Performance Based Design of Reinforced Concrete Plane Frames

Abstract eng:
The seismic analysis and design of reinforced concrete (RC) frames is still an unresolved issue due to its complex behaviour. Seismic design codes are traditionally based on the force-based approach wherein structures are designed with a certain minimum lateral strength. However, it has been observed that such an approach, which relates to the elastic response, does not produce consistent inelastic response in terms of the amount and distribution of damage in structural elements. In views of the above, the displacement based approach, also known as performance based design (PBD) approach, has been explored in recent times. In this approach, the prime response quantities of interest are the inter-storey drifts and the design process directly attempts to limit these drifts to an acceptable value. However, PBD is still not ready for codification as several issues need to be understood. These include the influence of parameters such as the strength, stiffness, energy dissipation capacity and detailing such as percentage of reinforcement and amount of confining steel on the local and overall damage. In this study, a small portion of the overall problem is studied extensively to arrive at meaningful conclusions which can be used to develop a suitable design approach. Over 700 RC regular frames of two, four and eight storeys, designed and detailed as per the Indian seismic codal provisions, are analyzed by varying the time period, response reduction factor and percentage of longitudinal reinforcement. Non-linear time history analyses for six different earthquake accelerograms are carried out using the Pivot hysteretic model. The response parameters considered are local and global ductility demand, local damage index and inter-storey drift index. Variation in the response parameters with time period, percentage of reinforcement and response reduction factor are presented in graphical form. It is shown that the percentage of reinforcement plays a major role in the seismic performance. Based on the study, a simple design procedure to implement performance based design is suggested.

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