Structural Dynamic Instability Due to Earthquake Loads

Abstract eng:
From a thorough observation of the images taken after major seismic events arises the conclusion that structures collapse vertically due to their lack of stability under vertical load amplification. Overturn of buildings due to earthquake effects happens in case of weak foundations or liquefaction effects (see Niigata, Japan 1964). Majority of collapses occurred due to structural instability as P-Delta effects under combined horizontal and vertical loads. Worse, there must be a dynamic effect due to vertical seismic oscillations that leads to amplification of the vertical loads. Vertical effects and P-Delta phenomena are mentioned in each seismic code but the effect is dealt statically for analysis and design purposes. It is indicated that dynamic analysis should be performed by means of step by step nonlinear analysis. The present work is intended to initiate a methodology to use the spectral capacity demand analysis to deal with the P-Delta effects compared with the results calculated by means of step by step analysis. The nonlinear effects develop at the bar ends (beams and columns) as plastic hinges with gradual plasticization due to the lateral displacements. Bending moments and shear effects in the structural elements are monitored during the simulations performed by means of the SAP2000 – Nonlinear Software.

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