Award-winning structural analysis and seismic retrofit design for four-story reinforced-concrete building. 50,000 sf.

Orange Coast College's Watson Hall was constructed in 1966 and served as the community college's library for several years. The floor consisted of waffle slab construction, and the building utilized concrete moment frames in both directions as the earthquake load resisting system. Like most concrete buildings designed in California before 1976, the 52,000-square-foot, four-story building presented a major earthquake risk because it would not survive the displacements induced by large earthquakes.

A previous retrofit plan that required the addition of shear walls had been rejected for its high cost and extensive foundation work. Weidlinger Associates was hired to assist the design team in developing a retrofit scheme that improved the seismic performance of the building while keeping the cost of construction low.

A computer model was developed, and a nonlinear analysis of the existing structure was performed to calculate the target displacement. The retrofit scheme selected involved the addition of strategically placed steel concentric braced frames in each principal building direction. The unique design provides the building with the stiffness and strength to resist displacements induced by a design level earthquake and requires only minor modifications to the existing foundations. Nonlinear computer analysis verified that the retrofit scheme drastically reduces earthquake induced displacements and limits the demand on structural elements to acceptable values.

Completion Date: 2008
Location: Costa Mesa, California
Owner or Client: Coast Community College District
Prime Consultant(s): Roessler Design Group