Evaluation of thermal stresses in a concrete box girder bridge.

摘要

Consideration of thermal effects required in bridge design includes distortions and stresses. Distortions include overall expansion and contraction along the longitudinal axis of the bridge, changes in the cross section shape due to differential expansion and contraction between elements, and curvatures induced by non-uniform temperature distributions. Stresses arise from restraint of free expansion, distortion, or curvature.; This thesis examines temperature distributions which may occur in concrete box girder bridges, methods to predict such distributions, and stresses arising from restraint of free response to arbitrary temperature distributions. It is argued that uni-dimensional heat flow analyses used in the past are not adequate for determination of restraint stresses in large box girder bridges. A simplified two dimensional analysis is proposed.; It is postulated that the magnitude-frequency relation for the occurrence of characteristic temperature distributions in concrete box girder bridges of typical proportions is related to the deviation of the daily maximum or minimum air temperature from the 2-day running mean air temperature. The magnitude-frequency relationship of this parameter is determined for two weather stations in the state of Washington. The magnitude for a 50-year return period was found to be 1.7 and 1.4 times the mean daily range for the summer months (June, July, August) when maximum solar radiation may be anticipated.; The methods used for prediction of temperature distributions and restraint stresses are tested against temperature and strain data obtained from a bridge in service. The significance for design is also examined by comparing stresses arising from thermal effects with stresses from other loading conditions.; Conclusions are drawn and recommendations for design and future research are presented.