Full-size wood-stud frame structure with sheathing, ties, and clay masonry veneer; gypboard inside
Full-size CMU structure with clay masonry veneer
For the past two years, the masonry industry has been working with university researchers under the National Science Foundation's Network for Earthquake Engineering Simulation (NEES) program to develop performance-based design provisions for masonry and masonry veneer. On Jan. 25-27, the research culminated with the seismic testing of a full-size wood-stud frame.
The wood frame structure with masonry veneer did not collapse under shaking that was in excess of maximum earthquake levels. Preliminary test results indicate masonry veneer can help the seismic performance of wood-stud structures, and should not be considered as mass only in the seismic design of a wood-stud frame. The testing also evaluated the performance of various masonry veneer connectors. (Visit our Web site for detailed observations from the first phase of the test.)
In March, a similar structure of load-bearing concrete masonry was to be tested. Both structures will be clad with clay masonry veneer and will be tested to failure on the NEES large outdoor shaking table of the University of California at San Diego.Test Results
The large-scale testing of the wood-frame structure at the NEES LHPOST facility at UCSD was successfully completed on January 26, 2009. Our most important observations are the following:1) The first major objective of the testing was to evaluate the safety of wood-stud frames with masonry veneer. That objective was achieved. The wood-frame structure with masonry veneer (clay masonry units, bonded by Type N masonry cement mortar and a variety of connection details meeting MSJC requirements), did not collapse under levels of shaking far in excess of the maximum considered earthquake (MCE, with a return period of 2500 years) for Seismic Design Category D (SDC D). This considerably exceeds the performance implied by our current design codes.2) The second primary objective of the testing was to see whether refinements are possible to current seismic design approaches for wood-frame structures with masonry veneer. Promising results were obtained regarding that objective. Preliminary test results indicate that masonry veneer can help the seismic performance of wood-stud structures, and should not be considered as mass only in the seismic design of the wood-stud frame. The researchers are using measurements and computer predictions to develop design recommendations that recognize the beneficial effects of masonry veneer on seismic performance of wood-stud frames.3) The third primary objective of the testing was to evaluate the performance of masonry veneer and masonry veneer connectors.
- a) On some parts of the structure, veneer fell off under levels of shaking consistent with the design-basis earthquake for SDC D (regions of high seismicity in the US). This behavior was due primarily to pullout of nailed wall ties from the wood-stud frame. On other parts of the structure, veneer fell off only at levels of shaking in excess of MCE. Researchers are evaluating the connector pullout forces and pullout capacities in different parts of the structure, with the objective of refining our current design provisions for fastening veneer connectors to wood-stud frames.
- b) Based on results obtained to date, researchers see a clear relationship between the method used to attach veneer connectors to the wood-stud frame, and subsequent seismic performance. Connectors attached by 8-penny electro-galvanized box nails almost always failed by nail pullout, while connectors attached by screws rarely failed by screw pullout. Researchers are evaluating the extraction capacities of different commercially available nails and screws, with the objective of refining our current design provisions for the types of fasteners used to attach veneer connectors to wood-stud frames.c) Based on results obtained to date, researchers do not see a clear relationship between the stiffness of veneer connectors (independent of their method of attachment to the wood-stud frame), and subsequent seismic performance. Researchers are continuing to study this using data and computer models.
- d) Based on results obtained to date, researchers do not see a clear relationship between the presence or absence of joint reinforcement in veneer, and the subsequent seismic performance of that veneer. Researchers are continuing to study the high-speed video of the test for additional information.