Performance-based direct displacement design of engineered timber building in seismic regions

This paper reports on a study to extend a recently proposed Direct Displacement Design (DDD) procedure for mid-rise engineered wood frame structures and develop a set of factors for use in the procedure to meet specified performance levels with certain target probabilities. Representative index multi-story building configurations were selected from the archetype buildings developed for the FEMA ATC-63 project. Seismic hazard levels and performance requirements recommended by ASCE 41-06 and modified for use in the recently completed NEESWood project were used. The archetype buildings, originally designed using current Force-Based Design (FBD) procedures, were re-designed using the simplified Direct Displacement Design procedure (also described herein) with a range of non-exceedance probability adjustment factors (C-NE). Specifically, the design inter-story shear forces and the sheathing nail spacings were determined for each structure designed using C-NE. Nonlinear Time-History Analysis (NLTHA) was performed for each archetype structure under the 2%/50 year seismic hazard level and peak inter-story drift distributions were developed. The non-exceedance probability at the 4% drift limit was then plotted against building height and design charts were developed for each different value of C-NE. Given the building height, target drift and desired non-exceedance probability, engineers/designers can select the appropriate minimum value of C-NE using these charts. Thus, a probability-based, multi-objective performance-based procedure for the seismic design of mid-rise wood frame structures is described.