Simultaneous Shear and Axial Failure of Reinforced Concrete Columns of Existing Substandard Buildings

Abstract eng:
Previous experience from earthquake events has shown that existing substandard Reinforced Concrete (R/C) buildings are particularly vulnerable to strong ground motions. One of the main causes of collapse of such structures is the axial failure of shear or flexure-shear critical vertical load bearing elements. In this context, the phenomenon of simultaneous shear and axial failure is of really high significance, because the collapse mode of the whole structure can be adversely affected by such members leading to redistribution of vertical loads at a very low lateral deformation level and the structure’s collapse probability can thus be greatly increased. Therefore, the cardinal priority in a pre-seismic retrofit programme for existing structures should be to prevent failure of these particularly vulnerable elements. Observations have been made in previous studies on possible circumstances leading to such a failure mode. However, the development of a reliable criterion is still an open issue. The main contribution of the present work is the proposal of the necessary conditions for the simultaneous shear-axial failure of a column in the form of a two-parameter classification criterion, constituting a handy tool for engineers working on assessment and retrofit of existing R/C structures. If not all member’s details are known or if a preliminary classification is only required, a simplified one-parameter criterion can be used, instead; nonetheless, the latter comes with a high uncertainty. Furthermore, criteria for “extra-safe zones” have also been extracted, in case a higher inter-storey drift capacity is to be ensured. Last but not least, two well-established predictive models are compared as to their ability to predict simultaneous failure of an R/C member. The one previously developed by the authors performs far better and would be recommended for use in relevant applications, with the aforementioned two-parameter criterion still being the optimal choice for a reliable classification of a column as safe from simultaneous failure.

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