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Lookup NU author(s): Michael Kyakula, Professor Sean Wilkinson
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SUMMARY This paper proposes an improved spread plasticity model that correctly identifies the initiation of yielding anywhere in the beam, takes into account the gradual spread of plasticity, the shift of the points of contra-flexure, the variable location and actual length of the yield zones. The model assumes that columns and beam column joints remain elastic. Beams are made up of elastic and spread plasticity sub elements connected in series. When a beam yields, its stiffness reduces and flexibility increases. Before yielding spread plasticity sub element has a null matrix, as the beam yields, the magnitude of its coefficients increase. At each time step, the model updates the flexibility matrices of the spread plasticity sub elements. Unlike existing spread and concentrated plasticity models, moments within the span are monitored and the effect of their yielding or “unyielding” taken into account. A number of examples are presented that demonstrate the limitations of the existing spread plasticity models. The paper concludes that spread plasticity models that only consider plasticity at the beam column connections are only accurate for lower stories and structures where the applied/design gravity load < 0.8. The examples also show that compared to existing spread plasticity models, the proposed model improves the accuracy in calculation of global displacements, joint rotations and inter story drift ratios by up to 25%, 69% and 55% depending on the ratios of applied/design gravity load and bottom/top reinforcement.
Author(s): Kyakula M, Wilkinson SM
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Unknown
Conference Name: 13th World Conference on Earthquake Engineering
Year of Conference: 2004
