horizontal direction (i.e., there are rollers on vertical boundaries

and pins at the bottom boundary). Therefore, the vertical direction

movement is restricted in the bottom boundary.

Appendix A shows more detail about the theories and the boundary

condition

32

Fig 3.8 Thermal and Structure Boundary Conditions for Thermal Analysis

33

CHAPTER FOUR

COMPARATIVE STUDY BETWEEN COSMOS & ANSYS

4.1 Overview

COSMOS and ANSYS are the two finite element based softeware

that are used to carry out the thermal analysis for the RCC AL-Wehdah

dam. The analysis was carried out for Jordanian Pozzolan RCC mix, with

placement temperature of 28°C. It is quite necessary to talk about these two

codes and what are the bases and theories that each code depends on, the

results after that will be presented and discussed.

4.2 COSMOS/M Software

COSMOS/M Thermal is a fast, robust, and accurate finite element

program for the analysis of linear static structural problems. The program

exploits a new technology developed at Structural Research for the solution

of large systems of simultaneous equations using sparse matrix technology

along with iterative methods combined with novel database management

techniques to substantially reduce solution time, disk space, and memory

requirements (Structural Research and Analysis Corporation , 1997).

COSMOS/M Thermal has been written from scratch using state of the

art techniques in FEA with two goals in mind: 1) to address basic design

34

needs, and 2) to use the most efficient possible solution algorithms without

sacrificing accuracy. The program is particularly suitable for the solution of

large models subjected to a variety of loading and boundary conditions

environments.

The program can analyze linear and nonlinear steady state and transient

heat conduction problems with convective and radiative type boundary

conditions in one, two, and three-dimensional geometries

Time curves facility is the most important option in the COSMOS

program. It enables the user to simulate any dependent time problems. For

example, many parameter in our model is time dependent; RCC casting, heat

generation due to the heat of hydration of RCC, and convection… etc. Killing

and living the elements are also done using the time curve option.

Figure 4.1 shows all the time curves that were used in model analysis.

For the first layer as shown, the heat generation started from time zero, while

for the next layer, zero values were given to the heat generation until the

placement time reached for this layer. The same thing done to apply the heat

convection on the layer surface, this convection continuing for ten days only,

so a time curves with zero values are made and a value of one (1) for 10 days

only is given to the time curve to alive the convection on this layer, the

convection on the outer surface will start when the layer placed but this

convection will continue, so the value (1) will extend from the placement to

the last time as shown.

35

0 10 20 30 40 50 60 70 80 90 100

Time (day)

Hea

t Gen

erat

ion

C

onve

ctio

n on

the

Laye

rs

C

onve

ctio

n on

Up

& D

ownS

tream

Fig 4.1 Time Curves Used in COSMOS/M for the 1st three layers

36

4.3 ANSYS Software

ANSYS is finite element analysis based software enables engineers to

perform the following tasks:

Build computer models or transfer CAD models of structures,

products, components, or systems.

Apply operating loads or other design performance conditions.

Study the physical responses, such as stress levels, temperature

distributions.

Optimize a design early in the development process to reduce

production costs.

The ANSYS program has a comprehensive graphical user interface

(GUI) that gives users easy, interactive access to program functions,

commands, and documentation and reference material. An interactive menu

system helps users to navigate through the ANSYS program. Users can input

data using a mouse, a keyboard, or a combination of both (Anonymous,

2002).

Birth and death of elements is also some of the effective facilities in

ANSYS program, it is used to simulate any dependent time problems. For

heat convection boundaries for instant, heat convection boundary condition

should be superimposed on the surface of conduction element. In the process

of adding the concrete, it should be given ‘birth’ to heat conduction elements

that correspond to the concrete. The heat convection boundary condition are

37

also given ‘birth’, which means apply convection on top of conduction

element at the same time, if the conduction elements include heat convection

boundaries as shown in Figure (3.7). However, the element which has

previously given the operation of ‘birth’’, should not given the ‘death’

operation in any of the following steps, only for convection boundary

condition, delete from the previous layer and apply to the next layer and so

on until the dam complete. Also for heat of hydration, as in Figure 4.2, which

shows from STEP, i to STEP i+1 is allowed. In this way, the analysis can be

done with a single computational mesh instead of several ones, one for each

stage of construction.

Convection

Conduction Conduction Conduction

Convection

Convection

Step i-1 Step i Step i+1

Birth

Death

Birth

Death

Figure 4.2 Births and Death of Elements

38

4.4 Model Analysis

4.4.1 Two-Dimensions Model Analysis using COSMOS

The dam was modeled as a two-dimensional transient heat transfer

model to simulate the real construction process of the dam. The time curve

option in the COSMOS/M Program that was discussed previously is used for

the heat of hydration and the heat convection effects to simulate the time lag

between the placements of the RCC layers. The dam is divided into 32 layers.

Each layer has thickness of 3 m constructed in 10 days. The total number of

elements and nodes are 2266 and 7074 respectively. Quadrilateral plane

element with eight nodes was used in the finite element analysis (Figure 4.3).

The element has one degree of freedom temperature at each node. This is a

high order element that has 8 nodes, is suitable for simulating irregular

shapes, and is applicable to the study of a two-dimension steady state or

transient thermal analysis. Figure 4.5 shows the finite element mesh of cross

section of dam.

4.4.2 Three-Dimensions Model Analyses using COSMOS

A 3-D analysis was also carried out for Al Wehdah RCC dam. The

length of the dam is divided into 16 blocks, each block 30 m long. Figure 4.6

shows the finite element mesh for 3D, the total number of elements and

nodes is 11330 and 14424 respectively. A solid element type was used for the

thermal analysis (see Fig 4.3). This element has 8 nodes with a single degree

of freedom temperature at each node.

39

4.4.3 Two-Dimensions Model Analysis using ANSYS

The dam was modeled as a two-dimensional transient heat transfer

model using a birth and death procedure (see Figure 4.2) to simulate the real

construction process of the dam. The dam is divided into 32 layers. Each

layer has thickness of 3 m constructed in 10 days; the rock foundation is

presented from 30 meters upstream, 30 meters downstream and 30 meters

under the dam. The rock elements simulate the heat dissipation through the

foundation. The total number of elements and nodes are 2266 and 7074

respectively. PLANE77 element type available in ANSYS element library

was used. The element has one degree of freedom temperature at each node

as shown in Figure 4.4. This element is a higher order element has 8 nodes

and it is suitable to simulate irregular shape and applicable to a two

dimension steady – state or transient thermal analysis. Also, the element can

be used to carry out structural analysis by replacing it by an equivalent

structural element called PLANE82, Figure 4.4. A plane strain model was

adopted for two-dimension analysis. Plane strain is the condition for which

the strains perpendicular to the plane of the analysis are maintain at zero.

Gravity loads due to self – weight of the rock foundation and the RCC and

thermal loads from thermal analysis were included in the structural analysis.

Figure 4.7 shows the finite element mesh of cross section of dam.

