ACI 437.2M-13: Code Requirements for Load Testing of Existing Concrete Structures (ACI ... · 2020....

ACI 437.2M-13

Code Requirements for Load Testing of Existing Concrete Structures

(ACI 437.2M-13) and CommentaryAn ACI Standard

Reported by ACI Committee 437

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First PrintingMay 2014

Code Requirements for Load Testing of Existing Concrete Structures and Commentary

Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI.

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ACI 437.2M-13

Code Requirements for Load Testing of Existing Concrete Structures (ACI 437.2M-13) and

Commentary

Reported by ACI Committee 437

Carl J. Larosche*, Chair J. Gustavo Tumialan*, Secretary

Joseph A. AmonNicholas J. Carino

Paolo CasadeiJohn A. Frauenhoffer

Nestore Galati*

Zareh B. GregorianPawan R. Gupta

Frederick D. HeidbrinkAshok M. Kakade

Danielle D. KleinhansAndrew T. KrauklisDaniel J. McCarthy

Javeed MunshiAntonio Nanni

Thomas E. Nehil*

Renato ParrettiK. Nam Shiu

Jeffrey S. West*

Paul H. Ziehl*

Consulting MembersMarco Arduini

Habib M. Zein Alabideen

*Member of the subcommittee that prepared this report

This code provides requirements for test load magnitudes, test protocols, and acceptance criteria for conducting a load test as a means of evaluating the safety and serviceability of concrete struc-tural members and systems for existing buildings as provided for by ACI 562-13. A load test may be conducted as part of a struc-tural evaluation to determine whether an existing building requires repair and rehabilitation, or to verify the adequacy of repair and rehabilitation measures applied to an existing building, or both. This code contains provisions for both a cyclic load test and a monotonic load test procedure.

Keywords: acceptance criteria; cyclic loading; load test; monotonic loading; test load magnitude; test protocol.

CONTENTS

CHAPTER 1—GENERAL, p. 31.1—General, p. 31.2—Scope, p. 31.3—Purpose, p. 31.4—Limitations, p. 41.5—Interpretation, p. 41.6—Language and units of measurement, p. 4

CHAPTER 2—NOTATION AND DEFINITIONS, p. 52.1—Notation, p. 52.2—Definitions, p. 6

CHAPTER 3—REFERENCED STANDARDS, p. 8

CHAPTER 4—TEST LOAD, p. 94.1—Service loads, p. 94.2—Test load magnitude, p. 9

1

ACI 437.2M-13 was adopted October 23, 2013, and published May 2014.Copyright © 2014, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any

means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.



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CHAPTER 5—LOADING PROTOCOL, p. 115.1—Safety, p. 115.2—Load arrangement, p. 115.3—Monotonic loading protocol, p. 125.4—Cyclic loading protocol, p. 125.5—Load application, p. 135.6—Response measurements, p. 145.7—Visual inspection, p. 14

CHAPTER 6—ACCEPTANCE CRITERIA, p. 156.1—Distress caused by load test, p. 156.2—Performance assessment at service load level, p. 166.3—Acceptance criteria for monotonic loading protocol,

p. 176.4—Acceptance criteria for cyclic loading protocol, p. 176.5—Provision for lower load rating, p. 19

R7—COMMENTARY REFERENCES, p. 21Cited references, p. 21

American Concrete Institute Copyrighted Material—www.concrete.org

2 CODE REQUIREMENTS FOR LOAD TESTING OF EXISTING CONCRETE STRUCTURES (ACI 437.2M-13)



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CHAPTER 1—GENERAL

1.1—General 1.1.1 The scope, purpose, applicability, limitations, inter-

pretation principles, and units of measure are defined in this chapter.

1.1.2 This code supplements and is part of the “Code Requirements for Evaluation, Repair, and Rehabilitation of Existing Concrete Buildings (ACI 562-13) and Commen-tary” through reference.

1.2—Scope 1.2.1 The requirements of this code shall govern for

the evaluation of safety and serviceability of members in existing concrete structures by load testing.

1.2.2 The requirements of this code shall apply to rein-forced concrete with prestressed reinforcement, nonpre-stressed reinforcement, or both.

1.2.3 Procedures and requirements provided in this code are not applicable to existing structures having concretes with compressive strengths above 55 MPa unless permitted by the licensed design professional.

1.2.4 For structures being erected under the requirements of a legally adopted general building code, of which ACI 318-11 forms a part, this standard shall not replace Chapter 20 of ACI 318-11.

1.3—Purpose1.3.1 The purpose of this code is to establish the minimum

requirements for the test load magnitudes, load test proce-dures, and acceptance criteria applied to existing concrete structures as part of an evaluation of safety and service-ability to determine whether an existing structure requires repair and rehabilitation, to verify the adequacy of repair and rehabilitation measures applied to an existing structure, or to provide for public health and safety through structural safety and serviceability.

1.3.2 Load tests shall be conducted according to load test procedures as described in Chapter 5.

R1—GENERAL

R1.1—General

R1.1.2 Through its reference by ACI 562-13, this code is to be used only when ACI 562-13 governs. In those cases in which the general building code governs, then the applicable provisions of Chapter 20 of ACI 318-11 dealing with load testing are to be used.

R1.2—Scope R1.2.1 The determination of situations where a load test

is required is outside the scope of this code. Furthermore, this code does not address procedures for analytical strength evaluations, condition evaluation of existing structures, or assessment of structural deterioration and its consequences. The licensed design professional should advise the owner and parties participating in the load testing of a structure of the potential for damage or even failure of the portions of the structure to be load tested in accordance with the procedures of this code. Refer to 5.1 for provisions relating to safety and shoring.

R1.2.4 Experience is lacking in the application of the procedures and requirements in this code to structures having high-strength concrete (concrete compressive strengths over 55 MPa). Structures with high-strength concrete may exhibit a more linear response as the structure approaches its load-carrying limit and may experience a more brittle failure in comparison to structures with strengths less than 55 MPa.


