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PCA R&D Serial No. 2403
In-Plane Lateral Load Resistance of WallPanels in Residential Buildings
by Armin B. Mehrabi
© 2000 Portland Cement Association
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TABLE OF CONTENTSPage
List of Tables................................................................................................................ iii
List of Figures............................................................................................................... iv
Glossary of Terms........................................................................................................ vii
Executive Summary ..................................................................................................... xi
Introduction .................................................................................................................. 1
Objective and Scope .................................................................................................... 1
Test Setup.................................................................................................................... 1
Instrumentation ............................................................................................................ 2
Test Procedure............................................................................................................. 3
Wall Panel 1, Wood-Frame Wall Panel ........................................................................ 3Structural Details ................................................................................................. 3Test Results ........................................................................................................ 3
Wall Panel 2, Steel-Frame Wall Panel.......................................................................... 4Structural Details ................................................................................................. 5Test Results ........................................................................................................ 5
Wall Panel 3, ICF Flat Wall Panel................................................................................. 6Structural Details ................................................................................................. 6Test Results ........................................................................................................ 7
Wall Panel 4, ICF Screen-Grid Wall Panel ................................................................... 7Structural Details ................................................................................................. 7Test Results ........................................................................................................ 9
Wall Panel 5, ICF Waffle-Grid Wall Panel .................................................................... 9Structural Details ................................................................................................. 10Test Results ........................................................................................................ 10
Comparison of Results ................................................................................................. 11
Summary and Conclusions........................................................................................... 12
Recommendations ....................................................................................................... 13
Future Study ................................................................................................................ 13
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TABLE OF CONTENTS (continued)
Acknowledgments ........................................................................................................ 14
References................................................................................................................... 15
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LIST OF TABLESPage
Table 1 - Comparison between Strength and Stiffness of Tested Panels ..................... 11
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LIST OF FIGURESPage
Figure 1(a) - Test Setup and Details ............................................................................ 16
Figure 1(b) - Test Setup and Details ............................................................................ 17
Figure 2 - Test Setup ................................................................................................... 18
Figure 3 - Lateral Support System................................................................................ 19
Figure 4 - Lateral Support Roller .................................................................................. 20
Figure 5 - Top Cross Beam .......................................................................................... 21
Figure 6 - Hydraulic Ram ............................................................................................. 22
Figure 7 - Instrumentation ............................................................................................ 23
Figure 8 - Load Cell...................................................................................................... 24
Figure 9 - Displacement Transducer T1 ....................................................................... 25
Figure 10 - Displacement Transducer T2 ..................................................................... 26
Figure 11 - Details of Wood-Frame Wall Panel ............................................................ 27
Figure 12 - Wood-Frame Wall Panel ............................................................................ 28
Figure 13 - Wood-Frame Wall Panel Test Setup .......................................................... 29
Figure 14 - Lateral Load–Lateral Displacement Curve for Wood-Frame Wall Panel..... 30
Figure 15 - Lateral Load–Shear Displacement Curve for Wood-Frame Wall Panel ...... 31
Figure 16 - Failure Mode of Wood-Frame Wall Panel................................................... 32
Figure 17 - Failure Mode of Wood-Frame Wall Panel; (a) General View; (b) Nailand Screw Pull-Out; (c) Base Separation; (d) Toe Crushing ....................... 33
Figure 18 - Details of Steel-Frame Wall Panel.............................................................. 34
Figure 19 - Steel-Frame Wall Panel ............................................................................. 35
Figure 20 - Steel-Frame Wall Panel Test Setup ........................................................... 36
Figure 21 - Lateral Load–Lateral Displacement Curve for Steel-Frame Wall Panel ...... 37
Figure 22 - Lateral Load–Shear Displacement Curve for Steel-Frame Wall Panel ....... 38
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LIST OF FIGURES (continued)Page
Figure 23 - Failure Mode of Steel-Frame Wall Panel.................................................... 39
Figure 24 - Failure Mode of Steel-Frame Wall Panel; (a) General View; (b) StudBuckling and Board Damage; (c) Base Separation ..................................... 40
Figure 25 - Buckling and Bending of Steel Studs ......................................................... 41
Figure 26 - ICF Flat Wall Forms ................................................................................... 42
Figure 27 - Details of ICF Flat Wall Panel .................................................................... 43
Figure 28 - Wall Panel Footing ..................................................................................... 44
Figure 29 - ICF Flat Wall Panel Test Setup .................................................................. 45
Figure 30 - Lateral Load–Lateral Displacement Curve for ICF Flat Wall Panel............. 46
Figure 31 - Uplift-Lateral Load Curve for ICF Flat Wall Panel....................................... 47
Figure 32 - Failure Mode of ICF Flat Wall Panel........................................................... 48
Figure 33 - Failure Mode of ICF Flat Wall Panel; (a) Base Separation; (b) GeneralView; (c) Pull-Out Cracks; (d) Toe Crushing ............................................... 49
Figure 34 - ICF Screen-Grid Wall Forms ...................................................................... 50
Figure 35 - Details of ICF Screen-Grid Wall Panel ....................................................... 51
Figure 36 - ICF Screen-Grid Wall Panel Test Setup..................................................... 52
Figure 37 - Lateral Load–Lateral Displacement Curve for Screen-GridWall Panel................................................................................................... 53
Figure 38 - Uplift–Lateral Load Curve for Screen-Grid Wall Panel ............................... 54
Figure 39 - Failure Mode of ICF Screen-Grid Wall Panel ............................................. 55
Figure 40 - Failure Mode of ICF Screen-Grid Wall Panel; (a) Shear and FlexuralCracks; (b) General View; (c) Base Separation and Flexural Crack; (d)Shear Crack and Toe Splitting .................................................................... 56
Figure 41 - ICF Waffle-Grid Wall Forms ....................................................................... 57
Figure 42 - Details of ICF Waffle-Grid Wall Panel ........................................................ 58
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LIST OF FIGURES (continued)Page
Figure 43 - ICF Waffle-Grid Wall Panel Test Setup ...................................................... 59
Figure 44 - Lateral Load–Lateral Displacement Curve for Waffle-Grid Wall Panel ....... 60
Figure 45 - Uplift–Lateral Load Curve for Waffle-Grid Wall Panel................................. 61
Figure 46 - Failure Mode of ICF Waffle-Grid Wall Panel............................................... 62
Figure 47 - Failure Mode of ICF Waffle-Grid Wall Panel; (a) General View; (b)Base Separation and Shear Crack; (c) Shear Crack and Toe Splitting ....... 63
Figure 48 - Comparison of Lateral Load–Lateral Displacement Curves........................ 64
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GLOSSARY OF TERMS
Anchorage - A device used to fasten and prevent the movement of a structural element relativeto its supporting structure.
Anchor Bolts - A bolt with the threaded portion projecting from a structure, generally used tohold the frame of a building secure against wind or seismic load.
Beams - A structural member, generally horizontal, subjected primarily to flexure.
Bearing - The contact between a bearing member, as a beam, and a pier, wall, or otherunderlying support.
Bond - Adhesion and grip of concrete or mortar to reinforcement or other surfaces against whichit is placed.
