Stability of unbraced concrete beams on bearing pads including wind loading

Abstract

Unbraced concrete beams supported temporarily at their ends by bearing pads are considered. Such beams may have horizontal curvature due to initial sweep and/or solar heating, and may be subjected to wind. These factors, along with creep and bearing eccentricity or slope, tend to cause the beam to roll (tilt) about the supports and possibly slide laterally, which may induce failure. Collapse of such unbraced bridge girders has occurred, and the problem is analyzed here. The beam is assumed to have small horizontal curvature (small sweep), and to behave elastically under gravity and wind loads. The equilibrium roll angle depends on the beam’s length, weight per unit length, modulus of elasticity, moment of inertia with respect to weak-axis bending, and height of the cross-sectional center of gravity above the roll axis, along with the lateral superelevation angle of the bearing pads, roll and yaw stiffness coefficients of the bearing pads, and wind loading. The effects of some of these quantities on the roll angle are investigated. Approximate formulas in the literature do not include the effect of wind. If a maximum allowable roll angle is specified, a factor of safety is determined and compared with the one used in the design of bridges. Finally, the critical value of the roll angle for sliding instability is obtained in terms of the coefficient of friction of the bearing pads.