Michael A. Riley and Fahim Sadek - NIST · 2009. 5. 7. · NISTIR 6938 EXPERIMENTAL TESTING OF ROOF...

NISTIR 6938

EXPERIMENTAL TESTING OF ROOF TO WALLCONNECTIONS IN WOOD FRAME HOUSES

Michael A. Riley and Fahim Sadek

April 2003

Building and Fire Research LaboratoryNational Institute of Standards and TechnologyGaithersburg, MD 20899-8611

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United States Department of CommerceDonald L. Evans, Secretary

Technology AdministrationPhillip J. Bond, Under Secretary for Technology

National Institute of Standards and TechnologyArden L. Bement, Jr., Director

Experimental Testing of Roof to Wall Connections in Wood Frame Houses

ABSTRACT

The majority of residential construction in the United States is wood-frame construction.These buildings perform well under gravity loads, but considerable damage has been observed in such structures after significant earthquakes and major hurricanes. This is due toweaknesses inherent in current wood-frame construction and underscores the need for improving the structural performance of typical homes. To enhance the resistance of houses tonatural disasters and to reduce the risk to life and property, the behavior of wood-frame buildings subjected to dynamic and lateral loads needs to be better understood. These buildingsare typically constructed from diaphragms that are joined by inter-eomponent connections,which can greatly influence the overall behavior of the structure. An understanding of the behavior of each of the structural components and connections is essential to accurately predictthe performance of a housing unit under different types of loading.

While the response of many of the components of wood-frame houses are well documented,there is a lack of performance data for inter-eomponent connections between intersectingwalls, roofs and walls, and walls and foundations. Since post-event investigations of severalrecent disasters indicate that failure of inter-eomponent connections played a large role in thefailure of many structures, the response of such connections needs to be better understood. Toachieve this, experiments are needed to investigate how these connections respond as they are

. loaded to failure. The resulting experimental data can be used to develop improved analyticalmodels of wood-frame structures, which can be used to design houses that are better able toresist extreme loads.

This report describes the results of a series of tests on two types of roof to wall connections.These test results show how the connections are likely to perform when subjected to strongwinds or seismic loads. The results of the tests provide data necessary for the development ofimproved analytical models of the connection response, which could in tum lead to improveddesign tools for wood-frame construction, and to stronger and more structurally efficient residential buildings.

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ACKNOWLEDGEMENTS

This effort was supported by the Materials and Construction Research Division, Building andFire Research Laboratory, National Institute of Standards and Technology, U.s. Department ofCommerce. The authors wish to thank Frank Davis, Andre Witcher, Mark Kile, and Max Peltzwho provided valuable assistance in the laboratory testing. Jason McCormick's assistance inanalyzing the experimental data is greatly appreciated.

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CONTENTS

Ab ...SITaet 111

Acknowledgements V

Contents vii

List of Figures ix

List of Tables xi

1 Inuoduction 1

1.1 Background : 21.1.1 Experimental Studies 31.1.2 Analytical Studies 3

1.2 Research Objectives 31.3 Scope of Current Effort 4

2 Overview of Test Pro~am 5

2.1 Test Specimens 52.1.1 Roof to Wall Connections Tested 7

2.2 Test Setup 82.3 Instrumentation and Data Acquisition 102.4 Test Protocols ..........................................................................................................•............. 14

3 Results of Uplift Load Tests 17

3.1 Response with Toe-nailed Connections 173.2 Response with Hurricane Clips 183.3 Comparison of Responses 18

4 Results of Monotonic Lateral Load Tests 27


5 Results of Cyclic Lateral Load Tests 39


6 Results of Combined Uplift and Lateral Load Tests 49


7 Conclusions 61

8 References 65

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LIST OF FIGURES

Figure 2.1. Sketch of a typical test specimen 5Figure 2.2. Typical test specimen before instrumentation 6Figure 2.3. Side view of specimen 7Figure 2.4. Front view of specimen 7Figure 2.5. Hurricane clip of the type used 8Figure 2.6. Dimensions of hurricane clips 8Figure 2.7. Sketch of specimen for lateral load test 10Figure 2.8. Sketch of specimen for uplift load test.. 9Figure 2.9. Sketch of specimen for combined vertical and lateral load test.. 11Figure 2.10. Locations of displacement sensors and load cells on the specimens 13Figure 2.11. Generic lateral displacement curve for cyclic lateral load tests 16Figure 3.1. Failure of toe-nailed truss to wall connection 17Figure 3.2. Vertical displacement applied to specimen with toe-nailed connections 19Figure 3.3. Vertical load applied to specimen with toe-nailed connections 19Figure 3.4. Connection deformation response of specimen with toe-nailed connections 20Figure 3.5. Load-deformation response of specimen with toe-nailed connections 20Figure 3.6. Failure of hurricane clip connection 21Figure 3.7. Vertical displacement applied to specimen with hurricane clips 22Figure 3.8. Vertical load applied to specimen with hurricane clips 22Figure 3.9. Connection deformation response of first test with hurricane clips 23Figure 3.10. Load-deformation response of first test with hurricane clips 23Figure 3.11. Connection deformation response of second test with hurricane clips 24Figure 3.12. Load-deformation response of second test with hurricane clips 24Figure 3.13. Comparison of responses with toe-nailed connections and hurricane clips 25Figure 4.1. Failure of toe-nailed connection with lateral load 28Figure 4.2. Lateral displacement applied to specimen with toe-nailed connections 29Figure 4.3. Lateral load applied to specimen with toe-nailed connections 29Figure 4.4. Lateral displacement responses for trusses with toe-nailed connections 30Figure 4.5. Uplift displacement respons~sfor trusses with toe-nailed connections 30Figure 4.6. Lateral force-displacement responses for trusses with toe-nailed connections 31Figure 4.7. Uplift force-displacement responses for trusses with toe-nailed connections 31Figure 4.8. Comparison of lateral and vertical responses for inner truss with toe-nailed

connections 32Figure 4.9. Comparison of lateral and vertical responses for outer truss with toe-nailed

connections 32Figure 4.10. Failure of hurricane clip connection with lateral load 33Figure 4.11. Lateral displacement applied to specimen with hurricane clips 34Figure 4.12. Lateral load applied to specimen with hurricane clips 34Figure 4.13. Lateral displacement responses for trusses with hurricane clips 35Figure 4.14. Uplift displacement responses for trusses with hurricane clips 35Figure 4.15. Lateral force-displacement responses for trusses with hurricane clips 36Figure 4.16. Uplift force-displacement responses for trusses with hurricane clips 36Figure 4.17. Lateral and vertical responses for inner truss with hurricane clips 37Figure 4.18. Lateral and vertical responses for outer truss with hurricane clips 37Figure 4.19. Comparison of responses of inner trusses 38

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Figure 4.20. Comparison of responses of outer trusses 38Figure 5.1. Failure of toe-nailed connection with cyclic load 40Figure 5.2. Lateral displacement applied to specimen with toe-nailed connections 41Figure 5.3. Lateral load applied to specimen with toe-nailed connections 41Figure 5.4. Lateral displacement responses for trusses with toe-nailed connections 42Figure 5.5. Uplift displacement responses for trusses with toe-nailed connections 42Figure 5.6. Lateral force-displacement responses for trusses with toe-nailed connections 43Figure 5.7. Uplift force-displacement responses for trusses with toe-nailed connections 43Figure 5.8. Lateral displacement applied to specimen with hurricane clips 44Figure 5.9. Lateral load applied to specimen with hurricane clips 44Figure 5.10. Lateral displacement responses for trusses with hurricane clips .45Figure 5.11. Uplift displacement responses for trusses with hurricane clips 45Figure 5.12. Lateral force-displacement responses for trusses with hurricane clips 46Figure 5.13. Uplift force-displacement responses for trusses with hurricane clips 46Figure 6.1. Failure of toe-nailed connection with combined load 50Figure 6.2. Displacements applied to specimen with toe-nailed connections 51Figure 6.3. Loads applied to specimen with toe-nailed connections 51Figure 6.4. Lateral displacement responses for trusses with toe-nailed connections 52Figure 6.5. Uplift displacement responses for trusses with toe-nailed connections 52Figure 6.6. Lateral force-displacement responses for trusses with toe-nailed connections 53

Figure 6.7. Uplift force-displacement responses for trusses with toe-nailed connections 53Figure 6.8. Lateral and vertical responses for inner truss with toe-nailed connections 54Figure 6.9. Lateral and vertical responses for outer truss with toe-nailed connections 54Figure 6.10. Failure of hurricane clip connection with combined load 55Figure 6.11. Displacements applied to specimen with hurricane clips 56Figure 6.12. Loads applied to specimen with hurricane clips 56Figure 6.13. Lateral displacement responses for trusses with hurricane clips 57Figure 6.14. Uplift displacement responses for trusses with hurricane clips 57Figure 6.15. Lateral force-displacement responses for trusses with hurricane clips 58Figure 6.16. Uplift force-displacement responses for trusses with hurricane clips 58Figure 6.17. Lateral and vertical responses for inner truss with hurricane clips 59Figure 6.18. Lateral and vertical responses for outer truss with hurricane clips 59Figure 6.19. Comparison of responses of inner trusses 60Figure 6.20. Comparison of responses of outer trusses 60

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LIST OF TABLES

Table 2.1. Displacement sensors used to measure the specimen motion 12Table 2.2. Load cells used to measure the uplift loads applied to the roof sheathing 14Table 2.3. Additional sensors measured during the tests 14

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1 INTRODUCTION

The majority of residential construction inthe United States is wood-frame buildings.These buildings perform well under gravityloads, but considerable damage has beenobserved after significant earthquakes andmajor hurricanes. Recent natural disastershave caused major damage to them, whichhas resulted in large economic losses. Asexamples, the tornado that struck Oklahoma City on 3 May 1999 demolished morethan 2200 homes and damaged over 7000more, while losses to residential construction represented about 72 % of the $15.3 billion in total insured losses from the 1994Northridge earthquake.

Such disasters highlight the weaknesses inherent in current wood-frame constructionand underscore the need for improving thestructural performance of typical homes.To enhance the resistance of houses to natural disasters and to reduce the risk to lifeand property, the behavior of wood-framebuildings subjected to dynamic and lateralloads needs to be better understood.

Wood-frame buildings are constructed fromseveral diaphragms such as walls, floors,and roofs; joined by inter-component connections such as nails, anchor bolts, metal

plates, and other proprietary connectors.The structural performance of these buildings is influenced by the behavior of theirindividual components and connections.Therefore, an understanding of the behaviorof the different structural components andconnections is essential to accurately predictthe performance of a housing unit underdifferent types of loading.

Analysis of the structural response of woodframe building components subjected tolateral loads is a difficult task due to severalsources of nonlinearity, the complex natureof the connections, and a wide variability in

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material properties and construction techniques. Since shear walls are the most important elements for resisting lateral loads,they have been experimentally and analytically studied since the early 1970s. Simplified methods of wall analysis and finiteelement models have been developed topredict the behavior of the walls understatic and dynamic lateral loading.

The development of tools for analyzingcomplete wood-frame houses started in themid-eighties, but few investigators haveattempted to analyze the different structuralcomponents and the inter-component connections in an assembled model. This isdue, in part, to the lack of performance datafor inter-component connections betweenintersecting walls, roof and walls, and wallsand foundations. Since post-event investigations of several recent disasters indicatedthat in many cases failure of the intercomponent connections played a large rolein the failure of the structure, such connections need to be incorporated into the performance models. To achieve this, experiments are needed to investigate how theseconnections behave, as they are loaded tofailure.