Buckling - Instability in the form of bending or warping under compression loading.
Calibration - To determine, check, or rectify the graduation of any instrument givingquantitative measurements.
Cast-in-Place - Concrete or mortar which is deposited in the place where it is required to hardenas part of the structure.
Cold Joint - A joint or discontinuity formed when a concrete surface hardens before the nextbatch is placed against it, characterized by poor bond unless necessary procedures are observed.
Columns - A compression member, generally vertical, the width of which does not exceed fourtimes its thickness and the height of which exceeds four times its least lateral direction.
Compression - A stress which causes a body to shorten in the direction of applied force.
Compressive Strength - The measured maximum resistance of a concrete or mortar specimen toaxial loading; expressed as force per unit cross sectional area.
Concrete - A composite material which consists essentially of a binding medium within whichare embedded particles or fragments of aggregate; in portland cement concrete, the binder is amixture of portland cement and water.
Cross Section - The section of a body perpendicular to a given axis of the body.
Dead Load - The weight of a structure or portion thereof.
Deformation - A change in dimension or shape due to stress.
Development Length - The length of embedment required to anchor a dowel or reinforcementbar.
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Diaphragm Action - The constraint provided by the in-plane stiffness of a plate element.
Displacement - Linear movement.
Displacement Transducer - An electro-mechanical instrument used to measure displacement ormovement.
Dowel - A steel pin or reinforcing bar which extends into two adjoining portions of a concreteconstruction so as to connect the portions and transfer shear or tension load.
Flat Panel - A concrete panel, reinforced in two or more directions, generally without beams orgirders to transfer shear loads to supporting members.
Footing - The portion of a foundation of a structure which spreads and transmits load directly topiles, or to the soil or supporting grillage.
Foundation - The material(s) through which the loads of a structure are transmitted to the earthor supporting structure.
Friction - Surface resistance to relative motion, as of a body sliding or rolling.
Gravitational Load - Vertical loads resulting from the weight of a structure or supportedobjects.
Gypsum - A mineral having the composition: calcium sulfate dihydrate (CaSO4 2H2O).
Hinge - A connection or joint that allows rotation but no separation of adjacent members.
Hold-Down Device - A device to anchor a wall or slab to its supporting member and preventuplift.
Hydraulic Ram - A mechanical device that uses hydraulic pressure to apply force or loads.
Incremental Loading - Loading performed in discrete intervals or stages.
In-Plane - In a direction tangential to a surface.
Insulating Concrete Forms (ICFs) - A concrete forming system using stay-in-place forms offoam plastic insulation, a composite of cement and foam insulation, wood chips, or otherinsulating material, used for constructing cast-in-place concrete walls. Some systems aredesigned to have one or both faces of the form removed after construction.
Kip - A unit of force equal to a kilopound (1000 lb; 454 kg).
Lateral - In the horizontal direction.
Leeward - The edge of the specimen toward which the lateral load acts.
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Linear - Consisting of, involving, or describable by terms of the first degree.
Live Load - Any load that is not permanently applied to a structure, typically transient andsustained gravity loads resulting from the weight of people, furnishings, and equipment.
Load - Mechanical force that is applied to a body.
Load Cell - An electro-mechanical instrument used to measure load or force.
Maximum Resistance - The stress at which a material or structural member ruptures or fails.
Monolithic - Concrete cast with no joints other than construction joints.
Monotonic - A load or function either increasing or decreasing.
Nominal Size - A size used for purposes of general identification; the actual size of the part willbe approximately the same as the nominal size, but need not be exactly the same.
Oriented Strand Board (OSB) - Structural sheathing composed of wood chips and fibersbonded in a resin.
Out-of-Plane - In a direction perpendicular to a surface.
Post-Tensioning Rods - Steel tendons or rods, generally high strength, that are used to applycompression to hardened concrete.
Reaction Wall - A frame or wall designed and constructed to react against and impart load to aspecimen.
Reinforced Concrete - Concrete containing reinforcement and designed on the assumption thatthe two materials act together in resisting forces.
Reinforcement - Metal bars, wires, or other slender members that are embedded in concrete insuch a manner that the metal and the concrete act together in resisting loads.
Residual Strength - The strength remaining in a structural member following yield.
Screen-Grid Panel - A perforated concrete wall with closely spaced vertical and horizontalconcrete members (cores) with voids in the concrete between the members created by the ICFform.
Seismic Load - A dynamic inertial load resulting from seismic or earthquake ground motions.
Seismic Zones - Designated areas associated with a particular level or range of seismic risk andassociated seismic design parameters (i.e., peak ground acceleration); seismic zones 0, 1, and 2generally correspond to low, yet successively greater seismic design loads.
Shear Load - A load tangential to the plane on which it acts.
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Splice - Connection of one reinforcing bar to another by overlapping, welding, mechanical endconnectors, or other means.
Splice Length - The length required to transfer the load between overlapped reinforcing bars in asplice.
Static Load - A load that does not vary as a function of time.
Steel Stud Framing - Framing composed typically of cold formed light gauge metal studs.
Stiffness - Resistance to deformation.
Stress - The force acting across a unit area in a solid material, resisting the separation,compacting, or sliding that is induced by external forces.
Studs - Slender, upright members of wood, steel, etc., forming the frame of a wall, generallycovered with plaster work, siding, etc.
Tension - A stress which causes a body to lengthen in the direction of applied force.
Tie - A region of a concrete panel reinforced to act as a beam or column.
Uplift - The separation of a wall panel from a footing at the windward edge due to overturningcaused by lateral load.
Waffle-Grid Panel - A solid concrete wall with closely spaced vertical and horizontal concretemembers (cores) with a concrete web between members created by the ICF form.
Wind Load - The force or pressure exerted on a building structure and its components resultingfrom wind.
Windward - The edge of the specimen from which the lateral load acts.
Wood Frame - Panels or walls framed from wood studs.
Yielding - The stress level at which plastic deformation occurs.
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EXECUTIVE SUMMARY
The performance of wall panels in residential buildings under wind and seismic loading is amajor concern. In addition to the forces resulting from dead and live gravitational loads, wallpanels are subject to in-plane shear and/or out-of-plane lateral forces when exposed to theseloading conditions. Several investigations have been conducted on the behavior of wall panelssubjected to out-of-plane loading, and there exist design guidelines and prescriptive methods forproportioning the wall panels for a satisfactory performance against this type of duress. For theperformance under in-plane forces, however, there is a need for additional investigation.
