The concept of intensity-based assessment for risk-based decision-making is introduced. It is realized by means of the so-called 3R method (response analysis, record selection and risk-based decision-making), which can be used to check the adequacy of design of a new building or of the strengthening of an existing building by performing conventional pushover analysis and dynamic analysis for only a few ground motions, which are termed characteristic ground motions. Because the objective of the method is not a precise assessment of the seismic risk, a simple decision model for risk acceptability can be introduced. The engineer can decide that the reliability of a no-collapse requirement is sufficient when collapse is observed in the case of less than half of, for example, seven characteristic ground motions. From the theoretical point of view, it is shown that the accuracy of the method is acceptable if the non-linear response history analyses are performed at a low percentile of limit-state intensity, which is also proven by means of several examples of multi-storey reinforced concrete frame buildings. The 3R method represents a compromise between the exclusive use of either pushover analysis or dynamic analysis and can be easily introduced into building codes provided that its applicability is further investigated (e.g. asymmetric structures and other performance objectives) and that the procedure for the selection of characteristic ground motions is automated and readily available to engineers (www.smartengineering.si)
COBISS.SI-ID: 7229793
The impact of factors which affect the performance of regular reinforced concrete frame buildings designed according to the Eurocodes is investigated. The introduction of a sequence of variants of a structure, which gradually takes into account the design factors, makes it possible to measure the level of impact of an individual design factor on the global structural and performance parameters. The proposed procedure was applied to regular several reinforced concrete frame buildings, which were designed for ductility class medium and located in a region with moderate seismicity. A comparison between the reduction factor and the behaviour factor revealed that the behaviour factor defined in Eurocode 8, which significantly affects the design seismic action, is based more on the expert elicitation rather than on a firm scientific basis. Furthermore, based on the results of the investigated buildings it is shown that the design factors which are simply adopted in the design often have a significant impact on the resulting structures and their performance, whereas some other design factors, which require analysis of the structure and a lot of labour by engineers, often have only a minor effect on the performance of a structure.
COBISS.SI-ID: 7339361
Design of structures to seismic loads according to current standards involves linear elastic analysis, the concept of reduction of seismic forces and the capacity design method. The basis for earthquake-resistant design of structures is peak ground acceleration with a return period of 475 years. Eurocode 8 assumes that the structures designed according to the standard are safe against collapse, even though it does not define the concept of safety. In this paper an alternative procedure for determination of the design ground acceleration is proposed. The procedure starts from the definition of target collapse risk. The design ground acceleration is then calculated by assuming reduction factor, the dispersion of peak ground accelerations causing collapse and the parameter which consider the continuum of seismic hazard. Risk-targeted peak ground acceleration for design of an eight-storey reinforced concrete frame building is then calculated in order to demonstrate the proposed procedure. Follows the check of force-based design of the structure by using a simplified nonlinear analysis where it is shown that the value of reduction factor was assumed with sufficient accuracy. The proposed procedure for determination of the risk-targeted peak ground acceleration for design is more general than the procedure prescribed by Eurocode. Therefore it can also be used for design of important structures, where it is more justifiable to start design by defining the tolerated collapse risk rather the target return period of design earthquake.
COBISS.SI-ID: 7074913