The NIST research plan is to develop experimentally validated, three-dimensional,analytical models to predict the performance of housing units during natural disasters. Such models can be used to establishperformance characteristics of conventionaland innovative housing systems. The current effort consisted of testing the intercomponent connections between rooftrusses and walls, in a full-scale roof andwall assembly. The intent is to determinethe performance of the connections whenthey are part of a complete system. The results of these tests can be combined with the


results of sub-component tests to developmore accurate analytical models.

1.1 Background

Although recent earthquakes and hurricanes in the United States have resulted infew casualties, they have caused substantialdamage, significant economic loss, and disruption of social and commercial activities.The performance of residential housing during such events has shown that wood-frameconstruction generally meets the life safetyobjective. Many houses, however, have experienced structural and nonstructuraldamage that prevented immediate occupancy, and resulted in expensive repairs.

Post-earthquake investigations have indicated that much of the seismic damage canbe attributed to construction flaws or inadequate quality assurance, including missing fasteners, overdriving of nails, improperplacement of anchor bolts, and misplacednails. The preference for more open interiorspaces, hillside homes, soft stories due togarage openings, and more irregularlyshaped structures may also be contributingfactors. Poor soil conditions (liquefaction,excessive settlement) and location (buildingon a hill-side) have been also cited as causesof damage. Houses built in accordance withseismic codes were generally found to perform well.

In general, poor seismic performance ofwood-frame houses has been observedwhen the house did not respond as a unit,due to discontinuous load paths. Commonpractices that lead to a lack of integrity include:

o Insufficient or poorly detailed intercomponent connections (anchorage tofoundation, wall-to-wall connections,wall-to-roof or floor connections).

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o Inadequate bracing (cripple walls, totalabsence of shear walls, large wall openings, inadequate let-in bracing).

o Component separation (masonry fireplaces and chimneys, masonry veneers,porch roofs and other overhangs, different house sections).

o Non-uniform or irregular distribution ofstiffness, due to irregular plans and elevations (split level house, setbacks),which leads to torsional movements.

o Poor detailing or quality of construction.

o Lack of continuous load path from roofto foundation.

In past hurricanes, the main cause of severedamage to wood-frame houses has beenroof damage, due to inadequate anchorageof the roof framing to the wall, damage tothe shingles and other roof coverings, andloss of roof sheathing. Foundation failureand inadequate anchorage of the structureto the foundation have also caused failures.Similar to earthquake performance, issuessuch as continuous load path and structuralintegrity are crucial for hurricane resistance,particularly because water damage fromroof failures is a major contributor towardthe economic losses. In addition to waterdamage, the internal pressure in a house isincreased due to breaches in the buildingenvelope from missiles, thereby contributing to roof failures. Properly installed plywood boards over windows or storm shutters, doors, and garage doors can alleviatethis problem, but improperly installedboards and shutters can contribute to thedamage from wind-borne debris.

NIST has published a comprehensive stateof-the-art report on the structural performance of single-family, wood-frame housing(Yancey et aL, 1998), which includes a detailed literature review of experimental and

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analytical studies conducted on completehouses, in addition to wood subassemblies,such as shear wall diaphragms, and variousconnections. While some of the salient findings are summarized below, greater detailmay be found in the NIST report.

1.1.1 Experimental Studies

Shear wall behavior under lateral loads hasbeen the focus of a significant number ofstudies. Tests have been conducted undermonotonic, cyclic, and dynamic loads toinvestigate the response characteristics ofthe walls. Several additional studies havetested the sheathing-ta-framing connectionsto determine their response characteristics,determine their resistance, and provide datafor analytical modeling, since they havebeen shown to be a critical element in thewall performance.

A relatively small number of full-scalehouses have been tested. Tests have beenperformed on single- and twa-story housesunder field and laboratory conditions.

Very few experimental studies have beenconducted on inter-component connections.See, for example, Rosowsky et aL (1998) andReed et aL (1996, 1997). Testing of theseconnections is important, since they are keyelements for the wood-frame buildings, andthey must perform well for the structure torespond in an integrated fashion. An invitational workshop on seismic testing, analysis, and design of wood-frame construction(Seible et al., 1999) recognized that the behavior of inter-component connections isnot well understood and recommended further testing of such connections.

1.1.2 Analytical Studies

Analyzing the structural components of awood-frame building subjected to lateralloads is essential to understand their performance during natural disasters. Since

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shear walls are the most important elementsin resisting lateral loads, several investigators have extensively studied them since theearly 1970s. Simplified analysis methodsand finite element models were developedto predict the nonlinear behavior of thewalls under static lateral loading. A fewresearchers also attempted to predict thedynamic behavior of the walls subjected toearthquake ground motion.

The development of analytical tools for analyzing complete wood-frame houses startedin the mid 1980s. This work included analyzing the different structural components,as well as the inter-component connectionsin an assembled modeL Comparisons withexperimental studies were performed toassess the validity of the proposed modelsand analyses. To date, only limited researchhas been directed toward the analysis of acomplete building or to the response of theinter-component connections (Polensek andSchimel, 1986, 1988; Groom and Leichti,1991, 1994).

1.2 Research Objectives

The long term objective of the NIST research is to develop the metrics and predictive tools necessary for evaluating the structural performance of housing systems during natural disasters, including earthquakesand strong winds. The program is expectedto lead to buildings that can better resist extreme loads and a reduction in constructioncosts for the housing industry.

To reach this objective, experimentally validated, three-dimensional finite elementmodels of typical systems and structuralperformance criteria for complete housesneed to be developed. The analytical models will need to include the interaction ofthe various diaphragms such as shear walls,floors, and roof, as well as inter-componentconnections. Data from prior testing con-

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ducted on wood diaphragms can be used inthe models, but as mentioned above, thereare minimal data on the performance of inter-eomponent connections. Therefore, experimental testing of various connectionsunder monotonic and cyclic loads is necessary to characterize their performance andprovide the necessary data for modeling.

1.3 Scope of Current Effort

The current research is intended to fill oneof the gaps in the understanding of thestructural behavior of wood frame buildings by experimentally testing two types ofroof to wall connections to determine theirbehavior and performance. The test resultswill provide data that are now lacking, butare necessary to develop analytical modelsof the connections. Such models will lead toimproved design tools for wood-frame construction, and to stronger and more structurally efficient residential buildings.

The two types of connections tested weretoe-nailed connections and hurricane clips.The simple toe-nailed connections are themost common type of roof to wall connection used in regions that are not routinelysubjected to hurricanes. The hurricane clips

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are one of the lightest and simplest versionsof a wide range of clips and straps that canbe used to increase the strength of roof towall connections.

In the current work, the specimens weresubjected to four types of loading. Monotonic uplift and monotonic lateral loadswere applied to determine the general failure response curves. Combined uplift andlateral load, and cyclic lateral loading wereapplied to obtain specific data on how theseconnections will respond when loaded tofailure by strong winds and seismic loads,respectively.

The objectives of these tests are to understand the in-situ behavior of the wall-to-roofconnections in the structure, explore thefailure mechanisms, and determine the displacements and forces that occur in the individual connections. The results of the experimental tests will allow more accuratesub-component connection testing and leadto improved analytical models.

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2 OVERVIEW OF TEST PROGRAM

This phase of the NIST effort consisted ofexperimental tests of full-scale wall-to-roofconnections. Tests will be performed onspecimens with toe-nailed connections andspecimens with hurricane clips. The objectives of this testing were to understand thein-situ behavior of the wall-to-roof connections in the structure, explore the failuremechanisms, and determine the displacements and forces that occur in the individual connections, so as to allow more accurate component connection testing andmodeling in the future.

2.1 Test Specimens

The specimens represent a center cutthrough a simple wood-frame house. Eachspecimen consisted of two 1.22 m (4 ft) longby 2.47 m (8 ft 1.25 in) high shear walls thatsupported four roof trusses with spans of4.88 m (16 ft). A sketch of a test specimen isshown in Figure 2.1, and a photo of onespecimen is shown in Figure 2.2

As can be seen in Figures 2.3 and 2.4, theframing for each shear wall consisted ofdouble top plates, a single bottom plate, and

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Figure 2.1. Sketch of a typical test specimen.

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four vertical studs spaced 0.40 m (16 in) oncenter. All framing members were constructed from 38 rnrn x 89 rnrn (2 by 4nominal) spruce-pine-fir, grade No.2 lumber. The outer wall sheathing was 11 rnrn(7/16 in) thick oriented strand board (OSB)panels. These were connected to the framing with 38 rnrn (1.5 in) cement coated staples spaced 76 rnrn (3 in) on perimeter and152 rnrn (6 in) on intermediate studs.

The pre-fabricated roof trusses, which areshown in Figure 2.4, had a top chord slopeof 4:12, and were spaced 0.41 m (16 in)apart. All truss elements were 38 rnrn x89 rnrn (2 by 4 nominal) members. The roofsheathing consisted of 11 rnrn (7/16 in)thick OSB panels attached to the trusses us-

ing 8d-<:ornrnon nails spaced 102 rnrn (4 in)apart.

Toe-nailed connections and hurricane clipswere used to tie the roof trusses to the shearwalls in these tests. Details about the connections are given in Section 2.1.1.

The shear walls and roof trusses were purchased pre-fabricated from a local supplier.They were thus fairly typical examples, inboth the material and quality, of woodframe construction in central Maryland.The quantity, spacing, length of the staplesused to connect the osB to the wall framingwere all standard, with respect to similarsized wood frame construction. The construction quality of these walls was gener-

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Figure 2.2. Typical test specimen before instrumentation.

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ally very good. The manufacturing techniques guaranteed that the quantity andspacing of the staples was consistent. Theonly aspect that was subject to human errorand variability was the positioning of thestaples relative to the studs. While the staples were properly driven in most cases, afew cases were observed where some of thestaples had missed a stud.

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2.1.1 Roof to Wall Connections Tested

Two types of roof to wall connections weretested - toe-nailed connections and hurricane clips.

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For the cases of the toe-nailed connections,each of the roof trusses were connected toeach wall using three 16d-common nailsdriven at approximately a 45°angle throughthe truss and into the top plate of the wall.Two of the nails were driven into one sideof the truss, while the third nail was driveninto the other side such that the nailscrossed at a 90° angle.

For the hurricane clip connections, two nails

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916.5 mm [3'-018"]

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1107.95 mm [4 1/4"]

61.91 mm [2 7/16"] ,

were toe-nailed through the truss and intothe top plate of the waIl for erection purposes. Then a simple, sheet metal hurricaneclip of the type shown in Figure 2.5 wasadded to provide the primary load path between the truss and the walls. The standarddimensions of the clips used are shown inFigure 2.6. These clips were attached to thetrusses and the top plate of the wall usingfour 8d common nails.

2.2 Test Setup

The shear walls were supported on steelfoundation frames rigidly attached to the

Figure 2.5. Hurricane dip of the type used.

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laboratory strong floor. The bottom platesof each of the walls were anchored to thefoundation frames with five 12.7 mm(1/2 in) diameter bolts, spaced 400 mm(16 in) on center.

The specimens were subjected to monotonicuplift, monotonic lateral, cyclic lateral, andcombined uplift and lateral loads.