Construction Technology Laboratories Inc. (CTL), was authorized by the Portland CementAssociation (PCA) to conduct an investigation on the performance of various types of residentialbuilding wall panels. The overall objective of this investigation was to compare the in-planeshear resistance of various types of wall panels commonly used in residential buildings. Fivepanel specimens with an aspect ratio (height/length) of 2 were tested. These were a wood-framewall panel, a steel-frame wall panel, and three ICF wall panels. One flat, one screen-grid, and onewaffle-grid ICF wall panel were tested. The structural details for the test specimens were adoptedbased on design recommendations and guidelines for typical exterior wall panels in earthquakezones 1 or 2, and for minimum wind speed of up to 70 miles per hour. The test setup andprocedure followed general guidelines of the ASTM Standard Practice for Static Load Test forShear Resistance of Framed Walls for Buildings, (E564-95). (1)
The test results indicated that, under similar restraint conditions, ICF wall panels are muchstronger and stiffer than similar wood- or steel-frame walls panels. The ICF wall panels resisted amaximum lateral load of 6 to 8.5 times the corresponding maximum loads resisted by the framedwall panels. The initial stiffness of the ICF wall panels was between 18 and 38 times the initialstiffness of the wood- or steel-frame wall panels. Under lateral loads of about twice as much asthe maximum resistance of the framed walls, the ICF panels behaved linearly, showing no signsof damage of any sort. The deformations under this level of loads were in the range of 0.05 to0.07 in. However, the maximum deflection provided by the ICF wall panels equaled or exceededabout 2 % of the story height. The higher strength of the ICF wall panels reinforces theresidential building’s ability to resist winds and earthquakes of much higher magnitudes.However, it should be pointed out that the effects of dynamic and out-of-plane loading, openingsin the panels, and various wall configurations have not been considered in this study, and oneshould be cautious in extending these results for the behavior of the panels during actual groundmotion.
The higher stiffness of ICF wall panels limits the lateral deformation and prevents potentialdamage to non-structural elements in buildings. In the case of moderate earthquakes (or winds),the repair cost of the damaged non-structural components is usually the major (or the only) partof the restoration costs. It should be pointed out that the connections between the wall panels andthe footings and between the panels and the roof/floor can strongly influence the behavior of thewall panels and the development of an efficient load transfer mechanism in the structure. Further,the positioning of the wall panels in the building plan and roof/floor diaphragm action cansignificantly influence the lateral load distribution to the wall panels.
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The results of this testing program have pointed out some design aspects that could be improved,with minimal cost, to enhance the in-plane shear behavior of the wall panels. For the wood-framewall panels, the use of screws (with pull-out resistance higher than nails) in place of nails forconnection of the OSBs to frame members would increase the maximum lateral resistance byproviding more integrity and preventing early separation of the boards from the frame. For thesteel-frame wall panels, the use of stiffening plates, reduced screw spacing, avoidance of webholes in the lower part of the vertical studs, and utilizing heavier gauge bottom tracks can preventearly buckling and bending of the frame members.
For the ICF wall panels, the use of dowels with longer development lengths between the footingand the wall will prevent early pull-out of the dowels and strengthen the base of the wall panels.To be effective, longer dowels should be accompanied by vertical reinforcing bars in the wallthat have adequate splice length with the dowel bars. The presence of minimal verticalreinforcement in the panels can also significantly improve the lateral behavior by providing moreductility and integrity in the case of shear/flexural cracking and a better interlock at the interfaceof the cracked sections.
This study, within its scope, demonstrated that ICF wall systems are highly advantageous oversome of the most common wall systems being used in construction of residential buildings,especially when subjected to lateral in-plane loading. However, to formulate and quantify thestrength and serviceability issues, a more detailed knowledge of the behavior of ICF wall panelsseems necessary. For this purpose, the investigation could be extended to include experimentaland analytical studies. Simulation of the structural behavior could be carried out using analyticalmodels to be developed based on available experimental results. Then, a broad-reachingparametric study could be conducted to deduce reliable code provisions and designrecommendations for the use of ICF wall panels in the areas of high seismicity.
Keywords
In-plane lateral resistance, wall panels, residential buildings, seismic loading, wind loading,insulating concrete forms, ICF wall panels, concrete walls, wood-frame walls, steel-frame walls,shear resistance, lateral stiffness, lateral strength.
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INTRODUCTION
The performance of wall panels in residential buildings under wind and seismic loading is amajor concern. In addition to the forces resulting from dead and live gravitational loads, wallpanels are subject to in-plane shear and/or out-of-plane lateral forces when exposed to theseloading conditions. Several investigations have been conducted on the behavior of wall panelssubjected to out-of-plane loading, and there exist design guidelines and prescriptive methods forproportioning the wall panels for a satisfactory performance against this type of duress. For theperformance under in-plane forces, however, there is a need for additional investigation. The lackof information is especially noticeable for relatively new types of wall systems, such asinsulating concrete form (ICF) wall panels.
Compared with other conventional wall systems, ICF wall panels have a significantly strongercross section for in-plane shear resistance when restrained against uplift. In a residential building,the restraint against in-plane uplift is provided by the dead load and diaphragm action of the roofor floors. Proper anchorage to the foundation and vertical reinforcement in the wall will alsohave a positive effect on the in-plane shear performance of ICF walls. In-plane shear resistanceof ICF wall panels can be compared to the resistance of other conventional wall panel systemsthrough experimental and/or analytical investigations. The present study focuses on theexperimental demonstration of the lateral in-plane performance of residential wall panels.
OBJECTIVE AND SCOPE
The overall objective of this investigation is to compare the in-plane shear resistance of varioustypes of wall panels commonly used in residential buildings. The scope of this study was limitedto demonstrating the lateral in-plane resistance of three types of major wall systems throughstandard static-load testing. Five panel specimens with an aspect ratio (height/length) of 2 weretested. These were a wood-frame wall panel, a steel-frame wall panel, and three ICF wall panels.One flat, one screen-grid, and one waffle-grid ICF wall panel were tested. The structural detailsfor the test specimens were adopted based on design recommendations and guidelines for typicalexterior wall panels in earthquake zones 1 or 2 and for minimum wind speed of up to 70 milesper hour. It should be noted that an extra measure was taken to strengthen the anchorage ofwood- and steel-frame wall panel specimens to their footing. The test setup and procedurefollowed general guidelines of the ASTM Standard Practice for Static Load Test for ShearResistance of Framed Walls for Buildings (E564-95). (1) Necessary modifications were applied tothe test procedure to better serve the objectives of this study.
TEST SETUP
The test setup shown in Figs. 1 and 2 complied with the recommendations of ASTM E 564. Theload reaction wall was a 10.5x6x1-ft reinforced concrete element anchored to the laboratorystrong floor with a 280-kip post-tensioning force. To transfer the lateral load along the top edgeof the panels, a beam was attached firmly to the top of the wall panels. The top beam was a 6-in.-deep timber member for the wood- and steel-frame walls. For the ICF wall panels, the top beamwas concrete with adequate anchorage (five 3/4-in.-diameter high-strength bolts) to the panels.
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Wall panels were anchored to a footing with structural details to be discussed later in this report.The footing, in turn, was anchored to the laboratory strong floor by applying vertical forcesthrough two spreader beams and four post-tensioning rods. This was to prevent the relativedisplacement between the footings and the lab floor.
To restrict the wall panels against out-of-plane movement, a railing system was provided for thetop beam attached to the specimens. This is shown in Fig. 3. The railing consisted of two channelsections supported laterally by the reaction frame at one end and by a reinforced concrete columnat the other. The reinforced concrete column was also anchored to the laboratory strong floor bya post-tensioning rod. As shown in Fig. 4, steel-ball roller systems were used between the topbeam of the specimens and the lateral support railing to restrict the out-of-plane motion and toallow a lateral in-plane motion with minimum friction.
