THE CUREE-CALTECH WOODFRAME PROJECT

Robert Reitherman1 and John Hall 2

1 Consortium of Universities for Research in EarthquakeEngineering, Richmond, California, USA; reitherman@curee.org.

2 Dept. of Civil Engineering, California Institute of Technology,Pasadena, California, USA; johnhall@its.caltech.edu

ABSTRACT

Funded by the Federal Emergency Management Agency (FEMA) through a grant administeredby the California Office of Emergency Services (OES), the CUREE-Caltech Woodframe Projectis a four-year $7 million effort to conduct engineering research and apply it to the practical goalof reducing earthquake losses to woodframe construction (or “two by four” construction). TheProject’s scope is wide-ranging, combining research and implementation. The elements of theProject are: Testing and Analysis, Field Investigations, Building Codes and Standards,Economic Aspects, and Education and Outreach.

The 1994 Northridge Earthquake

Prior to the Northridge Earthquake in the Los Angeles region in 1994, the general public as wellas engineers often generalized that woodframe buildings were highly earthquake resistant, eventhough not usually designed by an engineer, because of inherently favorable constructioncharacteristics. That generalization was challenged by the surprisingly large amount of damagethis class of construction sustained in the 1994 earthquake, although may woodframe buildingsperformed very well. Damage to woodframe construction predominated in all three basiccategories of earthquake loss in that disaster:

� Casualties: 24 of the 25 fatalities in the Northridge Earthquake that were caused bybuilding damage occurred in woodframe buildings (EQE, 1994);

� Property Loss: Half or more of the $40 billion in property damage was due to damage towoodframe construction (Kircher et al., 1997);

� Functionality: 48,000 housing units, almost all of them in woodframe buildings, wererendered uninhabitable by the earthquake (Perkins et al., 1998).

Woodframe construction represents one of society’s largest investments in the built environment,and the common woodframe house is usually an individual’s largest single asset. In California,99% of all residences are of woodframe construction, and even considering occupancies otherthan residential, such as commercial and industrial uses, 96% of all buildings in Los AngelesCounty are built of wood. In other regions of the country, woodframe construction is stillextremely prevalent, constituting, for example, 89% of all buildings in Memphis, Tennessee and87% in Wichita, Kansas, with "the general range of the fraction of wood structures to totalstructures...between 80% and 90% in all regions of the US….” (Malik, 1995).

The CUREE-Caltech Woodframe Project is a direct result of the Northridge Earthquake, and itsfunding was provided from FEMA to OES for the Project from hazard mitigation funds for thatparticular presidentially-declared disaster. Caltech is the direct recipient of the HazardMitigation Grant Program award, and under a subcontract to the Consortium of Universities forResearch in Earthquake Engineering (CUREE), most of the individual tasks are contracted. Thegoals of the Project, which began in 1998 and is concluding within the next few months, hasbeen to make woodframe construction more efficient and to make its engineering more scientific.Making the construction more efficient means keeping in mind that the industry that builds thistype of construction is decentralized, its competitive environment is fierce, and a largeproportion of its work is done under conventional (prescriptive rules) rather than engineeredconstruction code provisions. Making the engineering more scientific means conducting testsand analyses to provide guidance to structural engineers to improve the accuracy of their designprocedures.

Several kinds of integration were needed to make the Project a success. Research was combinedwith implementation; experimental work was designed with both the researcher and practicingengineers involved; an advisory committee representing a variety of agencies, constituencies,industries, and design professionals was valuable; research was conducted at the detailed and thesystem or macro scale; economic and social aspects were considered; and the large number ofindividually subcontracted scopes of work (over 70) had to be managed to keep them onschedule and within budget. The co-authors have served as the Project Director and ProjectManager respectively. All of the published or in-progress publications of the Project are listed inthe references of this paper and are available from CUREE. Information on the project,including photos and videos of experiments, can be accessed at http://www.curee.org.

Testing and Analysis

The first problem faced by the Woodframe Project was the fact that wood construction had been“under-researched” as compared to steel, concrete, and masonry structures. Within the scope ofthe project, a logically related set of testing and analysis tasks had to be devised to obtain avariety of information and yet to investigate individual topics in enough detail to produce reliableresults. The manager of this element, Professor André Filiatrault of the University of Californiaat San Diego, was the primary source for this plan, in addition to managing the variety of work inthis element over a four-year timespan. An initial workshop was held to which researchers fromthe US and other countries and especially practicing engineers and building code officials wereinvited.

