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WIND-RESISTANCE OF COMPOSITE STRUCTURAL INSULATED PANELS

(CSIPS)

by

LI DONG

NASIM UDDIN, COMMITTEE CHAIR JASON T. KIRBY TALAT SALAMA

A THESIS

Submitted to the graduate faculty of The University of Alabama at Birmingham, In partial fulfillment of the requirements for the degree of

Master of Science in Civil Engineering

BIRMINGHAM, ALABAMA

2012

Copyright by Li Dong

2012

iii

WIND-RESISTANCE OF COMPOSITE STRUCTURAL INSULATED PANELS (CSIPS)

LI DONG

DEGREE: MS PROGRAM: CIVIL ENGINEERING

ABSTRACT

Extreme windstorms are frequent and destructive natural hazards in the United

States. Each wind disaster proves that traditional wood houses are too fragile to withstand

high air pressures. The proposed Composite Structural Insulated Panels (CSIPs) are made

of a low-cost, thermoplastic orthotropic glass/poly-propylene (glass-PP) laminate as the

face sheet and expanded polystyrene (EPS) foam as the core, with a high face sheet/core

moduli ratio.

In order to evaluate the wind-resistance of CSIPs, panels with cores of 16 kg/m3

(1 PCF) and 48 kg/m3 (3 PCF) density were tested at the University of Florida. Stepwise

and dynamic simulated wind pressure was generated by the High Airflow Pressure

Loading Actuator. The connections of the CSIPs were 2”×6” lumbers as used in

traditional constructions. Top and bottom lumbers were fixed to steel plates with bolts. In

stepwise windstorm tests, step-by-step pressure was applied to CSIPs; the highest

pressure was equivalent to a wind speed of 124.44 m/s (280 mph). The CSIPs wall

system demonstrated superior capacity except local debonding between the face sheet

and core; there were connection failures at lumbers in all but one sample. In dynamic

windstorm tests, cyclic pressure was used to simulate actual exposure. Only one sample

failed at the lumber connection, and there were minor cracks in the lumber connections

and local debondings in three of the eight samples. The intact condition of all face sheets

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and cores after tests indicate the excellent wind-resistance of CSIPs for structural wall

applications.

Corresponding finite element modeling was developed and initially validated, in a

dynamic windstorm test, within the first second for the 1 PCF core density CSIP. The

modeling was further investigated with longer durations of exposure. The results were

compared, and modifications were projected for future modeling to improve the

precision.

Keywords: Wind resistance, Sandwich composite panel, Wind velocity, Stepwise

windstorm test, Dynamic windstorm test, Probability, Finite element modeling.

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DEDICATION

This thesis is dedicated to all my family members and my sincere friends.

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ACKNOWLEDGMENTS

First, thanks go to my advisor, the project Principal Investigator (PI) and

committee chair, Dr. Nasim Uddin, for all of his time and advice towards my graduate

study. Second, I appreciate the time input and guidance from my committee members,

Dr. Jason T. Kirby and Dr. Talat Salama. Further, I would like to acknowledge the

National Science Foundation for funding this project (NSF Grant #: CMMI-0825938).

Gratitude also goes to the project Co-PI, Dr. Forrest J. Masters, and his graduate

student, George Fernandez, from the University of Florida, who led and performed the

stepwise and dynamic wind storm tests described in the thesis.

To Xiaoxiao Song and all my sincere friends whose names have not been

mentioned here, your help and support are acknowledged as well.

Last and most importantly, I would like to thank my family for their continuous

and unconditional love and support, without which I could not have succeeded.

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TABLE OF CONTENTS

Page

ABSTRACT ……………………………………………………………………………..iii

DEDICATION…………………………………………………………………………....v

ACKNOWLEDGMENTS...……………………………………………………………vi

LIST OF TABLES……………………………………………………………………...x

LIST OF FIGURES……………………………………………………………………xii

CHAPTER

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

1.1 Background ......................................................................................................... 1 1.2 Literature Review................................................................................................ 2

1.2.1 Traditional Wood House ................................................................................. 2 1.2.2 Panelized Construction with Structural Insulated Panel (SIP) ....................... 2 1.2.3 Composite Structural Insulated Panel (CSIP) ................................................. 3

1.3 Research Objectives & Outline ........................................................................... 8

2 EXPERIMENT CONFIGURATION .............................................................................. 9

2.1 Test Panels .......................................................................................................... 9 2.2 The testing apparatus: High Airflow Pressure Loading Actuator (HAPLA) .... 10 2.3 Boundary Conditions ........................................................................................ 14 2.4 Instrumentation Setup ....................................................................................... 17

3 STEPWISE WINDSTORM TEST ................................................................................ 20

3.1 Target Load ....................................................................................................... 20 3.2 Panel S-0511-1 .................................................................................................. 22

viii

TABLE OF CONTENTS (Continued)

Page 3.3 Panel S-0506-3 .................................................................................................. 27 3.4 Panel S-0511-3 .................................................................................................. 32 3.5 Panel S-0512-3 .................................................................................................. 37 3.6 Panel S-0513-3 .................................................................................................. 42 3.7 Results ............................................................................................................... 46 3.8 Discussion ......................................................................................................... 47 3.9 Summary ........................................................................................................... 48

4 DYNAMIC WINDSTORM TEST ................................................................................ 50

4.1 Target Load ....................................................................................................... 50 4.2 Validation for Exposure Time of Fatigue Load ................................................ 52 4.3 Panel D-0926-1 ................................................................................................. 54 4.4 Panel D-1003-1 ................................................................................................. 59 4.5 Panel D-0912-3 ................................................................................................. 64 4.6 Panel D-0921-3 ................................................................................................. 68 4.7 Panel D-1025-3 ................................................................................................. 72 4.8 Panel D-1101-3 ................................................................................................. 77 4.9 Panel D-1102-3 ................................................................................................. 81 4.10 Panel D-1103-3 ................................................................................................. 86 4.11 Results ............................................................................................................... 90 4.12 Discussion ......................................................................................................... 93 4.13 Summary ........................................................................................................... 94

5 AS-BUILT CONDITIONS ............................................................................................ 96

6 FINITE ELEMENT MODELING ................................................................................. 98

6.1 Initial Modeling Validation ............................................................................... 98 6.1.1 Simulation Details ......................................................................................... 98

6.2 Further FE modeling and Experimental Results ............................................. 107 6.2.1 Stepwise Windstorm Test ........................................................................... 108 6.2.2 Dynamic Windstorm Test ........................................................................... 110

6.3 Summary ......................................................................................................... 114

7 SUMMARY AND CONCLUSION ............................................................................ 115

7.1 Summary ......................................................................................................... 115 7.2 Conclusion ...................................................................................................... 117

ix

TABLE OF CONTENTS (Continued)

Page

LIST OF REFRENCES ………………………………………………………………119

x

LIST OF TABLES

Table Page

Table 1 Mechanical properties of the face sheet ................................................................. 4

Table 2 Mechanical properties of the core .......................................................................... 4

Table 3 Test samples ........................................................................................................... 9

Table 4 Pressure to velocity conversion ........................................................................... 21

Table 5 S-0511-1 pressure to wind velocity conversion ................................................... 23





Table 10 Failure details of stepwise windstorm test ......................................................... 46

Table 11 Pressure to velocity conversion ......................................................................... 51

Table 12 Rayleigh probability of exposure at or above given wind speed ....................... 54

Table 13 D-0926-1 pressure to velocity conversion ......................................................... 55

Table 14 D-0926-1 exposure at or above given wind speed ............................................. 55




xi

LIST OF TABLES (Continued)

Page Table 18 D-0912-3 exposure at or above given wind speed ............................................. 65











Table 29 Failure details of dynamic windstorm test ......................................................... 91

Table 30 Material properties of face sheet ........................................................................ 99

Table 31 Material properties of core ................................................................................. 99

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LIST OF FIGURES

Figure Page

Figure 1 Panoramic view of CSIP sample ........................................................................ 10

Figure 2 High airflow pressure loading actuator [35] ....................................................... 12

Figure 3 Front view of HAPLA ........................................................................................ 13

Figure 4 HAPLA with sample ready ................................................................................ 13

Figure 5 Pressure Transducer ............................................................................................ 14

Figure 6 Panel installation ................................................................................................ 15

Figure 7 Connection detail sketch..................................................................................... 15

Figure 8 Disbonding ......................................................................................................... 15

Figure 9 Connection details .............................................................................................. 16

Figure 10 Connection details side view ............................................................................ 16

Figure 11 Fastener details ................................................................................................. 17

Figure 12 Strain gauges deployment ................................................................................. 18

Figure 13 Instruments setup .............................................................................................. 19

Figure 14 Pressure history of stepwise windstorm test ..................................................... 20

Figure 15 S-0511-1 pressure history ................................................................................. 23

Figure 16 S-0511-1 deflection plot ................................................................................... 24

Figure 17 S-0511-1 curvature ........................................................................................... 25

xiii

LIST OF FIGURES (Continued)

Page Figure 18 S-0511-1 top connection................................................................................... 26

Figure 19 S-0511-1 bottom connection ............................................................................ 26

Figure 20 S-0511-1 debonding sketch .............................................................................. 27

Figure 21 S-0511-1 strain plot .......................................................................................... 27




Figure 25 S-0506-3 top connection................................................................................... 31







Figure 32 S-0511-3 top connection................................................................................... 36







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Page Figure 39 S-0512-3 top connection................................................................................... 41








Figure 47 Deflection plots of stepwise windstorm test ..................................................... 47

Figure 48 Pressure history of dynamic windstorm test ..................................................... 51

Figure 49 Model estimated 500-year return period 3 sec gust wind speeds at a height of

10 m in open terrain including wind modeling uncertainty [39] ...................................... 53

Figure 50 D-0926-1 pressure history ................................................................................ 56

Figure 51 D-0926-1 100 second excerpt ........................................................................... 56

Figure 52 D-0926-1deflection plot ................................................................................... 57

Figure 53 D-0926-1 curvature .......................................................................................... 58

Figure 54 D-0926-1 debonding sketch ............................................................................. 59



Figure 57 D-1003-1deflection plot ................................................................................... 62

Figure 58 D-1003-1curvature ........................................................................................... 63

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Page Figure 59 D-1003-1 debonding sketch ............................................................................. 64



Figure 62 D-0912-3 deflection plot .................................................................................. 66












Figure 74 D-1025-3 bottom connection ............................................................................ 76






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Page Figure 80 D-1101-3 debonding sketch ............................................................................. 81





Figure 85 D-1102-3 top connection .................................................................................. 85

Figure 86 D-1102-3 bottom connection ............................................................................ 85







