Behaviour of reinforced concrete frames with lightweight blockwork infill panels
The current investigation concerns the behaviour of lightweight blockork infill panels bounded by reinforced concrete frames. A detailed and comprehensive review of the literature on different frame-inf ill combinations is presented. Details are given of tests on sixteen third-scale infilled frames and four open frames. These were tested under two types of loading: horizontal racking loading only and combined vertical loads on columns and racking loading. The complete load-deflection response is considered in detail including. initial elastic behaviour, influence of cracking and the formation of collapse mechanisms after the attainment of peak load. The variables investigated include the overall effects of the infill, the infill thickness, the vertical loads, the amount of reinforcement, the change in stiffness and strength of beams and of columns and the effect of reinforcement detailing. Those found to have a major influence are the vertical loads, the infill thickness, the reinforcement detailing particularly in the opening corners of the frame, and the workmanship. The principal parameters obtained from the tests are the initial racking stiffness, the infill cracking strength, the ultimate load and the plastic collapse load. Their values are compared to the available empirical and theoretical methods. None of these methods is found to safely predict the initial racking stiffness and the ultimate carrying capacity of this type of structure. A plastic analysis is presented to predict the two plastic collapse mechanisms identified in the tests. The penalty factor to allow for idealization of plasticity of the infill is found as part of the solution. A second penalty factor is introduced to allow for the limited ductility of the frame. The proposed method is found to yield satisfactory and safe predictions for the plastic resistance of these infilled frames. In conclusion some design recommendations are proposed for the initial racking stiffness and the cracking infill strength.