40

4.4.4 Three-Dimensions Model Analyses using ANSYS

A 3-D analysis was also carried out for Al Wehdah RCC dam. The

length of the dam is divided into 16 blocks, each block 30 m long. Figure 4.8

shows the finite element mesh for 3D analysis. A solid 70 element type was

used for the thermal analysis, Figure 4.4. This element has 8 nodes with a

single degree of freedom temperature at each node. A solid 65 element type

was used for the structural analysis. This element has three degrees of

freedom in each node, permitting movement in the x, y and z direction. Same

procedure in two dimensions was used for three dimensions to generate the

mesh. The total number of elements and nodes is 11330 and 14424

respectively. The step-by-step analysis of the construction simulation process

allows the determination of the temperature for each added lift.

41

Fig. 4.3 Element Types Used in COSMOS

Fig. 4.4 Element Types Used in ANSYS

42

Fig. 4.5 Two Dimension Model Mesh in COSMOS

Fig. 4.6 Three Dimension Model Mesh in COSMOS

43

Fig. 4.7 Two Dimension Model Mesh in ANSYS

Fig. 4.8 Three Dimension Model Mesh in ANSYS

44

4.5 Finite Element Results

4.5.1 Finite Element Results of COSMOS

Figure 4.9 shows the temperature contours in the dam body after 100

days for placement temperatures of 28°C and for RCC mix containing

Jordanian pozzolan using two and three dimensional analysis, it can be seen

that the maximum temperature in the dam core is 42.34 °C for 2D analysis

and 43.17 °C for 3D analysis. At the end of heat of hydration as shown in

figure 4.10 the temperature decreased to 42°C and 42.2°C for 2D and 3D

analysis respectively.

Figure 4.11 shows the predicted temperature history in the dam center at

different heights, this figure determines the elevation where the maximum

temperature was occurred. For 2D analysis as shown, 42.3 °C is the

maximum temperature that can occur in the dam during the construction; it is

at 12 m from the dam base. While in 3D analysis the peak temperature was

42.6 °C at the same elevation.

The temperature distribution shown in Figure.4.12 is for a specific

points located at a distance 12m from the dam base at different distance from

the dam upstream, once the RCC placed the temperature drop quickly to

23.2°C due to the convection on the layer surface then the temperature rise to

42.3°C for two dimensional analysis, the drop in 3D analysis was 23.1°C and

the maximum reached temperature was 42.6°C.

45

Fig 4.9 Temperature Contour after 100 days using COSMOS

46

Fig 4.10 Temperature Contour at the End of Heat of Hydration, 410 days using COSMOS

47

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)

At the dam base12 m from the dam base22 m from the dam base34 m from the dam base45 m from the dam base60 m from the dam base

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)


Fig 4.11 Predicted Temperature History in the Dam Center at Different Heights using COSMOS for 2D & 3D Analysis Respectively

48

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350 400

Time (Day)

Tem

pera

ture

(Deg

C)

3 m from UpstreamCenter of dam4 m from Downstream

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)


Fig 4.12 Predicted Temperature History at Different Nodal Point at 12m from the Dam

Base using COSMOS for 2D & 3D Analysis Respectively

49

4.5.2 Finite Element Results of ANSYS

Figure 4.13 shows the temperature contours in the dam body after 100

days for placement temperatures of 28°C and for RCC mix containing

Jordanian Pozzolan using two and three dimensional analysis, it can be seen

that the maximum temperature in the dam core is 43.6 °C for 2D analysis and

43.6 °C for 3D analysis. At the end of heat of hydration as shown in figure

4.14 the temperature was 43.7°C and 43.9°C for 2D and 3D analysis

respectively.

Figure 4.15 shows the predicted temperature history in the dam center at

different heights, this figure determines the elevation where the maximum

temperature occurs. For 2D and 3D analysis, 43.9 °C is the maximum

temperature that can occur in the dam during the construction; it is at 12 m

from the dam base as shown.

The temperature distribution shown in Figure.4.16 is for a specific

points located at a distance 12m from the dam base at different distance from

the dam upstream, once the RCC placed the temperature drop quickly to

24.1°C due to the convection on the layer surface then the temperature rise to

43.7°C for two dimensional analysis, the drop in 3D analysis was 24.1°C and

the maximum reached temperature was also 43.9°C.

50

Fig 4.13 Temperature Contour after 100 days using ANSYS

51

Fig 4.14 Temperature Contour at the End of Heat of Hydration, 410 days, using ANSYS

52

20222426283032343638404244464850

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)

At the dam base

12 m from the dam base




20222426283032343638404244464850

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)


Fig 4.15 Predicted Temperature History in the Dam Center at Different Heights using ANSYS for 2D & 3D Analysis Respectively

53

20222426283032343638404244464850

0 50 100 150 200 250 300 350 400

Time (Day)

Tem

pera

ture

(Deg

C)


20222426283032343638404244464850

0 50 100 150 200 250 300 350 400 450

Time (Day)

Tem

pera

ture

(Deg

C)


Fig 4.16 Predicted Temperature History at Different Nodal Point at 12m from the Dam Base using ANSYS for 2D & 3D Analysis Respectively

54

4.6 Summary and Discussion

Table 4.1 summarizes the models analysis for both COSMOS and

ANSYS codes, also it summarizes the results that were obtained from theses

programs and then the crack analysis for theses results is also summarized.

Figure 4.17 and 4.18 show the predicted temperature history using two

and three dimensional analysis by ANSYS and COSMOS at a nodal point in

the dam center and at a point near the upstream face; both points are at 12 m

from the dam base.

Figure 4.19 shows the temperature distribution along the dam cross

section at an elevation of 22 m from the dam base using two and three

dimensional analysis by ANSYS and COSMOS at the end of heat of

hydration (410 Days). And Figure 4.20 shows the vertical temperature

distribution at the dam center at the end of heat of hydration using also two

and three-dimensional analysis. It is clearly seen that both two and three

dimension analysis gave nearly the same results, for both COSMOS and

ANSYS, so discussing one of these analysis will be enough.

From all these figures, it can be seen that the maximum temperature

obtained from ANSYS program are higher than that obtained from COSMOS

by nearly one degree.

Since the two meshes for ANSYS and COSMOS has the same number

of elements and nodes, and the same material properties applied on both of

them, it can be concluded that this difference in temperature may

55

occur due to only two factors, the first is the heat generation due to the heat

of hydration, and the other is the temperature drop due to the convection

effects.

The values of heat of hydration at each 10 days were used in the two

programs according to Figure 3.6, but 1 day increment was used, the heat of

hydration at this increment was interpolated by the programs, the

interpolation process that is done by COSMOS differs from the ANSYS

interpolation.

Once the RCC placed, the temperature dropped from 28°C to 23°C in

COSMOS analysis, while it dropped to 24°C in ANSYS as shown in Figure

4.17, this is one of the factors that affect the maximum temperature results.

This difference refers to the theories that each code is based on.

From the crack analysis presented in Table 4.1, it can be concluded that

ANSYS gives more conservative results; 42 contraction joints must be placed

according to ANSYS results while 40 contraction joints is enough according

to COSMOS results.

