Seismic Design Coefficients for SpeedCore or Composite Plate Shear Walls

This report summarizes the results from FEMA P695 analytical studies conducted to verify the seismic design factors for composite plate shear walls – concrete filled (C-PSW/CF), also referred to as Speedcore. ASCE 7-16 provides the seismic design factors, which include the seismic response modification factor, R, deflection amplification factor, Cd, and overstrength factor, Ωo, for various approved seismic systems in Table 12.2-1. Steel and concrete composite plate shear walls (C-PSW/CFs) are in row 13 of Table 12.2-1 under building frame systems (item B). The value of R, Cd, and Ωo is 6.5, 5.5, and 2.5, respectively. The seismic design factors for C-PSW/CFs were selected based on the seismic performance of similar structural systems and engineering judgment of the committee. This analytical study investigated and verified the appropriateness of these seismic design factors.
The FEMA P695 procedure for evaluating seismic design factors consists of: (i) selecting the seismic design criteria and requirements for the system, (ii) designing several archetypes following the design requirements, (iii) developing and benchmarking a numerical modeling approach, (iv) conducting incremental dynamic analyses for 22 sets of ground motions, and (v) statistical analysis of the results to evaluate the system’s performance and adequacy of the seismic design factors.

C-PSW/CFs can be used as shear walls, or as part of the building’s elevator core to provide lateral force resistance. They can be either planar, C-shaped, or I-shaped walls. When used as part of the building’s core, the C-PSW/CF system may consist of walls that are coupled in one direction and uncoupled in the orthogonal direction. A previous FEMA P695 study was conducted (Kizilarslan et al. 2019) to establish an R-factor of 8 for coupled composite walls (CC-PSW/CF). This higher value was appropriate was coupled wall systems due to their additional ductility from the coupling beams and coupling action in the walls. The current study focuses on the uncoupled walls and builds on the coupled walls study by using similar structural floor plans for the archetype structures, and similar benchmarked numerical models for the composite (C-PSW/CF) walls.

The seismic design criteria for uncoupled C-PSW/CF walls were based on AISC 341-16, Section H7, with some minor modifications. Section H7 permits the use of walls without or with boundary elements, where the boundary elements are permitted to be half-circular or full-circular concrete filled tubes (CFTs). As part of this study, flange plates (also referred to as closure plates) are also permitted as boundary elements, based on the research and results of Wang et al. (2018). Based on the recommendations of the peer review panel, this study focuses primarily on C-PSW/CF walls with flange plates as boundary elements. Walls with half-circular or circular concrete filled steel tubes and walls without closure plates were not included due to perceived constructability issues and architectural considerations. The cyclic behavior of walls with half-circular or circular CFTs as boundary elements is typically better than that of walls with rectangular ends achieved using flange plates. Therefore, the findings from this study can be extended to those walls with half-circular or circular CFT boundary elements. A brief study on walls without closure plates was conducted, but this analysis concluded that walls without closure plates should be removed from AISC 341 Section H7 in the next code revision.

This study focused on the behavior and performance of four archetypes with planar walls (3-story, 6-story, 9-story, and 12-story) and three archetypes with C-shaped C-PSW/CF walls (15story, 18-story, and 22-story). The structural floor plans were developed based on the recommendations of the peer review panel to provide a reasonable representation of the feasible design space for low-rise and mid-rise buildings. The C-PSW/CF walls were designed following the requirements of AISC 341-16, Section H7, with minor modifications. These modifications will be recommended for the next revision of AISC 341.

OpenSees, an open-source structural analysis software, was used to develop nonlinear finite element (FE) models and conduct nonlinear time-history analyses of the archetype structures. The uncoupled walls were modeled using displacement-based fiber elements and appropriate steel and concrete material models developed by Shafaei et al. (2020) and recommended in Kizilarslan et al. (2019). The steel material model accounted for the effects of yielding, local buckling, stiffness and strength degradation due to cyclic loading, and low-cycle fatigue leading to fracture. The concrete material model accounted for the effects of tension cracking, compression softening, crushing, confinement, and crack opening and closing behavior under cyclic loading. The numerical models for the walls were benchmarked using experimental data.

The nonlinear models were used to conduct nonlinear static (pushover) analyses and nonlinear incremental dynamic (time-history) analyses. The static analyses were used to calculate the period, Tn, period-based ductility, μt, and overstrength factor, Ω. The dynamic analyses were used to assess median spectral acceleration collapse intensity, SCT, and collapse margin ratio, CMR. 44 far-field ground motions (for example Chi-Chi, Kobe, and Northridge) as specified in the FEMA procedure were used to conduct incremental dynamic analyses. The collapse of the uncoupled C-PSW/CF walls was assumed to occur at an inter-story drift ratio of 3%, which was conservative with respect to actual collapse.

Details

Title	Seismic Design Coefficients for SpeedCore or Composite Plate Shear Walls - Concrete Filled
Pages	161
Language	English
Format	PDF
Size	10 MB
Download Method	Direct Download
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