Seismic Resistance of RC Bent Caps in Elevated Mass Transit Structures

Abstract

This paper presents a study of the seismic resistance of two reinforced concrete cap beams in existing elevated guideway structures constructed in the 1960s. One beam has a regular configuration and the other has an irregular configuration. For each beam type, a half-scale model was designed, constructed, and tested. The irregular beam tested had a larger depth and a higher quantity of main longitudinal steel. While the regular beam had spiral confinement extending into the beam-to-column joint, the irregular beam did not. The beams were subjected to simultaneous bending, shear, and torsion in the tests, with the torsion induced by the vertical eccentricity of the horizontal load exerted at the top face of the beams. The test results underscore the importance of confinement steel in the beam-to-column joint of a cap beam and the critical role of the longitudinal reinforcement in the beams for torsional resistance. A numerical parametric study has been conducted with nonlinear finite element and strut-and-tie models, which have been validated with the experimental results. The study has indicated that the seismic load resistance of a cap beam can decrease with a reduced gravity load, which is an important consideration for design. [DOI: 10.1193/1.3533471]