The lateral railing system was also used to prevent the rigid body motion of the specimens due touplift. This was achieved by using a cross beam, shown in Fig. 5, which rested against the topbeam of the specimen near the windward end via a roller system. This cross beam was bolted tothe lateral railing system. The vertical load developed in the cross beam, and consequently in thelateral railing system was transferred to the reaction wall and to the strong floor through crossbeams. These cross beams held the top of the lateral railing and were connected to the lab floorwith post-tensioning rods. The rigid body motion prevention system restricted only the uplift ofthe windward side of the panel and did not apply any initial vertical loading. However, verticalload would be developed in the system as the specimen was subjected to racking load.
The loading apparatus consisted of a 60-ton-capacity hydraulic ram. The ram was attached to thereaction frame at the proper elevation such that the center of the ram was aligned with the centerof the specimen top beam, that is, 3 in. higher than the top edge of the wall panels. A horizontalhinge system was also positioned between the ram and the top beam. Figure 6 shows thehydraulic ram in setup.
INSTRUMENTATION
Instrumentation included a load cell and four displacement transducers. These are shown inFig. 7. As shown in Fig. 8, the load cell was installed between the top beam of the specimen andthe hydraulic ram. A 25-kip-capacity load cell was used for wood- and steel-frame wallspecimens, and a 50-kip-capacity load cell was used for ICF wall panels. The load cells werecalibrated for these tests. The maximum error in load reading was limited to about 1%, and theresolution was 1 lb.
The displacement transducers were positioned according to the instrumentation requirements ofASTM E 564. Transducer T1 measured the total horizontal displacement of the top of the panel,T2 measured the slip at the base of the wall panel with respect to the footing, T3 measured theuplift at the base of the panel in the windward side, and T4 measured the vertical displacement atthe toe of the wall. In addition to the electrical displacement transducers discussed above, amechanical dial gauge was also installed to assure zero displacement of the footing with respectto the lab floor. Figures 9 and 10 show the displacement transducers T1 and T3, respectively.
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TEST PROCEDURE
The wall panel specimens were subjected to monotonically increasing static lateral in-planeloads. Before data recording, a small initial load (200–300 lb) was applied to each specimen andwas held for a few minutes to seat the connections. The initial load was then removed and zeroreadings were taken. After zero readings, the main loading started, and the load was increasedgradually. Any major distress, cracking, or damage was observed and recorded. The loading wascontinued beyond the maximum resistance level. In most cases, the test was terminated after theresidual strength had been considerably reduced from the peak value, due to excessive damage inthe specimens. In one case, Wall Panel 3, the test was terminated after excessive lateraldeformation. As can be noticed, this test procedure did not precisely follow the incrementalloading and unloading process of ASTM E 564. Monotonically increasing loading wasconsidered more appropriate for the purposes of this study.
WALL PANEL 1, WOOD-FRAME WALL PANEL
Wall Panel 1 was a wood-stud-frame panel. Except for the base anchorage, the panelconstruction was according to the details of panels typically used in residential buildings for alow design wind speed (up to 70 miles per hour).
Structural Details
The structural details for this specimen are shown in Fig. 11. Figure 12 shows photographs of thespecimen before attachment of the gypsum wallboard. The frame of the panel was built using2x4, spruce-pine-fir, 254 stud-grade, S-dry, wood studs. The studs were joined together usingthree 12D direct nails. The framing was covered with a 7/16-in. OSB (oriented strand board) onone side and 1/2-in. gypsum wallboard on the other side. The OSB was attached to the framingusing 6D common nails with 6-in. spacing along the edges and 12-in. spacing along the interiorstuds. The gypsum wallboard was attached to the framing using 1-1/4-in., No. 6, coarse-threadscrews with 4-in. spacing along the edges and 8-in. spacing along the interior studs.
For lateral load distribution, a 6x6-in. timber top beam was connected to the specimen with five3/4-in. (A325) bolts. The panel specimen was anchored to an 80x16x16-in. reinforced concretefooting. Two Simpson HD-10A hold-downs were used at the two ends, and two 5/8-in.-diameteranchor bolts were used along the base with a 2-ft spacing as an extra measure to improve baseanchorage.
Test Results
Figure 13 shows a photograph of Wall Panel 1 in the test setup. The test procedure describedearlier was followed for testing of Wall Panel 1. Figure 14 shows the lateral load vs. lateraldisplacement (at the top of the specimen) response curve. Figure 15 shows the curve for lateralload vs. internal shear displacement of the panel. The shear displacement was calculated with thedata recorded from four displacement transducers installed on the specimen. The followingrelationship was used to calculate the shear displacement of the panel (ASTM E564):
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∆int = ∆1 - ∆2 - (∆3 - ∆4) a/b (1)
in which •int is the internal shear displacement, •1 is the horizontal displacement at the top of thepanel, •2 is the horizontal displacement at the bottom of the panel with respect to the footing, •3 isthe vertical displacement at the bottom of the wall at the windward side, •4 is the verticaldisplacement at the bottom of the wall at the leeward side, a is the height of the panel, and b isthe length of the panel.
At an applied lateral load of about 3,000 lb, separation of the wall panel from footing wasobserved at the windward side. This was followed by some noises indicating distress in the boardand nails/screws connecting the board to the frame. Up to this load, the panel shows a fairlylinear behavior. The maximum lateral resistance was achieved at a load of 4,553 lb and lateraldisplacement of 0.885 in. At this stage, crushing was observed in the OSB at the leeward bottomcorner near the footing, after which, with increasing lateral displacement, the load droppedgradually. With increasing displacement beyond that corresponding to the maximum resistance,the nails holding the OSB to the wood frame started to pull out, and consequently the OSBbulged and separated from the frame at higher displacements. The test was terminated at a lateraldisplacement of about 4.5 in. with a residual load of about 2,000 lb. The failure mode of thispanel is shown in Figs. 16 and 17. As indicated in these figures, at the end of the test, thecrushing and bulging of the OSB, as well as pull-out of the nails, extended to a large area in thebottom of the panel near the leeward side.
From the data collected, the shear stiffness of the panel was calculated according to therelationships suggested in ASTM E564. The global shear stiffness (G’), was calculated to be18,500 lb/in. using the following relation for the applied lateral load (P) equal to 1/3 of themaximum resistance:
G’ = (Pa)/(∆1b) (2)
The internal shear stiffness (Gint) was calculated to be 65,000 lb/in. using the following relationfor the applied lateral load (P) equal to 1/3 of the maximum resistance:
Gint = (Pa)/(∆intb) (3)
After the test, the gypsum board was stripped off the frame to afford inspection for damage toframe members. There was no apparent sign of damage to the wood studs. However, the nailsconnecting the vertical stud to the bottom horizontal stud at the windward side were pulled outslightly, leaving a gap of about 1/8 in. It was apparent that the Simpson hold-down device hadimproved the joint between vertical stud and horizontal bottom stud, as well as between verticalstud and footing, and added to the integrity of the whole panel. Without this device, the verticalstud in the windward side would have separated completely from the bottom stud.
