Cripple Wall Small-Component Test Program: Wet Specimens II (PEER-CEA Project), PEER Report 2020/18

Abstract: 

This  report  is  one  of  a  series  of  reports  documenting  the  methods  and  findings  of  a  multi-year,  multi-disciplinary  project  coordinated  by  the  Pacific  Earthquake  Engineering  Research  Center  (PEER  and  funded  by  the  California  Earthquake  Authority  (CEA).  The  overall  project  is  titled  “Quantifying the Performance of Retrofit of Cripple Walls and Sill Anchorage in Single-Family Wood-Frame Buildings,” henceforth referred to as the “PEER–CEA Project.”

The  overall  objective  of  the  PEER–CEA  Project  is  to  provide  scientifically  based  information  (e.g.,  testing,  analysis,  and  resulting  loss  models)  that  measure  and  assess  the  effectiveness of seismic retrofit to reduce the risk of damage and associated losses (repair costs) of  wood-frame  houses  with  cripple  wall  and  sill  anchorage  deficiencies  as  well  as  retrofitted  conditions that address those deficiencies. Tasks that support and inform the loss-modeling effort are: (1) collecting and summarizing existing information and results of previous research on the performance   of   wood-frame   houses;   (2)   identifying   construction   features   to   characterize   alternative  variants  of  wood-frame  houses;  (3)  characterizing  earthquake  hazard  and  ground  motions  at  representative  sites  in  California;  (4)  developing  cyclic  loading  protocols  and  conducting  laboratory  tests  of  cripple  wall  panels,  wood-frame  wall  subassemblies,  and  sill  anchorages to measure and document their response (strength and stiffness) under cyclic loading; and (5) the computer modeling, simulations, and the development of loss models as informed by a workshop with claims adjustors.

This report is a product of Working Group 4 (WG4): Testing, whose central focus was to experimentally investigate the seismic performance of retrofitted and existing cripple walls. This report  focuses  stucco  or  “wet”  exterior  finishes.  Paralleled  by  a  large-component  test  program  conducted  at  the  University  of  California,  Berkeley  (UC  Berkeley)  [Cobeen  et  al.  2020],  the  present  study  involves  two  of  multiple  phases  of  small-component  tests  conducted  at  the  University  of  California  San  Diego  (UC  San  Diego).  Details  representative  of  era-specific  construction, specifically the most vulnerable pre-1960s construction, are of predominant focus in the present effort. Parameters examined are cripple wall height, finish style, gravity load, boundary conditions, anchorage, and deterioration. This report addresses the third phase of testing, which consisted of eight specimens, as well as half of the fourth phase of testing, which consisted of six specimens where three will be discussed. Although conducted in different phases, their results are combined  here  to  co-locate  observations  regarding  the  behavior  of  the  second  phase  the  wet  (stucco)  finished  specimens.  The  results  of  first  phase  of  wet  specimen  tests  were  presented  in  Schiller et al. [2020(a)]. Experiments involved imposition of combined vertical loading and quasi-static reversed cyclic lateral load onto ten cripple walls of 12 ft long and 2 or 6 ft high. One cripple wall was tested with a monotonic loading protocol. All specimens in this report were constructed with the same boundary conditions on the top and corners of the walls as well as being tested with the same vertical load. Parameters addressed in this report include: wet exterior finishes (stucco over  framing,  stucco  over  horizontal  lumber  sheathing,  and  stucco  over  diagonal  lumber  sheathing), cripple wall height, loading protocol, anchorage condition, boundary condition at the bottom of the walls, and the retrofitted condition. Details of the test specimens, testing protocol, including instrumentation; and measured as well as physical observations are summarized in this report.  Companion  reports  present  phases  of  the  tests  considering,  amongst  other  variables,  impacts of various boundary conditions, stucco (wet) and non-stucco (dry) finishes, vertical load, cripple  wall  height,  and  anchorage  condition.  Results  from  these  experiments  are  intended  to  support  advancement  of  numerical  modeling  tools,  which  ultimately  will  inform  seismic  loss  models capable of quantifying the reduction of loss achieved by applying state-of-practice retrofit methods  as  identified  in  FEMA  P-1100,Vulnerability-Base  Seismic  Assessment  and  Retrofit  of  One- and Two-Family Dwellings.

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Author: 
Brandon Schiller
Tara Hutchinson
Kelly Cobeen
Publication date: 
November 1, 2020
Publication type: 
Technical Report
Citation: 
Schiller, B., Hutchinson, T., & Cobeen, K. (2020). Cripple Wall Small-Component Test Program: Dry Specimens II (Report No. 2020/18). Pacific Earthquake Engineering Research Center (PEER). https://apps.peer.berkeley.edu/publications/peer_reports/reports_2020/2020_18_Schiller_Wet_SpecimensII.pdf