Numerical Modeling of Soft-Story Woodframe Retrofit Techniques for Design

Soft-story woodframe buildings are recognizable by their large openings at the bottom story which are typically for parking or other storage. During an earthquake, these large openings lead to large inter-story drifts and potential collapse, even before the upper stories experience any significant drifts. In order to improve the seismic performance of these at-risk buildings, a retrofit technique is designed using a Performance Base Seismic Retrofit (PBSR) method which applies the direct displacement design (DDD) approach. Torsion is eliminated based on structural analysis and then the DDD procedure is applied. The seismic performance of the retrofitted building is evaluated through multi-record incremental dynamic analysis (IDA). This paper focuses on the retrofit of a full-scale three-story wood-frame building that will be tested in 2012 at the NEES@Buffalo laboratory as part of the NEES-Soft Project. Two different types of retrofits models were developed, namely the inverted steel moment frames (IMF) and wood shearwalls resulting in the building achieving the prescribed performance objectives at all stories.