Lateral system design philosophy within moderate seismic regions: Tozzer Library case study and angle connection component test program

Retrofit of an existing lateral force resisting system and development of an angle test program each contribute to discussion of design philosophy in moderate seismic regions. The addition and renovation to an existing two-story building with an existing moment resisting frame (MRF) provided an opportunity for the structural designers to study load path and potential reserve capacity. The final design included a combined MRF/braced frame system with reserve capacity greater than the seismic resistance required by code. Recent work on the seismic behavior of low-ductility braced frames suggests that top and seat angles may be used to increase reserve capacity, and therefore collapse performance. Concurrent with the retrofit, a comprehensive angle test program was developed to establish a baseline of ultimate capacities under monotonic and cyclic loading, and serve as verification for predictive models. The experimental data suggest that the distance from the heel of the angle to the centerline of the bolts is a key variable in predicting angle behavior. Furthermore, the completed tests indicate that top and seat angles have sufficient displacement capacity to merit consideration as potential sources for reserve capacity.