56

Table 4.1 Summary Results for COSMOS and ANSYS

COSMOS ASNYS DESCRIPTIONS

2D 3D 2D 3D

Output file size (GB) 0.24 1.6 0.14 0.72

Gen

eral

Run Time (hr) 1 4 0.5 3

No. of Elements 2266 11330 2266 11330

No. of Nodes 7074 14424 7074 14424

Element Type Plane 2D Solid Plane 77 Plane 70

Mod

el A

naly

sis

Time Simulation Time Curves Birth & Death

Peak Temperature 42.3 42.6 43.6 43.8

Elevation of Peak Temp (m) 12 12 12 12

Time of Peak Temp (days) 110 110 110 110 Res

ults

Temp. Drop due to Convection oC 23.2 23.1 24.2 24.1

∆T oC (Peak – Min. Ambient) 30.3 30.5 31.2 31.5

Induce strain (µmm) 142 143 148 149

No. of block 40 40 42 43

Cra

ck A

naly

sis

Length of block (m) 26 24 23 23

57

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300

Time (Day)

Tem

pera

ture

(Deg

C)

ANSYSCOSMOS

20

22

24

26

28

30

32

34

36

38

40

42

44

46

48

50

0 50 100 150 200 250 300 350

Time (Day)

Tem

pera

ture

(Deg

C)

ANSYS

COSMOS

Fig 4.17 Comparative Predicted Temperature History using ANSYS and COSMOS at the Dam Center and 12 m from the Dam Base using 3D Analysis

Fig 4.18 Comparative Predicted Temperature History using ANSYS and COSMOS at 3m from Upstream and 12 m from the Dam Base using 2D Analysis

58

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Distance (m)

Tem

pera

ture

(Deg

C)

ANSYS (2D)ANSYS (3D)COSMOS (2D)COSMOS (3D)

0

8

16

24

32

40

48

56

64

72

80

88

96

20 25 30 35 40 45 50

Temperature (Deg C)

Dis

tanc

e (m

) ANSYS (2D)ANSYS (3D)COSMOS (2D)COSMOS (3D)

Fig 4.19 Cross Section Temperature Distribution at 22 m from the Dam

Base using ANSYS and COSMOS

Fig 4.20 Vertical Temperature Distribution at the Dam Center using ANSYS and

COSMOS

59

CHAPTER FIVE

THERMAL AND STRESS ANALYSIS

5.1 Overview

Thermal analysis was carried out using both two and three-dimensional

Finite Element Method (FEM) in ANSYS program, the analysis done for

different RCC mix of different pozzolanic material (South Africa flyash,

Turkey flyash, Jordanian pozzolan, and rock flour) which have different heat

of hydration as discussed in the chapter three.

A parametric study to find the placement temperature that required

getting a 20 m spacing between contraction joints was also done by changing

the placement temperature (20, 24, 28, and 32 °C) and accordingly carrying

out the analysis.

One RCC mix using Jordanian pozzolan with 28°C placement

temperature were used to perform stress analysis using both two and three-

dimensional Finite Element Method (FEM). The analysis carried out using

ANSYS program only, some difficulties and insufficient time prevent us to

use COSMOS program for stress analysis.

60

5.2 Thermal Analysis for RCC Dam

5.2.1 Effect of Convection Coefficients

The forms are analytically removed (i.e., convection coefficients change

Values) one days after a lift is placed with lift placement proceeding at ten-

day intervals. This construction rate tends to be much faster than what

actually occurs on the job site. Nevertheless, the increased rate for form

removal will produce higher thermal gradients due to removal near the time

when peak temperatures are obtained producing a sudden cooling at the

surface. Also, placing lifts every ten days results in higher temperatures since

the new lift adds heat to the previous lift before a significant amount of

cooling can occur. The temperature of the convective medium, the air, is the

mean daily ambient temperature that is a function of time and represents the

project site conditions. A mean daily temperature is used because of the

difficulty in predicting changes in the temperature variations throughout the

day and to alleviate the need for an excessive number of time steps.

5.2.2 Effect of Heat of Hydration and placement Temperature

Heat of hydration of cementitious materials as well as placing

temperature is the principal parameters influencing the temperature rise in the

massive concrete structure.

5.2.3 Results and discussion of Thermal Analysis

Figure 5.1 shows the temperature contours at the end of heat of

hydration (410 days) for different placement temperatures (20, 24, 28°C) for

61

RCC mix containing South Africa flyash using two and three dimensional

analysis, it can be seen that the maximum temperature in the dam core

increases by increasing the placement temperature, for 2D analysis it is 41.16

°C when using 20°C placement temperature, increased then to 45.32 °C for

24°C placement temperature then increased to 47.5 for 28 °C placement

temperature, also for 3D analysis the peak temperature increased from 42.37

°C to 45.23 °C to 47.9 °C respectively, 21.3˚C which is equal to the average

ambient temperature is the minimum temperature reached in the dam, it is

located at the outer surface of the dam body where the ambient temperature

affects the dam.

Figures 5.2, 5.3, and 5.4 show also the temperature contours at the end

of heat of hydration for RCC mix of Turkey flyash, Jordanian Pozzolan, and

Rock Flour respectively. The peak temperatures in the dam core at the end of

heat of hydration for these different analyses are summarized in Table 5.1

62

Fig. 5.1 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28°C) for RCC mix of South Africa flyash

63

Fig. 5.2 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24 and 28 °C) for RCC mix of Turkey flyash

64

Fig. 5.3 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28 and 32 °C) For RCC mix of Jordanian pozzolan

65

Fig. 5.4 Temperature contour at the end of heat of hydration, 410 days for different placement temperature (20, 24, 28 and 32 °C) For RCC mix of rock flour

66

Table 5.1, Peak temperature in the dam core at the end of heat of hydration

Figure.5.5 shows the comparison temperature history at 22m from the

base of the dam (in the middle of the eighth layer) at the dam center where

the maximum temperature occurred during the construction process for three

different placement temperatures (20, 24, 28°C) and also for RCC mixes

containing South Africa flyash using two-dimensional analysis. For example

when using 28˚C placement temperature, the placement of this layer started

in the day 70, the temperature increased from 28˚C to 43.3˚C in the first ten

days when the heat of hydration is the maximum, and then the temperature

decreased by 0.2˚C due to the effect of convection on the layer surface, the

temperature after that started a new increase but with a rate smaller than the

first one due to the decreasing of the heat of hydration rate with time, the

temperature reached its maximum (47.5˚C) after 100 days from the

placement (in the day 170, as shown), then it remained constant for a long

period of time because heat transfer from the core of dam to the surface is

very slow, and further more the heat conduction due to the construction of the

overlying layers of RCC prevents internal heat loss from the constructed lift

2D Analysis 3D Analysis Placement temp. oC 20 24 28 32 20 24 28 32 South Africa flyash 41.16 45.32 47.5 * 42.37 45.23 47.9 * Turkey flyash 39.66 42.84 46.02 * 41.02 43.67 46.35 * Jordanian pozzolan 38.49 41.67 45.8 48 39.79 42.45 45.12 47.78 Rock Flour 37.58 40.76 43.9 47.12 38.85 42.45 45.16 46.82

67

surface. The maximum temperature for 20˚C and 24˚C placement

temperature was 41.1˚C, 45.3˚C respectively.