Table 1 lists the Testing and Analysis subcontractors to CUREE involved in the Project.

Fifteen different organizations (twelve universities and three consulting firms) carried out thetwenty-two Testing and Analysis Tasks, not counting the University of British Columbiaresearch that was separately funded in Canada but which made contributions to this Project. Onthe topic of international collaboration, it is also noteworthy that a significant, year-long effortwas invested in the Project by Dr. Hiroshi Isoda of the Building Research Institute of Japan,

Table 1: Testing and Analysis Investigators

Subcontractor TopicBryan Folz, UC San Diego International Benchmark (analysis contest)Chia-Ming Uang, UC San Diego Rate of Loading and Loading Protocol EffectsHelmut Krawinkler, Stanford University Testing ProtocolJames Beck, Caltech Dynamic CharacteristicsBryan Folz, UC San Diego Analysis Software DevelopmentHelmut Krawinkler, Stanford University Demand AspectsAndré Filiatrault, UC San DiegoKelly Cobeen, GFDS Engineers

Two-Story House (testing, analysis)Two-Story House (design)

Khalid Mosalam, UC BerkeleyBret Lizundia, Rutherford & Chekene

Three-Story Apt. Building (testing, analysis)Three-Story Apt. Building (design)

Frank Lam et al., U. of British Columbia Multiple Houses (funded separately in Canada, liaisonrole to CUREE-Caltech Project)

J. Mahaney, Wiss, Janney, Elstner Assoc. Anchorage (in-plane wall loads)Yan Xiao, University of Southern California Anchorage (hillside house diaphragm tie-back)James Dolan, Virginia Polytechnic Institute DiaphragmsRob Chai, UC Davis Cripple WallsGerard Pardoen, UC Irvine ShearwallsKurt McMullen, San Jose State University Wall Finish Materials (lab testing)Gregory Deierlein, Stanford University Wall Finish Materials (analysis)Michael Symans, Washington State University Energy-Dissipating Fluid DampersFernando Fonseca, Brigham Young University Nail and Screw Fastener ConnectionsKenneth Fridley, Washington State University Inter-Story Shear Transfer ConnectionsGerard Pardoen, UC Irvine Shearwall-Diaphragm ConnectionsDavid Rosowsky, Oregon State University Reliability of Shearwalls

as a visiting researcher at the University of California at San Diego. In addition, an InternationalBenchmark, in which teams attempted to blind predict the shake table response of a two-storyhouse using their preferred form of modeling, involved participants from Slovenia, Canada, Italy,Japan, New Zealand, and the United States.

Figure 1: Shake TableTesting of 2-story House atUC San Diego

Figure 2: Shake TableTesting of 3-storyApartment Building at UCBerkeley

Figure 3: Complete Collapse ofGround Story of Three-StoryApartment Building

Field Investigations

To take advantage of the opportunity to collect and studydata on building performance from the NorthridgeEarthquake, two related sets of investigations wereconducted under the direction of Professor G. G. Schierle ofthe University of Southern California: statistical studies andcase studies. The statistical studies involved a thorough andtime-consuming processing of data available in City of LosAngeles building department files (for example relating topost-earthquake inspections and permits for repair ordemolition work) and random samples of single-family andapartment buildings. The case studies were conducted byengineers who had already studied particular buildings to assess damage and design neededrepairs, and that body of knowledge was distilled into papers that were consistently organized totry to answer the same set of recurring questions as to the type of construction and its details, thedegree of damage, and causes of the damage (or in some cases, the good performance).

Figure 3 illustrates one extreme of damage on the performance scale, which was the completeground story collapse of an apartment building. The presence of automobile parking at theground level introduces a soft story and torsional irregularity that in a number of cases was notadequately counteracted by engineering enough earthquake resistance into the structure.

Building Codes and Standards

Along with serving as a lead designer and advisor for experimental specimens, structuralengineer Kelly Cobeen managed this element of the Project which is now nearing completion.Other key managers include James Russell, Building Codes Consultant, and Professor JamesDolan of the Virginia Polytechnic Institute. The chief product of this element of the Project is adocument containing recommendations for modifications to building codes (e.g., InternationalBuilding Code), standards (e.g. standards for materials or used for testing protocols), engineeringprocedures (e.g., guidance on calculation of the period of vibration), and construction practices(e.g., advice on quality control measures used in the field that can significantly improveearthquake performance. For each research task, for example a series of shake table experimentsor a large database of fastener testing results, this practice-oriented branch of the projectinterpreted the results and discussed them with the researchers to distill the implications.