CODE REQUIREMENTS FOR LOAD TESTING OF EXISTING CONCRETE STRUCTURES (ACI 437.2M-13) 3

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1.3.3 All references in this code to the licensed design professional shall be understood to mean persons who are licensed to practice structural design in the jurisdiction where this code is being used. The licensed design profes-sional for a project is responsible for and in charge of the evaluation of safety and serviceability.

1.4—Limitations 1.4.1 This code does not apply to foundations, slabs-

on-ground, structures whose responses are dominated by in-plane actions, or structures having unusual design concepts as determined by the licensed design professional.

1.4.2 This code shall not be used for product develop-ment testing where load testing is used for quality control or approval of mass-produced members.

1.4.3 Testing for resistance to load effects of fatigue, wind, and earthquakes is outside the scope of this code.

1.4.4 Load testing to determine design strength or load-carrying limit at failure is outside the scope of this code.

1.5—Interpretation1.5.1 The official version of the code is the English

language version published by the American Concrete Insti-tute using inch-pound units.

1.5.2 In case of conflict between the official version of the code and other versions of the code, the official version governs.

1.6—Language and units of measurementValues in this code are stated in inch-pound units. A

companion code in SI units is also available.

R1.4—Limitations R1.4.1 The procedures and requirements in this code have

been developed and applied to structural members subjected to gravity loads and where the structural response is domi-nated by flexure, such as typical elements of the gravity load-resisting system in a building. This code is not appli-cable to structures where the response involves significant in-plane or membrane action, where soil-structure interac-tion is present, or in situations where the structural behavior is not typical of building structural elements. Structures where the response may be inappropriate for use with the requirements of this code include shells, arches, bins and silos, blast-resistant structures, and chimneys.

R1.4.4 The procedures and requirements of this code are not intended to provide any indication of the design strength or load-carrying limit of a member or structure at failure. The term “design strength” refers to the strength of a member or cross section as used in the context of the basic require-ment for strength design, expressed as “design strength ≥ required strength” (based on factored load combinations of the general existing building code). The design strength is calculated in accordance with the provisions and assump-tions of the strength design method of the general existing building code and multiplied by the appropriate strength reduction factor φ.



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CHAPTER 2—NOTATION AND DEFINITIONS

2.1—NotationD = total dead load: Dw + Ds, or related internal moments

or forcesDs = superimposed dead load, or related internal

moments or forcesDw = load due to self-weight of the concrete structural

systemF = load due to weight and pressure of fluids with

well-defined densities and controllable maximum heights, or related internal moments or forces

IDL = deviation from linearity indexIPi = permanency index for the i-th cycle at specified

load level of a cyclic load testIP(i+1) = permanency index for the (i + 1)th cycle at specified

load level of a cyclic load testIpr = permanency ratio indexL = live load due to use and occupancy of the building

not including environmental load and superim-posed dead load, or related internal moments or forces

Lr = roof live load produced during maintenance by workers, equipment, and materials or during life of structure by moveable objects such as planters and people, or related internal moments or forces

lt = span of member under load test and taken as the smaller of: (a) distance between centers of supports; and (b) clear distance between supports plus thick-ness h of member; for a cantilever, it shall be taken as twice the distance from face of support to canti-lever end, mm

Pi = applied load corresponding to point i in load-deflection envelope in a cyclic load test, used for calculation of ai in IDL acceptance criterion, kN

Pmax = applied load corresponding to 100 percent of test load magnitude, kN

Pmin = minimum load to be maintained during a cyclic load test, kN

Pref = reference load corresponding to the peak load of the first cycle (reference point) in a cyclic load test, used for computation of aref in IDL acceptance crite-rion, kN

R = rain load, or related internal moments and forcesS = snow load, or related internal moments or forcesai = slope of secant line of point i in load-deflection

envelope, where secant line passes through origin and point of interest, i, in a cyclic load test, degrees

aref = slope of reference secant line in load-deflection envelope, where reference secant line passes through origin and peak load of the first cycle (reference point) in a cyclic load test, degrees

∆i = measured deflection corresponding to point i in load-deflection envelope in a cyclic load test, used for computation of ai in IDL acceptance criterion, mm.

R2—NOTATION AND DEFINITIONS



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∆l = maximum measured deflection (cyclic or mono-tonic load test), mm

∆l2 = maximum deflection measured during a retest rela-tive to the position of the structure at the beginning of the retest, mm

∆r = residual deflection measured after the 24-hour recovery period following complete removal of the load at the completion of the load test, mm

∆ref = measured reference deflection corresponding to the peak load of the first cycle (reference point) in a cyclic load test, used for computation of aref in IDL acceptance criterion, mm

∆rrt = permanent or residual deflection measured after the 24-hour recovery period following complete removal of the load at the completion of the repeat load test; residual deflection during the repeat test is relative to the position of the structure at the beginning of the repeat test, mm

∆1max = measured maximum deflection at the end of the i-th

cycle at a given load level of a cyclic load test, mm∆1

r = measured residual deflection after unloading to the minimum load, Pmin, at the completion of the i-th cycle at a given load level of a cyclic load test, mm

∆2max = measured maximum deflection at the end of the (i +

1)th cycle at a given load level of a cyclic load test, mm

∆2r = measured residual deflection after unloading to the

minimum load, Pmin, at the completion of the (i + 1)th cycle at a given load level of a cyclic load test, mm

2.2—Definitions acceptance criteria—set of explicit and quantitative rules

to establish whether or not a structure (or a portion of it) passes a load test.

applied test load (ATL)—load applied to the structure, in addition to dead load already in place, to produce test load magnitude.

cyclic load test—application of test load magnitude using a defined set of increasing, repeated load cycles and then maintaining the test load magnitude for at least 24 hours.

failure—when referred to the performance of a structure (or a portion of it) under load test, it indicates that one or more acceptance criteria are not met.

licensed design professional—engineer or architect who is licensed to practice structural design as defined by the statutory requirements of the professional licensing laws of a state or jurisdiction; or the architect or engineer, licensed as described, who is responsible for the structural design of a particular project.

load-deflection envelope—curve enclosing the points on a plot of applied load versus measured deflection from a cyclic load test. Only those loads that are greater than or equal to any previously applied load cycle are included.

load level—maximum load attained during a loading cycle in a cyclic load test or an intermediate load before the full test load magnitude is applied in a monotonic load test.