Figures 5.6, 5.7, and 5.8 show also the comparison temperature history

at 22m from the dam base but for RCC mix of Turkey flyash, Jordanian

pozzolan, and Rock Flour respectively. The maximum temperatures occurred

during the construction process for these different analyses are shown in

Table 5.2.

Table 5.2, Maximum temperatures occurred during the construction process

Fig. 5.5 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for

Different Placement Temperatures for RCC Mix of South Africa flyash

2D Analysis 3D Analysis Placement temp. oC 20 24 28 32 20 24 28 32 South Africa flyash 41.15 45.33 47.8 * 42.59 45.25 47.9 * Turkey flyash 39.67 43.12 46.3 * 40.58 43.7 46.4 * Jordanian Pozzolan 38.5 41.93 45.1 48.2 39.37 42.47 45.1 47.8 Rock Flour 37.59 41 45.2 47.3 38.4 41.5 45.2 46.84

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)

Placement Temp=20 deg C




Starting Placement Time

68

15.00

20.00

25.00

30.00

35.00

40.00

45.00

50.00

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)





Starting Placement

Time


Different Placement Temperatures for RCC Mix of Turkey flyash


Different Placement Temperatures for RCC Mix of Jordanian pozzolan

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)






69

Fig. 5.8 Predicted Temperature History in the Dam Center at 22 m from Base of Dam for Different Placement Temperatures for RCC Mix of rock flour

The temperature distribution shown in Figure.5.9 is for a specific points

located at a distance 12m from the dam base at two different distance from

the dam upstream for a placement temperature of 28oC, the analysis carried

for RCC mix of South Africa flyash using 2D and 3D analysis. The cleared

temperature drop down from 28 oC to 24 oC that is shown in the figure was

due to the convection on the layer surface, the drop as seen continued for one

day only, the temperature after that increased to 43 oC for the two nodal

points due to the heat generation, For the point near the upstream face (3m

from the upstream), once the temperature reached its maximum it started

decreasing because of the heat dissipation into the air, the temperature

15

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)






70

decreased to 23.5oC after 420 days and this will continue to reach the ambient

temperature(21.3oC). While for the point in the dam center, the temperature

was continuing in its increasing (47.8oC) because it is far away from the

surface, so it gets more temperature from the nodal points above it that

starting their heat generation. It also can be seen that the temperature

distribution for 28 oC placement temperature was the same for two and three

dimensional analysis, which implementing that the 2D analysis could be

convenient for this type of problems.

Fig 5.9 Comparison 2D & 3D Analysis for Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of South Africa

flyash

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)

3 m from Upstream (2D)Center of dam (2D)3 m from Upstream (3D)Center of dam (3D)


71

Figures 5.10, 5.11, and 5.12 show also the temperature distribution for

the same specific points but for RCC mix of Turkey flyash, Jordanian

Pozzolan, and rock flour respectively. The maximum temperature as shown

for the RCC mix of South Africa flyash is the highest, then Turkey flyash,

Jordanian Pozzolan, and rock flour respectively.

Fig 5.10 Comparison 2D & 3D Analysis for Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of Turkey flyash

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)



72

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)



Fig 5.11 Comparison 2D & 3D Analysis of Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of Jordanian

pozzolan

Fig 5.12 Comparison 2D & 3D Analysis for Predicted Temperature History at Different Points at 12 m from Dam Base, Using 28°C Place_Temp for RCC Mix of Rock Flour

20

25

30

35

40

45

50

0 100 200 300 400 500

Time (Day)

Tem

pera

ture

(Deg

C)



73

Figure 5.13 shows the temperature distribution along the dam cross

section at an elevation of 22 m from the dam base for different placement

temperatures for RCC mix of South Africa flyash using two dimensional

analyses at the end of heat of hydration (410 Days). At the both sides of the

dam the temperature was 21.5 which is close to the ambient temperature,

while it increased as we come close to the dam center, it reached 41.4˚C,

45.3˚C, 47.5˚C for 20°C, 24°C, 28°C placement temperature respectively.

The effect of placement temperature is cleared perfectly in this figure.

Figures 5.14, 5.15, and 5.16 show also the temperature along the dam

cross section at an elevation of 22 m from the dam base but for RCC mix of

Turkey flyash, Jordanian Pozzolan, and rock flour respectively; Also the

maximum temperature for the RCC mix of South Africa fly ash was the

highest one.

74

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Distance (m)

Tem

pera

ture

(Deg

C)

Placement Temp=20 deg CPlacement Temp=24 deg CPlacement Temp=28 deg CPlacement Temp=32 deg C

Fig 5.13 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of South Africa flyash

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Distance (m)

Tem

pera

ture

(Deg

C)


Fig 5.14 Cross Section Temperature Distribution at 22 m from the Dam Base for Different Placement Temperatures for RCC Mix of Turkey flyash

75

15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Distance (m)

Tem

pera

ture

(Deg

C)


15

20

25

30

35

40

45

50

0 10 20 30 40 50 60 70 80

Distance (m)

Tem

pera

ture

(Deg

C)


Fig 5.15 Cross Section Temperature Distribution at 22 m from the Dam Base for Different

Placement Temperatures for RCC Mix of Jordanian pozzolan

Fig 5.16 Cross Section Temperature Distribution at 22 m from the Dam Base for Different

Placement Temperatures for RCC Mix of Rock Flour

76

0

10

20

30

40

50

60

70

80

90

100

20 25 30 35 40 45 50

Temperature (Deg C)

Dis

tanc

e (m

)


Figure 5.17 and 5.18 and 5.19 and 5.20 show the vertical temperature

distribution at the dam center for different placement Temperatures at the end

of heat of hydration for the four RCC mix respectively using two dimensional

analyses. The temperature gradient is high at region near the foundation. This

is due to the heat loses by conduction into the foundation. The maximum

temperature is about 41˚C for the first placement temperature at 20m from

the base.