Table 2 summarizes this train of thought: Targets for implementation of research results wereidentified at the beginning of the Project, even before any research began, to identify the ways inthe which the Project could have a beneficial effect.

Table 2: Potentially Affected Codes and Standards

National Consensus StandardsNational Design Specification for Wood (NDS)Wood LRFD Design Specification (ASCE 16)Wood Frame Construction Manual (AF&PA)Loads for Buildings (ASCE 7)American Society for Testing and Materials (ASTM, various standards)

National GuidelinesNEHRP Recommended Provisions for Seismic Regulations for New Buildings and OtherStructures (FEMA 368)Handbook fro the Seismic Evaluation of Buildings (FEMA 310)Prestandard and Commentary for the Seismic Evaluation of Buildings (FEMA 356)Home Builders’ Guide to Seismic Resistant Construction (FEMA 232)

National Building CodesInternational Building CodeInternational Residential CodeGuidelines for Seismic Retrofit of Existing BuildingsTri-Services Manual

Product Evaluation CriteriaNational Voluntary Product Standards (PS-1, PS-2)ICBO Evaluation ServicesNational Evaluation Services

State and Local Building CodesCalifornia Building CodeAgency Amendments to California Building CodeLocal Jurisdiction Retrofit Measures

Seismic Design GuidelinesSEAOC Recommended Lateral Force Requirements (Bluebook)SEAOC Seismic Design ManualSEAOC Vision 2000

Economic Aspects

Managed by Thomas Tobin, this element of the Project focused its efforts on loss estimationwork that could test the benefits and costs of various proposed retrofits for existing buildings ordesign enhancements for new ones. Structural engineers, university researchers, cost estimators,insurance industry representatives, and others provided sources of expertise for this work.

Figure 4: Illustration of One Index BuildingUsed in the Woodframe Project

Figure 4 illustrates a central feature of theEconomic Aspects element of the Project:index buildings. These are hypothetical butrealistically designed buildings that representkinds of buildings frequently found in thebuilt environment. Each building wasdesigned with input from a committee toconsider what was typical of a particularvintage (e.g., one decade) of construction, for agiven size and type of use, ranging from asmall, older single family house to a newermulti-family apartment building ortownhouse. Using analytical techniquesdeveloped at UC San Diego, additional work byCaltech and ABS Consulting producedstatistical portraits of probable damage todifferent index buildings for differentearthquakes, with and without enhancements.A virtue of this approach is that the way the building stock is described is very precise—withdrawings and notes that are roughly comparable to construction blueprints—for individualarchetypes, rather than providing only verbal description.

Education and Outreach

This element, managed by Jill Andrews of Caltech (formerly of the Southern CaliforniaEarthquake Center, SCEC), has been wide-ranging. A brief list of the variety of activities isindicated below:

• Media relations for major shake table experiments (e.g., live CNN coverage)• Newsletters• Project update videos• Video programs produced for airing on television• Seminars for engineers, building officials, constructors• Museum exhibits

The last-named item is an interesting new area of involvement for earthquake engineeringoutreach. This element of the Project had the following kinds of exhibits built and installed inthe Riverside County (southern California) Youth Museum:

• Full-scale models of woodframe walls, showing construction details• Small models of vulnerable kinds of wood buildings, that could be shaken to collapse,

then quickly re-erected and “retrofitted” with bracing elements, then shaken again todemonstrate the beneficial effect

Figure 5: Hand-operated shake table with re-buildable model, Riverside County Youth Museum;this model has removable anchor bolts

• Architectural models of commonkinds of buildings with andwithout retrofits

• A detailed model of the collapsedNorthridge Meadows ApartmentComplex, where sixteen fatalitiesoccurred

• Posters explaining earthquakesafety lessons

• Teacher training for scienceteachers and students at theelementary school level

• Connections to earth scienceseducation and outreach

References CitedEQE International and the Governor’s Office of Emergency Services, The Northridge Earthquake ofJanuary 17, 1994: Report of Data Collection and Analysis, Part A, p. 5-18 (Sacramento, CA: Office ofEmergency Services, 1995).