R2.2—Definitions



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load step—load increment applied during a loading cycle to reach the load level for that cycle or the load decrement during the unloading portion of the cycle.

monotonic load test—application of test load magnitude in at least four approximately equal steps and then main-taining the test load magnitude for at least 24 hours.

reference point—point on a plot of applied cyclic load versus measured deflection corresponding to the peak load of the first load cycle.

reference secant line—line passing through the origin of a plot of applied cyclic load versus measured deflection and the reference point.

self-weight dead load, Dw—load due to self-weight of the concrete structural system only.

strip or patch test load—test load distributed over a limited portion of the tributary area of the structure or member to be tested and typically applied by means of hydraulic jacks.

superimposed dead load, Ds—load due to weight of construction materials other than self-weight of the struc-tural system that are already incorporated into the building or will be incorporated in the future.

test load magnitude (TLM)—total load to be used in conjunction with acceptance criteria in this code to deter-mine whether or not a structure, or a portion of it, passes a load test.

total dead load, D—total load due to self-weight, including superimposed loads.

superimposed dead load, Ds—this includes, but is not limited to, walls, roofs, ceilings, stairways, built-in parti-tions, finishes, cladding, and other similarly incorporated architectural and structural items; the weight of fixed service equipment such as cranes, plumbing stacks and risers, elec-trical, heating, ventilating and air-conditioning systems, and fire sprinkler systems.

test load magnitude (TLM)—this includes factored dead, live, snow, and rain loads, and is established using the load factors and combinations defined in Chapter 4 of this code. It includes dead load that is already in place in the structure, including self-weight and super-imposed dead load, plus additional applied test loads to reach the desired TLM.

total dead load, D—a distinction is made between dead load due to self-weight and superimposed dead loads in this code. The total dead load, D, includes both dead load due to self-weight and superimposed dead loads; that is, D = Dw + Ds.



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CHAPTER 3—REFERENCED STANDARDSAmerican Concrete InstituteACI 318-11—Building Code Requirements for Structural

Concrete and CommentaryACI 562-13—Code Requirements for Evaluation, Repair,

and Rehabilitation of Existing Concrete Buildings and Commentary

American Society of Civil Engineers (ASCE)ASCE/SEI 7-10—Minimum Design Loads for Buildings

and Other Structures



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CHAPTER 4—TEST LOAD

4.1—Service loads4.1.1 Service loads shall be determined in accordance

with the governing general building code requirements. The dead load portion of the service loads shall be separated into components Dw and Ds.

4.1.2 Unless documentation or tests are available to define the density of concrete used in the structure, the density of normalweight reinforced concrete shall be taken as 2400 km/m3 for calculation of Dw.

4.1.3 Fluid loads F, due to weight and pressure of fluids with well-defined densities and controllable maximum heights, are permitted to be included in the superimposed dead load, Ds, for defining the test load magnitude in 4.2. If fluid loads F are due to weight and pressure of fluids that do not have well-defined densities or controllable maximum heights, then F shall be included with live load L for defining the test load magnitude in 4.2.

4.2—Test load magnitude 4.2.1 Test load magnitude (TLM) shall be as defined in

4.2.2 and 4.2.3 except as modified by 4.2.4 and as permitted or required by the local building authority. For load testing and evaluation, live loads are permitted to be reduced in accordance with the general building code. If the general building code requires application of impact factors to the live loads, the same impact factors shall be included in the live load used in 4.2.2 through 4.2.4.

4.2.2 When load testing will evaluate only part of the portions of a structure that are suspected of containing deficiencies or that have been repaired or rehabilitated and whose adequacy is to be verified, and members to be tested are statically indeterminate, then Eq. (4.2.2a) through (4.2.2c) shall be used to determine the TLM.

TLM = 1.3(DW + DS) (4.2.2a)

TLM = 1.0DW + 1.1DS + 1.6L + 0.5(Lr or S or R) (4.2.2b)

TLM = 1.0DW + 1.1DS + 1.6(Lr or S or R) + 1.0L (4.2.2c)

4.2.3 When all suspect portions of a structure are to be load tested, or when the elements to be tested are determi-nate and the suspect flaw or weakness is controlled by flex-ural tension, the TLM (including dead load already in place) shall not be less than the largest value from Eq. (4.2.3a) through (4.2.3c). If the deficiency in statically determinate members is not tension-controlled, then Eq. (4.2.2a) through (4.2.2c) shall be used to determine the TLM.

TLM = 1.2(DW + DS) (4.2.3a)

R4—TEST LOAD

R4.2—Test load magnitude The required TLM follows the recommendations of ACI

437.1R. The value of the TLM is intended to be consis-tent with the factored load combinations of ASCE/SEI 7. The TLM is appropriate for evaluating concrete structures designed in accordance with the current or previous editions of ACI 318.

R4.2.3 Smaller load factors are permitted for determi-nate tension-controlled sections to reduce the potential for inelastic deformations as a result of the load test and because of the extra ductility and associated warning expected to develop before failure or collapse. Tension-controlled sections are also usually less sensitive to variations in concrete strength.