The uplift loads were applied using a vertical actuator with a steel load tree that distributed the load to ten points on the roofsheathing, as shown in Figure 2.7. The uplift point loads were further distributed using 38 mm x 184 mm (2 by 8 nominal) lumber members that were connected to theroof sheathing, but not the trusses. Theseboards spread the load over a larger area,and prevented local failure of the sheathing.

The lateral loads were applied using a horizontal actuator connected to a transferbeam, which was in turn connected to twosteel pipes that were bolted to a pair of

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Figure 2.6. Dimensions of hurricane clips.

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38 mm x 184 mm (2 by 8 nominal) lumbermembers that were screwed to the roofsheathing on either side of the ridge. Thisconfiguration, shown in Figure 2.8, allowedthe load to be applied through the roof'scenter of mass, without applying any un-

usually large lateral loads to any trussmembers.

For the tests with combined lateral and uplift loads, the two loading systems were

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Figure 2.7. Sketch of specimen for uplift load test

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combined, as shown in Figure 2.9.

Both the vertical and horizontal actuatorspush against a steel reaction frame, whichcan be seen in Figures 2.7 through 2.9. Forthe uplift loads an actuator with a 152 mm

(6 in) stroke and a 222 kN (50 kip) capacitywas used, while for the lateral loads asmaller actuator with a 152 mm (6 in) strokeand a 45 kN (10 kip) capacity was used.

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Figure 2.8. Sketch of specimen for lateral load test

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2.3 Specimen Instrumentation

The specimens were higWy instrumentedwith displacement transducers and loadcells to gain maximum information aboutthe response characteristics of the speci-

mens. The sensors consisted of twelve loadcells and forty-eight displacement sensors.

The displacement sensors consisted of fortysix linear variable differential transformers(LVDT) mounted on the specimen or one of

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Figure 2.9. Sketch of specimen for combined vertical and lateral load test.

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Table 2.1. Displacement sensors used to measure the specimen motion.

SensorSensorlD Type

Direction ReferenceStroke Length Measured Datum Sensor Location

Sensors on 1st (West Outer) TrussSOW1XG ACLVDT 203.2 mm (8 in) East-VIlest Absolute South wallMIL1XG ACLVDT 203.2 mm (8 in) East-West Absolute Center of truss, lower chordMIU1XG ACLVDT 203.2 mm (8 in) East-VIlest Absolute Center of truss, upper chordNOW1XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute North wall

Sensors on 2nd (West Inner) TrussSOL2XR DC LVDT 50.8 mm (2 in) East-VIlest Relative South end of truss, lower chordSOW2.YG DCLVDT 50.8 mm (2 in) North-South Absolute South wallSOl2YR ACLVDT 152.4 mm (6 in) North-South Relative South end of truss, lower chordSOL2ZRO AC LVDT 152.4mm (6 in) Up-Down Relative South end of truss, lower chord, outside of wallSOW2.ZG AC LVDT 152.4 mm (6 in) Up-Down Absolute South wallSOL2ZRI AC LVDT 101.6 mm (4 in) Up-Down Relative South end of truss, lower chord, inside of wallSQl2XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute South quarter of truss, lower chord, inside of wallSQL2ZG AC LVDT 101.6 mm (4 in) Up-Down Absolute South quarter of truss, lower chord, inside of wallSQU2XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute South quarter of truss, upper chord, inside of wallMIl2XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute Center of truss, lower chordMIl2ZG ACLVDT 101.6 mm (4 in) Up-Down Absolute Center of truss, lower chordNOl2XR DC LVDT 50.8mm (2 in) East-VIlest Relative North end of truss, lower chordNOW2.YG AC LVDT 152.4 mm (6 in) North-South Absolute North wallNOl2YR DC LVDT 50.8 mm (2 in) North-South Relative North end of truss, lower chordNOL2ZRI DC LVDT 50.8 mm (2 in) Up-Down Relative North end of truss, lower chord, inside of wallNOW2ZG DC LVDT 50.8 mm (2 in) Up-Down Absolute North wallNOL2ZRO AC LVDT 152.4 mm (6 in) Uo-Down Relative North end of truss, lower chord, outside of wall

Sensors on 3rd (East Inner) TrussSOL3XR DC LVDT 50.8 mm (2 in) East-VIlest Relative South end of truss, lower chordSO\lll3YG DC LVDT 50.8 mm (2 in) North-South Absolute South wallSOL3YR AC LVDT 152.4 mm (6 in) North-South Relative South end of truss, lower chordSOL3ZRO AC LVDT 152.4 mm (6 in) Up-Down Relative South end of truss, lower chord, outside of wallSO\lll3ZG ACLVDT 101.6 mm (4 in) Up-Down Absolute South wallSOL3ZRI ACLVDT 101.6 mm (4 i11) Up-Down Relative South end of truss, lower chord, inside of wallMIL3XG ACLVDT 203.2mm (8 in) East-VIlest Absolute Center of truss, lower chordMIL3ZG DC LVDT 152.4 mm (6 in) Up-Down Absolute Center of truss, lower chordNQL3XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute North quarter of truss, lower chord, inside of wallNQL3ZG AC LVDT 101.6 mm (4 in) Up-Down Absolute North quarter of truss, lower chord, inside of wallNQU3XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute North quarter of truss, upper chord, inside of wall

Sensors on 4th (East Outer) TrussSOW4XG AC LVDT 203.2 mm (8 in) East-VIlest Absolute South wallSOW4YG ACLVDT 152.4 mm (6 in) North-South Absolute South wallSOL4YR AC LVDT 152.4 mm (6 in) North-South Relative South end of truss, lower chordSOL4ZRO AC LVDT 152.4 mm (6 in) Up-Down Relative South end of truss, lower chord, outside of wallSOW4ZG AC LVDT 152.4 mm (6 in) Up-Down Absolute South wallSOL4ZRI DC LVDT 50.8 mm (2 in) Up-Down Relative South end of truss, lower chord, inside of wallSOL4XR DC LVDT 50.8 mm (2 in) East-VIlest Relative South end of truss, lower chordNOW4XG ACLVDT 203.2 mm (8 in) East-VIlest Absolute North wallNOW4YG ACLVDT 152.4 mm (6 in) North-South Absolute North wallNOW4ZG DC LVDT 50.8 mm (2 in) Up-Down Absolute North wall

Sensors at cornersSWC DC LVDT 152.4 mm (6 in) Up-Down Relative South-west corner top plateSEC DC LVDT 101.6 mm (4 in) Up-Down Relative South-east corner top plateNVVC DC LVDT 50.8 mm (2 in) Up-Down Relative North-west corner top plateNEC DC LVDT 152.4 mm (6 in) Up-Down Relative North-east corner top plate

three reference frames located next to thespecimen. These sensors were used tomeasure the displacements of the trusses

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and walls, and the deformation that occurred in the roof to wall connections.

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As listed in Table 2.1, twenty-six of the sensors measured the absolute motion of thespecimen, while twenty sensors measuredthe relative motion within the specimen.Twenty-one of the sensors were used tomeasure the vertical motions, and sixteenwere used to measure the lateral motion inthe east-west direction, which was the primary direction of motion during the lateralloading tests. The remaining nine sensorsmeasured out-of-plane motions in the

north-south direction. The positions ofthese sensors are shown in Figure 2.10.

Two additional LVDTs, permanentlymounted inside the hydraulic actuators,were used to measure the displacementsapplied to the specimen.

Ten strain gage-based load cells were usedto measure the uplift forces applied to theroof of the specimen. These sensors were

Notation:

~ LVDT measuring absolute displacement

~ LVDT measuring relative displacement

~ LoadCell

Figure 2.10. Locations of displacement sensors and load cells on the specimens.

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Table 2.2. Load cells used to measure the uplift loads applied to the roof sheathing.

L t"ReferenceDt S

DirectionM dc

SensorTIDSensor ype apacny easure aum ensor ocalon

LCS01 Load Cell 44.5 kN (10 kip) Up-Down Absolute South side, west end, outsideLCN01 Load Cell 44.5 kN (10 kip) Up-Down Absolute North side, west end, outsideLCS02 Load Cell 44.5 kN (10 kip) Up-Down Absolute South side, west end, insideLCN02 Load Cell 44.5 kN (10 kip) Up-Down Absolute North side, west end, insideLCS03 Load Cell 44.5 kN (10 kip) Up-Down Absolute South side, centerLCN03 Load Cell 44.5 kN (10 kip) Up-Down Absolute North side, centerLCS04 Load Cell 44.5 kN (10 kip) Up-Down Absolute South side, east end, insideLCN04 Load Cell 44.5 kN (10 kip) Up-Down Absolute North side, east end, insideLCS05 Load Cell 44.5 kN (10 kip) Up-Down Absolute South side, east end, outsideLCN05 Load Cell 44.5 kN (10 kip) Up-Down Absolute North side, east end, outside

Table 2.3. Additional sensors measured during the tests.

LcSSensor ID Tvpe troke or apacitv Sensor ocatlonCmdVAct Command Signal 10V jIIertical actuator command signalDispVAct ACLVDT 152.4 mm (6 in) jIIertical actuator displacementLCVAct Load Cell 222.4 kN (50 kip) jIIertical actuator applied loadCmdHAct Command Signal 10V Horizontal actuator command signalDispHAct AC LVDT 152.4 mm (6 in) Horizontal actuator displacementLCHAct Load Cell 44.5 kN (10 kip) Horizontal actuator applied load

located along the rods that transferred theloads from the load tree to the roof sheathing. As listed in Table 2.2, each of theseload cells had a capacity of 45 kN (10 kip).

Two additional load cells, attached to therods of the hydraulic actuators, were usedto directly measure the forces generated bythe actuators.

Table 2.3 lists the additional response signals that were recorded during testing. Asmentioned above, the forces and loads generated by each of the actuators were measured and recorded. The command signalsthat were used to drive the actuators werealso monitored. Each of these signals was adirect current voltage, with a 10 V full scale.Since each of the actuators was driven indisplacement control, the 10 V corresponded to the maximum displacement ofthe actuator.

2.4 Test Protocols

lateral, cyclic lateral, or combined uplift andlateral loads. The loads were applied withthe actuator driven in displacement control.During the monotonic load tests a constantrate of deformation was applied.

For the uplift loading tests, a number ofsmall deformation tests were performed toverify that the sensors were properly measuring the response, followed by a large deformation test to fail the connections. During the first small deformation test, a vertical deformation was applied at a constantrate of 2.54 mm/min (0.10 in/min) to a peakof 2.54 mm (0.10 in). A second small deformation test was performed with a vertical deformation applied at a constant rate of5.08 mm/min (0.20 in/min) to a peak of5.08 mm (0.20 in). If the results of these initial tests appeared reasonable, the specimenwas tested to failure. During the failuretest, the vertical deformation was applied ata constant rate of 6.35 mm/min(0.25 in/min), until the connections on oneside of the roof failed.

