Partial-interaction analysis of composite beams using the direct stiffness method

This thesis investigates the behaviour of composite beams with partial shear interactionby means of the direct stiffness approach. A model is derived to describe the behaviourof m-layered composite beams in the linear-elastic range (where m is an integer greaterthan or equal to two). This model is then applied to the particular case of compositebeams formed by two layers, as in the case of steel-concrete composite beams. Based onthis model, the direct stiffness approach is formulated and closed form solutions arederived for particular structural cases, such as for simply supported beams, proppedcantilevers and fixed ended beams, subjected to a uniformly distributed load.The direct stiffness formulation is extended to account for material nonlinearities andthe proposed nonlinear modelling technique is validated against experimental dataavailable in literature; the experiments considered include simply supported beamsloaded in positive and negative bending subjected to a point load applied at mid-spanand two-span continuous composite beams subjected to point loads.The behaviour of composite beams with partial shear interaction is then investigatedaccounting for time effects such as creep and shrinkage. The model derived in thelinear-elastic range for two-layered composite beams is further developed to account forthese time effects. In addition, the applicability of the direct stiffness approach isextended in the time domain based on this model and closed form solutions are derivedfor some structural systems, such as for simply supported beams, propped cantileversand fixed ended beams, subjected to a uniformly distributed load and to shrinkagedeformation. The use of the direct stiffness approach requires only one discretisation tobe carried out, which occurs in the time domain, instead of the two (i.e. onediscretisation in the time domain and one discretisation along the beam axis) requiredby modelling techniques available in literature. The time-dependent behaviour of theconcrete is modelled by means of the algebraic methods, such as the age-adjustedeffective modulus method and the mean stress method. The extension of the formulationto model the time-dependent behaviour of the concrete using the step-by-step procedureis also presented.