The impact of the type of target response spectrum and the number of ground motions on the response of buildings is investigated. The parametric study involves the selection of ground motions based on the Eurocode 8 spectrum, a conditional spectrum using the official seismotectonic model of Slovenia, a uniform hazard spectrum based on the seismotectonic model of the SHARE project, and the corresponding conditional spectrum. In addition, the number of selected ground motions was varied from 7 to 60. Selected sets of ground motions were used to investigate the seismic response of eight reinforced concrete buildings. The aim of the study was to analyse the variation of target displacements obtained by a pushover-based method and the median spectral acceleration causing collapse. It was found that the target spectrum and the number of ground motions have a limited impact on the target displacement. Additionally, the impact of the number of ground motions on the median spectral acceleration causing collapse is much lower than the impact of the target response spectrum. When the conditional spectrum was used as the target spectrum for ground motion selection instead of the design response spectrum prescribed by Eurocode 8, the resulting median spectral acceleration causing collapse increased by a factor of between 1.2 and 2.3.
COBISS.SI-ID: 8668513
A pushover-based seismic risk assessment and loss estimation methodology for masonry buildings is introduced. It enables estimation of loss by various performance measures such as the probability of exceeding a designated economic loss, the expected annual loss, and the expected loss given a seismic intensity. The methodology enables the estimation of the economic loss directly from the results of structural analysis, which combines pushover analysis and incremental dynamic analysis of an equivalent SDOF model. The use of the methodology is demonstrated by means of two variants of a three-storey masonry building, both of which have the same geometry, but they are built, respectively, from hollow clay masonry (model H) and solid brick masonry (model S). The probability of collapse given the selected design earthquake corresponding to a return period of 475 years was found to be negligible for model H, which indicates the proper behaviour of such a structure when designed according to the current building codes. However, the corresponding probability of collapse of model S was very high (46%). The expected total loss given the design earthquake was estimated to amount to 28,000 € and 290,000 €, respectively, for models H and S. The expected annual loss per 100 m2 of gross floor area was estimated to amount to 75 € and 191 €, respectively, for models H and S. For the presented examples, it was also observed that nonstructural elements contributed more than 50 % of the total loss.
COBISS.SI-ID: 21692931
A fatality risk-based decision model for the performance assessment of buildings is proposed as an alternative to the frequently used collapse risk-based verification format. Earthquake fatalities as a measure of the consequences of collapse are studied in order to introduce a model for the tolerated annual fatality risk. It is assumed that the tolerated annual fatality risk depends on the tolerated individual annual fatality risk and the expected number of fatalities given the collapse of a building. The latter parameter accounts for the consequences of the collapse of a building via the number of people exposed in the building and the performance of the structural system of a building in relation to the risk of death in the case of collapse. The use of the proposed decision model is demonstrated on an example of three reinforced concrete frames. It is shown that it is challenging to achieve a negligible fatality risk even if the structure is designed according to standards for earthquake-resistant design. Therefore further studies are needed to develop a firm scientific basis for the decision model, which will address safety as well as costs of construction and expected losses. The proposed fatality risk-based decision model can be the first step towards such improvements, and thus it can be used for the performance assessment of a building.
COBISS.SI-ID: 9029217
The improved fish-bone (IFB) model for the seismic analysis of predominantly plan-symmetrical reinforced concrete (RC) frame buildings and a simplified nonlinear model for the analysis of a simple RC wall-frame building consisting of the IFB model and a model of a cantilever wall are presented. The configuration of structural elements of the IFB model is equal to that of the basic fish-bone model, which is determined by a column to which beams are connected at both sides and in all storeys. The improvement of the basic fish-bone model refers to a new procedure for the estimation of the parameters of the structural elements, which allows to approximately account for the effect of the structural elements on the seismic response of a building. The ability of simplified nonlinear models for seismic analysis is then analysed. First, we show that the IFB model is sufficiently accurate to simulate the storey-based engineering demand parameters of a four-storey reinforced concrete frame building. This is followed by an analysis of the capability of the simplified nonlinear models for pushover analysis of three symmetric RC buildings. We found that the simplified models used in the analysis are sufficiently accurate for the calculation of the pushover curves and the storey-based damage assessment of structural elements.
COBISS.SI-ID: 8973921
An approach for the evaluation and communication of seismic risk is presented that is based on a five-grade grading system. Each of the grades (AA, A, B, C and D) indicates a level of long-term and short-term risk tolerance. Long-term risk tolerance is equivalent to the conventional concept of risk tolerance, while short-term risk tolerance corresponds to a specific period of time in which risk is allowed to be greater than in the long term. The grading process is performed in two steps. First, the initial grade is determined based on the comparison between the estimated risk and a set of risk boundaries. If the initial grade corresponds to long-term negligible or tolerable risk, the grading process is concluded. However, if risk is long-term intolerable, another step is performed, in which the initial grade is gradually reduced to the lowest grade. The time periods corresponding to the reduction of grades are determined by comparing the estimated cumulative risk to the cumulative risk boundaries. The use of the grading system is demonstrated by performing a risk evaluation of a precast reinforced concrete building. It is shown that the grading system can serve as a communication tool to enhance the public discussion about tolerable risk. However, it can also be used as the basis for disaster risk management by linking grades to specific sets of actions, which are scheduled after the risk evaluation.
COBISS.SI-ID: 37960707