Figure 93 Deflection plots of dynamic windstorm test ..................................................... 92

Figure 94 Corner disbonding ............................................................................................ 96

Figure 95 Simpson strong tie ............................................................................................ 97

Figure 96 Connection dimensions .................................................................................... 99

Figure 97 Panel dimensions ............................................................................................ 100

Figure 98 Load history: Pressure - Time ........................................................................ 101

Figure 99 Geometry ........................................................................................................ 101

Figure 100 Deflection - Time curves for different materials .......................................... 102

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Page Figure 101 Deflection – Time curve of explicit and implicit methods ........................... 104

Figure 102 Deflection – Time curve of different element numbers ............................... 105

Figure 103 Comparison between experiment and FE modeling ..................................... 106

Figure 104 Deflection contour ........................................................................................ 107

Figure 105 Deflection comparisons of 1 PCF core density CSIPs in stepwise windstorm

test ................................................................................................................................... 108


test ................................................................................................................................... 109

Figure 107 Deflection comparisons of 1 PCF core density CSIPs in dynamic windstorm

test ................................................................................................................................... 112

Figure 108 Deflection comparisons of 3 PCF core density CSIPs in dynamic windstorm

test ................................................................................................................................... 113

1

CHAPTER 1

INTRODUCTION

1.1 Background

In the United States (U.S.) from 1991 to 2010, the insured losses caused by w

indstorms such as hurricanes and tornadoes amounted for $258.6 billion (2010 dollars),

which accounts for 74% of all catastrophic losses, including those caused by winter

storms, terrorism, geologic events, wind, hail, flood, fires, etc. Eight of the ten most

costly catastrophes were hurricanes; the other two were the terrorist attacks on the World

Trade Center and the Pentagon and the California Northridge earthquake, which ranked

second and fourth, respectively. The top disaster, Hurricane Katrina in 2005, caused $41

billion in overall losses and 1320 fatalities [1]. Although windstorm shelters are

considered the safest structures in windstorm prone areas, such shelters may not be

available and there may be limited time to evacuate, preventing people from being secure

during windstorms. Since people tend to stay in houses during hazardous conditions,

building damage is closely associated with fatalities. Although the population along

coastal areas continues to increase, the residential structures in these areas are generally

not prepared for hurricanes [2]. From 2000 to 2011, tornadoes caused 1155 fatalities,

among which 37% of the people were killed in permanent houses [3]. This information

indicates that traditional wooden residential houses are not capable of resisting strong

2

windstorms. According to in-field investigations, building envelope failures are the most

common windstorm damages [4-7].

1.2 Literature Review

1.2.1 Traditional Wood House

Due to their low initial cost, relatively fast construction, and durability with

regular maintenance, most homes in the U.S. are traditional wood houses. However,

wood, a widely used material, has weaknesses. As an organic material, wood attracts

termites and can accumulate mold buildup in environments of high humidity.

Furthermore, wood can lose strength after it is immersed in water, which is common

during floods. The deficient performance of wood during windstorms makes it less

desirable as a construction material. In tornadoes, 37% of fatalities are for people in their

own houses. Investigations after hurricanes and tornadoes show that, in windstorms,

wooden structures have poor resistance to aerial debris and to high air pressure.

1.2.2 Panelized Construction with Structural Insulated Panel (SIP)

Residential home building is an essential component of the U.S. economic

system. Stick-built homes were formerly popular in traditional building. As advances

have been made in modular manufacturing, however, panelized construction has been

introduced. Factory-built modules are assembled onsite, which decreases the construction

time and the total cost. Structural Insulated Panel (SIP) is commonly used in such

construction. A typical example of SIP is the sandwich structure with an oriented strand

board (OSB) face sheet and a foam core, made of expanded polystyrene (EPS), extruded

polystyrene (XPS), or urethane, which have plasticity and low cost and provide insulation

for sound and temperature. Although extensive research has been accomplished on the

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structural behavior of SIP [8], there has not been an analytical model accurate enough

and convenient enough to apply in its design [9]. Further, the OSB face sheet retains

problems similar to those found for traditional wood houses, such as low wind resistance,

termite attack, mold buildup, and loss of strength after exposure to water.

1.2.3 Composite Structural Insulated Panel (CSIP)

Extensive research on CSIP has been conducted at the University of Alabama at

Birmingham. As investigations progressed, the focus of research shifted from “hard” core

sandwich panels [10-14] to “soft” core sandwich panels [9, 15-16]. The CSIP discussed

in this report is limited to the sandwich panel made of a thermoplastic E-glass fiber and

polypropylene (glass-PP) laminate face sheet and an expanded polystyrene foam core.

The characteristics of a high strength to weight ratio, low cost, and fewer required in-field

techniques make CSIP an ideal material for residential buildings.

1.2.3.1 Materials

Produced by the hot-melt impregnation process named DRIFT [17], the face sheet

consists of 60% (by weight) bi-directional E-glass fiber with a polypropylene matrix.

Expanded polystyrene (EPS) foam is used as the core because of its relatively low cost.

For the present research, the face sheet and core materials were ordered from U.S. Liner

[18] and Universal Foam Products [19], respectively, and were bonded by a hot-melt

thermoplastic spray adhesive on a casting and molding facility with quality control. The

mechanical properties of the face sheet and core are listed in Table 1 and Table 2.

4

Table 1 Mechanical properties of the face sheet

Property Value Fiber Reinforcement 60% Bi-Directional E-glass Fibers

Matrix Polypropylene Material Designation Orthotropic Nominal Thickness 3.04 mm (0.12 in)

Tensile Strength 290 MPa (42,061 psi) Tensile Modulus 12,414 MPa (1,800,498 psi) Flexural Strength 276 MPa (40,030 psi) Flexural Modulus 11,035 MPa (1,600,491 psi)

Table 2 Mechanical properties of the core

1.2.3.2 Laboratory Tests on CSIPs

Extensive research has been performed on CSIPs by Vaidya et al. [9] at the

University of Alabama at Birmingham. The results are summarized as follows.

Reduced Scale Flexural Test. The flexural test was conducted according to ASTM C-393

[20]. The traditional SIP with an OSB face sheet and the innovative CSIP with an E-

glass/PP face sheet were compared. SIPs failed by rupture of face sheets and shear

cracking of the core. CSIPs failed only in shear cracking of the core; the face sheets

Property Value

Foam Density 16 kg/m3 (1 pcf) 48 kg/m3 (3 pcf)

Elastic Modulus (Ec) 1.2-1.5 MPa (180-220 psi) 5.4-5.7 MPa (780-820 psi)

Flexural Strength 0.1-0.2 MPa (25-30 psi) 0.55-0.59 MPa (80-85 psi)

Shear Modulus (Gc) 1.9-2.2 MPa (280-320 psi) 5.65-5.93 MPa (820-860 psi)

Shear Strength 0.1-0.15 MPa (18-22 psi) 0.31-0.34 MPa (45-50 psi)

Tensile Strength 0.11-0.14 MPa (16-20 psi) 0.19-0.21 MPa(26-30 psi)

Compressive Strength 0.07-0.1 MPa (10-14 psi) 0.28-0.34 MPa (40-50 psi)

Poisson’s Ratio 0.25 0.25

5

remained intact. The results indicated that CSIPs had a greater strength-to-weight ratio

and more ductility than SIPs [9].

Reduced Scale Low Velocity Impact (LVI) Test. An Instron Model 8250 drop-weight

impact machine was used in the test. 20 J, 50 J, and 68 J of impact energy were evaluated

on SIP and CSIP samples. Under 68 J of impact energy, the top face sheet and the foam

core of SIP were pierced through, but there was only a minor dent on the top face of the

CSIP. Thus, CSIP absorbed more energy; there was only a slight indentation on the

impact surface [9, 21].

Full Scale High Velocity Impact (HVI) Test. A gas gun facility was used to shoot an

aluminum bullet toward a full-scale CSIP. Two impacts were conducted in order to

comply with standards established by the Federal Emergency Management Agency.

Although the front face was damaged severely, the back face was intact, demonstrating

that CSIP is capable of bearing the equivalent impact energy of 66.7 N of a 5.1 cm × 10.2

cm wind missile traveling at a speed of 44.7 m/s [9, 22].

Full Scale Wall Buckling Test. A full-scale wall CSIP was constructed according to

ASTM E-72 05 [23]. The damage modes were linear elastic range, initial delamination

near supports, and delamination between the core and obvious face sheet at failure load.

The concentric and eccentric buckling load and the wrinkling stress of the face sheet were

determined by the formula of Mousa and Uddin [24, 25]. The test proved that CSIP bears

6.25% more than the design load according to the APA design guide and meets the mid-

height deflection criteria in ACI 318-05 [9,16.22].

Full Scale Floor Flexural Test. As per ASTM E-72 05, a four-point load was used in the

test. The design load of CSIP is 0.0024 N/mm2 (50 psf), which is 25% higher than the

6

value in ASCE 7-05 [26]. The typical failure was localized delamination between the face

sheet and the core near the loading point. The test also revealed that the compressive

strains on the top face sheet were higher than the tensile strains at the bottom [9]. The

mid-span deflection, flexural strength, facing stress, and wrinkling stress were validated

[16, 27].

Full Scale Panel Flood Test. Four groups of CSIPs were tested in a flood experiment. Per

ASTM C 393, a flexural test was used to evaluate CSIPs after exposure to water. The

first group of samples were the control group and were tested as they were; the second

group of samples were submerged in water for three days and tested in dry condition; the

third group of samples were submerged in water for seven days and tested in dry

condition; the fourth group of samples were submerged in water for seven days and tested

in wet condition. The results showed that the largest degradation was 16% for panels

submerged in water for seven days and tested wet; there was only a 6% decrease for

panels in water for three days and tested dry. Therefore, the results proved that the

strength of CSIPs does not decrease substantially after exposure to water for several days.

Fire Resistance. CSIPs were evaluated for their flame retardant properties by two

approaches. The first involved use of FRTM Surmat Veil [28] impregnated with TSWBTM

[29] as the face sheet surface coating; the second involved use of a modified matrix

additive, Fyrebloc 400 [30]. Both approaches have passed ASTM E-162 [31] and E-662

[32], and the first approach has passed the recent ASTM E-84 [33] as well [29]. The first

coating material apparently does not affect the properties of CSIPs, but the second

additive increases the bending stiffness of CSIPs and is likely to decrease its impact

resistance [34].

7

1.2.3.3 Finite Element Analysis on CSIPs

In addition to the tests conducted on CSIPs, there was also finite element

modeling performed by ANSYS as described below. No debonding or slipping was

considered in the modeling.

