MODEL STUDY OF A PRESTRESSED CONCRETE BOX-GIRDER BRIDGE UNDER THERMAL LOADING

THE EFFECTS OF VERTICAL AND HORIZONTAL TEMPERATURE GRADIENTS HAVE LARGELY BEEN IGNORED, OR DEALT WITH BY OVERSIMPLIFIED THEORIES, IN THE DESIGN OF BRIDGE STRUCTURES. THE NONUNIFORM TEMPERATURE DISTRIBUTION INDUCED IN BRIDGES BY SOLAR RADIATION HAS TWO MAIN LONGITUDINAL EFFECTS. FIRST, INTERNAL STRESSES ARE INDUCED DUE TO THE NONLINEAR VERTICAL TEMPERATURE GRADIENT. SECOND, THE INCREASE IN TEMPERATURE OF THE BRIDGE DECK WITH RESPECT TO THE SOFFIT TEMPERATURE RESULTS IN AN UPWARDS HOGGING OF THE BRIDGE. IF THE BRIDGE IS CONTINUOUS, RESTRAINT OF THE UPWARD DEFLECTION IS PROVI- DED AT THE INTERNAL SUPPORTS, AND THE RESULTING REACTIONS INDUCE CONTINUITY STRESSES OF APPRECIABLE MAGNITUDE. AN EXPERIMENTAL PROGRAM IS REPORTED IN WHICH THEORETICAL CONSIDERATIONS WERE EXAMINED THROUGH THERMAL LOADING OF A MODEL FOR WHICH A TYPICAL, SINGLE-CELL, TRAPEZOIDAL, BOX- GIRDER SECTION WAS CHOSEN. THE TEST RESULTS SHOWED THAT THE EQUATIONS DEVELOPED FROM CONSIDERATION OF SIMPLE STATICS ACCURATELY PREDICT LONGITUDINAL STRESSES AND CURVATURES IN BOX-GIRDER BRIDGES. TO DATE THE MODEL HAS BEEN TESTED ONLY WITH A BARE CONCRETE DECK SLAB. FURTHER SERIES OF TESTS WITH A SCALED BITUMINOUS WEARING COURSE AND WITH A WHITE PAINTED SURFACE ARE PLANNED.