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Report No.: CCEER-98-5

Title: Cyclic Behavior of Richmond-San Rafael Retrofitted Tower Leg

Authors: Ahmad M. Itani, Bruce M. Douglas, and Jeremy P. Woodgate

Date: June 1998

Sponsoring Agency: California Department of Transportation (Caltrans)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557

Abstract

This report presents results of experimental investigation to evaluate the cyclic behavior of retrofitted Richmond-San Rafael Bridge tower legs. The retrofit strategy consisted of infilling the bottom steel section with 6000 psi concrete and adding two perforated steel cover plates at the open sides of the section. This investigation is limited to the cyclic behavior of the tower in the longitudinal directions, i.e. bending around y-y axis.

The objectives of the study are:

  1. Determine the cyclic response of the retrofitted tower leg under gravity load.
  2. Determine the ultimate strength, rotational capacity, and the failure mode of the retrofitted tower leg.

A one-half scale specimen that represented retrofitted Pier 20 was tested under a constant gravity load equal to 0.183 Py (330 kip) and an increasing lateral cyclic displacement. The specimen responded elastically up to displacement of 2 inches, which corresponded to lateral load equal to 27 kips. Yielding concentrated at the end of the specimen in the joint between the infill concrete and R/C block. The inelasticity did not spread inside the zone where the concrete infill was added. At a displacement equal to 5.75 inches a crack initiated in the top and bottom plates of the section along the net section of the first blot row at 2 inches inside the R/C block. At a displacement equal to 10 inches, the top and bottom plates including the outside angles were completely fractured.

The test results showed that the displacement ductility, which is defined as ratio of the displacement at which fracture is initiated, 5.75", to the yield displacement, 2", is equal 2.9. After the test, minor local buckling was noticed in the top and bottom cover plates. Vertical cracks inside the concrete infill could be seen at the location of the expansion joint filler. The ultimate moment section capacity at the base of the specimen was 41% higher the plastic moment capacity (Abstract by authors).

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