Floor Flexural Modeling. A finite element modeling of CSIP floor was created by

Vaidya [9] using ANSYS 10.0. The E-glass fiber face sheet was modeled with SHELL

99, and the EPS foam core was SOLID 186. The orthotropic face sheet was modeled by

defining local coordinates and assigning different values in different directions; the core

was regarded as isotropic. The model was validated using results of full-scale panel

flexural tests, the results of which were within acceptable variance. After validation, a

uniformly distributed load of 0.0024 N/mm2 (50 psf) was evaluated. Later, Mousa [16]

created similar finite element modeling for CSIP floor with ANSYS 12.0; the mid-span

strains from finite element analysis matched well with experiment values. In this

modeling, SOLID 45 was used for both the face sheet and the core. The span-to-depth

ratio was evaluated in a parametric study to give a design guide.

Wall Buckling Modeling. CSIP wall finite element modeling was created by Mousa [16]

with ANSYS 12.0 and was validated with results from a full-scale wall buckling test.

SOLID 45 was used for both the face sheet and the core. A comparison of mid-height

strains showed agreement between experimental results and modeling.

Windstorm Shelter Modeling. A windstorm shelter made of CSIP was modeled with

ANSYS 11.0 by Nguyen [15]. Unlike previous modeling, a layer stacking approach was

used to model the face sheet. Two layers were displayed bi-directionally to model the

orthotropic material. Element SOLID 191 for the face sheet and SOLID 95 for the core

8

were used. After analysis by Computational Fluid Dynamics, wind pressure was applied

to the shelter. The connection design was also evaluated. This modeling showed that

CSIP is an excellent material to resist extreme wind pressure.

1.3 Research Objectives & Outline

The research objectives of this study were to find the resistance capacity of CSIPs

under simulated stepwise and dynamic wind pressure tests, and to validate the finite

element modeling with the test results. The research outline was as follows.

• Summarize and analyze the stepwise and dynamic windstorm tests by converting

air pressure to wind velocity by ASCE 7-10, using appropriate probability

methods to determine exposure time for various designs.

• Validate the finite element modeling using the first second of the 1 PCF core

density CSIP in a dynamic windstorm test, and use the modeling to investigate

panel behaviors during long durations of stepwise and dynamic windstorm tests.

9

CHAPTER 2

EXPERIMENT CONFIGURATION

2.1 Test Panels

Five CSIPs were tested in a stepwise test and eight in a dynamic windstorm test, as

displayed in Table 3. Due to the limits of the test instrument, only one panel dimension of

145.8mm × 1219.2mm × 2438.4mm (5.74’’ × 4’ × 8’) was investigated. The thickness of

the face sheet was 3.04mm (0.12’’), and that of core was 139.7mm (5.5’’). Core densities

of 16.0 Kg/m3 (1 PCF) and 48.0Kg/m3 (3 PCF) were variables for the samples. Figure 1

shows the CSIP before being installed in the instrument. A hot knife was used to cut

sections of the foam, 50.8 mm (2’’) deep, out on both ends in order to nail in the wood

connection.

Table 3 Test samples

Panel Dimension Test TypeCore

Density Panel Type

Test Date

145.8mm × 1219.2mm × 2438.4mm (5.74” × 4’ × 8’)

Stepwise

16.0 Kg/m3

(1 PCF) S-0511-1 05/11/11

48.0Kg/m3 (3 PCF)

S-0506-3 05/06/11S-0511-3 05/11/11S-0512-3 05/12/11S-0513-3 05/13/11

Dynamic

16.0 Kg/m3 (1 PCF)

D-0926-1 09/26/11D-1003-1 10/03/11

48.0Kg/m3 (3 PCF)

D-0912-3 09/12/11D-0921-3 09/21/11D-1025-3 10/25/11D-1101-3 11/01/11D-1102-3 11/02/11D-1103-3 11/03/11

10

Figure 1 Panoramic view of CSIP sample

2.2 The testing apparatus: High Airflow Pressure Loading Actuator (HAPLA)

HAPLA, developed at the University of Florida, was used to generate simulated air

pressure. As shown in Figure 2, the HAPLA system was comprised of two 75-HP

Centrifugal Backward Inclined Class IV Single Width Single Inlet (SWSI) fans that could

be configured to operate in series or in parallel. Minimal air leakage was achieved by

operating them in series. The ducting and the air valve connected with each other at five

ports: supply (from fan), return (to fan), exhaust (open atmosphere), intake (open

atmosphere), and service (connecting to the test chamber). The amount of air traveling

from the test chamber to the exhaust (intake) port was modulated by the air valve. The air

leakage through the specimen was equivalent to the difference between the exhaust rate

and intake rate. The air valve was connected to a rotary actuation system, which consists

11

of a Metronix ARS2340 servo-positioning controller, a Sumimoto Drive Technologies

CHF 6135 Y-11 11:1 drive reduction, and a Metronix SBL-T6-2900 brushless servo

motor. A two-pole resolver in the motor provided positioning feedback. The pressure in

the chamber was controlled by a customized Labview 8.5 on a National Instruments PXI

system through a 100 Hz PID controller that received feedback from a pressure

transducer attached to the “airbox.” The test chamber was a stiff 2.4 m × 2.4 m × 0.3 m (8

ft x× 8 ft × 1 ft) hollow steel frame box lined with 14-gauge galvanized sheet steel on

five sides. The test specimen was placed on the sixth side, as shown in Figure 3 and

Figure 4. The CSIP was vertically installed, and the air inside the chamber was increased

slowly, creating horizontally distributed air pressure on the panel. A transparent plastic

membrane covering the sixth side of the airbox and a red rubber pipe along the edge of

the box were used to seal the chamber to prevent leaking. As indicated in Figure 5, the air

pressure in the chamber was measured through the small hole by use of a thin pipe

connecting to the data acquisition and control system [35].

12

Figure 2 High airflow pressure loading actuator [35]

Note: From “Water penetration resistance of residential window and wall systems subjected to steady and unsteady wind loading” by Lopez C., Masters, F. J., Bolton S., 2011, Building and Environment,46, p. 1333. Copyright 2011 by Elsevier Ltd. Reprinted with permission.

13

Figure 3 Front view of HAPLA

Figure 4 HAPLA with sample ready

14

Figure 5 Pressure Transducer

2.3 Boundary Conditions

Due to the limits of the HAPLA testing system, both the top and bottom

connections used the same assembly. Figure 6 and Figure 7 show the joint configuration

in detail. A hot knife was used to remove foam at the ends.

When cutting the foam with hot knife, the CSIP could be placed only horizontally.

The foam melted down due to gravity, which could produce an unsymmetrical bonding

between the two face sheets and the core. As shown in Figure 8, one side of the face sheet

disbonded slightly before the tests. It is possible that, during tests, this disbonding caused

earlier debonding failures. More details are presented in Chapter 5. Disbonding is due to

defects in manufacture and debonding is developed during loading.

15

Figure 6 Panel installation

Figure 7 Connection detail sketch

Figure 8 Disbonding

16

As stated previously, the foam core of the CSIP was 139.7 mm (5.5’’). In order to

fit it into the gap, 2” × 6” southern yellow pine lumber was used. As shown in Figure 9

and Figure 10, the wood connection was similar to the traditional wood wall assembly,

which can speed up construction because no new techniques are needed.

Figure 9 Connection details

Figure 10 Connection details side view

17

At both ends, the face sheet and the lumber were nailed together with a gas gun,

as shown in Figure 11.

Figure 11 Fastener details

2.4 Instrumentation Setup

Six strain gauges were attached at quarter points of both sides, as shown in Figure

13. The laser deflection measurement system on the black tripod monitored the mid-span

and provided a precision of 0.0001 inch. The lumber on the tripod made a perfect

horizontal angle for the laser. Figure 13 is a front view of all the instruments immediately

before a test. The yellow straps were used to keep the panel from crashing out when there

was a sudden connection failure at a high pressure; it did not touch the panel during tests.

18

To achieve minimal air leakage, several C-clamps were used to fix the sample onto the

chamber. All the stepwise and dynamic windstorm tests described in the thesis were led

and performed by the Co-PI of this project Dr. Forrest J. Masters, and his graduate

student, George Fernandez, from the University of Florida.

Figure 12 Strain gauges deployment

19

Figure 13 Instruments setup

20

CHAPTER 3

STEPWISE WINDSTORM TEST

3.1 Target Load

According to ASCE 7-10 [36], the wind load was determined with an assumption

of a building occupancy category II, an exposure classification of C, a building width of

14.33m (47’), a length of 42.67m (140’), a CSIP exterior wall, and a flat roof with a mean

height of 2.44m (8’). The topography was assumed to be homogeneous. The proposed

pressure is shown in Figure 14. The pressure started at 0.24 kPa (5 PSF) with increments

of 0.48 kPa (10PSF) every 90 seconds.

Figure 14 Pressure history of stepwise windstorm test

Equation 1 from Section 27.3.2 in ASCE 7-10 [36] was used to find the

equivalent wind velocity. = 0.00256 (lb/ft2) (Eq.1)

0 90 180 270 360 450 540 630 720 810 900 990 1080 1170 1260 13500

1

2

3

4

5

6

7

8Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

21

where

qz = velocity pressure from Figure 14

Kz = 0.85, velocity pressure exposure coefficient, see Section 26.6 in ASCE 7-10

Kzt = 1.0, topographic factor, see Section 26.8.2 in ASCE 7-10

Kd = 0.85, wind directionality factor, see Section 26.6 in ASCE 7-10

As determined by Equation 1, the highest wind velocity was 124.44 m/s (280

mph), at which point the pressure reached 6.94 kPa (145 PSF). 124.44 m/s (280 mph)

wind speed is considered to be an extreme wind load, which occurs in hurricanes and

tornadoes. Table 4 displays the corresponding wind velocity for the pressure of each step.

Compared to the highest basic wind speed of 80 m/s (180 mph) for inland US indicated

by Figure 26.5-1A in ASCE 7-10, the samples of this test bore greater pressure.

Table 4 Pressure to velocity conversion

Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph) 11 5.04 kPa (105 PSF) 106.39 m/s (238 mph) 12 5.52 kPa (115 PSF) 111.75 m/s (250 mph) 13 6.00 kPa (125 PSF) 116.22 m/s (260 mph) 14 6.48 kPa (135 PSF) 120.69 m/s (270 mph) 15 6.96 kPa (145 PSF) 124.44 m/s (280 mph)

22

3.2 Panel S-0511-1

As shown in Table 5, panel S-0511-1 was loaded up to 5.04 kPa (105 PSF), which

is equivalent to a wind velocity of 106.39 m/s (238 mph). The pressure was not in proper

control and fluctuating at the beginning, as seen in Figure 15. As indicated in Figure 16,

the sudden large deflection increase at the end of the test indicated that the bottom lumber

broke. The deflection at the failure moment was 9.63 cm. The approximate curvature of

the panel, depicted in Figure 17, refers to the recorded mid-span deflection. The intact top

plate and the cracked bottom plate are displayed in Figure 18 and Figure 19, respectively.

