UBC Theses and Dissertations
Numerical modelling of experimental data of reinforced concrete beam-to-column joints Baraka, Miljenko
Since the 1970's, increasing attention has been given to seismic design in building codes with emphasis on ductility. Ductile behaviour in reinforced concrete moment resisting frames is important from the point of view of an energy dissipating mechanism. Modern design codes today have stringent guidelines on the design of the beam to column joint region in order to achieve ductile behaviour without brittle shear failure. There are many older buildings, however, that are deficient in strength and ductility with respect to seismic loading. Deficient structures such as these may be retrofitted by encasing the beam to column joint in a steel shell. Cyclic testing of reinforced concrete beam and column sub-assemblies have proven that a very substantial increase in bending and shear strength can be achieved in the joint area by encasing the region with a steel tube and filling the cavity with cement grout. Failures were deflected from the joint area to adjacent members, which were intentionally weakened to form plastic hinges. Subsequent tests on the remaining joint specimens, which forced the failure mechanism into the joint region, provided strength and ductility data for the joint itself. Because experimental testing of scale models can be expensive and at times impractical for every situation that may arise in practice, a non-linear finite element program was written for the analysis of the joint area. The program utilizes plasticity based constitutive descriptions of the concrete and steel material models and intends to be able to predict the behaviour and peak values of the strength envelopes of the joints. Comparisons with available experimental results were encouraging insofar as the plastic behaviour of the concrete and steel were captured. Due to the complex nature of the problem the program was unable to accurately predict the maximum load carrying capacity and more research is required in "fine tuning" the material constitutive models and finite element models. Recommendations for continuing research are given.
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