Determination of seismic performance factors for cross laminated timber shear wall system based on FEMA P695 methodology
Date
2018
Authors
Amini, Mohammad Omar, author
van de Lindt, John W., advisor
Mahmoud, Hussam, committee member
Heyliger, Paul, committee member
Senior, Bolivar, committee member
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Volume Title
Abstract
Cross Laminated Timber (CLT) was initially introduced in Europe and has recently gained popularity in North America where it is seen as a sustainable alternative to steel and concrete in midrise construction. Although most CLT structures to date have been constructed in low seismic regions, recent tests have indicated that CLT based lateral force resisting systems can successfully be utilized in regions of higher seismicity. Despite the many advantages that CLT offers, the lack of a design code and systematic design procedure is one of many challenges inhibiting widespread adoption of CLT in the US. The purpose of this study was to investigate the seismic behavior of CLT based shear wall systems and determine seismic performance factors, namely, the response modification factor (R-factor), the system overstrength factor (Ω), and the deflection amplification factor (Cd), using the FEMA P695 procedure. The methodology is an iterative process that includes establishing design requirements, developing archetypes, performing a series of tests, developing and validating nonlinear models, nonlinear static and dynamic analysis, and evaluating performance; all in conjunction with a peer panel to provide input. Nine index buildings that include, single-family dwellings, multi-family dwellings, and commercial (including mixed-use) mid-rise buildings were developed. Archetypes were then extracted from these index buildings. Testing performed at the component and subassembly levels include connector tests and isolated shear wall tests. A subsequent full-scale shake table test was performed for system level demonstration. A critical aspect of this study is use of generic connectors whose properties are already addressed by a design specification to facilitate building code recognition. Test-based performance for these generic connectors is reported as part of this study to facilitate evaluation of proprietary alternatives for seismic equivalence. Connector tests were performed on angle brackets, used for attachment of the wall to the supporting element, and inter-panel connectors. These tests showed connector thickness to be important in achieving the desired ductile behavior with lesser thickness (12 gauge) being the more favorable. Quasi-static cyclic tests were conducted for a portfolio of CLT shear walls to systematically investigate the effects of various parameters. CLT demonstrated rigid behavior with energy dissipation concentrated in the connectors. Boundary constraints and gravity loading were both found to have a beneficial effect on the wall performance, i.e. higher strength and deformation capacity. Specific gravity also had a significant effect on wall behavior while CLT thickness was less influential. Higher aspect ratio panels (4:1) demonstrated lower stiffness and substantially larger deformation capacity compared to moderate aspect ratio panels (2:1). However, based on the test results there is likely a lower bound for aspect ratio (at 2:1) where it ceases to benefit deformation capacity of the wall. Multi-panel configuration comprised of high aspect ratio panels connected through vertical joint demonstrated considerably larger deformation capacity. Shake table tests showed the proposed system's potential to meet life-safety code requirements and its applicability in US seismic regions. A CLT shear wall design method was developed and refined based on the test results. Phenomenological models were used in modeling CLT shear walls. The archetypes were designed based on the proposed design method and were numerically evaluated by assessing their performance using nonlinear static and dynamic analyses. Based on the rigorous process, an R factor of 3 is proposed for the CLT shear wall systems and an R factor of 4 is proposed for the cases with high aspect ratio panels only. Results from the study will be proposed for implementation in the seismic design codes and standards in the US.
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Subject
earthquake
FEMA P695 methodology
shake table test
experimental wood testing
cross-laminated timber (CLT)
seismic performance factors