There was no damage to the EPS foam core. The interior face of the panel, which is the

compression side, showed considerable debonding at the bottom (Figure 20). Figure 21

shows all six strains at quarter points of both sides. The program recorded feedbacks,

including pressures, deflections, and strains at a frequency of 100 Hz.

Large volumes of data were generated in the test, including strain-related plots that

can hardly be seen without proper filtering because the strains did not vary appreciably

while pressure built up. The raw data overlaid each other and hid useful information.

There was a pressure increment every 90 seconds, and it took about 2 seconds for the

pressure to reach the next level, which means the pressure stayed “static” for 88 seconds

each period. Based on the periodic increment, a MatLab subroutine was used to process

the strain data collected directly from the experiment. As stated before, the irregular data

at the beginning reflects the corresponding poorly-controlled pressure. The strain gauge

at the exterior middle (SGEM) showed the largest tension before 3.60 kPa (75 PSF); the

strain gauges of exterior top (SGET) and bottom (SGEB) surpassed SGEM’s tension at

higher pressures. The strain gauge at the interior middle (SGIM) shows the largest

23

compression before 2.64 kPa (55 PSF); at higher pressures, the strain gauges at the

interior top (SGIT) and SGIM began to show decreasing compression and ended with

positive tension strain. The strain at SGIM ended a little higher than that at SGIT.

Throughout the test, the trace of the strain gauge at the interior bottom (SGIB) did not

change appreciably. The steady trace for SGIB after 3.60 kPa (75 PSF) reflects a large

deflection that broke the wire of that gauge; no more data were received after that point.

Table 5 S-0511-1 pressure to wind velocity conversion

Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph) 11 5.04 kPa (105 PSF) 106.39 m/s (238 mph)

Figure 15 S-0511-1 pressure history

0 90 180 270 360 450 540 630 720 810 900 990-2

-1

0

1

2

3

4

5

6Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

24

Figure 16 S-0511-1 deflection plot

0 90 180 270 360 450 540 630 720 810 900 990-10

4

8

12

16

20

24Deflection vs Time

Time/s

Defl

ecti

on

/cm

25

Figure 17 S-0511-1 curvature

26

Figure 18 S-0511-1 top connection

Figure 19 S-0511-1 bottom connection

27

Figure 20 S-0511-1 debonding sketch

Figure 21 S-0511-1 strain plot

3.3 Panel S-0506-3

As shown in Table 6, the lateral distributed load for panel S-0506-3 increased to

6.48 kPa (135 PSF), which simulated a 120.69 m/s (270 mph) wind speed. As displayed

in Figure 22, there was poor control in the later periods; the last period dropped instead of

increasing. The inadequate control caused the coarse deflection curve shown in Figure

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-200

0

200

400

600

800

Pressure/kPa

Str

ain

/1E

-6

Strain vs Pressure

SGITSGIMSGIBSGETSGEMSGEB

28

23; the failure deflection was 10.03 cm. Figure 24 illustrates the panel deflection at each

pressure stage. For this panel, the top plate cracked through (Figure 25). There was only a

small, short crevice at the bottom plate (Figure 26). Debonding occurred at all corners on

both sides (Figure 27). As shown by the strain pressure plot (Figure 28), the values for

SGEM were consistently higher, with increasing tension relative to those for SGET and

SGEB, which show matched strains at each stage. The SGIM also had the largest

compression strain among the interior three strain gauges until 3.12 kPa (65 PSF) was

reached. The wires of SGIM and SIGB broke at that point, and the wire of SGIT broke at

5.04 kPa (105 PSF). The SGIT showed an increasing trend after 3.12 kPa (65 PSF) and

ended up tension.


Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph) 11 5.04 kPa (105 PSF) 106.39 m/s (238 mph) 12 5.52 kPa (115 PSF) 111.75 m/s (250 mph) 13 6.00 kPa (125 PSF) 116.22 m/s (260 mph) 14 6.48 kPa (135 PSF) 120.69 m/s (270 mph)

29



0 90 180 270 360 450 540 630 720 810 900 990 1080 1170 1260 13500

1

2

3

4

5

6

7

8Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

0 90 180 270 360 450 540 630 720 810 900 990 1080 1170 1260 13500

4

8

12

16

20


Time/s

De

fle

cti

on

/cm

30


31



32



3.4 Panel S-0511-3

As shown in Table 7, panel S-0511-3 experienced failure at a pressure of 4.56 kPa

(95 PSF), which is equivalent to a 101.47 m/s (227 mph) wind speed. As determined

from the pressure trace (Figure 29), it was in relatively good control. The deflection plot

0 1 2 3 4 5 6 7-400

-200

0

200

400

600

800

1000

Pressure/kPa

Str

ain

/1E

-6

Strain vs Pressure


33

(Figure 30) is smooth; the panel achieved a deflection of 6.27 cm before failure. The

deflection curvature of the panel at all ten pressure stages is plotted in Figure 31. As seen

in Figure 32 and Figure 33, the top plate was in good condition, but the bottom plate

cracked through. Large debondings were evident in three corners of the interior side

(Figure 34). As shown in Figure 35, SGEM consistently had the largest tension strain,

although the values for SGEB increased at pressures greater than 2.64 kPa (55 PSF). At

this point, values for SGET decreased below those for the other exterior strain gauges.

Values for the three interior gauges began to increase at 2.16 kPa (45 PSF) and showed

tension at the end. The SGIM consistently displayed the largest compression strain.


Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph)

34



0 90 180 270 360 450 540 630 720 810 9000

1

2

3

4

5Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

0 90 180 270 360 450 540 630 720 810 9000

3

6

9

12

15

18


Time/s

De

fle

cti

on

/cm

35


36



37



3.5 Panel S-0512-3

Throughout all 15 pressure stages, no failure occurred in panel S-0512-3, as shown

in Table 8. The panel held its position at the highest pressure of 6.96 kPa (145 PSF),

which is equivalent to a wind speed of 124.44 m/s (280 mph). Figure 36 and Figure 37

show the pressure and deflection plots. The deflection curve is smooth for the first

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-300

-200

-100

0

100

200

300

400

500

600

700

Pressure/kPa

Str

ain

/1E

-6

Strain vs Pressure


38

several periods. The curve spiked as the pressure increased, but the values showed good

control, and the variation was not substantial. The largest deflection reached by the panel

was 11.38 cm. Figure 38 plots the curvature of the panel at each pressure stage. As shown

in Figure 39 and Figure 40, both the top and bottom plates are intact after the test, but

debonding was evident at three corners of both sides (Figure 41). As demonstrated by the

strain plots (Figure 42), SGEM had the largest tension strain throughout the test, and

values for SGEB were somewhat higher than those for SGET. SGIM showed the largest

compression strain, which was slightly higher than for SGIT. Instead of compression,

SGIB showed an increasing tension strain almost from the beginning. Plots for the

interior strain gauges began to move upward after 2.64 kPa (55 PSF). The changes for

SGIT and SGIM were more obvious. At higher pressures, interior stains increased at a

slower rate. Exterior strains were also decreased at pressures higher than 4.08 kPa (85

PSF).


Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph) 11 5.04 kPa (105 PSF) 106.39 m/s (238 mph) 12 5.52 kPa (115 PSF) 111.75 m/s (250 mph) 13 6.00 kPa (125 PSF) 116.22 m/s (260 mph) 14 6.48 kPa (135 PSF) 120.69 m/s (270 mph) 15 6.96 kPa (145 PSF) 124.44 m/s (280 mph)

39



0 90 180 270 360 450 540 630 720 810 900 990 1080 1170 1260 13500

1

2

3

4

5

6

7

8Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

0 90 180 270 360 450 540 630 720 810 900 990 1080 1170 1260 13500

2

4

6

8

10

12


Time/s

De

fle

cti

on

/cm

40


41



42



3.6 Panel S-0513-3

Panel S-0513-3 experienced the same pressure stages until, as shown in Table 9, it

failed at 5.04 kPa (105 PSF), which is equivalent to a 106.39 m/s (238 mph) wind speed.

Figure 43 shows the effective control of pressure, as does Figure 44, which displays a

smooth deflection curve. The panel failed at a mid-span deflection of 8.18 cm. The panel

0 1 2 3 4 5 6 7-200

0

200

400

600

800

Pressure/kPa

Str

ain

/1E

-6

Strain vs Pressure


43

curvature at each stage is illustrated in Figure 45. As demonstrated in Figure 46, value for

SGEM was larger than those for other strain gauges. Its tension strain increased at a

constant speed, while values for SGET and SGEB matched each other, and the tension

strains increased at the same speed. There were three paths for each of the interior strain

gauges. SGIM had the largest tension strain from beginning to end. The compression

strain value was lower for SGIT, and there was only slight compression for SGIB. At

pressures greater than 1.20 kPa (25 PSF), all three interior strain gauges showed

decreases in compression, which reflected increases in tension at a low speed. In regard

to the failure of this panel, the bottom plate cracked through at the end of the test. After

failure, the panel was stuck in the steel frame, requiring force to remove it. Thus, no

pictures were taken, and no debonding lengths were measured after unloading.


Step # Pressure Wind Velocity 1 0.24 kPa (5 PSF) 23.24 m/s (52 mph) 2 0.72 kPa (15 PSF) 40.23 m/s (90 mph) 3 1.20 kPa (25 PSF) 51.85 m/s (116 mph) 4 1.68 kPa (35 PSF) 61.69 m/s (138 mph) 5 2.16 kPa (45 PSF) 69.73 m/s (156 mph) 6 2.64 kPa (55 PSF) 76.88 m/s (172 mph) 7 3.12 kPa (65 PSF) 83.59 m/s (187 mph) 8 3.60 kPa (75 PSF) 89.85 m/s (201 mph) 9 4.08 kPa (85 PSF) 95.66 m/s (214 mph) 10 4.56 kPa (95 PSF) 101.47 m/s (227 mph) 11 5.04 kPa (105 PSF) 106.39 m/s (238 mph)

44



0 90 180 270 360 450 540 630 720 810 900 9900

1

2

3

4

5

6Pressure vs Time

Time/s

Pre

ssu

re/k

Pa

TargetMeasured

0 90 180 270 360 450 540 630 720 810 900 9900

3

6

9

12

15


Time/s

De

fle

cti

on

/cm

45


46


3.7 Results

For the panels, Table 10 contains a summary of failure details, including panel

number, failure mode, failure pressure, failure wind velocity, and failure deflection. The

failure deflections were chosen from the end of each 90-second period. A view of these

deflections at the end of every period is in Figure 47.