WALL PANEL 2, STEEL-FRAME WALL PANEL
Wall Panel 2 was a steel stud–frame panel. Except for the base anchorage, the panel constructionwas according to the details of typical panels used in residential buildings for a low design windspeed (up to 70 miles per hour).
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Structural Details
The structural details for this specimen are shown in Fig. 18. Figure 19 shows photographs ofthis specimen before the attachment of the gypsum board. The frame of the panel was built using2x4, 20 gauge, steel studs. The studs were joined together using two No. 6, 7/16-in. drill-point,pan-head screws. The framing was covered with a 7/16-in. OSB (oriented strand board) on oneside and 1/2-in. gypsum wallboard on the other. The OSB was attached to the framing using 1-1/4-in., No. 6, drill-point screws with 6-in. spacing along the edges and 12-in. spacing along theinterior studs. The gypsum wallboard was attached to the framing using 1-1/4-in., No. 6, drill-head screws with 4-in. spacing along the edges and 8-in. spacing along the interior studs.
For lateral load distribution, a 6x6-in. timber top beam was connected to the specimen with five3/4-in. (A325) bolts. The panel specimen was anchored to an 80x16x16-in. reinforced concretefooting. For anchorage, two Simpson HD-10A hold-downs were used at two ends and two 5/8-in.-diameter anchor bolts were used along the base with a 2-ft spacing. This detail was employedas an extra measure for the base anchorage.
Test Results
Figure 20 shows a photograph of Wall Panel 1 in the test setup. The test procedure describedearlier was followed for testing of Wall Panel 2. Figure 21 shows the lateral load vs. lateraldisplacement (at the top of the specimen) response curve. Figure 22 shows the curve for lateralload vs. internal shear displacement of the panel. The shear displacement was calculated usingEq. 1.
Separation of the wall panel from the footing was observed on the windward side at an appliedload of about 2,400 lb followed by some noises indicating distress in the board and screwsconnecting the boards to the frame. Up to a load of about 3,000 lb, the panel showed a fairlylinear behavior. Crushing was observed in the OSB at the leeward bottom corner near the footingat a load of about 3,500 lb. However, the board did not bulge and the load did not drop at thisstage due to the efficient connection of the board to the steel studs provided by the screws. Themaximum lateral resistance was achieved later at a load of 4,004 lb and lateral displacement of0.755 in., with local buckling of flanges of the vertical stud visible at the leeward side near thebolts connecting the stud to the Simpson hold-down devices. With further increases in the lateraldisplacement, the load dropped gradually to 2,500 lb. At maximum resistance, separation of thepanel from footing at the windward side had reached about 1/2 in. The crushing of OSB extendedalong the length of the panel touching the footing, and later some bulging/buckling was alsoobserved along this line. However, the screws were still holding the board to the frame firmly.With further increase in the displacement beyond 2.5 in., the resistance picked up once againgradually to the level of 3,500 lb. At this point (load of 3,500 lb and displacement of 4.5 in.), thelocal buckling of the vertical stud extended and, load dropped with a faster pace than before. Thevertical steel stud buckled totally at a lateral top displacement of about 5.2 in. and lateral load ofabout 2,500 lb, after which the OSB and gypsum board were separated from the frame. The testwas terminated shortly after this stage. The failure mode of this panel is shown in Figs. 23 and24. As indicated in these figures, at the end of the test, the crushing and bulging of the OSB wasextended to a large area in the bottom of the panel near the leeward side.
6
From the data collected, the shear stiffness of the panel was calculated using Eqs. 2 and 3. Theglobal shear stiffness (G’) was calculated to be 30,000 lb/in. and the internal shear stiffness (Gint,)to be 70,000 lb/in.
After the test, the gypsum board was stripped off the frame to allow for damage inspection of theframe members. There was major damage to the steel studs, mostly in the form of local andglobal buckling of the vertical studs. In addition, the bottom steel track was also bent up at thewindward side. Figure 25 shows the damage to the steel studs. Oservation indicated that theSimpson hold-down device had had some beneficial effects on the joint area by transferringdamage to the regions farther from the joint connections. However, the weak links introduced bythe local and global buckling and bending of the slender studs with thin flanges and webovershadowed the positive effects of the strong hold-down devices.
WALL PANEL 3, ICF FLAT WALL PANEL
Wall Panel 3 was an ICF flat wall panel with a 4-in. uniform thickness. The forms for thisspecimen were provided by LITE-FORM International. Figure 26 shows the forms used forcasting. This wall panel was designed for wind speed of up to 70 miles per hour, according to thePrescriptive Method for Insulating Concrete Forms in Residential Construction.(2)
Structural Details
Figure 27 shows the structural details of Wall Panel 3. This drawing depicts the dimensions andreinforcing details of the concrete panel and does not show the insulating concrete forms. The6x8-in. beam on the top of the panel was used for distribution of the lateral in-plane load and didnot constitute a structural part of the wall. This wall panel was cast on an 84x18x14-in.reinforced concrete footing (cast separately). Nominal compressive strengths of the concrete usedin the footing and the wall panel (as per the purchasing order to the ready mix companyproviding the concrete) were 3000 psi and 2500 psi, respectively. However, the 28-daycompressive tests conducted on cylindrical specimens indicated average strengths of 6144 psiand 5110 psi for footing and wall panel, respectively. The compressive strength of the concreteused for casting of the wall panel was tested again on and around the wall testing days (32-dayage). The average cylindrical compressive strength of the concrete in the wall panel at this agewas 5210 psi. Grade 60 reinforcing bars were used in both the wall panel and the footing. Toverify the strength of the steel bars, a tension test was also conducted on a No. 4 bar, whichresulted in a tensile yielding strength of 63 ksi and maximum tensile strength of 91 ksi. Thesevalues are consistent with Grade 60 material. The top surface of the footing was roughened andcleaned before casting of the wall to provide better friction and bond with the wall. Figure 28shows details of the wall footing. According to the requirements for cold joints (PrescriptiveMethod for Insulating Concrete Forms in Residential Construction), three No. 4 dowelsconnected the wall to the footing. The wall panel had three horizontal bars, one on top and two atabout 1/3 of the wall height from the bottom. Standard hooks were provided at the ends of thehorizontal bars. This was to simulate, as much as possible, the required continuity of thehorizontal bars. In this wall panel, three vertical bars were spliced with the dowels projected fromthe footing and terminated in the top beam with a standard bend. A 6x6x1/4-in. plate was
7
anchored to the side of the top beam to be used for application of the load and bearing of the loadcell.
Test Results
Wall Panel 3 was tested 31 days after casting. Figure 29 shows a photograph of Wall Panel 3 intest setup. The test procedure described earlier was followed. Figure 30 shows lateral load vs.lateral displacement (at the top of the specimen) response curve. An attempt was made tocalculate the internal shear displacement for ICF walls from the data collected with theinstrumentation using Eq. 1. However, the results were not reasonable, and negative internalshear displacements occurred during several stages. This can be attributed to the fact that Eq. 1 isdesigned for framed wall panels and does not apply to solid concrete walls. In concrete walls,sudden localization of cracks near the bottom would create discontinuities in the sheardisplacement curve and would subsequently result in negative displacements.