As described above, specimens were subjected to either monotonic uplift, monotonic

The lateral loading test sequence was similar to the vertical test sequence. Again, a

14 NIST


number of small deformation tests wereperformed to verify that the sensors wereworking properly, followed by a large deformation test to failure. Because thespecimens were more flexible in the lateraldirection, larger deformations and rateswere used. During the first small deformation test, the lateral deformation was applied at a constant rate of 6.35 mm/min(0.25 in/min) to a peak of 6.35 mm (0.25 in).During the second small deformation test,the deformation was applied at a constantrate of 12.7 mm/rnin (0.50 in/min) to a peakof 12.7 mm (0.50 in). Again if the results ofthese tests appeared to be reasonable, thespecimen was tested to failure. During thefailure test of the specimen with toe-nailedconnections, the lateral deformation wasapplied at a constant rate of 12.7 mm/min(0.50 in/min). This rate of loading resultedin a relatively long test. So, to reduce thetest length and to make the amount of datarecorded more manageable, during the failure test of the specimen with hurricaneclips, the lateral deformation was applied ata constant rate of 25.4 mm/min(1.0 in/min).

The combined lateral and uplift load testswere performed by applying a vertical deformation at a constant rate, and calculatingin real-tUne the lateral deforITlation that

would cause a lateral load that was proportional to the load caused by the vertical deformation. Based on the shape of the trussand the tributary area of the roof, the ratiobetween the uplift load and the lateral loadthat would occur during a strong windstorm was estimated as 0.295. The controlsystem attempted to maintain the ratios between the uplift and lateral forces at thislevel throughout the test; however, due tolimitations in the speed of the control computer, nonlinearities in the specimen response, and changes in the stiffness of thespecimen as it deformed, the actual loadratio varied slightly over the course of each

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test. As in the case of the monotonic loadtest, small deformation tests were performed to validate the sensor operation.During the failure test, the vertical deformation was applied at a rate of 6.35 mm/min(0.25 in/min).

The fourth test series was the cyclic lateralloading, which was intended to simulate theeffects of earthquake motion on the connections. The applied motion was a constantvelocity (CV) deformation waveform withincreasing amplitudes over time. The generic version of this waveform is shown inFigure 2.11. This waveform is based on thework of Krawinkler et al. (2001). Forapplication in a test, the waveform is scaledsuch that the unit amplitude of the genericwaveform is equal to 60% of the deformation in a specimen subjected to monotoniclateral loading at the point in the test afterthe peak capacity has been exceeded andthe response force has dropped to 80% ofthe peak value.

For the current tests, the period of the waveform was 30 s. The unit amplitude wasscaled to 37.24 mm (1.466 in) for the specimen with toe-nailed connections and to50.19 mm (1.976 in) for the specimen withhurricane clips. In both cases, the absolutepeak amplitude was liInited to 73.7 nun(2.90 in), due to the actuator stroke limits.

15

3.0 I

2.5

2.0

1.5

1.0 -

CI) 0.5 -'g:::J~ 0.0Q.E« -0.5 -

-1.0 -

-1.5 -

-2.0 -

-2.5 -

-3.0


VYVVVV'#VVVVYVVVyYV

Time

Figure 2.11. Generic (dimensionless) lateral displacement curve for cyclic lateral load tests.

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3 RESULTS OF UPLIFT LOAD TESTS

Two specimens were tested under upliftload to simulate the wind effects on thestructure, without any lateral component tothe load. The first specimen used the toenailed connection (three 16d-eommon nails)to tie the bottom chord of the roof trusses tothe walls, while the second used thestronger hurricane clip to connect the bottom chord of the trusses to the upper plateof the walls' top plate.

3.1 Response with Toe-nailed Connections

As described in section 2.4, a constantly increasing uplift deformation was applied to

the roof of the toe-nailed connection specimen at a rate of 6.35 mm/min (0.25 in/min)for a period of approximately 360 s. Thisdeformation is shown in Figure 3.2 and theresulting loads are shown in Figure 3.3. Thespecimen failed on one side at the connection between the trusses and the top plate ofthe wall after about 125 s. The failure modewas characterized as the nails withdrawingfrom the top plate, which resulted in separation in the bottom wood fibers of the bottom chord as can be seen in Figure 3.1. Thespecimen continued to exhibit some resistance, although the strength was relativelysmall after 200 s, and continued to decreaseas all of the connections on one side of the

Figure 3.1. Failure of toe-nailed truss to wall connection.

NIST 17


specimen failed completely.

Figure 3.4 shows the deformation that occurred at two connections during the test.The outer connection, truss 4, failed first.The drop in the deformation for this trussoccurred near the end of the test, when theopposite outer connection finally failed.Truss 2 is an inner truss, and was the thirdof the four connections to separate completely. The load-deformation curves forthese two connections are shown in Figure3.5.

3.2 Response with Hurricane Clips

The specimen with the stronger hurricaneclip connections was tested twice. The firstfailure occurred on the lightly instrumentedside of the specimen, and consisted of theentire top plate pulling loose from the wallstuds and cladding. The specimen was repaired and retested. During the second test,failure was observed on the other side in thewalls' top plate, as can be seen in Figure 3.6.The hurricane clip remained attached to theupper member of the top plate and thetruss, while the upper member of the topplate and a portion of the lower memberseparated from the rest of the wall. Thisfailure mode clearly illustrated the improved strength of the hurricane clip connection.

During both tests, this specimen was loadedin the same way as the toe-nailed connection specimen, except that the loading period was increased and, as can be seen inFigure 3.7, the applied deformation increased proportionally. During the firsttest, the connections began to lose stiffnessafter about 150 s, but they did not fail untilapproximately 225 s. Due to the nature ofthe failure, the resistance of the specimendropped by about half when the first failureoccurred. This response can be observed inFigure 3.8.

18

The deformation that occurred at one of theinner truss connections during the first testis shown in Figure 3.9, while the deformation at three connections during the secondtest is shown in Figure 3.11. The corresponding load-deformation curves areshown in Figure 3.10 (first test) and Figure3.12 (second test). As can be seen in thesetwo figures, the hurricane clip connectionsshowed good ductility, continuing to carrysignificant, but reduced, load at relativelylarge levels of deformation.

3.3 Comparison of Responses

A direct comparison of the responses withthe two types of connections is shown inFigure 3.13. The behavior of both of thesetypes of connections is highly nonlinear,and once either of these connections reachestheir ultimate load they lose a significantportion of their resistance. However, Figure3.13 clearly shows that the hurricane clipconnection has a significantly higher upliftcapacity, and in most cases a larger failuredeformation than the toe-nailed connections. In addition, the residual strength ofthe hurricane clip connection tended to begreater than the capacity of the toe-nailedconnection.

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60,Or50.0 ~

I

_ 40.01E :

~ ICDrOIis 20.0 l

!

!

10.0 -i

50045040035030025020015010050

0.0 -..L__--,---__~--___,__--

oTime (seconds)

Figure 3.2. Vertical displacement applied to specimen with toe-nailed connections.

30000 , 60.0,- Actuator Load

Commanded Displacement

25000 -;- 50.0

20000

~CD 15000u..0

LL

10000

400

-'- 40.0_E.§.cCD

30.0 ECDu

"ii.IIIis

-;- 20.0

I

!

t 10.0

I

---i- 0.0

450 500

Time (seconds)

Figure 3.3. Vertical load applied to specimen with toe-nailed connections.

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100 T;::::=======I -Truss2 l

90 - •• Truss 4 ICommanded Displacement

80-

70

E..§.. 60 ~

CGlE SO-BCll

~ 40is

30 -

20

10 -

50045040035030025020015010050o~---=--~--,---~-----~-----------

oTime (seconds)

Figure 3.4. Connection deformation response of specimen with toe-nailed connections.

40.0

5000

4500

4000

3500

3000

!:B 25000II.

2000

1500

1000

500

0-10.0 0.0 10.0 20.0

Displacement (mm)

30.0

--Truss21- - - Truss 4 1

50.0

Figure 3.5. Load-deformation response of specimen with toe-nailed connections.

20 NIST


Figure 3.6. Failure of hurricane clip connection.

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60.0

50.0

400E .§.cCDE 30.0CDUIIIis.III

C 20.0-

10.0 -

0.0

o 50 100 150 200 250 300 350 400 450 500

Time (seconds)

Figure 3.7. Vertical displacement applied to specimen with hurricane dips.

60.0

40.0 _E§.CCD

30.0 ECDUIIIis..!/!

_ 20.0 c

- 10.0

~ 50.0

0.0

500450400350

1-==============!- Actuator Load

~_C?mmanded Displacement

30025020015010050

o+L--._----..~~-, -----..,.._-

o

10000 -

,1

!

25000 1II

I

5000

30000 ,---!

20000

z2l 15000ou..

Time (seconds)

Figure 3.8. Vertical load applied to specimen with hurricane dips.

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90-1

100 -,-=~======::;----------------------~I I-Truss . ]

Commanded Displacement:

E.s 601:CDE 508III

~ 40is

30

20

10,

500450400350300250200100 15050

o·---"'~=-~---T·-----~-----'--------~---o

Time (seconds)

Figure 3.9. Connection deformation response of first test with hurricane clips.

5000

4500

4000

3500

3000Z8 25000u.

2000

1500

1000

500

o ~-

-10.0 0.0 10.0 20.0

Displacement (mm)

30.0 40.0 50.0

Figure 3.10. Load-deformation response of first test with hurricane clips.

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50045040035030025020015010050

o~__...~~~_~iiii~~_~§:_:~:=_=_,-:=_=-=-~=--= --,- _o

10 -

100 T,==~======-~1--Truss2i '- - - Truss 3

90 +1

,- 'Truss4

, i Command~_Qi.sfll_ace!:"~rrt_i80 1

i

70 -,

20 -

30 -

E.§. 60 c

-cellE 50ellUCll

~ 40i5

Time (seconds)

Figure 3.11. Connection deformation response of second test with hurricane clips.

--Truss 2

'- - - Truss 31- 'Truss4

5000 ,,-------------------------------------!i

4500 ~ii

4000 ~

3500 ~

_ 3000-1~ i

~ 2500 1~ !

2000 Ji

1500 ~

1000 ~

500

40.0 50.030.020.0

Displacement (mm)

10.00.0

o -,------------"------------~- ---------10_0

Figure 3.12. Load-deformation response of second test with hurricane clips.

24 NIST


5000

4500

4000 -

3500

3000

~~ 2500!;LL

2000

1500

1000 -

- Toe-nailed

-Hurricane Clip

500 -

50~040~030~020.0

Displacement (mm)

10.0

o-----~-~~~__+_-----~-----~--100 O~O

Figure 3.13. Comparison of responses with toe-nailed connections and hurricane dips.

NIST 25

26


This page intentionally left blank.

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4 RESULTS OF MONOTONIC LATERAL LOAD TESTS

Two specimens were tested with a monotonic lateral load to determine the ultimateshear capacity of the connections and theirpushover response. As in the case of themonotonic uplift tests, in one specimen thebottom chord of each roof truss was connected to the walls with toe-nailed connection, while in the other specimen hurricaneclips were used.


For the specimen with toe-nailed connections, the lateral deformation was applied ata constant rate of 12.7 mm/rnin(0.50 in/min) for a period of about 330 s, ascan be observed in Figure 4.2. The resultingload is shown in Figure 4.3. The specimenresisted the applied load with constantlydecreasing stiffness, until about 270 s intothe test. At this point, the tension, due tothe overturning moments, in the connections at one end caused the outer truss topull free of the top plate. This failure can beseen in Figure 4.1. As in the case of the uplift loading, the failure mode can be characterized as nail withdrawal from the topplate. This failure resulted in the woodsplitting in the bottom chord of one innertruss, but little damage to the wood of theouter truss.