When testing structures designed using the load factors and φ-factors in the 2002 and later editions of ACI 318, wherein load factors and φ-factors are changed from earlier editions, the test load may induce bilinear elastic (cracked)



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TLM = 1.0DW + 1.1DS + 1.4L + 0.4(Lr or S or R) (4.2.3b)

TLM = 1.0DW + 1.1DS + 1.4(Lr or S or R) + 0.9L (4.2.3c)

4.2.4 If serviceability is a criterion in the evaluation of the structure, a test load level equivalent to 1.0D + 1.0L + 1.0(Lr or S or R) shall be included in the loading cycles so that the behavior of the structure at service load level can be evaluated.

4.2.5 It shall be permitted to modify the load factors used in Eq. (4.2.2a) through (4.2.2c) and (4.2.3a) through (4.2.3c) in accordance with 4.2.5.1.

4.2.5.1 If the ratio of service live loads to service dead loads exceeds 2.0, that is, if (L + (Lr or S or R))/(DW + DS) > 2.0 and if the suspect deficiency is tension-controlled, it shall be permitted to reduce the load factor applied to the live load L in Eq. (4.2.2b) to 1.4 and in Eq. (4.2.3b) to 1.3, and to reduce the load factor applied to roof live loads, snow loads, or rain loads (Lr or S or R) in Eq. (4.2.2c) to 1.4 and in Eq. (4.2.3c) to 1.3.

or inelastic behavior for some structures. Discussion is provided in Chapter 6 regarding linearity of response as part of acceptance criteria.

When testing members not meeting the minimum shear reinforcement requirements on the basis of 11.4.6.1 of ACI 318-11, but meeting strength requirements on the basis of 11.4.6.2 through 11.4.6.4, an assessment of the test load at which cracking in the web-shear region will occur is recom-mended. Section R11.3.3 of ACI 318-11 indicates that Eq. (11-12) can be used to determine the shear force that will cause web-shear cracking in prestressed concrete members. Cracking that does not close after removal of the test load may occur where nonprestressed reinforcement yields during the load test. Precast/prestressed members with thin webs, such as double tees, can be a concern in this regard because they may be prone to developing permanent damage from full test loads.

R4.2.5.1 For buildings with large live loads compared with the structure’s self-weight and weight of superimposed dead loads, there may be a concern that an otherwise adequate structure could be loaded into the inelastic range during the load test, inducing permanent deformations. This could occur, for example, when testing a structure prestressed for a lower, more typical, service load condition but reinforced with bonded reinforcement to provide adequate design strength for full factored code-required live load. Section 4.2.5.1 provides some flexibility for moderating the TLM in such cases. This provision in effect permits reducing the TLM to approximately 85 percent of demand as defined in Eq. (9-2) of ACI 318-11 for the referenced equations of 4.2.2, and reducing the TLM to approximately 80 percent of demand for the referenced equations of 4.2.3. These reduc-tions are permitted only for those cases where the limiting strength being tested is tension-controlled, implying a ductile failure mode with large accompanying deflections.



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CHAPTER 5—LOADING PROTOCOL

5.1—Safety 5.1.1 Load tests shall be conducted in a manner to provide

safety to people and the structure during the test. Shoring shall be designed by a licensed design professional and installed prior to the start of the load test.

5.1.2 Safety measures shall be implemented in such a way as not to interfere with load test procedures or affect results.

5.2—Load arrangement 5.2.1 The areas loaded shall be selected to maximize

the response characteristics due to applied test load (ATL) specified in Chapter 4. More than one test load arrangement shall be used if a single arrangement will not simultaneously result in maximum values of the effects necessary to demon-strate the adequacy of the structure.

5.2.2 Either uniform or concentrated loads are permitted. In the case of uniform loading, arching of the applied load shall be avoided and concentrated load effects investigated. If concentrated loads are used to simulate distributed loading, they shall be of such magnitude and so located as to produce equivalent maximum internal moments and forces at critical cross sections as would be produced by uniform loads.

5.2.3 The load shall be applied at locations so that its effects on the structural elements for which safety or service-ability is in doubt are maximized and the probability of unloaded members sharing the applied load is minimized. If it is shown by analysis that adjoining unloaded elements will help resist some of the load, the contribution of these members shall be taken into account.

R5—LOADING PROTOCOL

R5.1—Safety R5.1.1 Shoring should be provided before a load test,

whether the entire structure or only a portion is involved, to support the structure in case of failure during the test. Shoring should be designed to support dead loads, the ATL, and all additional superimposed loads on the portion of the building for which collapse is possible. The effects of impact loading on the shoring, which is likely if a structure or member fails during the test, should be considered in the selection of shoring elements. This may be accomplished by designing the shoring to support at least twice the total test load plus the existing dead load.

For multistory structures, shoring more than one level to prevent progressive collapse in the event of failure should be considered. For example, if all floors below the test floor cannot support the weight of the test element, the loads it supports, and the imposed test loads, then the shoring should be extended to suitable bearing surface.

R5.1.2 For horizontal members, shoring should clear the underside of the structure by not more than the maximum expected deflection plus an allowance not to exceed 50 mm. Similar arrangements should be made for other types of members. Shoring should not influence or interfere with the free movement of the structure under the test load.

R5.2—Load arrangement

R5.2.2 Arching can be caused by the stacking of masses and refers to the tendency for the load to be transmitted nonuniformly to the flexural element being tested. For example, if a slab is loaded by a uniform arrangement of bricks with the bricks contacting each other, arching can result in reduction of the load on the slab near the midspan of the slab.

The internal moment and force diagrams due to concen-trated loads cannot exactly reproduce the ones due to uniform loads.

R5.2.3 The load arrangement should cause the maximum demands at the critical sections. In cases where it is shown by analysis that adjoining unloaded elements will help support some of the load, the load should be placed with consideration of the expected load sharing.



