In the presented practice-oriented probabilistic approach for the seismic performance assessment of building structures, the SAC-FEMA method, which is a part of the broader PEER probabilistic framework and permits probability assessment in closed form, is combined with the pushover-based N2 method The most demanding part of the PEER probabilistic framework, i.e. Incremental Dynamic Analysis (IDA), is replaced by the much simpler N2 method which requires considerably less input data and much less computational time, but which can, nevertheless, often provide acceptable estimates for the mean values of the structural response. Using some additional simplifying assumptions that are consistent with seismic code procedures, an explicit equation for a quick estimation of the annual probability of “failure” (i.e. the probability of exceeding the near collapse limit state) of a structure can be derived, which is appropriate for practical applications, provided that predetermined default values for the dispersion measures are available. In the paper, this simplified approach is summarized and applied to the estimation of the “failure” probability of reinforced concrete frame buildings representing both old structures, not designed for earthquake resistance, and new structures designed according to Eurocode 8. The results of the analyses indicate a high probability of the “failure” of buildings which have not been designed for seismic loads. For a building designed according to a modern code, the conservatively determined probability of “failure” is about 30 times less but still significant (about 1% over the lifetime of the structure).
COBISS.SI-ID: 5478241
An approximate seismic risk assessment procedure for building structures, which involves pushover analysis that is performed utilizing a deterministic structural model and uncertainty analysis at the level of the equivalent SDOF model, is introduced. Such an approach is computationally significantly less demanding in comparison with procedures based on uncertainty analysis at the level of the entire structure, but still allows for explicit consideration of the effect of record-to-record variability and modelling uncertainties. A new feature of the proposed pushover-based method is the so-called probabilistic SDOF model. Herein, the proposed methodology is illustrated only for RC frames, although it could be implemented in the case of any building structure, provided that an appropriate probabilistic SDOF model is available. An extensive parametric analysis has been performed within the scope of this study in order to develop a probabilistic SDOF model which could be used for the seismic risk assessment of both code-conforming and old, i.e. non code-conforming reinforced concrete frames. Based on the results of risk analysis for the four selected examples, it is shown that the proposed procedure can provide conservative estimates of seismic risk with reasonable accuracy, in spite of the employed simplifications and the relatively small number of Monte Carlo simulations with LHS, which are performed at the level of the SDOF model. An indication of the possible default values of dispersion measures for limit-state intensities in the case of low to medium-height RC frames is also presented.
COBISS.SI-ID: 6496353
Floor response spectra, which are used for the seismic design of equipment, are often based on the assumption that the behaviour of a structure and its equipment is linearly elastic. Significant reductions in the peak values of floor acceleration spectra can be achieved if inelastic behaviour of the structure is taken into account. This paper presents the most important results of an extensive parametric study of floor acceleration spectra, taking into account inelastic behaviour of the structure, and linear elastic behaviour of the equipment. The structure and the equipment were modelled as single-degree-of-freedom systems. The influences of the input ground motion, ductility, hysteretic behaviour and the natural period of the structure, as well as that of damping of the equipment, have been studied. A simple practice-oriented method for direct determination of floor acceleration spectra from an inelastic spectrum for the structure and an elastic spectrum for the equipment is proposed and validated. In this method, the floor response spectra in the resonance region, where the natural period of the equipment is close to the natural period of the structure, are based on the empirical values obtained in the parametric study, whereas the spectra in the pre- and post-resonance regions are based on the principles of dynamics of structures. The method is intended for a quick estimation of approximate floor acceleration spectra.
COBISS.SI-ID: 6747489
The objective of the study presented in this paper is to investigate the effects of masonry infills on the shear demand and failure of columns for the case when reinforced concrete frames with such infills are modeled by means of simplified nonlinear models that are not capable of the direct simulation of these effects. It is shown that an approximate simulation of the shear failure of columns can be achieved through an iterative procedure that involves pushover analysis, post-processing of the analysis results using limit state checks of the components, and model adaptation if shear failure of columns is detected. The fragility parameters and the mean annual frequency of limit state exceedance are computed on the basis of nonlinear dynamic analysis by using an equivalent SDOF model. The proposed methodology is demonstrated by means of two examples. It was shown that the strength of the four-story and seven-story buildings and their deformation capacity are significantly overestimated if column shear failure due to the effects of masonry infills is neglected, whereas the mean annual frequency of limit state exceedance for the analyzed limit states is significantly larger than that estimated for the case if the shear failure of columns is neglected.
COBISS.SI-ID: 6102113
The seismic performance assessment of existing masonry buildings involves many uncertainties, whose impact can be reduced to some extent by using nondestructive in-situ tests of such buildings, at least when destructive in-situ tests, which can provide more reliable results, cannot be performed. In this paper the extent of the potential beneficial effects achievable by calibration of a structural model of a building to its experimentally estimated vibration periods has been investigated. This was done by performing measurements of ambient and forced vibrations on an old two-storey masonry building, and by then assessing its seismic performance using a simplified nonlinear method. The results of numerical investigations revealed that the natural vibration periods of such buildings can be reproduced with sufficient accuracy, although it is possible that they will be overestimated or underestimated by analysts by up to around 40 %. This means that the accuracy of the prediction of the intermediate results of the seismic performance assessment of any particular building can be significantly increased by calibration of the structural model. Additionally, the beneficial effects of such calibration were observed even in the case of the final outcome of the nonlinear analysis, which is expressed through the near collapse limit state capacity in terms of the peak ground acceleration.
COBISS.SI-ID: 6420577