Analysis of bridge decks for thermal loading for the Sri Lankan industry

Abstract

Concrete bridge structures, which are exposed to the sun are subjected to complex thermal stresses, which may vary continuously with time. The magnitude of these stresses depends mainly upon the temperature variations that occur within the cross section of the bridge deck. The nonlinear temperature variation created over the cross section of a simply supported bridge produces longitudinal self-equilibrating stresses (eigen stresses). These can be determined by restraining the simply supported beam and then releasing the restrained structure by reversing and applying the stress resultants. Using the Principle of superposition gives the desired stresses. The resulting internal forces are unaffected but there is a re-distribution of stresses in different components of a cross-section under thermal loading. In a continuous bridge, additional continuity stresses also develop. In this situation internal forces as well as external reactions change. Overall results can be obtained using superposition of self-equilibrating stresses and continuity stresses. The procedure described can be used for any practical situation as long as there is symmetry of the cross section about a vertical axis. A section containing several layers made out of different materials can also be handled in a similar way. In the situation of a complex bridge deck consisting of a grid structure the above results can be combined with a normal grillage analysis to enhance the comprehensive nature of the approach.