Fig 5.17 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of South Africa flyash

77

0

10

20

30

40

50

60

70

80

90

100

20 25 30 35 40 45 50

Temperature (Deg C)

Dis

tanc

e (m

)


0

10

20

30

40

50

60

70

80

90

100

20 25 30 35 40 45 50

Temperature (Deg C)

Dis

tanc

e (m

)


Fig 5.18 Vertical Temperature Distribution at the Dam Center for Different Placement

Temperatures for RCC Mix of Turkey flyash

Fig 5.19 Vertical Temperature Distribution at the Dam Center for Different Placement

Temperatures for RCC Mix of Jordanian pozzolan

78

0

10

20

30

40

50

60

70

80

90

100

20 25 30 35 40 45 50

Temperature (Deg C)

Dis

tanc

e (m

)


Fig 5.20 Vertical Temperature Distribution at the Dam Center for Different Placement Temperatures for RCC Mix of Rock Flour

All the maximum temperatures that occurred in the dam during the

construction process using two and three-dimensional analysis are

summarized in Figure 5.21 for the different RCC mix using the four

placement temperature (20˚C, 24˚C, 28˚C, and 32˚C). It can be clearly seen

that South Africa flyash RCC mix has the highest temperature, and then the

mix of Turkey flyash, then Jordanian pozzolan mix, and rock flour RCC mix

has the lowest one. Also it can be seen that the three dimensional analysis

gives a values higher than two dimensional analyses for 20˚C, 24˚C, and

32˚C placement temperature, while for 28˚C placement temperature the

values are close to each other. The most important conclusion from this

figure is that for a maximum predicted temperature of 46˚C for example; the

79

36

37

38

39

40

41Pe

42

44

45

46

47

48

49

50

20 24 28 32

Placement Te perature oC

ak T

eat

ure

o C

43mpe

r

m

South Africa Flyash (2D)South Africa Flyash (3D)Turkey Flyash (2D)Turkey Flyash (3D)Jordanian Pozzolan (2D)Jordanian Pozzolan (3D)Rock Flour (2D)Rock Flour (3D)

placement temperature can be easily determined using this figure. It is

25.5˚C, 26.5˚C, 28˚C, 29.5˚C for the four RCC mix respectively.

Fig.5.21 Summary of the Maximum Temperatures in the Dam Body for Different RCC Mix and Different Placement Temperatures

5.3 Thermal Stresses in RCC Dam

5.3.1 Thermal Stress Due to Temperature Drop Near the Foundation

The case of RCC gravity dam is quite different from conventional

concrete gravity dam because there is no artificial cooling for joint grouting.

The dam is completed when the temperature in the interior of dam drops to

the final stable temperature. Thus, the temperature drop, the weight of

concrete must be superposed in the stress analysis for the study of

temperature control of RCC gravity dam.

80

5.3.2 Thermal Stresses Due to Temperature Deference between the

Surface and Interior of Dam.

The temperature in the interior of the dam rises after casting of concrete,

while the surface temperature is low because heat is dissipated in to the air.

As a result, there are tensile stresses in the surface of a concrete dam. There

is no artificial pipe cooling for joint grouting in RCC dams, so the internal

temperature drops very slowly, yet the surface temperature will be low in the

winter, thus, high tensile stresses will occur which may cause horizontal or

vertical cracks.

5.3.3 Thermal Stresses Due to Restraint of Foundation

Due to the conduction of heat from the dam body into the foundation,

the distribution of temperature drop in the concrete near the rock is not

uniform, thus the tensile stress is greater in a larger dam block.

5.3.4 Thermal Stresses Due to Vertical Temperature Difference

The vertical temperature difference is caused by the seasonal variation

of the placing temperature of the concrete and by stopping construction due

to flood or severe cold temperature in the winter. In RCC gravity dam, the

thermal stresses caused by vertical temperature difference may be large in

order to obtain the relation between the tensile stress due to vertical

temperature difference and the length of dam block. (Zhu B., et al. 1999).

81

5.3.5 Influence of Gallery in the Dam Body

In a solid gravity dam, the temperature difference inducing thermal

stresses is the difference between the highest temperature and the final stable

temperature. In a gravity dam with openings, such as gallery, the temperature

in the openings in winter is generally lower than the final stable temperature

for a solid gravity dam. So the thermal stresses around the openings may be

greater than those in a solid gravity dam. This is why cracks often appear

around the openings in a concrete dam. The influence of openings on thermal

stresses may be greater in a RCC gravity dam than in a conventional concrete

gravity dam with longitudinal joints because the length of dam block is

longer. (Zhu B., et al. 1999).

5.3.6 Results and Discussion of Structural Analysis

All the finite element results, which will be discussed, now were for the

RCC mix that contains Jordanian pozzolan using 28˚C as placement

temperature.

Figure 5.22 shows the stress envelope in the dam body in the direction

of river stream (x-direction) and in the dam axial direction (z-direction), and

also the major principal stress using two-dimensional structural analyses. For

the stress in x-direction, it can be seen that the tensile stress concentrated on

the gallery walls and also near the foundation surface, it was found from

figure 5.22 that the stress was about 0.94 MPa on the gallery walls and there

was some tensile stresses (0.5 MPa) developed near the foundation which

82

were caused by the external restraint by the foundation and the steeper

gradient of temperature. And also, it is about 0.6 MPa near the gallery for the

stress in z-direction, it can be seen also from the same figure for the axial

stress (z-direction) that the tensile stress mainly at the upstream and

downstream surface and at the surface of gallery. All theses results are

smaller than the allowable tensile strength to meet the demands against

cracking.

A plane strain model was adopted for two dimension structural analysis.

Plan strain is the condition for which the strains perpendicular to the plane of

the analysis are maintained at zero. Although, a plane strain analysis would

have given reasonable results, the actual effect of the finite dimension of

monolith was not observed. Accordingly, it is necessary to carry out the three

dimensional analysis. Figures 5.23 to 5.25 present three dimensional stress

contours at the end of heat of hydration. It can be noticed that the maximum

tensile stresses which were obtained from three-dimensional analysis were

high compared to that obtained from two-dimensional analysis, they were

0.88, 1.2, 1.2 MPa for σx, σ1, and σz respectively. For the stress in z-direction

it was found as shown in figure 5.25 that the tensile stresses concentrated also

at the upstream and downstream surface and at the surface of gallery, the

stresses reached a values more than the tensile strength of the RCC (1 MPa),

which may cause a cracks.

83

Fig 5.22 Different Stress Contour (σx, σz, N/m2) at the End of Heat of Hydration using 2D

Analysis.

84

Fig 5.23 3D Stress Contour (X-direction, N/m2) at the End of Heat of Hydration

Fig 5.24 3D Principal Stress Contour (σ1, N/m2) at the End of Heat of Hydration

85

Fig 5.25 3D Stress Contour (Z-direction, N/m2) at the End of Heat of Hydration

86

Stress history diagram of different stresses type (σ1 and σz) at 9m from

base of dam and at two different points, near the upstream face and near the

gallery are shown in Figures 5.26 and 5.27 respectively, using two dimension

analyses. It is obvious that the RCC near the gallery forcing a tensile stress

that is equal to 1.1 MPa and 0.9 MPa for (σ1 and σz) respectively. Which is

equal nearly to the tensile strength, the stress reached theses values after 150

days when the temperature decreased to its minimum. Also it can be seen that

the points at the upstream are in compression. While as shown in figure 5.28

and 5.29 for three dimension analysis that both points were in tension state

and have more stress compared with two dimension results.

Figure 5.30 shows a comparison in the axial stress (z-direction) between

two and three dimension structural analysis at 1.5m from base of dam at a

point near the upstream surface (2m from upstream). It can be seen from this

figure that the stresses which were obtained by three dimensional analysis

were higher than the stresses which were obtained by two dimensional

analysis, this is due to the assumption of a plain strain in two dimensional

analysis, which gives a zero value for strains perpendicular to the plane of the

analysis (εz=0.0). So using the two dimension structural model produces an

underestimate for axial stress developed in the dam body.

