1920s Office/Warehouse Conversion & Seismic Retrofit

1422 Harrison is an existing 1920s one-story reinforced concrete structure with a long-span wood truss and a rectangular footprint. The building’s owners plan to convert the current office/warehouse into an event space and indoor miniature golf course.

Axonometric view of analysis Model in Etabs Building Design Software.

Code Compliance Pathway

A-2 assembly with an occupant load less than 300 qualifies as a risk category II structure. Per CEBC 2022, in order to fulfill the change in occupancy, the seismic upgrade being performed in phase I is required to bring the building up to meet the seismic performance criteria for full seismic forces. Following CEBC§301.3.3 we will be using performance-based design. Following §304.3.1(2) of the CEBC, ASCE 41-17 tier 3 analysis shall be used and the performance objectives for the design shall meet:

• (S-3) Life-Safety at BSE-1N hazard level.
• (S-5) Collapse Prevention at BSE-2N hazard level.

Design

The lateral force resisting system for the proposed work includes the addition of Tectonus resilient friction dampers installed at the existing roof truss and wall piers.

Transverse section showing Tectonus friction damper and truss connection strengthening.

Such wooden truss buildings are common in the Bay Area and are characterized by weak connections and inadequate foundations. The seismic retrofit costs of such buildings can be prohibitive for the owner, particular when foundation work is involved.

The addition of Tectonus devices increased ductility and reduced seismic demand. As a result the only strengthening required is of the existing truss connections where the new timber braces with Tectonus devices attach.

The savings on additional strengthening and foundation work more than offsets the cost of the Tectonus devices and additional engineering and peer review costs.