One important parameter in the behavior of concrete wall panels, however, is separation of thewall from the footing, which follows the initiation of a localized crack at the wall footinginterface. To capture this event, the displacement reading of the transducer installed at the bottomof the wall in the windward side was plotted against the applied lateral load and is shown for theICF flat wall panel in Fig. 31. A major change in the slope of this curve would be an indicationof crack formation and separation at the bottom of the wall in the windward side.
The wall panel was loaded gradually to up to about 5,000 lb. At this level the loading was keptconstant and the wall panel was inspected for visible sign of damage or distress. No damage wasobserved. Also, the lateral load–lateral displacement curve up to this load level followed a linearpath indicating no sign of damage, which would create a nonlinear response otherwise. The firstcrack was visible at the wall panel/footing interface in the windward side at an applied load ofabout 10,000 lb. However, when reviewing Figs. 30 and 31, it becomes clear that the first crackhappened at about 8,500 lb, where the slope of the curves in both figures shows a considerablechange. This indicates that this wall panel resisted about twice as much load as the maximumstrength of wood- and steel-frame wall panels without exhibiting any sign of damage or distress.At higher applied loads, the crack at the bottom of the wall opened wider and extended towardthe leeward toe. At an applied load of about 16,000 lb, the crack opening was about 1/8 in,. andthe crack extended over about 2/3 of the base length. At an applied load of about 16,000 lb, avertical crack developed, starting from the bottom of the wall near the windward end andextending about 12 in. Location of this crack coincided with the position of the dowel barextending from the footing into the wall and was an indication of bond failure for this dowel. Ata load of about 22,000 lb, an inclined crack developed on the top of the earlier vertical crackextending from the windward side down to the base of the wall panel. Crushing was observed inthe leeward toe region of the wall at a load of about 28,000 lb, and a horizontal crack developednear the mid-height of the wall extending from the windward side to almost 1/4 of the walllength at about 30,000 lb load. In spite of extension of cracking and crushing in the wall base, thestrength increased gradually to a maximum of 34,245 lb at a lateral displacement of about 2.5 in.After this, the strength remained almost flat with a slight descend. The test was terminated at alateral displacement of nearly 3 in. The failure mode of this panel is shown in Figs. 32 and 33.As it can be noticed in these figures, the pull-out of the dowel bar between the footing and the
8
wall in the windward side is quite pronounced, with the separation of a conical crack in theconcrete in the wall base and vertical cracks along the bar. A vertical splitting crack alsodeveloped on the east side of the windward toe.
From the data collected, the global shear stiffness of the panel was calculated using Eq. 2. Theglobal shear stiffness (G’) was calculated to be 708,000 lb/in. for a 5,000 lb lateral load level and308,500 lb/in. for an 8,500 lb lateral load level.
WALL PANEL 4, ICF SCREEN-GRID WALL PANEL
Wall Panel 4 was an ICF screen-grid panel. The forms for this specimen were provided byReddi-Form, Inc. Figure 34 shows the forms used for casting. This wall panel was designed forwind speed of up to 70 miles per hour according to the Prescriptive Method for InsulatingConcrete Forms in Residential Construction.
Structural Details
Figure 35 shows the structural details of Wall Panel 4. This drawing depicts the dimensions andreinforcing details of the concrete panel and does not show the insulating concrete forms. Theconcrete wall panel consisted of a monolithic network of five vertical ties (columns) and sevenfull, plus two one-half horizontal ties (beams). The 6x8-in. beam on the top of the panel was fordistribution of the lateral in-plane load and did not constitute a structural part of the wall. Thiswall panel was cast on an 84x18x14-in. reinforced concrete footing, with details shown in Fig.28. Mechanical properties of concrete and reinforcing bars were as described for Wall Panel 3.The top surface of the footing was roughened and cleaned before casting of the wall to providebetter friction and bond. According to the cold joint requirements of the Prescriptive Methodcited above, three No. 4 dowels connected the wall to the footing. The wall panel had threehorizontal bars, one on top and two others at about the1/3 and 2/3 points along the height.Standard hooks were provided at the ends of the horizontal bars. This was to simulate, as muchas possible, the continuity of the horizontal bars as required. In this wall panel, no verticalreinforcing bar was used. However, three dowels similar to those in the footing were insertedbetween the wall panel and the top beam. A 6x6x1/4 -in. plate was anchored to the side of the topbeam to be used for application of the load and bearing of the load cell.
9
Test Results
Wall Panel 4 was tested 32 days after casting. Figure 36 shows a photograph of the test setup.The test procedure described earlier was followed for this panel. Figure 37 shows the lateral loadvs. lateral displacement (at the top of the specimen) response curve. Displacement readings of thetransducer installed at the bottom of the wall in the windward side were plotted against theapplied lateral load and are shown in Fig. 38.
The wall panel was loaded gradually to up to about 5,000 lb. At this level the loading was keptconstant and the wall panel was inspected for visible signs of damage or distress. No damage wasobserved. Also, the lateral load–lateral displacement curve up to this level followed a linear path,indicating lack of damage. The first crack was visible at the wall panel to footing interface in thewindward side at an applied load of about 9,000 lb. When reviewing Figs. 37 and 38, it is clearthat the first crack happened at about 8,600 lb, where the slope of the curves in both figuresshows a drastic change. This indicates that this wall panel resisted about twice as much lateralload as the maximum load attained in wood- and steel-frame panels without any sign of damageor distress. At an applied load of about 11,000 lb, a horizontal crack developed starting from thewindward side of the wall about 12 in. from the footing. This crack inclined toward the base ofthe wall after passing the position of the first dowel bar along the interface of the wall andfooting. The formation of this crack suggests that the dowel action of the bar between the footingand the wall resulted in separation of a large chunk of concrete from the wall, and can beconsidered as failure of the wall to footing joint. Formation of this crack dropped the loadslightly, however, the load increased with increasing the lateral displacement. Shortly after thisstage, at a lateral load of about 12,000 lb, an inclined crack developed starting from thewindward side at about 1/3 of the wall height from the bottom. This shear crack reduced thelateral load considerably, to about 7,500 lb. With increasing lateral displacement, the loadgradually increased almost linearly. As the load increased, significant opening and extensionwere observed in the existing cracks. The inclined shear crack developed earlier extended towardthe leeward toe of the wall. At the maximum lateral resistance of 27889 lb, the shear crackextended all along the wall, resulting in complete shear failure and an abrupt drop in lateral load.Lateral displacement at the maximum load was about 1.7 in. The test was terminated after shearfailure. The failure mode of this panel is shown in Figs. 39 and 40. These figures clearlydemonstrate the shear-dominated failure pattern for this wall panel.
From the data collected, the global shear stiffness of the panel was calculated using Eq. 2. Globalshear stiffness (G’) was calculated to be 526,000 lb/in. for a 5,000 lb lateral load level and320,000 lb/in. for an 8,600 lb lateral load level.
WALL PANEL 5, ICF WAFFLE-GRID WALL PANEL
Wall Panel 5 was an ICF waffle-grid panel. The forms for this specimen were provided byAmerican Polysteel Forms. Figure 41 shows the forms used for casting. This wall panel wasdesigned for wind speed of up to 70 miles per hour according to the Prescriptive Method forInsulating Concrete Forms in Residential Construction.