Charles Kircher, Robert Reitherman, Robert Whitman, and Christopher Arnold, “Estimation ofEarthquake Losses to Buildings,” Earthquake Spectra, Vol. 13, No. 4, November 1997, p. 714, and

Robert Reitherman, “Overview of the Northridge Earthquake,” Proceedings of the NEHRP Conferenceand Workshop on Research on the Northridge, California Earthquake of January 17, 1994, Vol. I, p. I-1(Richmond, CA: California Universities for Research in Earthquake Engineering, 1998).

Jeanne B. Perkins, John Boatwright, and Ben Chaqui, “Housing Damage and Resulting Shelter Needs:Model Testing and Refinement Using Northridge Data,” Proceedings of the NEHRP Conference andWorkshop on Research on the Northridge, California Earthquake of January 17, 1994, Vol. IV, p. IV-135(Richmond, CA: California Universities for Research in Earthquake Engineering, 1998).

Ajay Malik, Estimating Building Stocks for Earthquake Mitigation and Recovery Planning, CornellInstitute for Social and Economic Research, 1995.

References CUREE-Caltech Woodframe Project--- Publication Date: 2000 ---

W-01: Proceedings for the Invitational Workshop on Seimic Testing Analysis and Design of WoodframeConstruction (edited by F. Seible / A. Filiatrault / C.-M. Uang) - 173 pages

--- Publication Date: 2001 ---

W-02: Development of a Testing Protocol for Woodframe Structures (H. Krawinkler / F. Parisi / L. Ibarra /A. Ayoub / R. Medina) - 87 pages

W-03: Woodframe Project Literature Reviews (edited by A. Filiatrault) – 261 pages

W-04: Woodframe Project: Case Studies (edited by G. G. Schierle) - 433 pages

W-05: Two-Story Single Family House Shake Table Test Data (5-CD set) (D. Fischer / A. Filiatrault / B.Folz / C.-M. Uang / F. Seible) [includes the 88 page report: Shake Table Test Descriptions, Test PhaseDescriptions, Instrumentation, and Construction Drawings (D. Fishcher / A. Filiatrault)

W-06: Shake Table Tests of a Two-Story Woodframe House (D. Fischer / A. Filiatrault / B. Folz / C.-M.Uang / F. Seible) - 611 pages

W-07: Fall/Winter 1999 / Summer 2000 - Earthquake Hazard Mitigation of Woodframe Construction (2-VHS) (J. Andrews) - 25 min.

W-08: CASHEW: a computer program for the Cyclic Analysis of wood SHEarWalls (B. Folz / A.Filiatrault) - includes 58-page report

--- Publication Date: 2002 ---

W-10: Reliability Studies (D. Rosowsky / J. H. Kim) - 69 pages

W-11: Dynamic Characteristics of Woodframe Structures (V. Camelo / J. Beck/ J. Hall) - 94 pages

W-12: Seismic Modeling of Index Woodframe Buildings (H. Isoda / B. Folz /A. Filiatrault) - 144 pages

W-13: Cyclic Response of Woodframe Shearwalls: Loading Protocol and Rate of Loading Effects(C.-M. Uang / K. Gatto) - 219 pages

W-14: Anchorage of Woodframe Buildings: Laboratory Testing Report (J. Mahaney / B. Kehoe) + CD-ROM? - 124 pages

--- In press, summer 2002 ---

W-09: Northridge Statistical Reports (G. G. Schierle) - 140 pages

W-15: Seismic Performance of Gypsum Walls (K. McMullin / D. Merrick) - 151pages

W-16: Nail, Wood Screw, and Staple Fastener Connections (F. Fonseca, S. Rose, S. Campbell) - 161pages

W-17: Seismic Behavior of Level and Stepped Cripple Walls (R. Chai / T. Hutchinson / S. Vukazich) -153 pages

W-18: Improving Loss Estimation for Woodframe Buildings (K.A. Porter, J.L. Beck, H.A. Seligson,C.R. Scawthorn, L.T. Tobin, R. Young, and T. Boyd) - 314pages

W-19: Seismic Evaluation of an Assymmetric Three-Story Woodframe Building (K.M. Mosalam, C.Machado, K.-U. Gliniorz, C. Naito, E. Kunzel, and S. Mahin) -295 pages