Suggested Improvements on Mandatory Wood “Soft Story” Retrofits

October 17, 2019
Publication: 2019 SEAOC Convention
Author(s): Russell McLellan Keith Palmer Kenneth Tam Daniel Zepeda Michael Mehrain Garrett Hagen Jonathan Buckalew Milad Oliaee

The “soft story” wood frame retrofit ordinances adopted by many California cities including Los Angeles and San Francisco are the largest of their kind. These ordinances mitigate a deficiency known to cause collapse in past earthquakes. When writing seismic retrofit ordinances that cover thousands of unique buildings, it is not possible to anticipate all issues that may arise during implementation. As issues arise, it is common for building departments to write bulletins to resolve or clarify issues. Today, a substantial amount of soft story wood frame retrofit projects have been completed in the Los Angeles and San Francisco areas with many more currently in plan check.

As more research has surfaced and new retrofit techniques have been employed, several issues have been identified in mandatory soft story retrofits. These issues can be categorized into three categories: (1) Design Requirements (scope clarifications, R values, Cd factors, drift limits, strength of first story relative to second story), (2) Detailing (load path, existing LFRS alteration, deformation compatibility, shear transfer, eccentric load transfer, foundation connection) and (3) QA/QC Improvements (design review and inspection). This paper highlights the authors’ observations about wood soft story retrofit ordinances currently underway in both southern and northern California and offers suggestions on how to improve the design and construction of these retrofits.