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5.3—Monotonic loading protocol 5.3.1 Applied test load (ATL) shall be applied in a prede-

termined pattern in at least four approximately equal incre-ments. If serviceability is a criterion in the evaluation of the structure, a load level equivalent to 1.0D + 1.0L + 1.0(Lr or S or R) shall be included so that the behavior at service load level can be evaluated. The tolerance for the applied sustained load shall be ±5 percent of the full ATL.

5.3.2 Load level and load steps are shown in Fig. 5.3.1. After applying each load level, deflection measurements shall be made at equal time intervals until the deflections stabilize. Deflections shall be considered stabilized when the difference between successive deflection readings taken no less than 2 minutes apart does not exceed 10 percent of the initial deflection recorded for the current load step. Each load step shall be held for at least 2 minutes. The full ATL shall be maintained for at least 24 hours.

5.3.3 A set of response measurements shall be made at the beginning and the end of the 24-hour sustained load period.

5.3.4 After response measurements are made at the end of the 24-hour sustained load period, the test load shall be removed as quickly as practicable.

5.3.5 A final set of response measurements shall be made at least 24 hours after removal of the load. If the structure has met the acceptance criteria at the conclusion of the loading cycle, it is not necessary to wait the full 24-hour period to make the final set of response measurements.

5.4—Cyclic loading protocol 5.4.1 Applied test load (ATL) shall be applied in repeated

loading and unloading cycles of increasing magnitude. At least six repeated loading cycles shall be used with the following magnitudes:

a) Cycles A and B—Service load level if serviceability is a criterion, otherwise 50 percent of ATLb) Cycles C and D—Halfway between Cycle A and 100 percent of ATLc) Cycles E and F—100 percent of ATL

R5.3—Monotonic loading protocol

R5.3.4 Intermediate response measurements should be made at selected intervals to determine whether significant creep is occurring during the hold period.

R5.4—Cyclic loading protocol In the cyclic loading procedure, the loads are applied in

loading-unloading cycles of increasing magnitude using hydraulic jacks. Using a sequence of loading and unloading cycles up to the predetermined maximum load level provides the opportunity to evaluate the structure at different load levels. The load sequence is intended to identify, in an explicit manner, any undesirable response. Because the structure is initially loaded and unloaded at low levels, the licensed design professional has the ability to better under-

Fig. 5.3.1—Loading protocol for monotonic load test procedure.



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The tolerance for the applied load shall be ±5 percent for each load cycle.

5.4.2 Load levels and load steps for each loading cycle are shown in Fig. 5.4.1 and are described in 5.4.4 through 5.4.6. After applying each load step, deflection measurements shall be made at equal time intervals until the deflections stabilize. Deflections shall be considered stabilized when the differ-ence between successive deflection readings taken no less than 2 minutes apart does not exceed 10 percent of the initial deflection recorded for the current load step. Each load step shall be held for at least 2 minutes.

5.4.3 At the end of each unloading phase, which shall use similar steps as the loading phase, a load Pmin of at least 10 percent of ATL shall be maintained to keep the test devices engaged. Pmin shall not exceed 15 percent of ATL.

5.4.4 Load Cycles A and B—For Load Cycle A, the load steps shall be initiated at Pmin. The first load cycle consists of five approximately equal load steps beyond Pmin. Load Cycle B is a repeat of Load Cycle A.

5.4.5 Load Cycles C and D—For Cycles C and D, the load at the first of five steps shall be at the same level as the third step of Cycle A, and the load at the second step shall be at the level of maximum load attained in Cycle A. The remaining three steps are of approximately equal magnitude.

5.4.6 Load Cycles E and F—For Cycles E and F, the load at the first of five steps shall be at the same level as the third step of Cycle C, and the load at the second step shall be at the level of maximum load attained in Cycle C. The remaining three steps shall be of approximately equal magnitude.

5.5—Load application 5.5.1 Load shall be applied in accordance with either 5.3

or 5.4, as determined by the licensed design professional.

stand end fixity and load transfer characteristics of the tested member by comparing actual deflection responses with calculated deflection responses. For statically indeterminate structures in particular, this ability allows checking the accu-racy of the assumptions on fixity and load sharing made in the structural analysis.

R5.5—Load application R5.5.1 The cyclic loading protocol allows performing

a real-time assessment of member characteristics such as linearity and permanency of deformations at different load levels. Hydraulic loading devices are generally required

Fig. 5.4.1—Loading protocol for cyclic load test procedure.



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5.5.2 Load shall be applied without impact and without causing vibration of the structure.

5.5.3 The loading differential for the twin cycles in the cyclic load test shall not exceed a maximum range of 10 percent.

5.6—Response measurements 5.6.1 Response measurements shall be taken beginning

10 minutes before the application of the first load level and continued throughout the loading and unloading cycles. Deflections shall be measured. The resolution of deflection measurement devices shall not exceed 1/100 of the expected deflection.

5.6.2 Measurements shall be made at locations where maximum response is expected as established by the licensed design professional.

5.7—Visual inspection5.7.1 The structure shall be inspected following appli-

cation of each load level for the formation, widening, or lengthening of cracks and other forms of distress; as well as for the presence of excessive deformations or rotations.

5.7.2 The licensed design professional shall assess the significance of any distress and determine whether it is safe to continue with the test.

to complete the cyclic loading protocol within a reason-able period of time. In some instances, the use of hydraulic loading devices may not be practicable. Examples of such instances may include thin shell structures and structures having inadequate existing members to be used as reaction members.

R5.6—Response measurements R5.6.1 In addition to deflection, response measurements

may include rotation, strain, and crack widths. If electronic data acquisition is used, the measurements can generally be taken at a rate of once each second. The data acquisition rate can be reduced to once each minute during the 24-hour sustained load period. In some cases, mechanical instrumen-tation could be used, such as analog dial gauges. In such cases, the measurements should be made after each load step.