The lateral deformations in the toe-nailedconnections of three of the trusses areshown in Figure 4.4, while the uplift deformations in the same connections are shownin Figure 4.5. From these results it is clearthat the connections were quite stiff inshear, but more flexible in tension. The corresponding force displacement responsesare shown in Figures 4.6 and 4.7. The responses of all three connections were quitesimilar in shear, but the outer connection,which failed first, was clearly carrying

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greater tension due to the overturning moments.

The lateral and vertical components of theresponse of the east inner truss are shownin Figure 4.8. These curves clearly show adifference in the lateral and vertical stiffnessof the connection, and how much more deformation occurred in the vertical directionthan the lateral. Figure 4.9 shows the sameresponse for the east outer truss. In thiscase the difference in the stiffnesses beforefailure is not as great, but again the verticaldeformation is much greater than the lateraldeformation. It is notable that the peak vertical load carried by this connection isnearly as large as the load carried by thetoe-nailed connections tested with upliftloading.


For the specimen with hurricane clips, thelateral deformation was applied at a constant rate of 25.4 mm/rnin (1.0 in/min) for aperiod of about 250 s, as can be observed inFigure 4.11. The load that resulted is shownin Figure 4.12. The specimen resisted theapplied load with a near constant stiffness,until about 170 s into the test. At this point,the outer truss pulled free of the top plate.As in the case of the toe-nailed connections,the tension due to the overturning momentsappeared to playa major role in the failure,which can be seen in Figure 4.10. Also as inthe prior test, the failure mode can be characterized as nail withdrawal from the topplate.

The lateral deformations in the connectionsof three of the trusses are shown in Figure4.13, and the uplift deformations in theseconnections are shown in Figure 4.14. Fromthese results it is clear that like the toenailed connections, the hurricane clip con-

27


nections were quite stiff in shear, but relatively flexible in tension. The corresponding force displacement responses are shownin Figures 4.15 and 4.16. Again, the responses of all three connections were quitesimilar in shear, but the outer connection,which failed first, was clearly carryinggreater tension due to the overturning moments, and the westernmost connectionnever reached its failure capacity.

Figure 4.17 shows the lateral and verticalcomponents of the response of the east inner truss. These curves clearly· show a difference in the lateral stiffness of the connection was greater than the vertical stiffness,and how much more deformation occurredin the vertical direction than the lateral.Figure 4.18 shows the same response for the

east outer truss. In this case, the stiffnessesare similar to the inner truss, and again thevertical deformation is much greater thanthe lateral deformation. While the peak vertical load carried by this connection isnearly twice as large as the peak lateralload, it is somewhat smaller than the loadcarried by the hurricane clip connectionstested with uplift loading. One reason forthis last result may be the difference in thefailure modes between the two tests.

Figure 4.1. Failure of toe-nailed connection with lateral load.

28 NIST


120

100

E80

.§.-c:GlE 60Gluellii.VI

C40 -

20 -

o ~=-----o 50 100 150 200 250 300 350

Time (seconds)

Figure 4.2. Lateral displacement applied to specimen with toe-nailed connections.

- Actuator Load ,I Actuator Displacement!

====~1202000 i

!

0

-2000

-4000

g -6000Glu~

0 -8000IL

-10000

-12000

-14000

-16000

0 50 100 150 200 250 300

- 100

-, 80E.§.1:Gl

60 EGluellii.VI

C40

-1- 20I

o350

NIST

Time (seconds)

Figure 4.3. Lateral load applied to specimen with toe-nailed connections.

29


10 ~~~~--r~~~-'-~~--

0r-----~""""""'''''''''''''==~~~~~

-10 T - - - - - - - - - - - - - - - - '- - - - - - - - - - - - - - - - -- - - - - - - - - - - - -~-20

1:GlEGlUIIIiiUI

C

_______ -.1 , _

,

,

-40 ~ - - - - - - - ~ - - - - - - - - - - - - - - - ---r - - - - - - - - - - -- - - - - ~ - - - - - - - -:- - - - - - - - ~

-50 - - - - - - - - ~ - - - - - - - -!- - - - - - - - - - - - - - - -

-60--------~-------

~o-----------------~------------------------~----------------

-80----------------- --------- --- -- --- --.--.-----------------

-90---- -----------------------West Inner Truss i

- - ,--East Inner Truss C -!

~- East Outer Truss:

300 350250

"~----·'-T·"-~~--~--

~~~~~~~~---,-~~

150 200Time (seconds)

10050

-100 ~~--~---~---~.

o

Figure 4.4. Lateral displacement responses for trusses with toe-nailed connections.

100'- - - . - West Inner Truss I

90 - ,-East Inner Truss .~ - - - - - --

;--East Outer TrussJ80 - - - - - - - - ~ - - - - - - - - - - - - - - - -

,------------- .--------------

70 - -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -! - - - - - - - - - -- - - - - -

~-~.~-_.~._-_.~.~.~~~~._._--------------o

10 ----------

3QT-------------

,

50 - - - - - - - - ~ - -- - -- - -

40--------~--------

20 ~- - - - - - - - - - - - - - - - - - - - - - - - - -, - - -

E 60 - - - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -! - - - - g1:GlEGlUIIIiiUI

C

300 350250150 200Time (seconds)

10050

-10 ---------c

o

Figure 4.5. Uplift displacement responses for trusses with toe-nailed connections.

30 NIST


West Inner Truss

i-East Inner Truss

--East Outer Truss

0

-500

-1000

-1500

-2000

Z"8 -2500 ~0LL

-3000

-3500

-4000I

-4500 iI

-5000 I-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 o 10

Displacement (mm)

Figure 4.6. Lateral force-displacement responses for trusses with toe-nailed connections.

West Inner Truss

:-East Inner Truss!--East Outer Truss

100908070605040302010

5000

4500

4000

3500

3000ZGl 2500u...0u.

2000

1500

1000

500

0-10 0

Displacement (mm)

Figure 4.7. Uplift force-displacement responses for trusses with toe-nailed connections.

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i Horizontal I I

i-Vertical i I

5000 --

4500 -

4000 -

3500 -

3000 -

!.8 2500 -...0IL

2000 -

1500 --

1000

500 --

0

-10 0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)

Figure 4.8. Comparison of lateral and vertical responses for inner truss with toe-nailed connections.

10090

I Horizontal I

i-vertical I

8070605040302010

5000

4500

4000 '

3500

3000 -

~8 2500...0IL

2000 ~

1500 -

1000 -

500 -

0

-10 0

Displacement (mm)

Figure 4.9. Comparison of lateral and vertical responses for outer truss with toe-nailed connections.

32 NIST



A direct comparison of the responses at theinner trusses with the two types of connections is shown in Figure 4.19, while the responses at the outer trusses are shown inFigure 4.20. The behavior of both of thesetypes of connections is highly nonlinear,with most of the deformation occurring inthe vertical direction. These figures clearlyshow that the hurricane clip connections

have a significantly higher capacity for bothuplift and shear. As in the case of themonotonic uplift loading, the residualstrength of the hurricane clip connectiontended to be similar to or greater than thecapacity of the toe-nailed connection.

Figure 4.10. Failure of hurricane clip connection with lateral load.

NIST 33


120 ---

100

E80

.§.

....I:G)

E 60 ~G)UftIa.l/I

Ci40

20 -

o ---L__

o 50 100 150 200 250 300 350

Time (seconds)

Figure 4.11. Lateral displacement applied to specimen with hurricane dips

2000i=Actuator Load--,

Actuator Displacement:o

~----------- -------,- 120

100

-2000

-4000

~ -6000"

~

~ -8000

-10000

80ES~II

60 EIIUftIa.l/I

Ci-, 40

-12000

-I- 20

-14000

----Lo35030025020015010050

-16000 ~-----~--------------,-----

oTime (seconds)

Figure 4.12. Lateral load applied to specimen with hurricane dips

34 NIST


10

-20 1 -

-10 +I

o-- --..-~;;..;;,-~~-~;;,,:,;,:.:~~

I ~ __ ~:---~---~"-----' _------,---------1----- I ----~I I I '. ",

I I

__ ~ ' ------- 1 -------------------,

I

,-------------------

~O~-------~--------~-----------------------------------------

-60~-------~-------- ---------- -----

-40 1- - - - - - - - ~ - - - - - - - -- - - - - - - - - -- - - - - - - -:- - - - - - - - - - - - - - - - - - - - - - - - -I I I I

...c:IIIEIIIUIIIQ.Ul

C

E -30 t,- ~ - ~ - - - - , - - - - - - - - i - - - - - - - ~ - - - - - - - -:- - - - - - - - , - - - - - - - -, - - - - - - - -

.s

-70 .- - - - - - - - , - - - - - - - - ,- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -, - - - - - - - -

-80------,

-------------------------------------------------

I

------~--------~----

I

I1- - -- - West Inner Truss

- - --r - - - - - - - - ,- - - - - - - - ~ - - !--East Inner Truss

1--East Outer Truss

-90 --

-100o 50 100 150 200

Time (seconds)250 300 350

Figure 4.13. Lateral displacement responses for trusses with hurricane clips.

100 --,-----------,---------

I

I- - - - - - - t- - - - - - - - -I

--~-~~~.~.~~-~------------------------

___' L ,_

,- - - - - _. -, - - - - - - - - ,- - - - - - - - -I

I----------------

30 ~ - - - - - - - -: - - - - - - ~ - - - - - - - - - - - - - - - - - '- - -

40 ~ - - - - - - - -j - - - - - - - - r - - - - - - - -- - - - - - - - ~ - - --

I

I

• ~--Westlnner TruSSi90 -i-- I-East Inner Truss r -

,--East Outer Truss I

80 ~ - - - - - - ~ , - - - - - ~ - - , - - - - - - - - - - - - - - - - ~ - - - - - - -

50

I

I20 - - ~ -- - - ~ - -j - - - - - - - - - - - - - - - - - - -

70

CIIIEIIIUIIIQ.Ul

C

E 60.s

-10

o 50 100 150 200 250Time (seconds)

300 350

Figure 4.14. Uplift displacement responses for trusses with hurricane clips.

NIST 35


o .------------------------------------------y-----

10-10 0

West Inner Truss

-East Inner Truss

--East Outer Truss

-20-30-40-50-60-70-80-90

-1000

-500

-1500

-2000

i -2500 i,f I

-3000 I-3500 ~

I-4000I-4500 1-5000 -I-J---------,.----,.----,.-------,---~-----~--

-100

Displacement (mm)

Figure 4.15. Lateral force-displacement responses for trusses with hurricane clips.

- West Inner Truss i

--East Inner Truss _

--East Outer Truss

908070605040302010

5000

4500

4000

3500

3000

~CD 2500u...0

La.2000

1500

1000

500

0-10 0

Displacement (mm)

Figure 4.16. Uplift force-displacement responses for trusses with hurricane clips.

36 NIST


-Horizontal

-=-~~~~-

5000

4500

4000

3500

3000-zB 2500...0II.

2000 ~

1500 -

1000 ~

500 c

O~

-10 0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)

Figure 4.17. Lateral and vertical responses for inner truss with hurricane clips.

5000 I

4500 ~

I4000 -1

3500 ~

3000gB 2500...0II.

2000

1500 ~

1000

500

0-10 0 10 20 30 40 50 60 70 80

'-Horizontal'-Vertical

90 100

NIST

Displacement (mm)

Figure 4.18. Lateral and vertical responses for outer truss with hurricane clips.

37


:r------~-

4000 i-Toe-nailed - Horizontal---- Toe-nailed - Vertical-Hurricane Clip - Horizontal- Hurricane Clip - Vertical

3500 ~

3000 ~

ZQl 2500u...0u..

2000

1500 -

1000 ..,

500 -1!

0!

~10 0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)

Figure 4.19. Comparison of responses of inner trusses.

100908070

I-Toe-nailed - Horizontali -- Toe-nailed - Vertical

-Hurricane Clip - Horizontal- Hurricane Clip - Vertical

605040302010

___.L- ~ -------------------

5000 ,

,

I

4500 i

4000 ~

3500 -

3000 ~

Z

Ql 2500 ..,u...0u..

2000 .,

1500 -

1000 -

500 -

0

-10 0

Displacement (mm)

Figure 4.20. Comparison of responses of outer trusses.

38 NIST


5 RESULTS OF CYCLIC LATERAL LOAD TESTS

Two specimens were tested with a cycliclateral load to determine their response toan earthquake type loading. Again in onespecimen the bottom chords of the rooftrusses were connected to the walls withtoe-nailed connections, while in the otherspecimen hurricane clips were used.


For the specimen with· toe-nailed connections, the waveform described in section 2.4,was applied with a cycle period of 30 s andthe unit amplitude of the generic waveformscaled to 32.24 mm (1.466 in). The resultingdisplacement curve is shown in Figure 5.2,and the resulting load is shown in Figure5.3. Although the specimen's stiffness decreased during the test, the specimen resistance continued to increase until the finallarge cycle of motion, about 1220 s into thetest. At this point, the connections at tension end of the specimen pulled free of thetop plate. This failure can be seen in Figure5.1. As in the case of the previous tests withthe toe-nailed connections, the failure wasdue to the nails withdrawing from the topplate. This failure resulted in some woodsplitting in the top plate of the wall, but lit

tle damage to the wood of the trusses.

The lateral deformations in the toe-nailedconnections of four connections for three ofthe trusses are shown in Figure 5.4. Notethat the failure occurred on the north side ofthe specimen, so three of the four curvesrepresent the non-failing response. Fromthis figure it can be noted that the outertruss connection on the south side, whichdid not completely fail, began to deformsignificantly after about 600 s. The innertruss connection on the north side had relatively moderate shear deformations untilthe last cycle before it failed.

NIST

The corresponding uplift deformations inthe connections are shown in Figure 5.5.From these results it is clear that the connections were more flexible in tension, and thatboth the outer truss connection on the southside and the inner truss connection on thenorth side began to deform more than theother connections after about 600 s.

The corresponding force-displacemet:lt responses are shown in Figures 5.6 and 5.7.The responses of all four connections exhibit significant hysteresis, indicating thatthese connections would dissipate a significant amount of seismic energy before failure. For all connections except the eastouter truss connection, the envelopes of thelateral and uplift responses during this testwere similar to the responses observed during the monotonic lateral load test. However, the east connection on the outer trussexhibited more lateral deformation and lesslateral stiffness than the other connections,while carrying more vertical load than wastypical in prior tests.


For the specimen with hurricane clips, thewaveforlll described in section 2.4, was ap

plied with a cycle period of 30 s and the unitamplitude of the generic waveform scaledto 50.19 mm (1.976 in), as can be observed inFigure 5.8. The load that resulted is shownin Figure 5.9. The specimen resisted the applied load with some degradation in stiffness, but increasing resistance, until the lastlarge deformation cycle, which occurredapproximately 1220 s into the test. At thispoint the specimen's north wall began tofail at the sill plate, with the studs and cladding pulling free of the sill. The hurricaneclip connections had not yet failed when thetest was stopped.

39


The lateral deformations in the connectionsof three of the trusses are shown in Figure5.10, and the uplift deformations in theseconnections are shown in Figure 5.11.While none of the connections failed, theresponses shown in Figure 5.10 clearly indicate that the connection in the east innertruss may have begun to fail at about 950 sinto the test. Based on the responses shownin both figures, it is clear that, as in themonotonic lateral load test, the hurricaneclip connections were quite stiff in shear,but relatively flexible in tension.

The corresponding force displacement responses are shown in Figures 5.12 and 5.13.As in the case of the toe-nailed connections,the responses of all four connections shownin these figures exhibit significant hystere-

sis. The east inner truss connection, whichmay have begun to fail early in the test, hadthe largest hysteresis. All of the connectionsresponses· had envelopes that were similarto the responses observed during the monotonic lateral load test. Since none of theconnections failed entirely, the ultimateload capacity for the connections with thistype of loading was not determined. However, it is clear for this load case the hurricane clips were stronger than the wall itself.

Figure 5.1. Failure of toe-nailed connection with cyclic load.

40 NIST


80

60

40

E 20.§.c:GlE 0 ~ /, /," /,"" 1\ " ," /'\ ""

GloIIIQ.Ul -20 c

is

-40 -

-60 -

-80

o 200 400 600 800 1000 1200

Time (seconds)

Figure 5.2. Lateral displacement applied to specimen with toe-nailed connections.

15000 ---------------------------~80,-----_._-----~,

i-LoadI

L- A~.':'~~DisJJl_ac~ment

10000+60i

-7- 40

5000

ZGl 00

0IL

-5000

20 E.§.c

o ~GlUIIIQ.

-20 isI '

-40

-10000-60

12001000800600400200

-15000 +-------------------------------------.,-----'- -80

oTime (seconds)

Figure 5.3. Lateral load applied to specimen with toe-nailed connections.

NIST 41


, :, ,

: : : ,t, - - - - - - -- - - - ,- - - - - - - - - T - - - - - - - - - - - - - - ~ - - -,t- --

I I I.. I A: :. . I:

,

2.0 :;====:'::::::::===:::;-~--i - - West Inner Truss - North I

, ..... West Inner Truss - South i

--East Inner Truss1.0 T __ East Outer Truss

EE::- -1.0 - - - - - - - - - - - - - - - - - -l:GlEGlU-a -2.0 - - - - - - - - - - - - - - - -IIIC

-3.0 - - - - - - - - - ~ - - - - - - - - - - - - - - - - - - ,- - - - - - - - - ~ - - - - - - - - .., - - - - - -

..

..,,, ,

- - -,- - - - - - - - - ~ - - - - - - - -, - - - - - - - - -,- .. - ---4.0 - - - - - - - - - ~ - - - - - - - -

-5.0 -----~-------o 200 400 600 800

Time (seconds)1000 1200


18 -,------

,,

-----_._,+---,,,

- -->- - - - - - - - - -1- - - - - - - - - t- - -

,

6 ~ - - -- - - - - - - - - - - - - - - - - - - - - - - - - " - - - - - - - - -,- - - - - - - - - - -,,,

_______________ ...L 1 _

,4 -

-2 ----------...;...-----

12 - - - - - -

2------------------

Eg 10 - - - - - - - - - .., - - - - - - - - -- - - - - - -l:GlE 8GlUIIIQ.IIIC

o 200 400 600 800Time (seconds)

1000 1200


42 NIST


• • West Inner Truss - North

. - - - - West Inner Truss - South

--East Inner Truss--East Outer Truss

5000 T

4000 ~,

I

3000 ~

2000 ~

1000 ~

~CD 0- -.(J -...0u.. . . - .

-1000 -. - ....

-2000 -

-3000 -

-4000 -

-5000

-5.0 -4.0 -3.0 -2.0 -1.0

Displacement (mm)

0.0 1.0 2.0


5000

-1000 '

~CD~ou..

4000

3000

2000,

1000

o

-2000 ~

-3000

• • West Inner Truss - North

- - - - West Inner Truss - South

'--East Inner Truss

- East Outer Truss

..

--~-~---~--~------

-4000

-5000

-2 o 2 4 6 8 10 12 14 16 18

Displacement (mm)


NIST 43


80

60

40 -

E.§. 20-

-l:CDE 0CD()ClIc..Ul -20-is

-40 -

-60-

200

-80----

o 400 600

Time (seconds)

800 1000 1200

Figure 5.8. Lateral displacement applied to specimen with hurricane dips.

15000----- -------------------- 80

10000

5000

~CD 0()

0II.

-5000 -

-10000 -

~-_._---

;-Load ;

; ActlJ~or Displacement i

I I

60

40

- 20 E.§.1:

- 0 ~GluCllC.

- -20 15i I

- -40

- -60

-15000

o 200 400 600

Time (seconds)

800 1000

--------80

1200

44

Figure 5.9. Lateral load applied to specimen with hurricane dips.

NIST


•.- - - -' - - - II

, I

- --------T-----------.-·-

2.0 1-=======:::====::::-'------------, --:- - West Inner Truss - North i

," .. - West Inner Truss - South,:~-East Inner Truss

i--East Outer Truss1.0

EE:::;- -1.0 - - - - - - - -l - - - - - - - - -; - - - -

c

~CDu-a -2.0 T - - - - - - - + - - - - - - - -

IIIo-3.0 - - - - - - - - - ~ - - - -

,----T-----

,,

i

-4.0 .'.. - - - - - - - - - - - - - - - - - - - - - -

~~~~~~--,"--..-~~----_._--5.0 ~

o 200 400 600Time (seconds)

800 1000 1200


18 T== __-====---.---

ti- - West Inner Truss - North !

16 :..... West Inner Truss - South f _l---East Inner Truss I

!-- East Outer Truss !