Table 10 Details of stepwise windstorm test

Panel # Damage Mode Final

Pressure Final Wind

Velocity Final

Deflection

S-0511-1 Bottom lumber failure,

interior bottom debonding 5.04 kPa

(105 PSF) 106.39 m/s (238 mph)

9.63 cm

S-0506-3

Top lumber failure, bottom lumber partial cracking,

debonding on 4 corners of both sides

6.48 kPa (135 PSF)

120.69 m/s (270 mph)

10.03 cm

S-0511-3 Bottom lumber failure,

debonding on 3 corners of interior side

4.56 kPa (95 PSF)

101.47 m/s (227 mph)

6.27 cm

S-0512-3 Debonding on 3 corners of

both sides 6.96 kPa

(145 PSF) 124.44 m/s (280 mph)

11.38 cm

S-0513-3 Bottom lumber failure 5.04 kPa

(105 PSF) 106.39 m/s (238 mph)

8.18 cm

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5-400

-200

0

200

400

600

Pressure/kPa

Str

ain

/1E

-6

Strain vs Pressure


47

Figure 47 Deflection plots of stepwise windstorm test

3.8 Discussion

• Because the curve slope is consistent and no evident permanent deformation was

found after removing the CSIPs from the frame, the materials work within elastic

range.

• As seen in Table 10, S-0511-1, S-0511-3, and S-0513-3 have the same failure

mode of bottom lumber failure. Both S-0511-1 and S-0511-3 have large

debonding at the interior bottom side. It is obvious that plate failure can cause

debonding at the moment of cracking, but there is not enough evidence to show

the reverse process. Although the failure details of S-0513-3, such as debonding

lengths, are not available, there is a good probability that at least the interior

bottom debonds considerably.

48

• S-0506-3 suffered the most serious damage, where its top lumber failed, the

bottom one cracked partially, and all corners of both sides debonded. The

deflection drop at 85 PSF reflects the poor pressure control corresponding to

Figure 25. On the other hand, the fluctuating control may explain the extensive

damage.

• In the stepwise windstorm tests, S-0512-3 was the strongest sample. It remained

intact through all fifteen pressure steps. Neither of the plates was damaged,

although three corners of both sides debonded appreciably. As Figure 50 shows,

its deflection slope changed slightly after 45 PSF, which may indicate developing

damages such as debonding. The consistent deflection slope suggests the potential

of the panel to deflect more.

• Nearly all strain gauges on the compression side showed decreasing compression

after reaching pressures of 2 to 3 kPa. A reasonable assumption is that the face

sheet wrinkled at the location of strain gauge on the compression side [37], but

this assumption cannot be confirmed at present because the compression side is

inside the chamber and is difficult to observe during tests.

3.9 Summary

• The materials in CSIPs were strong enough that everything worked within the

elastic range in all stepwise tests.

• On the average, the CSIP with 1 PCF core density deflected more than those with

3 PCF core densities at each pressure step.

• From the test results, conclusions are that the proposed CSIPs are able to

withstand equivalent wind velocities at least as high as 101.47 m/s (227 mph), and

49

that it is reasonable to expect more potential from the performance of the panel of

S-0512-3.

• The bonding strength between the face sheet and core was set to equal to the

tensile strength of the core. However, the test proves the link is weaker than the

tensile strength, because there was no damage to the core.

• Although debonding was evident in every test, it did not significantly influence

the deflection.

• The CSIP is strong and ductile enough to bear large surface pressures, but the

wood connection is probably the weakest part of the structure. An improved

connection is expected to be found in future research.

• Due to the limited quantity of 1 PCF core density panel for this test, more 1 PCF

core density panels are expected to be tested in order to produce more convincing

results.

• In order to prove the assumption about the decreasing compression, measures will

be taken in future tests, such as placing more strain gauges on the compression

side to see if they have consistent results or using an infrared camera to capture

the wrinkling during tests.

50

CHAPTER 4

DYNAMIC WINDSTORM TEST

4.1 Target Load

In real life, the pressure produced by windstorms changes continuously. Fast-

changing pressure sometimes is more destructive to structures than a small-variation,

long-term load. In a hurricane or tornado, under repetitive pressure, the buildings are

susceptible to fatigue failure. From the Aerodynamic Database of National Institute of

Standards and Technology (NIST), the load histories were obtained. These are from

boundary layer wind-tunnel tests on scale building models. The load not only acts as

wind pressure to simulate the real scenario, but also tests the fatigue-resistance of CSIP.

The pressure history obtained from the database is shown in Figure 48. There were

sixteen peak loads. Each peak load was considered as one stage, and the duration of each

stage varied from approximately 500 seconds to 800 seconds. The higher the peak

pressure, the shorter the stage duration, which is realistic. Except for the first stage, which

had no trough pressure, each later stage contained one trough pressure, one minor peak

pressure, and one major peak pressure. The minor peak was smaller than the two major

peaks beside it. The last six stages were repeated high pressure periods, during which the

same pressure was applied six times. Due to the limit of the HAPLA system, an instant

high pressure after stage 7 was not available, which means the repeated high pressure

period was seven to sixteen in the field tests and that the trough pressure was not reached

51

in any of the stages. Using Equation 1, the equivalent wind velocity for corresponding

major peak pressure was converted (Table 11). All panels with 3 PCF core densities were

supposed to go through all sixteen stages, and the first eight stages were enough for

panels with 1 PCF core.

Figure 48 Pressure history of dynamic windstorm test

Table 11 Pressure to velocity conversion

Step # Pressure Wind Velocity 1 1.50 kPa (31.25 PSF) 58.10 m/s (130 mph) 2 1.83 kPa (38.12 PSF) 64.18 m/s (144 mph) 3 2.17 kPa (45.21 PSF) 69.88 m/s (156 mph) 4 2.55 kPa (53.12 PSF) 75.76 m/s (169 mph) 5 2.96 kPa (61.67 PSF) 81.62 m/s (183 mph) 6 3.38 kPa (70.42 PSF) 87.22 m/s (195 mph) 7 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph) 8 4.28 kPa (89.17 PSF) 98.15 m/s (220 mph) 9 4.75 kPa 98.96 PSF) 103.39 m/s (231 mph) 10 5.24 kPa (109.17 PSF) 108.60 m/s (243 mph)

11-16 5.74 kPa (119.58 PSF) 113.66m/s (254 mph)

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

1

2

3

4

5

6Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

52

4.2 Validation for Exposure Time of Fatigue Load

As stated above, the load data were collected from the aerial dynamic database in

NIST. In order to quantitatively prove the capability of the dynamic windstorm test, the

Rayleigh distribution was employed to provide the theoretical exposure time of the

dynamic load, which means fatigue load as well, in a 500-year return period [38]. The

Rayleigh probability distribution function is displayed here. ( ) = 1 − exp − ( ) (Eq.2)

Where:

P (V) = the probability of a wind gust of a given speed or less occurring at a given

moment

V = the wind speed under consideration V = the average mean wind speed for the location under consideration

Thus:

[1-P (V)]*Lifetime = Probable exposure time at or above a given wind velocity

The Rayleigh distribution is a special form of the Weibull probability distribution,

which is typically used to model the probability of occurrence for certain wind velocities,

with a shape factor of 2.0 and constant ratio of standard deviation to mean value. In this

case, a 500-year return period, a 170 mph design wind speed, and a mean annual wind

speed of 13.7 mph were used to determine the probable exposure time. The 170 mph

wind speed is the largest value in Figure 49. The predicted exposure times are displayed

in Table 12.

53

Figure 49 Model estimated 500-year return period 3 sec gust wind speeds at a height of 10 m in open terrain including wind modeling uncertainty [39]

Note: From “U.S. hurricane wind speed risk and uncertainty” by Vickery, P. J., Wadhera, D., Twisdale, L. A., Lavelle, F. M., 2009, Journal of Structural Engineering, 135, 3, p. 318. Copyright 2009 by ASCE Reprinted with permission.

54

Table 12 Rayleigh probability of exposure at or above given wind speed

Percent of 170 mph Design Wind Speed

Given Wind Speed / mph

Probability Probable Exposure

Time / s

30% 51 0.0018756% 295739 35% 60 0.0000287% 4523 40% 68 0.0000004% 62 50% 85 0.0000000% 0 60% 102 0.0000000% 0 70% 119 0.0000000% 0 80% 136 0.0000000% 0 90% 153 0.0000000% 0 100% 170 0.0000000% 0 110% 187 0.0000000% 0 122% 208 0.0000000% 0

4.3 Panel D-0926-1

Panel D-0926-1 experienced seven whole stages and part of the eighth stage. As

Table 13 displays, this panel withstood an equivalent wind velocity as high as 92.84 m/s

(208 mph). Table 14 shows the actual exposure time at or above different percentages of

design wind speed. The eighth stage did not finish because a major peak pressure was

omitted. The duration of pressure (Figure 50) was slightly more than 6000 seconds. The

data for Figure 51 was excerpted from 850 seconds to 950 seconds in order to show the

controlled load path. The mid-span deflection reached 12 cm at the end the test (Figure

52). The first deflection jump, at about 5500 seconds was caused by the seventh peak

pressure of about 3.8 kPa at the corresponding point in Figure 50. Before the end of the

test, the deflection curve continually reached 12 cm, which may reflect a developing

failure. To provide a clearer view of the panel deflection, the deflection value at the end

55

of each stage was used to plot Figure 53, which gives a more apparent side view of the

panel curvature. The debonding lengths are illustrated in Figure 54.

