DESIGN FOR TORSION IN BEAM

Abstract

This paper investigates the torsional load capacities of two reinforced concrete cap beams in the elevated
guideway structures. One beam has a regular configuration and the other has an irregular configuration. For
each beam type, a 1/2-scale model was tested. The failure mechanisms of both beams were dominated by
torsion. The load capacity of the regular beam was governed by the yielding of the main longitudinal
reinforcement induced by a truss action. The capacity of the irregular beam was governed by a torsional crack through the columns zone, which can be attributed to the lack of confinement in the region. The large spacing of the top horizontal ties in the regular beam led to vertical splitting cracks when the beam was loaded through the shear keys. Nonlinear finite element analyses have been conducted on the beams. The finite element models are able to reproduce the nonlinear behaviors observed in the tests with reasonably good accuracy. Based on the experimental observations and numerical results, strut-&-tie models have been developed to evaluate the load capacities of the beams. Both types of models have indicated that the horizontal load resistance of a cap beam under bending and torsion will decrease with the decrease of the vertical load.