Seismic design of RC structures: A critical assessment in the framework of multi‐objective optimization

Abstract

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. The objective of this work is to evaluate the European seismic design code, i.e. the Eurocode 8 (EC8), when used for the design of 3D reinforced concrete buildings, versus a 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 an RC 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. N. D. LAGAROS AND M. PAPADRAKAKIS disastrous earthquakes. Most of the current seismic design codes define a single design earthquake that is used for assessing the structural performance against earthquake hazard. As a consequence, these codes have many inherent assumptions built in the design procedure regarding the behaviour of the structure against earthquake loading. Severe damages caused by recent earthquakes made the engineering community to question the reliability of current seismic design codes [1,2]. Given that the primary goal of contemporary seismic design is the protection of human life in connection with the economic design, it is evident that additional performance targets and earthquake intensities should be considered in order to assess the structural performance in many hazard levels. In the last decade the concept of performance-based structural design (PBD), subjected to seismic loading conditions, was introduced [3-5]. In PBD more accurate analysis procedures are implemented based on nonlinear structural response.Most of the current seismic design codes belong to the category of the prescriptive design procedures (or limit-state 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. A typical limit state-based design can be viewed as one (i.e. ultimate strength) or two (i.e. serviceability a...

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“…Only a small fraction of these articles dealt with the optimal drift design due to seismic loads. The published work on the optimal drift design of tall buildings (Park and Park, 1997; Park and Kwon, 2003; Chan, 2004; Chan and Wang, 2005; Lagaros and Papadrakakis, 2007) used structural optimization algorithms, which are based on sensitivity coefficients rather than practical optimizations, and require extensive computational requirements.…”

Building design based on energy dissipation: a critical assessment

“…A number of studies have been published on the optimum design of RC structures (Frangopol 1986;Moharrami and Grierson 1993;Sarma and Adeli 1998;Li and Cheng 2001;Chan and Zou 2004;Lagaros and Papadrakakis 2007) taking into account different types of constraints during the design optimization procedure. However, none of them has taken into consideration the behaviour factor q.…”

“…In the work by Li and Cheng (2001) the optimal decision model of the target value of performance-based structural system reliability of RC frames is established according to the cost-effectiveness criterion. Chan and Zou (2004) presented an optimization technique for the elastic and inelastic drift performance-based design of reinforced concrete buildings, while (Lagaros and Papadrakakis 2007) critically assessed the designs of a 3D reinforced concrete building, obtained according to the European seismic design code and a performance-based design procedure, in the framework of a multi-objective optimization problem. The results revealed that the designs based on the European seismic design code violated safety requirements for different hazard levels.…”

Life-Cycle Cost Model and Design Optimization of Base-Isolated Building Structures

“…Following this general description of the optimization problem, the formulation of the performance-based design optimization problem for fixed-based RC-framed structures used in the current study is defined as follows (Lagaros and Papadrakakis, 2007):…”