Table 13 D-0926-1 pressure to velocity conversion

Step # Pressure Wind Velocity 1 1.50 kPa (31.25 PSF) 58.10 m/s (130 mph) 2 1.83 kPa (38.12 PSF) 64.18 m/s (144 mph) 3 2.17 kPa (45.21 PSF) 69.88 m/s (156 mph) 4 2.55 kPa (53.12 PSF) 75.76 m/s (169 mph) 5 2.96 kPa (61.67 PSF) 81.62 m/s (183 mph) 6 3.38 kPa (70.42 PSF) 87.22 m/s (195 mph) 7 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)

Table 14 D-0926-1 exposure at or above given wind speed



Predicted Probable Exposure Time / s

Actual Exposure Time / s

35% 60 4523 5572.91 40% 68 62 4882.26 50% 85 0 2955.99 60% 102 0 1362.49 70% 119 0 460.01 80% 136 0 116.20 90% 153 0 23.05 100% 170 0 3.84 110% 187 0 0.72 122% 208 0 0.01

56

Figure 50 D-0926-1 pressure history

Figure 51 D-0926-1 100 second excerpt

0 1000 2000 3000 4000 5000 6000 70000

1

2

3

4Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

850 860 870 880 890 900 910 920 930 940 9500

0.2

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0.8

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Pre

ss

ure

/kP

a

TargetMeasured

57

Figure 52 D-0926-1deflection plot

0 1000 2000 3000 4000 5000 6000 70000

2

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8

10

12


Time/s

De

fle

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/cm

58

Figure 53 D-0926-1 curvature

59

Figure 54 D-0926-1 debonding sketch

4.4 Panel D-1003-1

Panel D-1003-1 went through eight entire stages (Table 15). Table 16 shows the

actual exposure time at or above different percentages of design wind speed. As shown in

Figure 55, and, as stated before, the peak pressure of the eighth stage was not reached,

but a same load track as stage seven was accomplished instead, which means the repeated

high pressure period started from stage seven instead of theoretical stage eleven. Figure

56 shows an excerpt between 850 seconds and 950 seconds; the pressure path was

consistent in comparison to Figure 51. The difference between target pressure and

measured pressure was within tolerance. Figure 57 and Figure 58 show a deflection

increase from 12 cm to more than 20 cm at the end of the test. The deflection jump

corresponded to a severe connection failure. The bottom plate broke into two pieces

longitudinally, and there was a partial crack in the top plate. Debonding was large at the

interior bottom and exterior top corners, as shown in Figure 59. The 355.6-mm (14

60

inches) debonding at the top exterior was not a typical failure pattern, because it was not

observed in any other tests.


Step # Pressure Wind Velocity 1 1.50 kPa (31.25 PSF) 58.10 m/s (130 mph) 2 1.83 kPa (38.12 PSF) 64.18 m/s (144 mph) 3 2.17 kPa (45.21 PSF) 69.88 m/s (156 mph) 4 2.55 kPa (53.12 PSF) 75.76 m/s (169 mph) 5 2.96 kPa (61.67 PSF) 81.62 m/s (183 mph) 6 3.38 kPa (70.42 PSF) 87.22 m/s (195 mph)

7-8 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 5668.06 40% 68 62 4979.42 50% 85 0 3073.76 60% 102 0 1481.60 70% 119 0 538.01 80% 136 0 144.16 90% 153 0 31.96 100% 170 0 5.60 110% 187 0 1.62 122% 208 0 0.03

61



0 1000 2000 3000 4000 5000 6000 70000

1

2

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4

5Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

850 860 870 880 890 900 910 920 930 940 9500

0.2

0.4

0.6

0.8

1Pressure vs Time

Time/s

Pre

ss

ure

/kP

a

TargetMeasured

62

Figure 57 D-1003-1deflection plot

0 1000 2000 3000 4000 5000 6000 70000

4

8

12

16

20


Time/s

De

fle

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/cm

63

Figure 58 D-1003-1curvature

64


4.5 Panel D-0912-3

The 3-PCF core density panel D-0912-3 was structurally intact after all sixteen

stages, among which are the first six increasing stages and the ten repeated high-pressure

stages as shown in Table 17 and Figure 60. Table 18 shows the exposure time at or above

different percentages of design wind speed. Figure 61 shows the consistency of the load

track in the 100-second period. There was a deflection jump at about 7500 seconds

(Figure 62), which is at the end of the tenth pressure stage and in the middle of the

repeated high-pressure period. The deflection trace was almost flat before and after the

sudden increase. The deflections were the same for stages eleven to fourteen, which made

the curvature plots overlay each other. The mid-span point of the last panel curvature

(Figure 63) was 10 cm. Because both end lumbers showed no damage, and there was no

debonding (Figure 64), some bubbling and/or wrinkling may have occurred in the middle

of the panel, where it could not be seen.

65



7-16 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 9948.69 40% 68 62 9261.30 50% 85 0 7292.79 60% 102 0 5384.29 70% 119 0 3538.02 80% 136 0 1859.83 90% 153 0 730.45 100% 170 0 229.49 110% 187 0 73.81 122% 208 0 9.77


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

1

2

3

4

5

6Pressure vs Time

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Pre

ss

ure

/kP

a

TargetMeasured

66


Figure 62 D-0912-3 deflection plot

850 860 870 880 890 900 910 920 930 940 9500

0.2

0.4

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0.8

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ure

/kP

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8

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Defl

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/cm

67


68


4.6 Panel D-0921-3

The case for panel D-0921-3 was similar to that for panel D-0912-3. It finished all

sixteen stages (see Table 19 and Figure 65). Table 20 shows the actual exposure time at

or above different percentages of the design wind speed. The 100-second excerpt shows

the consistent pressure history (Figure 66). The deflection increased gradually at a

relatively flat slope for all stages until the end of the test, where there was an abrupt

increase from 9 cm to nearly 15 cm in the mid-span (Figure 67 and Figure 68). The slope

of the deflection curve became flat at about 8000 seconds. Although the deflection was

high at the end of the test, the panel showed no debonding (Figure 69). No crevices

appeared at the top plate or bottom plate. Like the failure pattern for D-0912-3, there may

have been, within the panel, bubbles or wrinkling, causing the deflection to increase at

the end.

69



7-16 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 9911.65 40% 68 62 9221.34 50% 85 0 7269.71 60% 102 0 5345.11 70% 119 0 3540.75 80% 136 0 1876.56 90% 153 0 763.96 100% 170 0 246.00 110% 187 0 77.40 122% 208 0 11.77


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

1

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5

6Pressure vs Time

Time/s

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ure

/kP

a

TargetMeasured

70



850 860 870 880 890 900 910 920 930 940 9500

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0.8

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/kP

a

TargetMeasured

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

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71


72


4.7 Panel D-1025-3

Panel D-1025-3 experienced all sixteen stages, as shown in Table 21 and Figure 70;

the pressure path of the 100-second excerpt is shown in Figure 71. Table 22 shows the

actual exposure time at or above different percentages of the design wind speed. Figure

72 shows a relatively smooth mid-span deflection curve, with the slope increasing

slightly after 5000 seconds, corresponding to the start of the seventh stage. The slope

dropped at about 8000 seconds, which was during twelfth stage. There was a small drop

before 10000 seconds and a sudden increase at the end of the test. The largest mid-span

displacement was 8.5 cm. The speed for developing a deflection is apparent in Figure 73.

The slim crevice in the bottom plate shown in Figure 74 was the failure pattern for this

panel. All sides and corners showed no debonding (Figure 75). The debonding within the

panel was likely to have happened during the test.

73



7-16 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 9938.32 40% 68 62 9251.95 50% 85 0 7295.75 60% 102 0 5382.15 70% 119 0 3545.92 80% 136 0 1857.78 90% 153 0 730.46 100% 170 0 236.22 110% 187 0 76.91 122% 208 0 6.38


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

1

2

3

4

5

6Pressure vs Time

Time/s

Pre

ssu

re/k

Pa

TargetMeasured

74



850 860 870 880 890 900 910 920 930 940 9500

0.2

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0.8

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Defl

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75


76

Figure 74 D-1025-3 bottom connection


77

4.8 Panel D-1101-3

Panel D-1101-3 experienced all sixteen pressure stages (see Table 23 and Figure

76). Table 24 shows the actual exposure time at or above different percentages of the

design wind speed, and Figure 77 shows the 100-second measured tract and the target

pressure tracks, which were well-matched. As shown in Figure 78, the deflection plot of

D-1101-3 was different from the plots of the other panels. First, the deflection

corresponding to a peak pressure in each stage was not obvious. Second, the slope of the

deflection curve for the first 500 seconds was steep, and it became almost flat until 1000

seconds. After a short and steep increase, the deflection continued upward at a constant

but slow rate until about 8000 seconds, at which point the deflection essentially stopped

increasing. This panel had the least deflection, slightly more than 4 cm. The panel

curvature plotted in Figure 79 shows a slowly developing mid-span displacement. The

top plate has a partial crack, but there was no debonding, as shown in Figure 80.



7-16 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)

78






35% 60 4523 9953.80 40% 68 62 9273.96 50% 85 0 7312.69 60% 102 0 5393.89 70% 119 0 3558.06 80% 136 0 1850.86 90% 153 0 717.45 100% 170 0 235.92 110% 187 0 61.24 122% 208 0 0.05


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

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6Pressure vs Time

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79



850 860 870 880 890 900 910 920 930 940 9500

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5Deflection vs Time

Time/s

Defl

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/cm

80


81


4.9 Panel D-1102-3

Panel D-1102-3 experienced thirteen pressure stages, as shown in Table 25 and

Figure 81. Table 26 shows the actual exposure time at or above different percentages of

the design wind speed. The 100-second excerpt is shown in Figure 82. From the different

slopes (Figure 83), the response can be divided to four periods. From 0 to about 30

seconds, the deflection increased; from about 30 seconds to about 4000 seconds, it was

almost flat; and from about 4000 seconds to about 7500 seconds, it had a sharp slope;

afterwards, the response was nearly flat and ended at 7 cm. The curvature of this panel is

plotted in Figure 84. Figure 85, Figure 86, and Figure 87 show the intact condition of the

connections and the bonding.

82



7-13 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 8550.94 40% 68 62 7862.55 50% 85 0 5907.47 60% 102 0 4056.97 70% 119 0 2471.14 80% 136 0 1209.80 90% 153 0 449.19 100% 170 0 139.81 110% 187 0 43.78 122% 208 0 4.42


0 1000 2000 3000 4000 5000 6000 7000 8000 90000

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6Pressure vs Time

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83



850 860 870 880 890 900 910 920 930 940 9500

0.2

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0.8

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0 1000 2000 3000 4000 5000 6000 7000 8000 90000

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8Deflection vs Time

Time/s

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fle

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84


85

Figure 85 D-1102-3 top connection

Figure 86 D-1102-3 bottom connection

86


4.10 Panel D-1103-3

Panel D-1103-3 experienced all sixteen stages (see Table 27 and Figure 88). Table

28 shows the actual exposure time at or above different percentages of the design wind

speed. Figure 89 shows a 100-second excerpt from the test. The deflection increased

during the entire test, but there was a lower rate of increase between 7500 seconds and

9000 seconds (Figure 90), which corresponds to the first three repeated high-pressure

stages. During the repeated high-pressure period, the panel fluctuated more than other

panels, although there was no difference in the application of pressure. This panel may

have had some unusual configuration involving bonding, connection installation, nailing

pattern, or bolt fastening, which led the frequency of the panel to near the frequency of

the high repeated pressure. The final deflection was more than 10 cm (Figure 91). The

top interior face sheet debonded almost to the mid-span (Figure 92), which may have

caused the partial crack in the top lumber.