87

-0.50

-0.30

-0.10

0.10

0.30

0.50

0.70

0.90

1.10

1.30

1.50

0 50 100 150 200 250 300 350

Time (Day)

Prin

cipa

l Stre

ss (

S1

) MPa

10 m from upstream face(Gallary Face)At Upstream

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 50 100 150 200 250 300 350

Time (Day)

Cro

ss v

alle

y St

ress

MPa

10 m from upstream face(Gallary Face)at Upstream

Fig 5.26 Principal Stresses History at Different Nodal Points at 9m from the Dam Base Using 2D Analysis

Fig 5.27 Cross Valley Stresses ( z-direction ) History at Different Nodal Points at 9m from

the Dam Base Using 2D Analysis

88

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 100 200 300 400

Time (Day)

Prin

cipa

l Stre

ss (

S1

) MPa

10 m from upstream face(Gallary Face)At Upstream

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 100 200 300 400 500

Time (Day)

Cro

ss v

alle

y St

ress

MPa

10 m from upstream face(Gallary Face)at Upstream

Fig 5.28 Principal Stresses History at Different Nodal Points at 6m from the Dam Base Using 3D Analysis

Fig 5.29 Cross Valley Stresses ( z-direction ) History at Different Nodal Points at 6m from the Dam Base Using 3D Analysis

89

-1.00

-0.90

-0.80

-0.70

-0.60

-0.50

-0.40

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0 50 100 150 200 250 300

Time (Day)

Cro

ss v

alle

y S

tress

(M

Pa)

3D Analysis

2D Analysis

Fig 5.30 Comparison Cross Valley Stresses ( z-direction ) History for 2D & 3D Analysis

at 1.5 m from base of dam and 2.5 m from upstream

Figure 5.31 shows the stress distribution (in z-direction) along the dam

cross section at an elevation of 9m from the base (top gallery surface) at

different period. It can be seen that the stresses inside the dam body are in

compression while the tensile stresses located at the outer surface and around

the gallery where the heat decreased rapidly and so the temperature gradient

increase. In the other hand, it can be seen that all the stresses along this

section tend to move to a compression state except the stresses on the gallery

surface, they were moved towered tension state, because the temperature

gradient in this location increasing with time. Figure 5.32 shows a

comparison principal stress across the same previous section using two and

three dimension analysis. It is clear that for the first 15m where the RCC

90

1.50

2.00

-1.00

-0.50

0.00

0.50

1.00

0 10 20 30 40 50 60 70 80 90 100

Distance (m)

Prin

cipa

l stre

ss (

S1

) MP

a

50 DayEnd of Heat of Hydration

-1.00

-0.50

0.00

0.50

1.00

1.50

2.00

0 10 20 30 40 50 60 70 80 90 100

Distance (m)

Prin

cipa

l stre

ss (

S1

)

2D Analysis3D Analysis

MP

a

exposed highly to the air; the stresses obtained from 2D was the highest,

while after that distance the principal stresses obtained from 3D analysis is

the highest.

Fig 5.31 Principal stresses across dam section at different time period (9 m from the dam

base) Using 2D Analysis

Fig 5.32 Comparison Principal stresses across dam section using 2D and 3D (9 m from the

dam base)

91

Figure 5.33 and 5.34 represent a comparison between the principal

stresses (σ1) and the cross valley stresses (σz) for a vertical section at the

center of the dam at different period of the dam construction using 2D and

3D analysis. It is cleared that most of the cross valley stresses is compression

stress which will not cause problems. After long time (410 days) the

temperature of RCC inside the dam body decreased which lead the tensile

stress to increase and the compression stress to decrease. The tensile stresses

at the top surface of the dam body are due to exposing the outer surface to the

ambient condition. Also, the zero stress temperature was developed near the

foundation at the end of construction of the dam, due to the difference in

stiffness between the foundation and the young RCC and the heat transfer

between the RCC face and the foundation. The maximum tensile stress is

reached 1.5 MPa at the end of construction and reduces to 0.6 MPa at the end

of heat of hydration due to the decreasing of temperature. The tensile stresses

obtained from 3D analysis are occupying more areas than that for 2D

analysis.

92

0

10

20

30

40

50

60

70

80

90

100

-2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00

Stress MPa

Elev

atio

n (m

)

S1 End of ConstructionS1 End of Heat of HydrationSZ at End of ConstructionSZ End of Heat of Hydration

0

10

20

30

40

50

60

70

80

90

100

-0.50 0.00 0.50 1.00 1.50 2.00

Stress MPa

Ele

vatio

n (m

)

S1 End of ConstructionS1 End of Heat of HydrationSZ at End of ConstructionSZ End of Heat of Hydration

Fig 5.33 Principal and Cross Valley Stresses Distribution at Vertical Section at the Dam Centre Using 2D Analysis

Fig 5.34 Principal and Cross Valley Stresses Distribution at Vertical Section at the Dam Centre Using 2D Analysis

93

-1

-0.9

-0.8

-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 50 100 150 200 250 300

Time (Day)

Cro

ss v

alle

y S

tress

(M

Pa)

15

20

25

30

35

40

45

Tem

pera

ture

(Deg

C)

StressTemperature

A comparison between temperature and cross valley stress distribution at

1.5m from the dam base and 2.5m from upstream surface is shown in Figures

5.35 and 5.36 for 2D and 3D analysis. It can be seen from these figures that

the stress (z-direction) adversely proportional with the temperature; stress

curve will rise up (decrease compression and increase tensile stresses) with

decreasing the temperature and vice versa. This behavior occurred because as

temperature of RCC increases due to heat generation, expansion in concrete

develops, but due to restraints on movement of RCC layers the expansion

leads to compression stresses in the concrete. And when temperature

decreases, this expansion will transform to contraction that leads to

decreasing the compression stresses and increasing tensile stresses.

Fig 5.35 Comparison between temperature and stresses in z-direction at 1.5 m from base

of dam and 2.5 m from upstream Using 2D Analysis

94

-0.50

-0.40

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0 50 100 150 200 250 300 350 400

Time (Day)

Cro

ss v

alle

y S

tress

(MP

a)

15

20

25

30

35

40

45

Tem

pera

ture

(Deg

C)

StressTemperature

Fig 5.36 Comparison between temperature and stresses in z-direction at 1.5 m from base of dam and 2.5 m from upstream using 3D Analysis

5.4 Cracking Analysis

5.4.1 Introduction

Thermal expansion of the outer face and temperature increase of the

interior concrete due to cement hydration are two mechanisms that cause the

cracks at the face of concrete dams as result of their combination. The surface

of the dam cools faster than the interior body. This causes a temperature

gradient between the cooled surface and the hot interior mass. Such a

difference will result in a thermal gradient that is likely to generate

undesirable thermal stresses which may cause cracks at the exterior surface.