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CHAPTER 6—ACCEPTANCE CRITERIA

6.1—Distress caused by load test 6.1.1 The portions or sections of the structure tested using

the cyclic loading protocol or monotonic loading protocol shall show no evidence of failure.

6.1.2 Deflections due to the test loads that exceed precal-culated deflections shall be evaluated by the licensed design professional. Based on this evaluation, a decision on whether to continue the load test shall be made by the licensed design professional.

6.1.3 Cracking shall be evaluated by the licensed design professional who shall decide on whether to continue the load test.

6.1.4 If at any time during the load test a member develops cracks indicating imminent shear failure, it shall be consid-ered as having failed the load test. Retesting of the failed member is not permitted.

6.1.5 In regions of anchorage and lap splices, the appear-ance of a series of short cracks inclined to the axis of the reinforcement or cracks parallel to the axis reinforcement shall be evaluated by the licensed design professional who shall decide on whether to continue the load test.

R6—ACCEPTANCE CRITERIA

R6.1—Distress caused by load test R6.1.1 A general acceptance criterion to assess the

behavior of a structure under test load is that no evidence of failure is observed. Evidence of failure includes cracking, crushing in compression zones, and deflections that are incompatible with the serviceability or safety requirements of the structure. No simple rules have been developed for application to all types of structures and conditions.

R6.1.2 Load tests are typically undertaken when it is not possible to evaluate by analytical means the performance of a structure with reasonable certainty due to the degree of deterioration or uncertainties in analysis. Thereby, calcula-tions to estimate deflections under the test loads may not be sufficiently accurate to be used as mandatory acceptance criteria. The licensed design professional should, however, make calculations to estimate deflections due to the test loads, considering as-built information for the structure. If the measured deflections exceed the calculated deflections, careful consideration should be given before continuing the load test to higher load levels. The calculated deflections need to be used to assess the performance during the load test and to interpret the load test results. Recommendations for the calculation of deflections are available in ACI 435R.

R6.1.3 Even though it is recognized that calculations regarding crack widths may not be sufficiently accurate to justify using them as mandatory acceptance criteria, the licensed design professional is to include their assessment under service load and other load levels as an integral part of the structural performance evaluation process.

The purpose of this recommendation is to caution the licensed design professional conducting the load test that the occurrence or excessive growth of cracks under service loads may be an indication of structural deficiencies.

R6.1.4 Shear forces are transmitted across a shear crack plane and are resisted by a mechanism combining the effects of the transverse reinforcement crossing the crack, if present; aggregate interlock; and dowel action of the reinforcement crossing the crack. As crack lengths increase to approach a horizontal projected length equal to the depth of the member and concurrently widen to the extent that aggregate interlock cannot occur, and as transverse stirrups, if present, begin to yield or display loss of anchorage, the member is assumed to be approaching imminent shear failure.

R6.1.5 Cracking along the axis of the reinforcement, at lap splices, and in anchorage zones may be related to high stresses associated with the transfer of forces between the reinforcement and the concrete. These cracks may be indica-tors of pending brittle failure of the element. The licensed design professional is required to evaluate the consequences of the observed cracking.



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6.2—Performance assessment at service load level

6.2.1 If serviceability is a criterion in the evaluation of the structure, deflections, crack spacing, and crack widths under a test load equivalent to the service condition shall be recorded and checked against limit values that are estab-lished by the licensed design professional before conducting the load test. If the limit values are exceeded at the service load level, the licensed design professional shall determine whether to terminate the load test.

R6.2—Performance assessment at service load level

R6.2.1 Irrespective of the loading procedure (that is, monotonic or cyclic load) and type of load (that is, uniformly distributed load over the entire tributary area, or concentrated loads), if the measured deflection or crack width exceed limits set before the load test by the licensed design profes-sional, careful consideration should be given as to whether to continue the load test to higher load levels. It is recog-nized that the variable nature of cracking and the challenges in accurately measuring and predicting crack width make the corresponding limits difficult to implement. The intent of the provision is to caution the licensed design professional that the occurrence or growth of excessive cracks under service loads may be an indication of structural deficiencies. Influ-ence of crack width is of particular significance for some members or structures, such as those exposed to aggressive environments.

Guidance for establishing possible limit values for deflec-tion and crack width at service load is as follows:

1. Maximum measured deflection should not exceed the permissible values given in Table 9.5(b) of ACI 318-11 for the various types of members. This recommendation is only applicable if the load distribution pattern reflects the one used for design, which is typically not the case for test loads of the strip or patch type. Furthermore, the first two values in Table 9.5(b) are intended for immediate live load deflections, while the third and fourth deflection limits are for the additional deflection occurring after attachment of nonstructural members due to long-term deflection caused by all sustained loads plus any immediate live load deflection. This makes these limits difficult to apply in the setting of a load test where only the immediate deflection due to applied loads can be measured. Additional long-term deflection due to sustained loads can be calculated and then added to the load test deflection results for live loading to arrive at a value that can be compared with the latter two limits of Table 9.5(b).2. The maximum width of new flexural cracks formed during the course of the load test or the change in width of existing flexural cracks should not exceed a limiting width determined by the licensed design professional before the load test. Consideration should be given to the intended use and exposure conditions for the structure or member. Limiting crack widths should be selected based on the following:

a) Suggested tolerable crack widths as reported in ACI 224Rb) The value of the analytical width calculated as the product s times ∆es (where s is the average spacing between cracks and ∆es represents the difference in strain in the longitudinal steel reinforcement when the cross section of interest is considered cracked and uncracked and subject to an applied moment at that location resulting from the service load)



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6.3—Acceptance criteria for monotonic loading protocol

6.3.1 Deflection limits6.3.1.1 The member or structure shall be considered to

have passed the load test if the residual deflection, ∆r, satis-fies Eq. (6.3.1) and the maximum deflection, ∆l, measured during the test satisfies Eq. (6.3.2).