87



7-16 3.83 kPa (79.79 PSF) 92.84 m/s (208 mph)






35% 60 4523 9942.79 40% 68 62 9266.98 50% 85 0 7310.56 60% 102 0 5390.19 70% 119 0 3561.59 80% 136 0 1868.47 90% 153 0 716.62 100% 170 0 227.07 110% 187 0 70.06 122% 208 0 0.95


0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

1

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6Pressure vs Time

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/kP

a

TargetMeasured

88



850 860 870 880 890 900 910 920 930 940 9500

0.2

0.4

0.6

0.8

1Pressure vs Time

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Pre

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ure

/kP

a

TargetMeasured

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

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/cm

89


90


4.11 Results

The test results of the entire dynamic windstorm test are given in Table 29, and

deflection plots for all eight tests are summarized in Figure 93. The table contains sample

designations, pressure stages, corresponding pressure, wind speed, final mid-span

deflections, and damage modes for each test.

91

Table 29 Failure details of dynamic windstorm test

Panel # Final Stages

Final Pressure

Final Wind

Velocity

Final Deflection Damage Mode

D-0926-1 8

3.83 kPa (79.79 PSF)

92.84 m/s (208 mph)

12.2 cm Interior bottom and one corner of top exterior

debonding

D-1003-1 8 12 cm

Interior bottom and exterior top debonding, bottom plate failure, and partial crack on top plate

D-0912-3 16 10 cm No debonding, intact connections

D-0921-3 16 14.8 cm No debonding, intact connections

D-1025-3 16 8.6 cm No debonding, partial crack on bottom plate

D-1101-3 16 4.2 cm No debonding, partial crack on top plate

D-1102-3 13 7 cm No debonding, intact connections

D-1103-3 16 10.3 cm Interior top debonding, and partial crack on top

plate

92

Figure 93 Deflection plots of dynamic windstorm test

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 110000

3

6

9

12

15

18


Time/s

De

fle

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on

/cm

D-0926-1D-1003-1D-0912-3D-0921-3D-1005-3D-1101-3D-1102-3D-1103-3

93

4.12 Discussion

• Because no evident permanent deformation was found after removing the CSIPs

from the frame, the materials work within elastic range.

• Except for a control problem with panel D-1102-3, which caused it experience

only thirteen stages of the dynamic windstorm tests, all of the panels completed

the pre-programmed pressure stages.

• Only one panel, D-1003-1, experienced a connection failure. The bottom lumber

cracked through longitudinally. Before the final increase, indicating plate failure,

the mid-span deflection was about 12 cm.

• Debonding was observed in the tests for both panels with 1 PCF core density and

one 3 PCF core density panel, D-1103-3. Although the bonding of CSIP with the

rigid core showed no defects on its sides and corners, and both connection

lumbers of some panels remained intact during the tests, the slope changes in the

deflection plot indicate there are debondings in the middle of the panel, which

were not visible.

• Panels D-0912-3, D-0921-3 and D-1102-3 were completely intact. No debonding

was evident on the sides and corners, and there was no crevice on the wood

plates.

• D-1025-3 and D-1101-3 had partial cracks on the bottom and top lumbers,

respectively, but neither had debondings.

• The mid-span deflection was similar for the two 1 PCF core density CSIPs, but it

varied considerably for the 3 PCF core density CSIPs, ranging from 4.2 cm to

14.8 cm. Some samples showing similar conditions after the tests had different

94

deflections. D-0921-3 and D-1102-3 had no obvious damage, but the former panel

had a mid-span deflection of 14.8 cm; the deflection for the latter was only 7 cm.

A reasonable explanation for the inconsistency is that more debondings in the

middle of the panel, which were not visible, developed in D-0921-3 than in D-

1102-3.

• Typically, the dynamic windstorm tests lasted for about 100 min for 1 PCF core

density panels and about 175 min for 3 PCF core density panels. The repeated

load cycles, especially stage 7 to stage 16, make this experiment an effective

check for fatigue load.

4.13 Summary

• Although the HAPLA system did not match the high-peak pressures in later

stages from 8 to 16 and the trough pressure in each stage, the control system

worked well in most load traces, as shown in figures of 100-second excerpts.

• In the dynamic windstorm tests, all materials of the CSIPs were strong and ductile

enough to function in the elastic range.

• The CSIPs with 1 PCF core density deflected more and were more prone to face

sheet debonding and connection failures; only slight damage occurred in a few of

the 3 PCF core density CSIPs.

• All CSIPs were able to bear an equivalent wind velocity as high as 92.84 m/s (208

mph). They have the potential to bear even higher wind loads and remain

structurally intact.

• Under repeated pressures as high as 3.83 kPa (79.97 PSF), the CSIPs

demonstrated effective fatigue resistance.

95

• In the dynamic windstorm tests, face sheet debonding was not a substantial

problem for 3 PCF core density CSIPs. Nevertheless, in future research,

nondestructive techniques may be used to determine debondings in the middle of

the panels.

• Debonding in the middle of the panels may account for the discrete mid-span

deflections.

• The connections performed well in the dynamic windstorm tests. Only one

connection failure occurred in CSIPs, D-1003-1.

• The deflection plots (Figure 96) proved the repeatability of the test.

96

CHAPTER 5

AS-BUILT CONDITIONS

During the tests, debonding between the face sheet and the core is caused

primarily by wrinkling of the face sheet in compression. But “disbonding,” a preexisting

condition due to defects in manufacture, will be covered in this chapter.

For an instance, Figure 94 shows one of four disbonding corners of CSIP S-0513-

3 before the stepwise test. Such disbonding is large enough to be considered. The

disbonding probably contributed considerably to the deflection, and may account for the

fact that curve S-0513-3 (Figure 50) is different from the other 3 PCF core density CISPs.

Figure 94 Corner disbonding

The connection is expected to model the realistic fixed condition in order to find

the wind resistance of the CSIPs. The ideal fixed boundary condition with no rotations

97

can hardly be achieved. Figure 95 shows the fixtures, including ½’’ Simpson strong ties

and bolts after a test. The warpage is insignificant, which means the fixed boundary

condition was essentially achieved.

Figure 95 Simpson strong tie

98

CHAPTER 6

FINITE ELEMENT MODELING

The commercial software package LS-DYNA was used to perform the finite

element analysis for CSIPs.

6.1 Initial Modeling Validation

Because the relatively long test duration and the time-sensitive calculation

characteristics of LS-DYNA, only the first one second of the dynamic windstorm test on

CSIP with 1 PCF core density was selected to validate the finite element modeling in

order to perform modeling efficiently.

6.1.1 Simulation Details

The dimensions of the CSIP are in Figure 96 and Figure 97. Through the finite

element modeling, material models, explicit and implicit methods, and element quantity

were investigated in order to find the model that generated the best matched deflection-

time curve. Because the debonding stress between the face sheet and the core was

unknown, it was assumed that the two components were bonded well through the test,

thus CONTACT_TIED_SURFACE_TO_SURFACE was used. The load was modeled as

a uniformly distributed surface load, and LOAD_SEGMENT_SET and SET_SEGMENT

were used to produce the time-changing pressure, which varied every 0.01 second. The

load history is seen in Figure 98. For simplicity, the wood connection was not considered

in the modeling, and the edge nodes were constrained for all six degrees of freedom

99

(Figure 99). The material properties used in the model are in Table 30 and Table 31. Due

to the long time of the experiment and the computation characteristics of LS-DYNA, only

data for the first second were used for the validation.

Table 30 Material properties of face sheet RHO EX EY EZ PRXY PRYZ PRXZ GXY GYZ GXZ

16 kg/m3

11035 MPa

11035 MPa

1030 MPa

0.11 0.22 0.22 1800 MPa

750 MPa

750 MPa

Table 31 Material properties of core

RHO EX PRXY

1783 kg/m3 1.2 - 1.5 MPa 0.25

Figure 96 Connection dimensions

100

Figure 97 Panel dimensions

101

Figure 98 Load history: Pressure - Time

Figure 99 Geometry

102

6.1.1.1 Material Models

MAT161 and MAT54 were evaluated for the 3.04-mm glass fiber / PP face sheet,

and MAT003, MAT012, and MAT063 were evaluated for the EPS foam core. The stress-

strain curve for MAT012 was obtained from Croop et al. [40]. The baseline material

models for the core and face sheet are MAT003 and MAT054, which, after several trials,

were determined to be the optimum types (see Figure 100).

Figure 100 Deflection - Time curves for different materials

Shell element was used instead of solid element because the element with an

aspect ratio closer to unity yields better results [41] and considering the cost of central

processing units (CPU). Although MAT161 was considered as a great fit for fiber

polymer materials, it did not show appropriate behavior in this modeling. MAT161 may

be better for modeling fiber failure, but the relatively low pressure did not cause any

103

damage to this model. Further, MAT161 is not applicable for 4-node shell element. Due

to the thin (3.04-mm) face sheet and the large dimensions of the model, the CPU cost

would be substantial if the element aspect ratio meets the unity requirement.

6.1.1.2 Explicit and Implicit Solver

The terms implicit and explicit refer to time integration algorithms. For explicit

analysis, the maximum time-step size is limited by the Courant condition. It is well suited

for dynamic simulations but can become prohibitively expensive in conducting static

analyses or those of long duration. For implicit analysis, the time-step size may be

selected by the user, but extensive efforts are required to form, store, and factorize the

stiffness matrix [42]. CONTROL_IMPLICIT_GENERAL was used to activate the

implicit solver. The comparisons among experiments, explicit and implicit, can be seen in

Figure 101. For the two methods, the results do not vary appreciably. However, the CPU

cost for implicit calculations was larger than that for the explicit method. Thus, the

explicit method was chosen for modeling.

104

Figure 101 Deflection – Time curve of explicit and implicit methods

For the implicit solver, the default iterative nonlinear solver used is the BFGS

method that employs a ‘Quasi-Newton’ method, in which the global stiffness matrix is

reformed only at each ILIMIT step. This default method often fails to converge when the

non-linearity of the problem grows or when there is substantial contact involved [43].

This specific modeling has a substantial amount of contact between the face sheet and the

core. In this case, as Suri Bala [43] recommends, a more expensive Full-Newton method

is used by setting ILIMIT = 1 to force LS-DYNA to reform the stiffness matrix at every

iterative step and to yield a more accurate estimation of stiffness. Further, the MAXREF

was set to 50 to allow a sufficient number of stiffness reformations before terminating or

reducing the solution time step.

