A closed-form solution of the risk equation incorporating intensity bounds is derived and analysed. The new equation, compared to the well-known risk equation developed in the 1990s, includes a correction factor, which has a value less than one if the effect of the intensity bounds is significant. The lower bound of ground-motion intensity represents a minimum ground-motion intensity, which causes a designated limit state, whereas the upper bound of ground-motion intensity is, in general, related to the physics of earthquakes, the tectonic regime, and the geology of the terrain in the region from the epicentre to the site of the building. In the paper typical values of the minimum collapse intensity and of the fragility parameters of code-conforming frames are discussed. An approximate procedure for assessing the upper bound of ground-motion intensity on the basis of ground-motion prediction models is also proposed. Finally, the procedure for seismic risk assessment is demonstrated by assessing the collapse risk for a 4-storey and a 15-storey building. It is shown that the collapse risk assessed on the basis of peak ground acceleration can be significantly affected by the lower bound of the collapse intensity, whereas the impact of the upper bound of the ground-motion intensity on the collapse risk can be more pronounced when the assessment of the collapse risk is based on the spectral acceleration at the first vibration period.
COBISS.SI-ID: 6723937
The simulation of the nonlinear seismic response of structures is uncertain due to the lack of data regarding the future earthquakes and the imperfection of nonlinear models. One of the uncertain parameter of the structural model is the effective width of the beam flange, which is addressed in this paper. First, several approaches for determination of the beam effective width are presented and analyzed by means of assessing the effective width of beams of the four-storey reinforced concrete frame. The simulations of the nonlinear response of the structure are then presented by taking into account four different values for the beam effective width. The results of simulations are compared with the results of the pseudo-dynamic test. It is shown that the beam effective width could have great impact on the building’s strength and ductility. Based on the simulations and results obtained from ELSA laboratory it is shown that the use of the rectangular section of the beam is inappropriate for the seismic performance assessment of such buildings.
COBISS.SI-ID: 6507617
Prepared was an entry for Encyclopedia of Earthquake Engineering. The entry has been organized into three subentries. The theoretical background for the prediction of the parameters of SDOF models is first described. This subentry is subdivided into two parts. The transformation of the equations of motion to a conventional equation of motion of an SDOF model is presented in the first part, while in the second part the procedure to determine the parameters of the SDOF model using pushover analysis is described. The first subentry provides an insight into the SDOF model, which represents a key link between the pushover analysis and seismic demand. Quite precise instructions are given how to determine an SDOF model which can be used to assess the seismic demand by nonlinear dynamic analysis. The first subentry is followed by an overview of the different types of pushover analysis, and the limit states. Some variants of pushover analyses are only mentioned, since it is not the aim of this entry to provide an insight into different types of pushover analysis. In the final subentry, pushover-based fragility analysis is explained with emphasis on the step by step procedure, which is also demonstrated by means of an example of fragility analysis for a four-storey reinforced concrete frame building. The EDP-based and IM-based formulations of the fragility function are introduced. This is followed by explaining three procedures for the estimation of the fragility parameters using pushover-based methods. Finally, the most comprehensive procedure, which takes into account the ground-motion randomness and modelling uncertainty, is demonstrated by explaining each step of the pushover-based fragility analysis.
COBISS.SI-ID: 6970977