American Society of Civil Engineers

Innovative Hi-Tech Solution for a Concrete Residential High-Rise Tower

by Saiful Islam, (Saiful/Bouquet Structural Engineers, Inc., Pasadena, CA), Matthew Skokan, (Saiful/Bouquet Structural Engineers, Inc., Pasadena, CA), and Sampson Huang, (Saiful/Bouquet Structural Engineers, Inc., Pasadena, CA)
Section: Selected Building Case Studies, pp. 1-10, (doi:

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Document type: Conference Proceeding Paper
Part of: Structures Congress 2006: Structural Engineering and Public Safety
Abstract: This paper describes the innovative seismic retrofit of the Webb Tower located on the campus of the University of Southern California in Los Angeles. The existing 14-story residential structure was constructed circa 1972 using light-weight concrete. The lateral system for the building consists of perimeter non-ductile post-tensioned concrete moment frames supported on isolated spread footings. A preliminary evaluation of the building revealed several seismic deficiencies, including the following: (1) non-ductile detailing, (2) excessive building deflection and (3) joint shear overstress. After considering several alternate retrofit schemes, a unique retrofit scheme was developed utilizing a single bay of buckling-restrained steel braces in combination with a reinforced concrete beam-column frame on each side of the building. The selection of this system provides several advantages for this project over other retrofit schemes, including: (1) provides partial views from the existing windows, (2) requires significantly less demolition than an interior scheme, (3) more cost-effective than an interior solution, (4) reduces building drift and demands on the non-ductile moment frames, and (5) buckling-restrained braces do not exhibit strength degrading and aesthetically unacceptable post-buckling deformations. A three-dimensional nonlinear computer model was developed capable of capturing the nonlinear behavior of the buckling-restrained braces, the existing concrete beams and columns with consideration for the post-tensioning effect, and the new concrete beams and columns. The seismic performance of the retrofitted building was investigated by time history analyses using seven sets of ground motion records.

ASCE Subject Headings:
Concrete structures
High-rise buildings
Residential buildings