American Society of Civil Engineers

Seismic Strengthening of a Four-Story Nonductile Concrete Flat Slab Structure

by Gary R. Searer, (Wiss, Janney, Elstner Associates, Inc. E-mail:, Mahmoud M. Hachem, (Wiss, Janney, Elstner Associates, Inc. E-mail:, and Douglas L. Gadow, (Wiss, Janney, Elstner Associates, Inc. E-mail:
Section: Rehabilitation and Upgrade of Structures 2, pp. 1-9, (doi:

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Document type: Conference Proceeding Paper
Part of: New Horizons and Better Practices
Abstract: This paper documents the design and construction of a voluntary seismic upgrade for a four-story, nonductile concrete flat slab structure. The structure was designed in the early 1970s and lacked detailing necessary to ensure ductile behavior — both in the lightly reinforced concrete columns and in the flat post-tensioned concrete slabs. Since the structure is a modernist landmark and is located in the historic Fisherman’s Wharf area of San Francisco, any strengthening had to have minimal impact on the historic fabric of the structure. After examining a number of possible options, addition of column capitals and fiber-wrapping of the non-ductile columns were selected as the upgrade that best suited the project. The new column capitals use a relatively unusual design that relies on shear-friction between the capital and the column — rather than typical epoxy-dowels — and this method of construction is described in detail. The intent of the upgrade was to satisfy prescriptive requirements as well as desired performance goals.

ASCE Subject Headings:
Seismic effects
Concrete structures