Finite element analysis of temperature effects concrete bridge

Abstract

The present study is an attempt to understand the thermal effects in concrete bridge decks with special attention to Bangladesh. Thermal effects in a bridge deck are consequence of non-linear temperature distribution over the deck cross section. As a result, stresses, movements, and even cracks are initiated, the order, magnitude and significance of which are still not fully understood. Although over the past two decades a number of studies have been carried out, codes provide little or no guidance whatsoever on this matter. The earlier studies demonstrated that thermal effects are comparable in magnitude to dead and live load effects. Since the governing factors influencing temperature distribution vary geographically, the results of any such study become limited to specific geographic and meteorological condition. Therefore, previous results cannot be applied to any other situation. This study aims at investigation of thermal effects in the context of Bangladesh. Particular attention is given on the non-linear temperature variation over the cross section of concrete bridge decks and on the resulting longitudinal eigenstresses. Additional continuity stresses that develop in a continuous bridge are also addressed. An analytical model is developed to find out the influence of various parameters on the temperature induced stresses. A method for two-dimensional finite element transient heat transfer analysis is formulated. The mathematical model incorporates as many as 40 factors or parameters, some are interdependent, affecting temperature distribution which are related to the material, geometrical, meteorological and geographical conditions. On the basis of the model a computer program is developed to predict the temperature and stress distributions over bridge cross sections. Results derived from the analytical model are compared with the experimental and theoretical results obtained by other investigators. Several analyses are carried out in order to establish the critical values of parameters causing extreme thermal effects in concrete bridge decks constructed in Bangladesh. Special attention is given to model the seasonal and diurnal variation in boundary conditions. Statistical analysis of extremes is carried out to determine the extremes of meteorological parameters for 30-yr return period. Finally, temperature distributions to be applied in Bangladesh in slabs, beams and webs of box girder of various depths encountered in practice are proposed. Simplified hand calculation method is also presented to calculate the magnitude of thermal stresses due to proposed distributions.