14 T -=-=-=-=-=-=--~- ----------I

~~~~~~--~~~~~~-------~-

- - ~ - - - - - - - - -I

I

12

2 ------------------------

4+--------------- - --------------

- - - - - - - - -; - - - - - - - - - 1- - - - ._ - - - - -+ - - - - - - - - -I - - - - - - -,

E.§.. 10

c:CDE 8~III

Q. 6.!!C

-2-"-----o 200 400 600 800

Time (seconds)1000 1200


NIST 45


!. • West Inner Truss - North!

I- -_. -West Inner Truss - South!I--East Inner Trussi--East Outer Truss

------------------'r==~======'

5000

4000

3000 -

2000 -

1000 -

~III 0-u...0u..

-1000 -

-2000 -

-3000 -

-4000 -

-5000-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0

Displacement (mm)


1816141210864

. =-.."

5000 -=======::===I '. • West Inner Truss - North i

' .... - West Inner Truss _South i

4000 ;--East Inner Truss

--East Outer Truss

2000-

3000 -

1000 -

-1000 -

-2000 -

-3000 -

-4000 -

-5000

-2 0 2

~

~ 0-...ou..

Displacement (mm)


46 NIST



A direct comparison of the results is difficult, because the hurricane clip connectiondid not completely fail. As was the casewith the monotonic lateral load, the behavior of both of these types of connections ishighly nonlinear, which lead to significanthysteresis in the response. This hysteresiswill help to provide significant energy dissipation during seismic events. The resultsshow that the hurricane clip connectionshave a higher capacity to withstand suchloading, but how much greater the capacityis could not be determined.

NIST 47

48



NIST


6 RESULTS OF COMBINED UPLIFT AND LATERAL LOAD TESTS

The final two specimens were tested with acombined uplift and lateral load to simulatethe wind effects on the structure, includinga lateral load component due to pressure onthe outside walls. As describe in section 2.4,a constant uplift deformation was appliedto the roof at a rate of 6.35 mrn/min(0.25 in/min). At the same time the appliedvertical load was measured, and a lateraldisplacement applied to produce a lateralload equal to 29.5% of the vertical load.Limitations in the speed of the control computer and the highly nonlinear nature of thespecimens limited the accuracy of the lateralloads as the displacements became large,but generally the peak lateral loads wereabout 25% of the peak vertical loads. Thesame loading sequence was used for bothspecimens.


The two deformations applied to the specimen with toe-nailed connections are shownin Figure 6.2. The resulting loads are shownin Figure 6.3. As in the previous tests, thespecimen's stiffness decreased throughoutthe test, but the resistance continued to increase until connections began to fail about250 s into the test. At this point the nails inthe connection that was being placed in tension by the overturning moment from thelateral portion of the load pulled free fromthe top plate of the wall, as shown in Figure6.1. This failure resulted in some woodsplitting in the top plate of the wall, but little other damage to the material.

The lateral deformations in the toe-nailedconnections of three of the trusses areshown in Figure 6.4 and the uplift deformations in the same connections are shown inFigure 6.5. The corresponding force displacement responses are shown in Figures

NIST

6.6 and 6.7. The responses of all three connections were quite similar in both shearand tension, although the outer connection,which failed first, was carrying slightlymore tension, due to the overturning moments caused by the lateral load.

The lateral and vertical components of theresponse of the east inner truss are shownin Figure 6.8, while Figure 6.9 shows thesame response for the east outer truss.These curves clearly show that during thistest there was little difference in the initiallateral and vertical stiffnesses of the connection. The curves also illustrate how muchmore deformation occurred in the verticaldirection than the lateral. The peak verticalloads carried by these connections weregreater than the loads carried by similarconnections subjected to uplift loadingalone.


The two deformations applied to the specimen with hurricane clips are shown inFigure 6.11, and the applied loads areshown in Figure 6.12. As was the case inthe monotonic lateral load test, the specimen resisted the applied load with a nearconstant stiffness, until the first connectionbegan to fail at about 180 s into the test. Thefailure occurred at the connection on theouter truss that was in tension from boththe uplift and the overturning moment dueto the lateral load. The failure consisted ofthe top plate of the wall splitting, which allowed the hurricane clip to pull free, as canbe seen in Figure 6.10. The connection ofthe inner truss next to the one that failedfirst, failed by the nails withdrawing fromthe intact top plate.

The lateral deformations in the connectionsof three of the trusses are shown in Figure

49


Figure 6.1. Failure of toe-nailed connection with combined load.

6.13, and the uplift deformations in theseconnections are shown in Figure 6.14. Thecorresponding force displacement responses are shown in Figures 6.15 and 6.16.Again, the responses of the two innerconnections were quite similar, but theouter connection, which failed first,exhibited much less stiffness in both shearand uplift, and failed at a relatively lowload. In fact, the capacity of this connectionwas only slightly greater than the toe-nailedconnections and much less than otherhurricane clip connections. The reducedcapacity may have been due to an inherentweakness in the wood of the top plate, or asplit in the wood caused by a poorly drivennail.

50

Figure 6.17 shows the lateral and verticalcomponents of the response of the east inner truss. These curves clearly show thatthe initial lateral and vertical stiffnesses ofthe connection were nearly equal, and howmuch more deformation occurred in thevertical direction than the lateral. Figure6.18 shows the same response for the eastouter truss. In this case, both of theconnection stiffnesses are much less thanthose of the inner truss. As mentionedabove, the outer truss connection failed at arelatively small load, and the deformationsat failure were much greater than for theother connections.

NIST


60 -,--------------------Lateral

'-Vertical

50

_ 40

E.§.1:Q)

E 30Q)UIII'ii.enC

20 ~

10 -

35030025020015010050

0-""'"'-----------·----

oTime (seconds)

Figure 6.2. Displacements applied to specimen with toe-nailed connections.

35000 F" .1'=__ Lateral Load (inverted)~

!'--Vertical Load I

,i •••••. Lateral Actuator Displacement30000, . . 1il- - Vertical Actuator Displacement,

------------------- 60

~ 50

!

250001

~ 20000Q)

~II.. 15000

10000

5000

40E.§...cQ)

+ 30 EQ)UIII'ii.enC

20

~ 10

300250200150

-----~-------------- 0

35010050o--'-=---~-------

oTime (seconds)

Figure 6.3. Loads applied to specimen with toe-nailed connections.

NIST 51


10 ~------'-----------r-----'-----------

,- - -, - - - - - - - - -;- - - - _. - - - - j- - - - - - - - - - - •. - - - - - t- - - - - - - - -I - - - - - -

,,

o~---~ =~=~~~ ~ ~ ~,~ ~ ~ ~ ~ ~ ~ ~"

i :::::::±>-sJ-10-~~~~

-20 - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - - ~ ~ T ~ ~ ~ ~ ~ ~ ~ ----------------------,

-60 - - - - - - - - - - - - - - - ~ - - ~ ~ - - - - - - - -

E.§.-CGlEGlUIIIQ.11l

C

-30 - ~ ~ ~ ~ ~ ~ ~ ~I ~ ~ ~ ~ ~ ~ ~ ~ c ~ ~ - ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ - - - - - ~ - - ~ ~ ~ ~ - - - - - - - - -, - - - - -, ,, ,

-40 - - - - - - - - -' - -- - ~ ~ ~ - - - ~ - - - - - - -, - - ~ - ~ - - - - - - - - - - - - ~ - - - - - -- - -: - - ~ - - - - -

-50 - - - - - - - - -' - - - - - - ~ - - ~ ~ - - - - - -:- - - -

, ,

---~--------~--------I-----

,,

-70 - - ~ - - - - - -; - - - - - - - -- -- ~ ~ ~ - - - - - - - - - - ~ - - ~ - - - - - - - - '- - - - - - - - -' - - - - ~ ~ - - -

-80 - - - ----------------~-----

,

-90--------

-100

-- - West Inner Truss-- - - - - - - - - - - - - - - j- - - - - - - - ---. - - - - - - - - - - - ~-East Inner Truss

,--East Outer TrussI

o 50 100 150 200Time (seconds)

250 300 350


100 -,--------~

i j - -- -- West Inner Truss 1 ; " i90 t '-East Inner Truss 1- - ~ - - - - - - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - ~ - -

i :--East Outer Truss 1 "

80 1.. - -- -- -- '- - -- -- ~ - '- -- -- -- -- -- -- - - - -- -- -- -- ~ -- - -- - -- -- -- - -I

70 - - - ~ - - ~ - ~ - - - - - - - T - -- - - - - - c ~ - - ~ - - - - - - - - - - - ~ - - - - - - -

: i~ - - - - - - -, - - - - - - - - - ~ - - - ~1

, •• ' i

- - - -- - - ~ - - - - - - - ---: - - - - - - -. - - - .-..=-' - -!- i

,

. - ~_- =-" =-. L ...L -.l -.J ---.J _,

40 - - -

50 --~-------------~---~~--

30 T-

o----~

E 60 ~ - ~ ~ ~ - - ~ c ~ ~ - - - - - ~ - - - - - - ~ " ~ - ~ - - - - ~ - - - - - - - ~ - - - - - - - - - - ~.§.CGlEGlUIIIQ.Ul

i5

20 - - - - - - - - - - - - - - -- - , ~ ~ ~ - - - - - - - - - - - --

,

10 - - - - - - - - - - - - - - - - , - - -~-~.--;

-10o 50 100 150 200

Time (seconds)250 300 350


52 NIST


10-10 0-20-30-40-50-60-70-80-90

-1500

-500

-2500

-4500

-~I-6500 ~ 1· .... West Inner Truss '

I '!-East Inner Truss I

1 ~~ast O.l:!!~2~~~~~-7500 -LI -~-----,_------------_----~

-100

z- -3500GluoIL

Displacement (mm)


West Inner Truss

'-East Inner Truss--East Outer Truss

7000

6000

5000

~ 4000GlU...0IL

3000

2000

1000

0

-10 0 10 20 30 40 50 60 70

Displacement (mm)


NIST 53


I-Horiz~~tal

-Vertical7000

6000 -

5000 -

-~ 4000 -Q)UToo.0u.

3000 -

2000 -

1000

0

-10 0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)

Figure 6.8. Lateral and vertical responses for inner truss with toe-nailed connections.

i7000 i

I

6000 J

5000 -:

~ 4000 ~Q)UToo.0u.

3000 -

2000 -

1000 c

0

-10 0 10 20 30 40 50 60 70 80

-Horizontal

-Vertical

90 100

54

Displacement (mm)

Figure 6.9. Lateral and vertical responses for outer truss with toe-nailed connections.

NIST



A direct comparison of the responses at theeast imler trusses with the two types ofconnections is shown in Figure 6.19, whilethe responses for the outer trusses areshown in Figure 6.20. The behavior of theimler trusses matches the behavior seen inother loading cases, with the hurricane clipsproviding a much greater capacity than thetoe-nailed connections. However, as discussed above, and clearly visible in Figure6.20, the outer truss hurricane clip connection that failed when the top plate of thewall split provided only a slightly greatercapacity than the toe-nailed connection.These curves highlight the great variabilitythat can occur in the response of woodframe construction, due to both the variabil-

ity in the materials and in the quality ofworkmanship. Note, however, that theoverall strength of the specimen was notgreatly compromised by the weak outerconnection. The combined strength of theother three hurricane clips on that wall ofthe specimen allowed the specimen to resistalmost 45% more load than the specimenwith toe-nailed connections.

Figure 6.10. Failure of hurricane clip connection with combined load.

NIST 55


60

1II

50 ~

40 c

E.s...CGlE 30 ~

~IIIIi.IIIC

20 -

10 -

oo 50 100 150 200 250

-lateral!

.-:-Vertical i

300 350

Time (seconds)

Figure 6.11. Displacements applied to specimen with hurricane clips.

35000 ---------=-=----~60,--Lateral Load (inverted)

! i--Vertical Load!

! !.•..•. Lateral Actuator Displacement ,

30000 i l-=-Vertical Actuator Displacement! ._-

25000

~ 20000~

~15u.. 15000-

10000 ~

5000

....

..

50

40E.scGl

30 E~IIIIi.IIIC

- 20

- 10

56

o __.....-:c ,---. -----,_~__ ----.-~ 0

o 50 100 150 200 250 300 350

Time (seconds)

Figure 6.12. Loads applied to specimen with hurricane clips.

NIST


10 ~~~~----~ .~~~~~~~~~~~-~----~

o II--"""'==~:::::======:--/~...-.;;..;;..,;,.;,.~.:;..:,.:,.::..:..:.~"""-~-10 + -

-20-"--------,----------------,------~------~~ - ----- -----------

E -30·.s-40~-----

-60

-c::GlE~ -50IIIii.UI

is

,--------------------- -----------

-70 - - - - - - 1- --

,

-80

-90West Inner Truss

--East Inner Truss -

--East Outer Truss

150 200Time (seconds)

-100 ----------------- ..-~~---------~~

o 50 100 250 300 350


100 -,----------~-,--.~--------~~----.------;-i ,---~--_: ,- - - - - West Inner Truss

90 T ~--East Inner Truss - - - ~ - - .~ - - - - - - - - - - - - - - - ~~

,--East Outer Truss80 -------~-------->--------

10- --------

70

E 60.s~ 50GlEB 40IIIii.UIis 30

20

o

- ~ - - - - - - I - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - -- - -

,

_______ ~ L I L _,

- -- - - - - - - - - - - - - - - ~ - - - - - - - -I - - - - - - - - t- - - - - - - - - - - - - - - - - - - - - - - -

