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Wilshire Grand: Outrigger Designs and Details for a Highly Seismic Site
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Wilshire Grand: Outrigger Designs and Details for a Highly Seismic Site
Joseph, Leonard M.; Gulec, C. Kerem; Schwaiger, Justin M.;
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The 1100 foot [335 m] tall Wilshire Grand Center tower under construction in Los Angeles illustrates many key outrigger issues. The tower has a long, narrow floor plan and slender central core. Outrigger braces at three groups of levels in the tower help provide for occupant comfort during windy conditions as well as safety during earthquakes. Because outrigger systems are outside the scope of prescriptive code provisions, Performance Based Design (PBD) using Nonlinear Response History Analysis (NRHA) demonstrated acceptability to the Los Angeles building department and its peer review panel. Buckling Restrained Brace (BRB) diagonals are used at all outrigger levels to provide stable cyclic nonlinear behavior and to limit forces generated at columns, connections and core walls. Each diagonal at the lowest set of outriggers includes four individual BRBs to provide exceptional capacities. The middle outriggers have an unusual `X-braced Vierendeel` configuration to provide clear hotel corridors. The top outriggers are pre-loaded by jacks to address long-term differential shortening between the concrete core and concrete-filled steel perimeter box columns. The outrigger connection details are complex in order to handle large forces and deformations, but were developed with contractor input to enable practical construction.
Tall building;Core;Outrigger;Belt truss;Buckling Restrained Brace (BRB);Nonlinear Response History Analysis (NRHA);Performance Based Design (PBD);Seismic design;
 Cited by
Choi, H. S. and Joseph, L. (2012). Outrigger system design considerations. International Journal of High-Rise Buildings, 1(3), 237-246

LATBSDC. (2011). An Alternative Procedure for Seismic Analysis and Design of Tall Buildings Located in the Los Angeles Region. Los Angeles Tall Buildings Structural Design Council, Los Angeles, California, USA.