4

lr

∆∆ ≤ (6.3.1)

180

tl

l∆ ≤ (6.3.2)

6.3.1.2 If the maximum deflection measured during the test, ∆l, is less than 1.3 mm or the deflection as a fraction of the span length, lt, is less than lt/2000, the residual deflection requirements given by Eq. (6.3.1) shall be permitted to be waived.

6.3.2 Retesting6.3.2.1 If the measured residual deflection ∆r does not

satisfy Eq. (6.3.1), it shall be permitted to repeat the load test if the maximum deflection ∆l satisfies Eq. (6.3.2).

6.3.2.2 The repeat test shall be conducted not earlier than 72 hours after removal of the test load for the first test.

6.3.2.3 The portion of the structure tested in the repeat test shall be considered acceptable if the residual deflection ∆r, measured at least 24 hours after removal of the load, satisfies Eq. (6.3.3), where deflections are measured relative to the position of the structure at the start of the repeat test.

2

10l

rrt

∆∆ ≤ (6.3.3)

where ∆l2 is the maximum deflection measured during the second test relative to the position of the structure at the beginning of the second test.

6.4—Acceptance criteria for cyclic loading protocol

6.4.1 Deviation from linearity index—The deviation from linearity index, IDL, calculated in accordance with Eq. (6.4.1), shall be monitored during all the cycles of the cyclic load test.

tan( )

1tan( )

iDL

ref

Iα

= −α

(6.4.1)

where tan(ai) is the secant stiffness of any point i on the increasing loading portion of the load-deflection envelope, and tan(aref) is the slope of the reference secant line for the load-deflection envelope, as shown in Fig. 6.4.1.

6.4.1.1 The deviation from linearity index shall be consid-ered acceptable if it does not exceed 0.25 for any point on the loading portion of the load-deflection envelope.

R6.3—Acceptance criteria for monotonic loading protocol

R6.3.1 The residual deflection for the monotonic load test limit follows past practice. If the structure shows no evidence of failure, recovery of deflection after removal of the test load is used to determine whether the performance of the structure is satisfactory. As a departure from past prac-tice, Eq. (6.3.2) sets an upper limit to the absolute measured deflection that, if exceeded, rules out retesting or the option of using deflection recovery as an acceptance criterion (ACI 437.1R). If Eq. (6.3.2) is satisfied and the member or struc-ture fails the residual deflection criterion on the first test, retesting is permitted. All deflections measured during retesting are relative to the position of the structure at the start of the repeat test.

If the member or structure is sufficiently stiff, deflection recovery is not relevant. In fact, it may even be unfeasible to measure the deflection recovery due to limitations in the resolution or accuracy of the deflection measurement equip-ment. To avoid penalizing a satisfactory structure in such a case, recovery measurements are waived and no check on deflection recovery is required if the absolute deflection is lower than 0.05 in. or the deflection as a fraction of span length is less than lt/2000 (ACI 437.1R).

R6.4—Acceptance criteria for cyclic loading protocol

R6.4.1 The deviation from linearity index should be checked at the critical locations of the member being load tested. The deviation from linearity index represents the measure of the nonlinear behavior of a member or struc-ture being tested. As a member becomes increasingly more damaged, its behavior may become more nonlinear, and its deviation from linearity increases. To define deviation from linearity, linearity is defined first as the ratio of the slopes of two secant lines intersecting the load-deflection enve-lope (Fig. 6.4.1). The load-deflection envelope is the curve constructed by connecting the points of the load-deflection data in the first of the two cycles of each load cycle.

If a member or structure is initially uncracked and becomes cracked during the load test, the change in flex-ural stiffness as a result of a drastic change in moment of inertia at the crack location(s) can produce a high deviation



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6.4.2 Permanency ratio—The permanency ratio Ipr, calcu-lated in accordance with Eq. (6.4.2a), shall be monitored during all the cycles of the cyclic load test.

( 1)p ipr

pi

II

I+= (6.4.2a)

where Ipi and Ip(i+1) are the permanency indexes calculated for the i-th and (i + 1)th load cycles, respectively, at the same load level using Eq. (6.4.2b) and (6.4.2c) and deflections as defined in Fig. 6.4.2.

ir

pi imax

I∆

=∆

(6.4.2b)

( 1)

( 1) ( 1)

ir

p i imax

I+

+ +

∆=

∆ (6.4.2c)

6.4.2.1 The permanency ratio shall be considered accept-able if it does not exceed 0.50 for all pairs of load cycles.

6.4.3 Residual deflection—The residual deflection ∆r, measured at least 24 hours after removal of the load at the completion of the load test, shall be considered acceptable if it satisfies Eq. (6.3.1), where ∆l is the maximum deflection measured during the test as shown in Fig. 6.4.1.

from linearity that is not necessarily related to degradation in strength (Nehil et al. 2007).

If the member/structure remains uncracked during the load test, the deviation from linearity should be computed under uncracked conditions.

If the transition between uncracked and cracked condition is experienced at a load cycle other than Cycle A, the load test may be restarted and Cycles A to E performed.

R6.4.2 Permanency ratio is evaluated considering the maximum deflection and the residual deflection for two cycles at each load level. If the permanency ratio exceeds the specified limit, it may be an indication that load applica-tion has damaged the member or structure and that inelastic behavior is taking place. High permanency ratios at low load levels (generally below service loads) might not be indicative of inelastic behavior when the measuring instru-ment resolutions are of the same order of magnitude as the actual deflections and deflection recovery. The permanency ratio might not be of significance if the absolute deflection measured for the twin cycles is lower than 1.3 mm or, as a fraction of span length, is less than lt/2000.