,

.~.~'--.=-.-.---=-.-~.- '- - - - - - - - -'- - - - - - - - -i-- - - - - - - - - - --

350300250150 200Time (seconds)

-10 --------~---____,--~-----~----------. ----------.- ~- -----

o 50 100


NIST 57


-500

-1500

-2500

z- -3500Glu...o

LL.

-4500

-5500

-6500 - , , - . West Inner Truss I

-East Inner Truss i

--East Outer Truss:

10o-10-20-30-40-50-60-70-80-90

-7500 -"--------,-----------,--------..,__-----,

-100

Displacement (mm)


West Inner Truss--East Inner Truss

--East Outer Truss

7000

6000

5000

~ 4000GlU...0

LL.

3000

2000

1000

0

-10 0 10 20 30 40 50 60 70 80 90 100

Displacement (mm)


58 NIST


7000

6000 ~

5000

~ 4000B..ou.

3000

2000

1000 -

,-Horizontal

-Vertical '~~~~

1009080706050403020

o--~-- --~~~---c---~~~~,.--~-~~-~~~~~~~~~~-10 0 10

Displacement (mm)

Figure 6.17. Lateral and vertical responses for inner truss with hurricane dips.

10090

-Horizontal

-Vertical

8070605040302010

+--~---''-----~~---- --,,--- -- ----,----------~-~~~~~~~-

7000 [i

Ii

6000 I!

5000 ~

~ 4000CIlu..0u.

3000

2000

1000

0-10 0

Displacement (mm)

Figure 6.18. Lateral and vertical responses for outer truss with hurricane dips.

NIST 59


7000

6000·

5000·

z- 4000·B..olL

3000·

2000·

1000 .

- - Toe-nailed - Horizontal..... Toe-nailed - Vertical

-Hurricane Clip - Horizontal~-Hurricane Clip - Vert~cal

•.100908070605040302010o

o_~--'L--~~_-10

Displacement (mm)

Figure 6.19. Comparison of responses of inner trusses.

7000 ~

6000 ~

- - Toe-nailed - Horizontal. - - _. Toe-nailed - Vertical

-Hurricane Clip - Horizontal~-Hurricane Clip - Vertical~,

5000 -

~ 4000 c

B..olL

3000 -

2000

1000 -

o-··~··

-10 0 10 20

............

30 40 50 60 70 80 90 100

Displacement (mm)

Figure 6.20. Comparison of responses of outer trusses.

60 NIST


7 CONCLUSIONS

Recent disasters in the United States haveresulted in few casualties, but they havecaused substantial damage and significanteconomic loss to residential housing. Aninvestigation of the state-of-the-art in experimental and analytical research onwood-frame housing found that while significant progress has been made in analytical modeling and testing of shear walls anddiaphragms, only limited progress has beenmade on the testing and modeling of complete houses and inter-eomponent connections.

The research reported herein attempts tohelp improve the performance of woodframe housing by filling one of the gaps inthe understanding of the structural behavior of wood frame buildings subjected toextreme loads. This work consisted of experimentally testing two types of roof towall connections to determine their performance and to provide the data, whichare now lacking but are necessary for thefuture development of analytical models ofthe connections and for complete 3-D numerical models of entire houses. Such models will lead to improved design tools forwood-frame construction, and to strongerand more structurally efficient residentialbuildings.

The two types of connections tested included toe-nailed connections and hurricane clips. The simple toe-nailed connections represent the most common type ofroof to wall connection in areas that are notroutinely subjected to hurricanes. The hurricane clips represent the lightest and simplest version of a wide range of clips andstraps that can be used to increase thestrength of roof to wall connections.

The specimens with these connections weresubjected to four types of loading: mono-

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tonic uplift, monotonic lateral load or pushover, combined uplift and lateral load, andcyclic lateral loading. The first two loadtypes provide general failure responsecurves, while the third and fourth loadtypes provide specific data on how theseconnections will respond when loaded tofailure by strong winds and seismic loads,respectively.

The results of the monotonic uplift load testshowed that the behavior of both types ofconnections tested is nonlinear under thisform of load. The results also showed thatonce either of these connections reachestheir ultimate load they lose a significantportion of their resistance. However, thehurricane clip connection had a significantlyhigher uplift capacity, and in most cases alarger failure deformation than the toenailed connections. The results showed thatthe residual strength of the hurricane clipconnection tended to be greater than thecapacity of the toe-nailed connection.

The tests with monotonic lateral loadingshowed that the behavior of both of thesetypes of connections tended to be stiffer inshear than in tension (or uplift). Becausethe loads on the individual connectionswere a combination of shear and uplift,with the uplift caused by overturning moments in the specimen, the performance ofthe specimens in pure shear was not observed. However, the performance with arealistic combination of shear and uplift indicated that the uplift component tended togovern the failure of the connections. Theresults clearly show that the hurricane clipconnections have a significantly higher capacity for both uplift and shear than the toenailed connections. As was the case withthe monotonic uplift loading, the residualstrength of the hurricane clip connectionstended to be similar to or greater than the

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ultimate capacity of the toe-nailed connections.

Tests with a cyclic lateral displacementwere performed to assess the performanceand behavior of the connections when subjected to seismic loads. While the toe-nailedconnections failed after numerous cycles,the hurricane clips proved to be strongerthan other components of the specimen.The hurricane clips were still intact whenthe wall studs and cladding began to separate from the base plate. As was the casewith the monotonic loads, the behavior ofboth types of connections was nonlinear,which produced significant hysteresis in theresponse. Such hysteresis can providesignificant energy dissipation duringseismic events. The results indicated thatthe hurricane clip connections have a highercapacity to withstand seismic loading, butthe magnitude of the increased capacitycould not be determined.

Finally, tests were performed with combined uplift and lateral loading to determine the performance and behavior of theconnections when subjected to strongwinds. During the test with hurricane clipconnections one of the connections failed ata relatively low load when the top plate ofthe wall split where the connection was anchored. The load at which this connectionfailed was still slightly larger than the loadsat which the toe-nailed connections failed.The behavior of the other hurricane connections was similar to the behavior seen inother loading cases, with the hurricane clipsproviding a much greater capacity than thetoe-nailed connections. This response highlights the great variability that can occur inthe response of wood frame construction,due to both the variability in the materialsand in the quality of workmanship. However, the overall strength of the hurricaneclip specimen was not greatly compromisedby the single weak connection. The com-

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bined strength of the other three hurricaneclips on that wall of the specimen allowedthe specimen to resist almost 45% more loadthan the specimen with toe-nailed connections.

The most important conclusion that can bereached from this effort is the great improvement in performance that was gainedwhen using the hurricane clips instead ofthe toe-nailed connections. These simpleclips tended to increase capacity by morethan 40%. As observed in the cyclic loadingtests, the hurricane clip connections hadstrengths that were similar to the strengthof the walls themselves. Further increasesin the connection capacity would requireclips or straps that connect the trusses directly to the wall studs, and should probably be paired with straps that anchor thestuds directly to the foundation.

There is, unfortunately, a significant uncertainty associated with these results. Due tothe limited number of tests and specimens,a statistical analysis of the results and anaccurate determination of their uncertaintyare not practical. In general, there is a largevariation in the response of wood-framehousing components due to variations inthe material properties of the wood members and inconsistencies in the quality ofconstruction. The wood properties can varyconsiderably, and are dependent on thewood type, dryness, and density, as well ascracks or other physical defects. The qualityof construction can vary considerably depending on the experience and skill of thebuilders. The uncertainty of the results between test specimens was minimized bypurchasing all materials at the same timeand from the same distributor, and havingthe walls and roof trusses pre-fabricated. Inaddition, the same two people performedthe final assembly of all of the specimens.Although the individual results have someuncertainty, the general trends in the over-

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all performance were quite consistent andthe uncertainty of the relative response between the specimens with toe-nailed connection and those with hurricane clips isestimated to be small.

The data obtained in these tests can providethe basis for limited analytical models of theconnection response. Additional testing isrequired to fully quantify the response ofroof to wall connections. Some gaps thatstill need to be filled include tests of additional types of connections and tests ofspecimens with longer wall lengths. Component tests of single, directly loaded connections would allow numerous tests with aparticular load pattern and connection type,to determine the statistical mean, variance,and uncertainty of the response. Tests ofwall-to-foundation and wall-to-wall connections are also necessary to fully determinethe response of wood-frame construction.

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8 REFERENCES

Groom, K M. and Leichti, R. J. (1991), "Fi_nite-Element Model of a Nonlinear intercomponent connection in LightFramed Structures," Proceedings of the1991 International Timber EngineeringConference, London, England, September, Vol. 4, pp. 4.346-4.353.

Groom, K M. and Leichti, R. J. (1994),"Transforming a Comer of a LightFrame Wood Structure to a Set ofNonlinear Springs, Wood and Fiber Science, Vol. 26, No.1, Society of Wood Science and Technology, pp. 28-35.

Krawinkler, H., Parisi, F., Ibarra, L., Ayoub,A, and Medina, R. (2001), "DevelOpment of a Testing Protocol for WoodFrame Structures," Technical Report W02, CUREE- Consortium of Universitiesfor Research in Earthquake Engineering,Richmond, CA

Polensek, A and Schimel, B. D. (1986), "Ro_tational Restraint of Wood-Stud WallSupports," Journal of Structural Engineering, Vol. 112, No.6, American Society ofCivil Engineers, NY, June, pp. 12471262.

Polensek, A. and Schimel, B. D. (1988),"Analysis of Nonlinear Connection Systems in Wood Dwellings," Journal ofComputing in Civil Engineering, Vol. 2,No.4, American Society of Civil Engineers, NY, October, pp. 365-379.

Rosowsky, D.V., Reed, TD. and Tyner, KG.(1998), "Establishing Design Values forUplift Connections in Light-Frame Construction," Journal of Testing and Evaluation, ASTM, 26(4), pp. 426-433.

Reed, T., Rosowsky, D. and Schiff, S. (1997),"Uplift Capacity of Light-Frame Rafter

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to Top-Plate Connections," Journal ofArchitectural Engineering, ASCE, 3(4), pp.156-163.

Reed, T.D., Rosowsky, D.V. and Schiff, S.D.(1996), "Roof Rafter-Top Plate Connection in Coastal Residential Construction," Proceedings: International Wood Engineering Conference, IWEC'96, New Orleans, LA

Seible, F., Filiatrault, A., and Uang, C. M.(1999), Proceedings of the InvitationalWorkshop on Seismic Testing, Analysis andDesign of Woodframe Constnlction,CUREe - California Universities for Research in Earthquake Engineering,Richmond, CA

Yancey, C. W., Cheok, G. 5., Sadek, F., andMohraz, B. (1998), "A Summary of theStructural Performance of SingleFamily, Wood-Frame Housing," Technical Report NISTIR 6224, National Institute of Standards and Technology,Gaithersburg, MD.

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Michael A. Riley and Fahim Sadek - NIST · 2009. 5. 7. · NISTIR 6938 EXPERIMENTAL TESTING OF ROOF...

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