Evaluation and comparison of ultimate deformation limits for RC columns

The ultimate deformation capacity assigned to structural elements of reinforced concrete structures is an essential parameter in the determination of their structural performance especially under seismic attack. Various ultimate deformation capacity limits were proposed for RC columns in the previous studies and were accommodated in the current building codes. However, the reliability of the existing deformation limits is still a matter of considerable debate. This study mainly focuses on the evaluation of the accuracy of the existing damage limits and aims to develop a new definition with a higher reliability in comparison to the existing limits. In this purpose, the study was composed of four major steps. Firstly, the existing building codes, standards, regulations and previous studies were reviewed and evaluated in terms of ultimate deformation criteria for RC columns. Secondly, actually tested sixty-nine RC columns were selected from PEER Structural Performance Database and were numerically modelled by using finite element method. The selected RC columns have different dimensions, aspect ratios, concrete and steel strength, longitudinal and transverse reinforcement amounts and axial load ratio. Third stage includes the comparison of the results obtained from the experimentally verified numerical models with the existing ultimate deformation limits to reveal the shortcomings of existing criteria. The numerical modelling facilitated the consistent comparison of strains and curvatures that are rarely available and difficult to measure in tests. A new concrete compressive strain prediction equation was proposed to determine the ultimate deformation capacity of rectangular RC columns. It was concluded that there is need for further comprehensive analytical and experimental studies on deformation limits of reinforced concrete columns.