Drying and Cracking Effects in Box-girder Bridge Segment

This paper deals with the effect of drying as a moisture diffusion process in a segment of a typical box-girder bridge. Pore relative humidity distributions throughout the cross sections of the plates of the girder are calculated from the diffusion equation, taking its nonlinearity and aging into account. The effect of creep with aging on the stresses produced by drying shrinkage is taken into account assuming a creep law based on the principle of superposition and described by an aging spring-dashpot chain model. The cross effects between creep and drying, expressed as stress-induced shrinkage (equivalent to drying creep), are considered. Tensile strain softening (smeared cracking) is taken into account in the form of an additive cracking strain. Localization of cracking and energetic fracture-mechanics aspects are neglected. A general algorithm for step-by-step integration in time is presented and verified by a convergence study. An example of analysis of the cross section of one recently built bridge confirms the feasibility of the analysis and indicates that the effect of the diffusion process of drying on the stress distributions is very large, in fact, so large that the stress values obtained by customary methods are merely fictitious.