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Structural Details
Figure 42 shows the structural details of Wall Panel 5. This drawing depicts the dimensions andreinforcing details of the concrete panel, and does not show the insulating concrete forms. Theconcrete wall panel consisted of a monolithic network of four vertical ties (columns) and fivefull, plus two one-half horizontal ties (beams), with a 2-in. thick web filling between ties. The6x8-in. beam on the top of the panel was for distribution of the lateral in-plane load and did notconstitute a structural part of the wall. This wall panel was cast on an 84x18x14-in. reinforcedconcrete footing, with details shown in Fig. 28. Mechanical properties of concrete andreinforcing bars were as described for Wall Panel 3. The top surface of the footing wasroughened and cleaned before casting of the wall to provide better friction and bond. Accordingto the cold joint requirements of the Prescriptive Method cited above, three No. 4 dowelsconnected the wall to the footing. The wall panel had three horizontal bars, one on top and twoothers at about the1/3 and 2/3 points along the height. Standard hooks were provided at the endsof the horizontal bars to simulate, as much as possible, the required continuity of the horizontalbars. In this wall panel, no vertical reinforcing bar was used. However, three dowels similar tothose in the footing were placed between the wall panel and the top beam. A 6x6x1/4-in. platewas anchored to the side of the top beam to be used for application of the load and bearing of theload cell.
Test Results
Wall Panel 5 was tested 33 days after casting. Figure 43 shows a photograph of the test setup.The test procedure described earlier was followed. Figure 44 shows the lateral load vs. lateraldisplacement (at the top of the specimen) response curve. Displacement readings of thetransducer installed at the bottom of the wall in the windward side were plotted against theapplied lateral load and are shown in Fig. 45.
The wall panel was loaded gradually up to about 5,000 lb. At this level the loading was keptconstant and the panel was inspected for visible signs of damage or distress. No damage wasobserved. Also, the lateral load–lateral displacement curve up to this level followed a linear path,indicating lack of damage. The first crack was visible at the wall panel to footing interface in thewindward side at an applied load of about 9,000 lb. When reviewing Figs. 44 and 45, it is clearthat the slope of the curves in both figures shows a drastic change. This indicates that this wallpanel resisted about twice as much lateral load as the maximum strength of wood- and steel-frame wall panels, without any sign of damage or distress. Formation of this crack reduced theload slightly. However, the load increased further as the lateral displacement increased. Withincreasing lateral displacement, the load gradually increased almost linearly. As the loadincreased, considerable opening and extension was observed in the wall base crack. At a load of26,000 lb, this crack opened approximately 1/2 in. and extended over almost 3/4 of the baselength. At a lateral load of 28,000 lb, a horizontal/diagonal crack developed, starting from thewindward side at distance of about 1/4 the wall height from the footing. The shape of the cracksuggested initiation of a shear failure in the wall. This event resulted in a considerable drop in thelateral load, down to about 18,000 lb. With further increase in the lateral displacement, theresistance increased gradually, for a second time following a linear path. During this stage, inaddition to extension of the shear and base cracks toward the leeward toe, concrete spalling was
11
also observed along the shear crack and near the toe. At the maximum lateral resistance of28,946 lb, the shear crack extended all along the wall, resulting in complete shear failure of thewall and an abrupt drop in the applied load. Lateral displacement at the maximum load was about1.6 in. The test was continued after the shear failure with a residual resistance of about 22,000 lb.Relative displacement of the two sides of the shear crack was clearly visible at this stagesuggesting that the residual resistance was maintained only due to friction forces along the crackline, resulting from the normal forces generated by the vertical restraint of the test setup. Also inthis stage, crushing and more spalling of concrete were observed in the leeward toe region of thewall panel. The test was terminated at a lateral displacement of about 2.2 in. The failure mode ofthis panel is shown in Figs. 46 and 47. These figures clearly show the shear-dominated failurepattern for this wall panel.
From the data collected, the global shear stiffness of the panel was calculated using Eq. 2. Theglobal shear stiffness (G’) was calculated to be 662,000 lb/in. for a 5,000 lb lateral load level and264,000 lb/in. for a 9,000 lb lateral load level.
COMPARISON OF RESULTS
Figure 48 compares the lateral responses of the five wall panels tested. As can be seen in thisfigure, the lateral strength and lateral stiffness of the ICF wall panels are consistently higher thanthose of the wood- or steel-frame wall panels. Table 1 compares some of the important strengthand stiffness parameters for the walls tested.
Table 1 - Comparison Between Strength and Stiffness of Tested Panels
Wall panel
Globallateral
stiffness*(lb/in.)
Load at firstmajor
damage(lb)
Displacementat first major
damage(in.)
Maximumlateral
resistance(lb)
Displacement atmaximum lateral
resistance(in.)
Wood-frame 18,500 3,500 0.51 4,553 0.89
Steel-frame 30,000 3,500 0.54 4,004 0.76
ICF flat+ 708,000 8,500 0.06 34,245 2.66
ICF screen-grid 526,000 8,600 0.05 27,889 1.71
ICF waffle-grid 662,000 9,000 0.07 28,946 1.64
* At 1/3 of the maximum resistance for wood- and steel-frame walls and at a lateral load of5000 lb for ICF walls.
+ Only ICF flat wall panel had vertical continuous # 4 bars (see Fig. 27).
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SUMMARY AND CONCLUSIONS
In-plane lateral load tests were conducted on five wall panel specimens with an aspect ratio(height/length) of 2. The panels represented some of the typical wall systems being used forconstruction of residential buildings. These were a wood-frame wall panel, a steel-frame wallpanel, and three ICF wall panels. One flat, one screen-grid, and one waffle-grid ICF wall panelwere tested. The structural details for the test specimens were adopted from the designrecommendations and guidelines for a typical exterior wall panel in the earthquake zone 1 or 2,with a minimum wind speed of up to 70 miles per hour. The test setup and procedure followedgeneral guidelines of ASTM E564-95, Standard Practice for Static Load Test for ShearResistance of Framed Walls for Buildings. Necessary modifications were applied to the testprocedure to better serve the objectives of this study.
The tests resulted in important information about the strength, stiffness, and failure patterns ofthe wall systems tested. The results indicated that, under similar restraint conditions, ICF wallpanels are much stronger and stiffer than similar wood- or steel-frame walls panels. The ICF wallpanels resisted a maximum lateral load of about 6 to 8.5 times the corresponding maximum loadsresisted by the framed wall panels. The initial stiffness of the ICF wall panels was between 18and 38 times the initial stiffness of the wood- or steel-frame wall panels. Under lateral loads ofabout twice as much as the maximum resistance of the framed walls, the ICF panels behavedlinearly, showing no damage of any sort. The deformations under this level of loads wereextremely small and were in the range of 0.05 to 0.07 in. However, the maximum deflectionprovided by the ICF wall panels equaled or exceeded about 2 % of the story height.
