Prediction of residual stress of an orthotropic plate due to welding

Abstract

Orthotropic steel decks are widely used in bridge construction nowadays, especially in case of long span bridges. One of the main problems of bridges that utilize this technology is the susceptibility to fatigue failure. Cyclic loading due to wheel loads, in combination with the complex network of welded details, make such types of decks prone to fatigue cracking, which poses a threat to the structure's integrity.
One of the factors that contribute to crack initiation and propagation under cyclic loading are welding-induced residual stresses. The localized heat input, due to welding, and the subsequent cooling, force the adjacent area to undergo expansion and shrinkage, which are, however, restricted by the surrounding material. As a result, residual stresses are formed, which can reach the yield strength of the material in the region near the weld. When these are tensile, they can accelerate the crack propagation rate, thus severely reducing the fatigue life and endangering the structure's safety. Knowing the residual stress distribution in welded joints of orthotropic steel decks can prove to be useful in the evaluation of resistance against fatigue.
In this research project, a finite element model which is able to predict residual stresses in normal strength steel weldments, has been developed. In the first stage of the research, a small-scale welding experiment has been conducted, during which temperature and distortion measurements were derived. The welding procedure was then modelled in the finite element software ABAQUS. Experimental data have been used to validate the accuracy of the adopted heat source model and parametric studies have been carried out, in order to investigate the influence of the heat source parameters and the heat losses on the temperature distribution.
The validated methodology was then applied on a trough-to-deck plate welded connection of an orthotropic steel deck. Longitudinal and transverse residual stresses have been calculated at various positions of the deck and stiffeners. The influence of the welding sequence on the residual stresses has been investigated, by considering two welding scenarios; parallel and sequential welding. The effect of the adopted stress-strain relationship under elevated temperatures on the residual stress field has been examined, by considering an ideal plastic material model and one that includes strain hardening. In addition to these, the impact of the boundary conditions has also been studied. Finally, the effect of welding on the appearance of imperfections is discussed, by considering the deflection of the deck plate, after the process. As a result, valuable information is obtained about the shape of residual stresses, the associated deformations, and the factors that affect them, in a welded connection of an orthotropic steel deck.