Performance-Based Procedure for Direct Displacement Design of Engineered Wood-Frame Structures

Abstract

This paper reports on a study to extend a recently proposed direct displacement design (DDD) procedure for midrise 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 multistory building configurations were selected from the archetype buildings developed for the FEMA ATC-63. Seismic hazard levels and performance requirements recommended by ASCE 41-06 and modified for use in the National Science Foundation sponsored NEESWood project were used. The archetype buildings, originally designed using current force-based design procedures, were redesigned using the simplified DDD procedure (also described herein) with a range of nonexceedance (NE) probability adjustment factors (CNE). Specifically, the design interstory shear forces and the sheathing nail spacings were determined for each structure designed using CNE. Nonlinear time-history analysis was performed for each archetype structure under the 2%/50 year seismic hazard level and peak interstory drift distributions were developed. The NE probability at the 4% drift limit was then plotted against building height and design charts were developed for each different value of CNE. Given the building height and desired NE probability, engineers/designers can select the appropriate minimum value of CNE using these charts. Additional analyses could be performed to consider other hazard levels and performance requirements. Using design charts of this type, engineers/designers are able to specify a target drift limit as well as a target NE probability when using the simplified DDD procedure. Thus, a true performance-based procedure for the seismic design of midrise wood-frame structures is described.