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Seismic Retrofits

Santa Ana State Office Building, Santa Ana, CA

Santa Ana State Office Building, Santa Ana, CAThis nine story concrete frame office building, originally constructed in 1972, was investigated as part of the State of California’s State Seismic Program. Due to unfavorable beam versus column geometry and the lack of interior joint reinforcing, it was determined that under a relatively low level seismic force that the frames would suffer joint yield and failure. Four distinctly different seismic retrofit strategies were investigated, with the exterior concrete buttress shear wall scheme selected, as it provides sufficient stiffness to protect the existing frame joints, while minimizing the disruption to occupants. The building was featured as a case study in the Fourth Conference on Tall Buildings in Seismic Regions.

Stent Hall, Menlo School, Atherton, CA

Stent Hall, Menlo School, Atherton, CAThis existing 3-story historic concrete mansion now functions as the administration building for Menlo School. To seismically retrofit this building, a solution was devised that minimized the intrusions into the existing building by bracing it with a new 2-story classroom and library building framed with structural steel and concrete shear walls.

Marin Executive Center, San Rafel, CA

Marin Executive Center, San Rafel, CAThis 5 story steel moment frame building was voluntarily seismically upgraded to reduce its damageability in a major earthquake. The selected scheme allowed the vast majority of the work to be completed from the exterior of the building and the building to remain essentially fully occupied during the duration of construction. The retrofit solution largely consisted of the construction of exterior buttresses which served the dual function of providing alternate lateral support for a weak soft story at the ground level and exterior walls for a new mechanical enclosure.

Construction of the upgrade was substantially complete within 8 months of Hohbach-Lewin’s initial involvement. Construction was by Rossi Builders, the architectural design was provided by Legacy Partners; peer review and PML evaluation services were by Telesis Engineers.

Crothers Memorial Hall, Stanford University, Stanford, CA

Crothers Memorial Hall, Stanford University, Stanford, CAThis 1940’s era dormitory was constructed with an unconventional laticed steel stud system that relied on the plastered interior room demising walls as the primary transverse vertical lateral force resisting system. This archaic (and ill advised) structural system was deemed inadequate to provide sufficient seismic resistance. The original strengthening scheme described in an evaluation report prepared by others, recommended removing all existing roof tiles so the straight sheathed roof could be sheathed in new plywood; additional recommendations called for the removal of all exterior stucco so that the exterior walls could also be sheathed.

By utilizing performance based techniques, Hohbach-Lewin was able to devise a scheme which eliminated the need for both of these costly retrofit measures. Intermittent wood framed cross walls were introduced into the attic space and a system of discreet and strategically located concrete shear walls were introduced in to the building footprint. To account for the low overhead clearance in the basement, the new concrete walls were supported by a network of new micro pile supported grade beams.

Historic Hoover Middle School, San Jose, CA

Historic Hoover Middle School, San Jose, CAThis 1930’s vintage concrete building has been retrofitted and returned to public educational use utilizing performance-based seismic design methods per the FEMA 273 and ATC-40 guidelines as permitted by Division III-R of the California Building Code. These methods allowed preservation of the buildings historic fabric, which is highly valued by the community, and also yielded significant savings in construction cost for the San Jose Unified School District, which made it feasible for the project to proceed. Testing of existing construction materials was undertaken to meet DSA requirements as well as to obtain accurate values for analysis. The architect for the project was the Steinberg Group; the general contractor was Toeniskoetter & Breeding, Inc. both of San Jose, CA.

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