The Whittier Narrows, California Earthquake of October 1, 1987—Damage to the I-5/I-605 Separator

Abstract

The I-5/I-605 separator, a major nine span bridge, was severely damaged in the Whittier earthquakes. All columns of Bent 6, which is supported on the median strip of the Santa Ana Freeway (I-5) suffered shear failures, and the supported spans came close to collapse. Other minor damage included minor column hinging at more flexible bents, abutment pounding, and fracture of keeper plates at abutment rockers. Apparently much of this minor damage occurred during a major aftershock. Preliminary calculations indicate that the shear failures of Bent 6 resulted from disproportionate flexural and shear strengths of the columns, attributable to the working stress philosophy adopted in design, and the much greater stiffness of Bent 6 than adjacent bents. Movement joints with cable restrainers, at both ends of spans founded on Bent 6, make estimation of lateral load transfer from more flexible regions difficult.