105

6.1.1.3 Element Quantity

To balance the relationship between CPU cost and consistency of results, different

element numbers were investigated for this model. With different mesh sizes, 32

elements, 96 elements, 1128 elements, and 64843 elements were evaluated. Results for

the four modeling did not differ appreciably, and were consistent with the experiment

curve (Figure 102). Also the computation time for the modeling with 32 elements, 96

elements and 1128 elements were similar. Thus, it was appropriate to use the model with

1128 elements.

Figure 102 Deflection – Time curve of different element numbers

Although the model had dimensions of 2.4 m × 1.2 m × 0.14 m (8 ft × 4 ft × 5.5

in), the results were consistent with mesh size of 100 mm and element number of 1128.

106

The reason why this model is not sensitive to the element size may be due to its simple

geometry and load pattern.

Results

As all the validation modeling shows, a finite model with MAT054 for face sheet,

MAT063 for core, CONTACT_TIED_SURFACE_TO_SURFACE between face sheet

and core, and a mesh size of 100 mm with element number of 1128 were consistent with

the experiment using explicit solver. The variance is within an acceptable range (Figure

103). The deflection contour can be seen in Figure 104.

Figure 103 Comparison between experiment and FE modeling

107

Figure 104 Deflection contour

6.2 Further FE modeling and Experimental Results

After validation of the first one second of the CSIP with 1 PCF core density, the

modeling was further developed in stepwise and dynamic windstorm tests of longer

duration. In the following, fixed and simply supported conditions and material models

MAT003 and MAT063 were evaluated in a parametric study of 1 PCF core density

CSIPs in stepwise tests; only boundary conditions were investigated for 3 PCF core

density CSIPs in stepwise tests. In dynamic windstorm tests, all models were in fixed

condition, and different material models were investigated only for 1 PCF core density

108

CSIPs. Due to the lack of debonding-related data, debonding was not considered in

modeling.

6.2.1 Stepwise Windstorm Test

The pressure history in Figure 105 was the input to the load-modeling file. The

deflections from experiment and finite element modeling for all fifteen stages of CSIPs

with 1 PCF core density can be seen in Figure 10. There was little difference between

different boundary conditions, and MAT003 gave a slightly better result than MAT063.

Nevertheless, after the first three stages, there were large divergences between deflections

from the experiment and the finite element analysis.


test

109

With the load input described in Figure 14, the deflections of experiment and

modeling for 3 PCF core density CSIPs were obtained (Figure 106). Again, fixed and

simply supported conditions were investigated. From this plot, it can be seen that the

modeling matches well with the experiment for only the first two stages; the difference

between them is greater at later stages.


test

The total deflection of the mid-span is the sum of bending deflection and shear

deflection, which are described by the first and second terms, respectively, of the

following formula.

U

PLk

D

PLk sb +=Δ3

(Eq. 3)

110

In the formula, P is total load acting perpendicular to neural axis, L is span, D and

U are bending and shear stiffness, and bk and sk are bending and shear constants

depending on loading, boundary conditions, and points of interest. For example, if mid-

span is the point of interest, the boundary condition changes from fixed to simply-

supported, and other conditions stay the same. In this case, bk changes from 1/384 to

5/384. In Figure 105 and Figure 106, the difference between fixed and simply supported

boundary conditions was not substantial, indicating that the deflection due to bending

was small enough to be ignored.

6.2.2 Dynamic Windstorm Test

Because the load file of LS-DYNA had an input limit and also considering the

expensive CPU cost and large volume of result files, only the first 300 seconds were used

as load input for the modeling (Figure 48).

The deflections of experiment and modeling of dynamic windstorm test of 1 PCF

core density CSIPs are illustrated in Figure 107. The deflections of experiment and

modeling followed a similar up-and-down pattern, and the FE63 modeling curve on top,

which used MAT063, gave a less noisy curve. The peak values of experiment and FE

modeling, which used MAT003 as core material (as evaluated previously in initial

validation), were within an acceptable difference; the mean values of the two varied

considerably, especially after 100 seconds.

Figure 108 shows the deflections of experiment and modeling for CSIPs with 3

PCF core densities. The deflection of modeling is at the bottom of all curves. The

111

modeling matched well with D-1101-3 before 150 seconds; thereafter it may not be a

validated model due to the relatively large variance.

112

Figure 107 Deflection comparisons of 1 PCF core density CSIPs in dynamic windstorm test

0 50 100 150 200 250 3000

0.5

1

1.5

2

2.5

3Deflection vs Time

Time/s

De

fle

cti

on

/cm

FEEX0926EX1003FE63

113

Figure 108 Deflection comparisons of 3 PCF core density CSIPs in dynamic windstorm test

0 50 100 150 200 250 3000

0.5

1

1.5

2

2.5Deflection vs Time

Time/s

De

fle

cti

on

/cm

FEEX0912EX0921EX1005EX1101EX1102EX1103

114

6.3 Summary

Although the modeling did not match well with the experimental work, there are still

points that can be made:

• MAT003 gave smaller deflections than experiments. Consequently, MAT063 was

tried because of its realistic behavior in other engineering modeling [40], and

more importantly it gave a larger deflection than MAT003.

• In stepwise windstorm tests, the small differences between different boundary

conditions may indicate that the deflection due to bending is small enough to be

ignored and that the deflection due to shear dominates. This is reasonable because

the foam is weak in shear resistance, and debonding between the face sheet and

the core also contributes.

• In dynamic windstorm tests, the modeling with MAT003 as core matched well

with the experiment for 1 PCF CSIPs, although the modeling with MAT063 was

less noisy. More closely matched results with MAT063 may be achieved with

stress-strain data from the mechanical test of the foam.

• The modeling will be more realistic when debonding-related data are obtained

from future tests and included in the analyses.

115

CHAPTER 7

SUMMARY & CONCLUSION

7.1 Summary

Composite Structural Insulated Panels (CSIPs) are proposed as a substitute for

traditional wood-made structural insulated panels (SIPs), which are typically used for

building envelopes. Made of composite materials, the CSIPs possess various structural

merits, most of which have been established by laboratory tests that have been described

in previous statements. By addressing the increasing loss due to wind hazards in recent

years, this thesis concentrated on the wind resistance of CSIPs. Simulated wind pressure

was applied, in stepwise and dynamic ways, to full-scale CSIPs using the High Air

Pressure Load Actuator (HAPLA) system developed at the University of Florida. The

commercial finite element software, LS-DYNA, was used to evaluate the modeling

validation of the experiments.

In stepwise windstorm tests, the HAPLA system produced simulated air pressure

starting from 5 PSF with increments of 10 PSF up to 145 PSF with 90 seconds for each

pressure period. During tests, CSIPs ended with equivalent wind velocities ranging from

227 mph to 280 mph. This stepwise test was considered conservative because it is an

extremely rare case that a structure is subject to a large wind load for 90 seconds.

Although four of five specimens failed at their connections, one CSIP experiencing the

largest velocity of 280 mph showed no cracks at the connections, which demonstrates the

116

wind resistance potential of CSIPs. For all specimens, debonding was observed at most

corners. The mid-span deflections were significant in tests, and CSIPs with thicker or

denser cores should solve that problem. An assumption of wrinkling of the face sheet on

the compression side was made due to the decreasing compression strain values. Future

tests can evaluate this possibility.

In dynamic windstorm tests, the HAPLA system generated fluctuating wind

pressure. The input data were obtained from the Aerodynamic Database of National

Institute of Standards and Technology (NIST). The peak equivalent wind velocity ranged

from 130 mph to 208 mph, which is 22% greater than the largest wind speed in the 500-

year hurricane map based on uncertainty calculations. The Rayleigh distribution was used

to predict the probable exposure time during the 500-year period. This dynamic

windstorm test was considered conservative because the actual exposure time during

dynamic windstorm tests was larger than the predicted time from the Rayleigh

distribution. In dynamic windstorm tests, four of eight CSIPs experienced connection

failures. Three of the four were 3 PCF core density samples that had minor cracks; the

other was a 1 PCF core density sample, which had a crack through the lumber. Three of

eight samples experienced corner debondings, two of the three were in 1 PCF core

density panels. Because the deflection plots for the 3 PCF core density panels were not

consistent, an assumption was made that debondings appeared in the middle of the face

sheet during tests, which would not be noticed but could be evaluated by nondestructive

techniques.

The stepwise and dynamic windstorm tests validate the wind resistance of the

CSIPs as a single full-scale wall panel. The connection details, construction problems,

117

and the performance of CSIPs after the cut for the windows, doors, wire line, plumbing

etc. will be the focus of this project in the next phase.

The commercial finite element software LS-DYNA was used to perform finite

element analysis. Due to the expensive CPU cost and computing time, initial modeling

validation was performed for the first second of the dynamic windstorm tests of 1 PCF

core density CSIP. After several trials, a 4-node shell element and MAT054 for face

sheet, 8-node solid element and MAT003 for core,

CONTACT_TIED_SURFACE_TO_SURFACE, element size of 100 mm, and explicit

solver were considered to be a good fit. With the load input from stepwise windstorm

tests and the first 300 seconds of dynamic windstorm tests, further modeling validation

was performed. Due to the uncertain stress-strain curve of the foam core and the

unknown debonding stress between the face sheet and the core, the modeling merely

developed a similar plot pattern. The results from stepwise windstorm test modeling led

to an assumption that the deflection due to shear dominates the total deflection and that

the weak shear-resistance foam core and the weak bonding between the face sheet and the

core justified the assumption.

7.2 Conclusion

• The results of stepwise and dynamic windstorm tests prove that the full-scale

CSIPs are capable of resisting an equivalent wind velocity of more than 200 mph

without showing substantial structural damage.

• In the tests, debonding was a typical damage mode for CSIPs, but the wind-

resistance capacity of CSIPs did not decrease appreciably after debonding.

118

• CSIPs with 1 PCF core density deflected more at the mid-height of panels than

the ones with 3 PCF core density. Denser or thicker foam cores are expected to

decrease the mid-height deflection to more comfortable criteria.

• For future tests, nondestructive techniques are recommended to determine if any

debondings fall away from the edges of the panels. At present, this cannot be

visually observed.

• The finite element modeling indicates that the deflection due to shear is a primary

factor in the structural behavior of CSIPs.

• The finite element modeling gave similar patterns in deflection plots. More

mechanical properties of foam cores, which are expected to be found in future

tests, will likely make the modeling more consistent with experiments.

119

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