This is not expected to be a structural problem unless the cracks extend

through to the drainage gallery, where the leakage of water may increase.

95

5.4.2 Transverse Contraction Joints.

Joints are required in most RCC dams. The potential for cracking may

be slightly lower in RCC because of the reduction in mixing water and

reduced temperature rise resulting from the rapid placement rate and lower

lift heights. In addition, the RCC characteristic of point-to-point aggregate

contact decreases the volume shrinkage. Thermal cracking may, however,

create a leakage path to the downstream face that is aesthetically undesirable.

Thermal studies should be performed to assess the need for contraction joints.

Contraction joints may also be required to control cracking if the site

configuration and foundation conditions may potentially restrain the dam. If

properly designed and installed, contraction joints will not interfere or

complicate the continuous placement operation of RCC.

5.4.3 Construction Joint Spacing Assessment

In order to assess the number of contraction joint, a crack analysis

should be performed in order to determine the predicted crack width and

consequently the number of required joints. Herein, a simplified method is

used to predict the crack with and number of contraction joints. The mass

gradient strain usually is determined by the following equation:

Induced strain= (Cth) (∆T) (KR) (Kf) 5.1

Where Cth= Coefficient of thermal expansion,

96

∆T= temperature difference, i.e., difference between the peak

temperature and the average annual ambient temperature.

KR= structure restraint factor, and

Kf= foundation restraint factor.

The coefficient KR is to be equal to 1.0 for conservative assumption and

maximum strain at the foundation base (Tatro and Schrader, 1992). The

coefficient Kf is determined form the following formula

ff

cgf

EAEAK

+=

1

1 =0.55

Where

Ag=gross area of concrete cross section at foundation plane

Af=area of foundation or zone restraining contraction of concrete,

Af= 2.5 Ag

Ef=modulus of elasticity of foundation or restraining element and it is taken

5.9 GPa

Ec= modulus of elasticity of mass concrete and it is taken 10 GPa.

The coefficient of thermal expansion (Cth) is strongly influenced by the

type of aggregate in the RCC mix, for Al Wehdah dam the aggregate is

basalt. A typical value for the coefficient of thermal expansion for the RCC

mass for Al Wehdah dam is taken as 8.6 E-6/ deg C. Table 5.3 summaries

the cracking analysis for Al Wehdah dam. As shown in this table, the number

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of blocks depends on the placement temperature as well as the assumed width

of cracks that assumed to be 2mm. theses calculations made assuming that

the tensile capacity is 60 µmm, and the minimum ambient temperature (12.3

oC) was used to calculate the temperature differences.

Experience show that some superficial cracks with depth of 5~20cm

may appear on the upstream face of concrete dam during construction. Some

of these superficial cracks may develop suddenly into large cracks at some

time after completing of dam. The extending of superficial crack into large

crack may be illustrated by the mechanics of fracture (Zhu, et al. 1999).

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Table 5.3 Crack Analysis in Al Wehda Dam for Different RCC Mix and Placement Temperatures.

South Africa Flyash 2D Analysis 3D Analysis

Placement temperature oC 20 24 28 20 24 28 Peak Temperature oC 41.15 45.33 47.8 42.59 45.25 47.9 ∆T oC 28.85 32.03 35.5 30.29 32.95 35.6 Induce strain (µmm) 136.46 151.50 167.92 143.27 155.85 168.39 Exceed strain (µmm) 76.46 91.50 107.92 83.27 95.85 108.39 Total Crack Width (mm) 37.08 45.38 52.34 40.39 46.49 52.57 No. of block 18 22 26 20 23 26 Length of block (m) 27 22 19 24 21 19

Turkey Flyash 2D Analysis 3D Analysis

Placement temperature oC 20 24 28 20 24 28 Peak Temperature oC 39.67 43.12 46.3 40.58 43.7 46.4 ∆T oC 27.37 30.82 34 28.28 31.4 35.1 Induce strain (µmm) 2 129.46 145.78 160.82 133.76 148.52 161.29 Exceed strain (µmm) 69.46 85.78 100.82 73.76 88.52 101.29 Total Crack Width (mm) 33.69 41.60 48.90 35.78 42.93 49.13 No. of block 16 20 24 17 21 24 Length of block (m) 30 24 20 29 23 20

Jordanian Pozzolan 2D Analysis 3D Analysis

Placement temperature oC 20 24 28 32 20 24 28 32 Peak Temperature oC 38.5 41.93 45.1 48.2 39.37 42.47 45.1 47.8 ∆T oC 26.2 29.63 32.8 35.9 27.07 30.17 32.8 35.5 Induce strain (µmm) 2 123.93 140.15 155.14 169.81 128.04 142.70 155.14 167.92Exceed strain (µmm) 63.93 80.15 95.14 109.81 68.04 82.70 95.14 107.92Total Crack Width (mm) 31.00 38.87 46.14 53.26 33.00 40.11 46.14 52.34 No. of block 15 19 23 26 16 20 23 26 Length of block (m) 32 26 21 19 30 24 21 19

Rock Flour 2D Analysis 3D Analysis

Placement temperature oC 20 24 28 32 20 24 28 32 Peak Temperature oC 37.59 41 45.2 47.3 38.4 41.5 45.2 46.84 ∆T oC 25.29 28.7 31.9 35 26.1 29.2 31.9 35.54 Induce strain (µmm) 2 119.62 135.75 150.89 165.55 123.45 138.12 150.89 163.37Exceed strain (µmm) 59.62 75.75 90.89 105.55 63.45 78.12 90.89 103.37Total Crack Width (mm) 28.92 36.74 45.08 51.19 30.77 37.89 45.08 50.14 No. of block 14 18 22 25 15 18 22 25 Length of block (m) 35 27 22 19 32 27 22 19

99

CHAPTER SIX

CONCLUSIONS AND RECOMMENDATIONS

6.1 Conclusions

The following conclusions may be drawn;

1. Thermal analysis is one of the most important analysis that should be

done for the RCC dam to provide the engineer with a means of predicting

excessive tensile stresses and strains, which could indicate possible cracking,

therefore, allowing the designer to take appropriate measures to limit or

control such potential cracks

2. The Al Wehdah RCC dam is to be constructed with a crest length of

485 m and 12 contraction joints at approximately 20 m spacing if Jordanian

Pozzolan is to be used to form the RCC mix.

3. Finite element models is becoming an increasingly powerful tool for

civil engineers to more accurately predict behavior of unprecedented

structures for which limited experience is available, such as RCC dams.

4. Using a commercially available finite element program such as

ANSYS and COSMOS and the available laboratory data, the incremental

100

construction process of mass-concrete structure can be modeled to produce

results that can be used in practical applications

5. The thermal results that obtained from ANSYS are more conservative

than the COSMOS results, the maximum temperature which were obtained

by ANSYS are higher than the temperature that were obtained by COSMOS

by one degree.

6. The thermal results for both 2D and 3D analysis are very close to each

other. So there is no need to do the 3D finite element analysis to estimate the

temperature distribution in the dam body.

