Carquinez Senior Apartments

400 Harbor Way
Richmond, CA

  • Architect: Weir Andrewson Associates, Inc
  • Contractor: Saarman
  • Developer: BRIDGE Housing
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Credit: Keith Baker

For under $1 million, we created a ground-floor retrofit that achieved life-safety performance at the DBE hazard and collapse prevention at the MCE hazard.

The Carquinez, a historic landmark located in Richmond, CA, was constructed in 1926 and served as a hotel until 1990, when it was converted to low-income housing. The five-story reinforced-concrete structure recently underwent a remodel that included seismic strengthening. As with many similar buildings of its era, the ground floor façade along the streets is largely open, while the rear facing walls are essentially solid. Above, the exterior concrete walls are mostly solid with a regular pattern of window openings. This configuration creates both a weak story and a large torsional irregularity at the ground floor, making the building extremely susceptible to earthquake damage.

The challenge was twofold: to develop a seismic strengthening scheme that would provide shelter-in-place for the tenants in the 36 housing units located above the ground floor and at the Alzheimer day-care center that occupied the rear half of the ground floor; and to provide a life-safety level of seismic performance on a $1,000,000 budget.

BRIDGE Housing had considered two retrofit designs based on prescriptive methods: One met the performance goals but would cost $4–6 million, potentially six times the available budget. The second met the budget but not the performance goals. Before proceeding with the affordable, second option, BRIDGE asked us to reexamine the problem.

Given their constraints, limited budget, and wish for immediate-occupancy performance, we did not consider a traditional solution a viable option. Instead, recognizing the large difference in strength and stiffness between the upper stories and the ground floor, we developed a seismic bracing scheme that provided strength and toughness at the ground floor while limiting the seismic forces transmitted to the upper floors. This system consists of four concrete walls carefully placed and proportioned to eliminate the torsional irregularity and provide the required strength and ductility needed to meet a life-safety performance level.

We conducted a nonlinear response history analysis using PERFORM 3D to evaluate the existing building and calibrate the new walls. We applied the insights that we learned while evolving the "relative-strength" concept underlying ATC 71-1: Guidelines for the Seismic Retrofit of Weak-Story Wood-Famed Buildings (now known as FEMA-P807.)

Our solution created a ground-floor retrofit for the Carquinez that achieved life-safety performance at the DBE hazard (475-year return period) and collapse prevention at the MCE hazard (2,475-year return period) and came in under BRIDGE's budget of $1 million. What's more, in the event of a large earthquake, tenants will not have to be displaced for BRIDGE to institute and complete repairs.





Executed as Tipping Mar