EVALUATION OF THE CURRENT CALTRANS SEISMIC RESTRAINER DESIGN METHOD

Abstract

The focus of this study was to understand the implications of the current Calif. Department of Transportation (Caltrans) hinge restrainer design procedure. Two aspects were studied. One was the effects of changing the cross sectional area of restrainers and the restrainer gap on the nonlinear response of a bridge with several hinges. The second was the sensitivity of the number of required restrainers to changes in some of the simplifying assumptions which are made in the current Caltrans restrainer design method. The focus of the nonlinear analyses was the relative displacements at the joints, restrainer forces, and restrainer stresses. The level of ductility demand in the piers was also examined to identify the extent of nonlinearity. Different earthquake records were used for insuring that conclusions reflect the effects of a variety of ground excitations. In addition to the input earthquake, the number of restrainers at each hinge, the restrainer gap, and the hinge gap were also varied. Only longitudinal bridge response was considered to be consistent with the design method. In order to study the effects of design assumptions on the required number of cables, several manual calculations of the design example in the Caltrans restrainer design guidelines were carried out. The deviations from the method included a different treatment of mass and stiffness as different hinges closed as a result of the earthquakes. Another variable was the simultaneous change in the restrainer and the hinge gaps.