Deaggregation of Seismic Safety in the Design of the Reinforced Concrete Buildings Using Eurocode 8

Abstract eng:
Design of earthquake-resistant structures according to Eurocod 8 is not based on the concept of acceptable/tolerable probability of exceedance of the near collapse limit state. Rather than that standard introduces fundamental non-collapse and damage limitation requirements, which are associated with the design seismic action. It is foreseen that the noncollapse requirement is satisfied when the regular structure does not collapse in the case of an earthquake with a return period of 475 years. Probability of such an even in 50 years is 10%. Therefore it is obvious that probability of failure of structures, which would be designed strictly according to the fundamental non-collapse requirement, would be unacceptable for society. Due to factors of safety involved in design the structures withstand much stronger earthquakes in comparison to an earthquake with a period of 475 years. In order to assess which factor of safety have the greatest impact on the overall safety of code-conforming buildings, two multi-storey reinforced concrete buildings were investigated. The strength and the system ductility of the six variants of the structures were evaluated on the basis of the pushover analysis gradually taking into account the requirements of the Eurocode 2 and 8, as well as gradually excluding the design assumptions. Safety in design of the buildings was evaluated by the difference between the calculated and prescribed behaviour factor, by the ratio between the design ground acceleration and that associated with the near collapse limit state, which was assessed using the N2 method, and by the escalation of safety in terms of probability of exceedance of the near collapse limit state. The results of this analysis are discussed in the paper. For the investigated buildings it is shown that the design seismic action has the greatest impact on the yield strength of the structure and the peak ground acceleration, which cause the near-collapse limit state. On the other hand, the partial factors of material strength contribute around 50% to the return period of the near-collapse limit state, whereas the contribution of the capacity design principles to overall safety is minor.

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