Keywords: prescriptive design procedures, performance-based design, limit state fragility, multi-objective optimization, reinforced concrete buildings.

The assessment of seismic design codes has been the subject of intensive research work in an effort to reveal weak points that originated from the limitations in predicting with acceptable precision the response of the structures under moderate or severe earthquakes. Most of the current seismic design codes belong to the category of the prescriptive design procedures where if a number of checks, expressed in terms of forces, are satisfied, then the structure is considered safe and no collapse will occur. However, prescriptive design procedures have many inherent assumptions built in the design procedure regarding the behaviour of the structure against earthquake loading because, most of them, define a single design earthquake that is used for assessing the structural performance against earthquake hazard. In the last decade the concept of performance-based structural design (PBD) [1], subjected to seismic loading conditions, was introduced. In PBD more accurate analysis procedures are implemented based on nonlinear structural response in order to assess the structural performance in many hazard levels. The objective of this work is to evaluate the European seismic design code, i.e. the Eurocode 8 (EC8) [2], when used for the design of three-dimensional reinforced concrete buildings, versus the performance-based design (PBD) procedure, in the framework of a multi-objective optimization concept. The initial construction cost and the maximum interstorey drift for the 10/50 hazard level are the two objectives considered for the formulation of the multi-objective optimization problem.

The solution of such optimization problems is represented by the Pareto front curve which is the geometric locus of all Pareto optimum solutions. Limit-state fragility curves for selected designs, taken from the Pareto front curves of the EC8 and PBD formulations, are developed for assessing the two seismic design procedures. Through this comparison it was found that a linear analysis in conjunction with the behaviour factor q of EC8 cannot capture the nonlinear behaviour of a reinforced concrete structure. Consequently the corrected EC8 Pareto front curve, using the nonlinear static procedure, differs significantly with regard to the corresponding Pareto front obtained according to EC8. Furthermore, similar designs, with respect to the initial construction cost, obtained through the EC8 and PBD formulations were found to exhibit different maximum interstorey drift and limit-state fragility curves [3].

1

Applied Technology Council (ATC), "NEHRP Guidelines for seismic rehabilitation of buildings", Report No. FEMA-273, Federal Emergency Management Agency, Washington, DC, 1997.

2

Eurocode 8, "Design provisions for earthquake resistance of structures", ENV1998, CEN European Committee for standardization, Brussels, 1996

3

Lagaros N.D., Papadrakakis M., "Seismic design of RC structures: a critical assessment in the framework of multi-objective optimization", Earthquake Engineering and Structural Dynamics, 2007.

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