Simplified Numerical Model for Seismic Collapse of RC Frame Structures

Abstract eng:
Collapse of buildings due to an earthquake is completely unacceptable. The combination of wide usage of Reinforced Concrete (RC) framed structures for residential buildings in earthquake prone areas and shoddy design and construction practices exposes the high vulnerability of this type of buildings to a seismic hazard. For practical engineering purposes, the following characteristics are desirable in a collapse simulation, (i) capturing the complete behavior of a structure i.e. from its normal state to a complete collapsed state during an earthquake, (ii) should be accurate and reliable, (iii) computationally efficient, (iv) ease of modelling, comprehending and workability, and, (v) good visualization of the analysis results. Considering the above requirements, an effective two-phase numerical collapse simulation model of structures is proposed. The first phase consists of a Finite Element Mapped Spring Network which simulates the small deformation nonlinear behavior of the RC frames. In the second phase, the aforementioned spring network is adopted into the Extended Distinct Element Method (EDEM) to predict the large deformation behavior of structures till collapse. To model concrete non-linearity, spatially averaged material models for concrete and steel are used. A secant stiffness based formulation is used for the nonlinear analysis of RC, through implicit numerical integration. The results obtained from numerical analysis using the nonlinear spring network are compared with results obtained from the experimental testing of RC beams and frame. Good agreement was observed between experimental and analytical data even when the element size was increased. Crack pattern matched the experimentally observed cracks in an averaged sense. Once the structure has been subjected to significant damage, the analysis shifts to the EDEM phase. Analysis is performed through explicit numerical integration and simplified material models. The spring properties are adopted from the damaged springs from the first phase. The validity of the damaged spring network into the EDEM framework is checked. The complete collapse analysis of a 11-storey RC frame is performed. Through this two-phase analysis method, a new, relatively simple method for RC frames is proposed which can, (i) model elastic behavior accurately, (ii) simulate the small deformation non-linear RC behavior, (iii) predict cracking, (iv) perform large deformation analysis, (v) model separation, collision and collapse, (vi) perform collapse analysis in a mediocre computing environment, due to less computation demand owing to the usage of large rigid circular elements, and, (vii) be used to analyze a large building stock with large material randomness, that requires a large number of analysis.

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