7. The RCC mix which affects the heat of hydration, and the placement

temperature have the highest effect on the maximum temperature that will

develop in the dam body

8. The use of rock flour RCC mix allows us to use a higher placement

temperature than the use of Jordanian pozzolan or Turkey flyash or South

Africa flyash RCC mixes.

9. The temperature in the interior of a RCC gravity dam drops very

slowly, cracks may appear on the upstream and downstream face especially

in the winter, thus some measures must be taken to prevent these cracks. The

most effective measure is to insulate the concrete surface.

10. At the early age, RCC properties have significant effect on peak

stresses developed in RCC dam body.

101

11. In the contrary of thermal analysis, there are differences in stress

results between 2D and 3D structural analysis, the two dimensional structural

analysis overestimates the stresses.

6.2 Recommendations

The mathematical models should be closed to reality as possible as it

can be, for instant, The model should divides the RCC dam in to 320 layers,

each layer was 30 cm high and constructed within 1 day according to the

construction schedule instead of 32 layer in our model. The daily ambient

temperature should also be modeled instead of the average annual

temperature. Using the actual placement schedule and actual boundary

conditions in finite element analysis, certainly will lead to accurately

determine the actual maximum temperature anticipated in dam body. Also,

using the non-linear model for modulus of elasticity produces better estimate

for stresses develop in dam body.

Effort is recommended to improve the thermal analysis of RCC dam,

so that, the time and cost of the projects can be reduced.

102

References

American Concrete Institute (ACI). (1978). "Prediction of creep, shrinkage and temperature effects in concrete structure." ACI #209-78,2nd Draft, Detroit Andriolo, Francisco, (2002) "RCC- Materials Availability-Properties and Practices in Differnet Regions". Anonymous, (2002) “ANSYS User’s manual for revisions 5.4 and 7.0”. Swanson Analysis System Inc., Houston, PA, (1997, 2002). Ayotte E., Massicotte, B., Houde, J. and Gocevski V.(1997) “Modeling the Thermal Stresses at Early Ages in A Concrete Monolith,” ACI Material Journal, Vol. 94, No. 6, pp. 577-587. Crichton A.J., Benzenati, I., Qiu, T.J. and Williams, J.T. (1999) “Kinta RCC Dam- Are Over-Simplified Thermal-Structure Analysis Valid,” ANCOLD Conference on Dams, Australia, November. Forbes B. A. and Williams, J. T.(1998) “Thermal Stress Modeling, High Sand RCC Mixes and In-situ Modification of RCC Used for Construction of Candiangullong Dam NSW,” ANCOLD Bulletin, Sydney. Ishikawa M. (1991),“Thermal Stress Analysis of Concrete Dam,” Computers & Structures, Vol. 40, No. 2, pp. 347-352. Luna R. and Wu Y.(2000) "Simulation of Temperature and Stress Field During RCC Dam Construction," Journal of Construction Engineering and Management, September/October. Malkawi A.I.H., Mutasher S.A., and Qiu T.J.(2002) "Thermal-Structural Modeling and Temperature Control of RCC Gravity Dam,", Journal of Performance of Constructed Facilities, ASCE, Vol.17 , No.4, November. Malkawi A.I.H., Shaia H.A., and Mutasher S.A (2003)"A comparative study of mechanical properties of RCC trial mix using two different cementitious materials (fly ash and natural pozzolan)" Proceeding of the fourth international symposium on Roller Compacted Concrete (RCC) Dam, 17-19 November, Madrid, SPAIN.

103

Marulanda A.,Castro A., and Rubiano N. (2002) "RCC Quality Control for MIEI I Dam" Proceeding of International Conference on RCC Dam Construction in Middle East 7th-10th April 2002, Irbid, Jordan Nollet, M.J. (1994) " General Aspect of Design and Thermal Analysis of RCC Lac Robertson DAM". Schindler, A.K., (2003) “Effect of Temperature on the Hydration of Cementitious Materials,” ACI .Materials Journal, accepted for publication. Structural Research and Analysis Corporation (1997) “COSMOS/M CAD Interface User Guide version 2.0” December 1997 Truman K. Z., Petruska, D., Abdelkader F. and Barry F.(1991) “Nonlinear, Incremental Analysis of Mass-Concrete Lock Monolith,” Journal of Structural Engineering, Vol. 117, No. 6, June, pp. 1834-1851. U. S. Army Corps of Engineers "Engineering and Design GRAVITY DAM DESIGN," Engineering Manual (EM) 1110-2-2200, Washington, DC 20314-1000,1995 Zhu B., PingXu and Wang S.(1999) “Thermal Stresses and Temperature Control of RCC Gravity Dams,” CHINA * RCC'99. Zhu B., PingXu. ,(1999) “Thermal Stresses in Roller Compacted Concrete Gravity Dams,” Dam Engineering Vol VI Issue 3.

104

APPENDIX A

NUMERICAL EQUATIONS

105

108

108

لسدود الخرسانية المدحولة والاجهادات الحرارية في اإيجاد التوزيع الحراري للعناصر الحديّة مختلفين بإستخدام برنامجين

)دراسة مقارنة (

ايهاب سالم شطناوي: إعداد عبداالله ملكاوي. د.أ: إشراف

:ملخص

دة في الاردن ذو في هذه الرسالة تم انجاز التحليلين الانشائي و الحراري لسد الوح

ة )ANSYS + COSMOS (الخرسانة المدحولة ، باستخدام برنامجين للعناصر الحديّ

ى مجموعة من اثير الحراري عل م الت اد من اجل فه ة الابع ة و ثلاثي لكلتا الطريقتين ثنائي

ى تعناصر السد و مكوناته، و آذلك ل قييم تأثير تميه حرارة الخرسانة و ظروف صبها عل

.رارة و الاجهادات في جسم السدتوزيع الح

انة شاء صب الخرس ال ان ة و جدول اعم الخصائص الحرارية و الظروف المناخي

سابقة ال ال ا من الاعم م فرضها او حصل عليه ذه الدراسة ، ت ا في ه م .التي تم اعتباره ت

ة من عدة مضيفات اد (استخدام خلطات خرسانية مختلفة مكون ي، رم اد جنوب افريق رم

ى تصميم ) ولان اردني، و طحين صخور ترآي، بوز ه الحراري عل أثير التمي ، لدراسة ت

.فواصل الانكماش

ودج ل نم ن تحلي سوبة م رارة المح ائج الح أن نت ة ب رت الدراس (ANSYS)اظه

ك المحسوبة من نموذج ر حذرا من تل ى و اآث ، وان استخدام (COSMOS)آانت اعل

درجات حرارة طحين الصخور آمضيف لخلطات الخرسانة يسمح ل انة ب ا بصب الخرس ن

تم الحصول اعلى من استخدام رماد جنوب افريقيا او رماد ترآي اوالبوزولان الاردني ،

سد ي ال ادات ف رارة و الاجه ع الح ن توزي صيلية ع ات تف ى معلوم .عل

112

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