Numerical modelling of time-dependent cracking and deformation of reinforced concrete structures

For a structure to remain serviceable, crack widths must be small enough to beacceptable from an aesthetic point of view, small enough to avoid waterproofingproblems and small enough to prevent the ingress of water that may lead to corrosion ofthe reinforcement. Crack control is therefore an important aspect of the design ofreinforced concrete structures at the serviceability limit state. Despite its importance,code methods for crack control have been developed, in the main, from laboratoryobservations of the instantaneous behaviour of reinforced concrete members under loadand fail to account adequately for the time-dependent development of cracking.In this study numerical models have been developed to investigate timedependentcracking of reinforced concrete structures. Two approaches were adopted tosimulate cracking in reinforced concrete members. The first approach is the distributedcracking approach. In this approach, steel reinforcement is smeared through theconcrete elements and bond-slip between steel and concrete is accounted for indirectlyby including the tension stiffening effect. The second approach is the localized crackingapproach, in which concrete fracture models are used in conjunction with bond-slipinterface elements to model stress transfer between concrete and steel.Creep of concrete has been incorporated into the models by adopting the principleof superposition and the time-dependent development of shrinkage strain of concrete ismodelled using an approximating function. Both creep and shrinkage were treated asinelastic pre-strains and applied to the discretized structure as equivalent nodal forces.Apart from material non-linearity, non-linearity arising from large deformation wasalso accounted for using the updated Lagrangian formulation.The numerical models were used to simulate a series of laboratory tests forverification purposes. The models were assessed critically by comparing the numericalresults with the test data and the numerical results are shown to have good correlationswith the test results. In addition, a comparison was undertaken among the numericalmodels and the pros and cons of each model were evaluated.A series of controlled parametric numerical experiments was devised and carriedout using one of the numerical models. Various parameters were identified andinvestigated in the parametric study. The effects of the parameters were thoroughlyexamined and the interactions between the parameters were discussed in detail