The failure of the wood-frame wall panel was dominated by the crushing and bulging/buckling ofthe OSB in the leeward bottom corner, and with the pull-out of the nails connecting the board tothe frame members. In the steel-frame wall panel, the failure was governed by the OSB in thesame manner as in the wood-frame panel, and with the local and global buckling/bending of thesteel studs. The ICF flat wall panel failed in a flexural mode by separation of the wall from thefooting in the windward side and crushing of the concrete in the leeward toe. The failure of ICFscreen-grid and waffle-grid wall panels involved a shear failure in the form of an inclined crackin the lower 1/3 of the wall.
These results suggest that when subjected to lateral in-plane loading from sources such as windor earthquake, ICF wall panels are not only considerably stronger, but also much stiffer thanframed wall panels. The higher strength of ICF wall panels reinforces a residential building’sability to resist winds and earthquakes of much higher magnitudes. The higher stiffness of ICFwall panels limits lateral deformation and prevents potential damage to non-structural elementsin buildings. In the case of moderate earthquakes (or winds), repair of damaged non-structuralcomponents is usually the major (or the only) part of restoration costs. It should be pointed outthat the connections between wall panels and footings, and more importantly, between panelsand roofs/floors can strongly influence the behavior of wall panels. The lack of well-designedand adequate connections can interrupt the development of an efficient load transfer mechanismbetween the structural members and could result in early collapse, even when the wall panels arefavorably strong. Further, the positioning of the wall panels in a building plan and roof/floordiaphragm action can significantly influence the lateral load distribution to the wall panels.
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Therefore, proper positioning of shear walls and minimum diaphragm action for roof/floor panelsshould be provided in the architectural and structural design of buildings.
RECOMMENDATIONS
The results of this testing program have pointed out some design aspects that could be improvedto enhance the in-plane shear behavior of wall panels. These improvements can be implementedwith minimal cost and would not necessarily complicate or alter the construction proceduresignificantly.
For wood-frame wall panels, the use of screws (with pull-out resistance higher than nails) inplace of nails for connection of OSBs to frame members would increase the maximum lateralresistance by providing more integrity and preventing early separation of the boards from theframe.
For steel-frame wall panels, the use of stiffening plates or members connected to the lower partof vertical studs and utilizing heavier gauge bottom tracks could prevent early buckling andbending of frame members. Also, reduced screw spacing for OSB to frame member attachmentin the lower part of vertical studs would shorten the unsupported length of the studs in the criticalcompression region and provide better integrity of board and frame. Avoiding web holes, asmuch as possible, in the lower part of the vertical studs would also help to reduce thesusceptibility of steel studs to local and global buckling.
For ICF wall panels, the use of dowels between footing and wall with longer developmentlengths will prevent early pull-out of the dowels and strengthen the base of the wall panels. Pull-out of these dowels and damage to the concrete in the wall near the footing were observed in thetests. To be effective, longer dowels should be accompanied by vertical reinforcing bars in thewall that have adequate splice length with the dowel bars. Otherwise, flexural cracks willdevelop past the termination point of the dowels, as was the case for the screen- and waffle-gridwall specimens. The presence of minimal vertical reinforcement could also significantly improvelateral behavior by providing more ductility and integrity in the case of shear/flexural cracking,and a better interlock at the interface of cracked sections.
In addition to the above specific recommendations, general considerations such as properpositioning of shear walls in building plans, providing an appropriate diaphragm action forroof/floor panels, and adequately engineered connections between floor/roof and wall panels forlateral load transfer are essential for any type of wall panel system.
FUTURE STUDY
This study, within its scope, has proven that ICF wall systems are highly advantageous oversome of the most common wall systems being used in construction of residential buildings,especially when subjected to lateral in-plane loading. However, to formulate and quantify thestrength and serviceability issues, a more detailed knowledge of the behavior of ICF wall panelsseems necessary. To better understand the behavior of ICF wall panels subjected to lateral in-plane loading, the investigation should be extended in different directions. This could include
14
experimental as well as analytical studies. Simulation of structural behavior could be carried outusing models to be developed based on the experimental results. Then, a broad-reachingparametric study could be conducted to deduce reliable code provisions and designrecommendations for the use of ICF wall panels in areas of high seismicity. Following is a list ofsome of the activities that could be developed for future studies on ICF wall panels:
• In-plane shear testing of ICF panels to investigate the improving effects of themodifications recommended in this study.
• In-plane shear testing of ICF panels with different aspect ratios.
• In-plane shear testing of ICF panels with window or door openings.
• In-plane shear testing of ICF panels damaged by out-of-plane loads.
• Testing of conventional and improved ICF wall panel connections.
• Development of finite element models for ICF wall panels.
• Development of simple analytical models for ICF wall panels.
• Calibration of analytical models using the results of the experimental study.
• Parametric studies on the behavior of ICF wall panels using the developed analyticalmodels.
• Code provisions and design recommendations based on the results of the parametric studyon ICF wall panels to be used in the regions of high seismicity.
• Development of simplified seismic design procedures and examples.
ACKNOWLEDGMENTS
The project described in this report was sponsored by the Portland Cement Association (PCA,Project No. 98-14). However, the opinions and findings expressed in this report are those of theauthor, and do not necessarily reflect the views of the Portland Cement Association. Thecontributions to this project of LITE-FORM International, American Polysteel Forms, andReddi-Form Inc., are greatly appreciated. The author thanks Mr. Lionel Lemay and Mr. DonnThompson of PCA for their direction and guidance. The author would also like to express hisgratitude to Mr. Felix Gonzales, Mr. Brad Anderson, and Mr. Greg Neiweem of CTL for theirassistance in the testing aspects, and Ms. Nancy Adams and Mr. Ralph Reichenbach of CTL fortheir part in preparation of the report.
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REFERENCES
1. ASTM E 564 - 95, “Standard Practice for Static Load Test for Shear Resistance of FramedWalls for Building,”ASTM Standards, Vol. 04.11, pp. 556–559.
2. Prescriptive Method for Insulating Concrete Forms in Residential Construction, NationalAssociation of Home Builders Research Center, Inc., Upper Marlboro, MD, 1998
FIGURE 2 TEST SETUP
FIGURE 3 LATERAL SUPPORT SYSTEM
FIGURE 4 LATERAL SUPPORT ROLLER
FIGURE 5 TOP CROSS BEAM
FIGURE 6 HYDRAULIC RAM
FIGURE 8 LOAD CELL
FIGURE 9 DISPLACEMENT TRANSDUCER T1
FIGURE 10 DISPLACEMENT TRANSDUCER T2
FIGURE 12 WOOD-FRAME WALL PANEL
FIGURE 13 WOOD-FRAME WALL PANEL TEST SETUP
FIG
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FIGURE 19 STEEL-FRAME WALL PANEL
FIGURE 20 STEEL-FRAME WALL PANEL TEST SETUP
FIGURE 24 FAILURE MODE OF STEEL-FRAME WALL PANEL
FIGURE 25 BUCKLING AND BENDING OF STEEL STUDS
FIG
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FIGURE 29 ICF FLAT WALL PANEL TEST SETUP
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FIGURE 36 ICF SCREEN-GRID WALL PANEL TEST SETUP
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FIGURE 43 ICF WAFFLE-GRID WALL PANEL TEST SETUP
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