| Summary: | This report describes an analytical study to investigate the seismic performance of single-story tilt-up structures with steel deck roof diaphragms. A review of current practice in North America for the seismic design of tilt-up structures reveals two points of interest; the flexibility of the roof diaphragm is not considered in calculation of the fundamental building period for the design, and that a force-based approach is used for seismic design that does not incorporate the principles of capacity-design currently used in other building systems, such as moment frames, braced frames, and shear walls.
To explore the application of capacity design for tilt-up structures, three possible failure mechanisms are investigated and compared: rocking of wall panels, sliding of wall panels, and frame action for buildings with wall panels incorporating large openings. Based on results of an industry survey, two building archetypes are created to represent the most common building types found in seismically active areas; one including solid panels and the second incorporating panels with large openings. Consideration of the sliding mechanism suggests it would be difficult to incorporate into common applications due to building geometry irregularities, difficulties in estimating sliding resistance, and permanent deformation resulting from the mechanism.
Analytical results from this study are compared with findings from previous research; the most interesting comparison showed the period from the analytical model to be within 10% of the estimated building period from ASCE 41 when the weight of the out-of-plane walls are considered in the estimate.
The rocking mechanism and frame mechanism are studied further by carrying out a preliminary assessment of seismic performance factors (R-values) utilizing concepts from the ATC-63 Methodology. Various analyses, including non-linear time history analyses for a suite of earthquakes, are carried out on 3D models of the building archetypes. Based on analysis results, the adequacies of some building components are evaluated, including the strength of the roof deck connectors and the strength of wall panel to roof connections both in-plane and out-of-plane. Further research is required to provide a recommendation for R-values, however, preliminary recommendations are provided and limitations of the study are discussed.
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