Studies On Theory Of Solar Radiation Thermal Effects On Concrete Bridges With Application

Environmental exposure to complex climatic conditions such as solar radiation and air temperature variation induces nonlinear temperature distributions in concrete bridges, which produce thermal stresses and deformations. The thermal stresses, which can be comparable in magnitude to external load stresses, contribute significantly to the cracking and consequent deterioration of the bridge concrete and therefore there are great emphases laid on solar radiation-induced thermal effects on concrete bridges. However, owing to the complexity characteristic of thermal effects, the current theory and computational methods for the problem are not yet fully developed. In practice, bridge designers may often proceed with over-simplified computational idealizations and methods to predict the thermal effects, which may result in thermal loadings and thermal stresses of insufficient accuracy. This thesis presents more thorough studies on solar radiation-induced thermal effects on concrete bridges. Improvements are made on the theory and methods that are currently available and used. The issue of solar radiation thermal load evaluation is also analyzed and discussed.Based on solar physics, general astrology and heat transfer theory, the mechanism of heat transfer between concrete bridges and their surroundings is studied. The boundary conditions of heat transfer in concrete bridges subjected to solar radiation are systematically defined, and computational models are established for analyzing the thermal response of concrete bridges of arbitrary complicated structural type to solar radiation.Studies are conducted on the finite element analysis of the solar radiation thermal effects. FEM modules are developed for analyzing the solar radiation thermal affects on concrete bridges of various structural types with the FEM package ANSYS as their running platform. The FEM modules developed are applied with emphases to the analyses of the temperature fields and thermal stresses within concrete box-girders subjected to solar radiation. Parametric studies are conducted to investigate the effects of various factors on the thermal responses of concrete box-girders in respect with solar radiation intensity, wind velocity, air temperature, location, orientation, geometry and material.Analysis of solar radiation temperature distributions in concrete bridges has frequently been performed by using sophisticated numerical techniques such as finite element method and finite difference method, which require a large expenditure of computational efforts and time. In this thesis, proposed are closed-form analytical solutions to temperature distributions within thin-walled concrete structures such as box-girders and hollow piers subjected to solar radiation. The temperature field is assumed to be periodic in time and one- dimensional through the wall depth. By resolving the equation of heat conduction, an analytical solution to the temperature field in Fourier series is obtained. Only a few terms out of the Fourier series are required to give results with sufficient accuracy due to the fast convergence of such series.Studies on computational methods for the 3-D thermal stresses in concrete bridges are presented. Based on the theory of thermoelasticity, an integration property of thermal stresses is derived, which is utilized to develop a general method of computing the 3-D thermal stresses. The 3-D problem is transformed into a plane one, where the coupling between different stress components is taken into account. Emphasis is laid on research on the 3-D thermal stresses in concrete box-girders, for which a practical method is proposed. With this method only technique of structural mechanics is required for calculating the 3-D thermal stresses with the stress component coupling taken into account, which offers considerable facility and simplicity. Examples are given to verify the validity and feasibility of the method; in the meantime the results from the examples reveal that the conventional methods can yield results with significant error.Reference is made to bridge design codes home and abroad with review and discussion on the specifications related to thermal loadings and thermal stress computation. With investigation into Chinese railway concrete bridge design code TB 10002.3—2005 and highway concrete bridge design code JTG D62—2004, suggestions for temperature gradient specification and thermal stress computation are proposed. Probability models and statistical methods are established and used to analyze the variability of the nonlinear temperature distributions in concrete bridges at different locations in China on the basis of historical meteorological data from typical weather stations over the country. Values of design temperature gradient loadings for concrete bridges at different locations are suggested.