R6.4.3 If the structure shows no evidence of failure, recovery of deflection after removal of the test load is used to determine whether the performance of the structure is satisfactory. The residual deflection ∆r is the difference between the initial and final (after the 24-hour recovery period following complete load removal) deflections for the load test. The residual deflection limit for concrete struc-tures with nonprestressed reinforcement follows past prac-tice. Bares and FitzSimons (1975) suggest that 25 percent residual deflection is acceptable for reinforced concrete

Fig. 6.4.1—Schematic load-versus-deflection curve for cyclic load test.



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6.4.4 Retesting6.4.4.1 If any of the acceptance criteria in 6.4.1 to 6.4.3 is

not satisfied, the member or structure shall be considered to have failed the load test except as provided in 6.4.4.2.

6.4.4.2 It shall be permitted to retest the member or struc-ture if the maximum deflection, ∆l, measured during the test satisfies Eq. (6.3.2).

6.4.4.3 The repeat test shall be conducted not earlier than 24 hours after complete removal of the test load for the first test.

6.4.4.4 The portion of the structure that is retested shall be considered acceptable if the residual deflection ∆rrt, measured at least 24 hours after removal of the load, satisfies Eq. (6.3.3), where ∆l2 is the maximum deflection measured during the second test relative to the position of the structure at the beginning of the second test.

6.5—Provision for lower load rating 6.5.1 If the structure under investigation does not satisfy

conditions of 6.1 and 6.2 and the criteria of 6.3 or 6.4, the structure shall be permitted for use at a lower load rating based on the results of the load test or structural analysis, if approved by the building official.

structures and 20 percent is acceptable for prestressed concrete structures.

R6.5—Provision for lower load rating R6.5.1 Except for load-tested members that have failed

or show extensive distress due to the load test, the building official may permit the use of a structure or member at a lower load rating that is judged to be safe and appropriate on the basis of the test results. When the lower load rating is achieved through structural analysis, the structural model used to analyze the structure should represent the actual behavior and, therefore, it should be calibrated to replicate the load test.

Fig. 6.4.2—Schematic of load-versus-deflection curve for two cycles at same load level.



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6.5.2 If the cyclic loading protocol is used, a number of twin load cycles at increasing load levels shall be applied until either the deviation from linearity index or perma-nency ratio fails. The safe live load shall be established by subtracting the factored dead load from the critical load at which one of the acceptance criteria was not met, and dividing that difference by the live load factor. Load factors used for the determination of the safe live load shall be deter-mined in accordance with the general building code. After unloading, the residual deflection shall satisfy Eq. (6.3.3).

6.5.3 If the structure or member has undergone significant damage, as determined by the licensed design professional, the distressed structure or members shall not be put into service, even at a lower load rating.



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R7—COMMENTARY REFERENCESAmerican Concrete InstituteACI 224R-01—Control of Cracking in Concrete Struc-

tures (Reapproved 2008)ACI 318-11—Building Code Requirements for Structural

Concrete and CommentaryACI 435R-95—Control of Deflection in Concrete Struc-

tures (Reapproved 2000)ACI 437.1R-07—Load Tests of Concrete Structures:

Methods, Magnitude, Protocols, and Acceptance CriteriaACI 562-13—Code Requirements for Evaluation, Repair,

and Rehabilitation of Existing Concrete Buildings and Commentary

American Society of Civil Engineers (ASCE)ASCE/SEI 7-10—Minimum Design Loads for Buildings

and Other Structures

Cited referencesBares, R., and FitzSimons, N., 1975, “Load Tests of

Building Structures,” Journal of the Structural Division, V. 101, No. 5, May, pp. 1111-1123.

Nehil, T.; Nanni, A.; and Masetti, F., 2007, “Strength Evaluation by Load Testing,” Concrete International, V. 29, No. 3, Mar., pp. 53-58.



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http://www.asce.org/

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As ACI begins its second century of advancing concrete knowledge, its original chartered purpose remains “to provide a comradeship in finding the best ways to do concrete work of all kinds and in spreading knowledge.” In keeping with this purpose, ACI supports the following activities:

· Technical committees that produce consensus reports, guides, specifications, and codes.

· Spring and fall conventions to facilitate the work of its committees.

· Educational seminars that disseminate reliable information on concrete.

· Certification programs for personnel employed within the concrete industry.

· Student programs such as scholarships, internships, and competitions.

· Sponsoring and co-sponsoring international conferences and symposia.

· Formal coordination with several international concrete related societies.

· Periodicals: the ACI Structural Journal and the ACI Materials Journal, and Concrete International.

Benefits of membership include a subscription to Concrete International and to an ACI Journal. ACI members receive discounts of up to 40% on all ACI products and services, including documents, seminars and convention registration fees.

As a member of ACI, you join thousands of practitioners and professionals worldwide who share a commitment to maintain the highest industry standards for concrete technology, construction, and practices. In addition, ACI chapters provide opportunities for interaction of professionals and practitioners at a local level.

American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701

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Code Requirements for Load Testing of Existing Concrete Structures and Commentary

The AMERICAN CONCRETE INSTITUTE

was founded in 1904 as a nonprofit membership organization dedicated to public service and representing the user interest in the field of concrete. ACI gathers and distributes information on the improvement of design, construction and maintenance of concrete products and structures. The work of ACI is conducted by individual ACI members and through volunteer committees composed of both members and non-members.

The committees, as well as ACI as a whole, operate under a consensus format, which assures all participants the right to have their views considered. Committee activities include the development of building codes and specifications; analysis of research and development results; presentation of construction and repair techniques; and education.

Individuals interested in the activities of ACI are encouraged to become a member. There are no educational or employment requirements. ACI’s membership is composed of engineers, architects, scientists, contractors, educators, and representatives from a variety of companies and organizations.

Members are encouraged to participate in committee activities that relate to their specific areas of interest. For more information, contact ACI.

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ACI 437.2M-13: Code Requirements for Load Testing of Existing Concrete Structures (ACI ... · 2020....

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