1,721,112 research outputs found
Seismic vulnerability assessment of “Sion cathedral” (Switzerland). An integrated approach to detect and evaluate local collapse mechanisms in heritage buildings
Full text linkSeismic assessment of existing heritage buildings remains a challenging task. There is a
high level of complexity and uncertainty compared with the assessment of standard buildings.
Heritage masonry churches are usually prone to partial collapses during earthquake due to local loss
of stability, and exhibit particular seismic vulnerabilities. An important step in the seismic analysis of
heritage masonry buildings is the detection of local mechanisms. The Italian Building Code provides a
simplified approach (LV1-churches) to assess the vulnerability of heritage churches evaluating and
comparing 28 potential mechanisms. A general index of vulnerability and hierarchy between
mechanisms is thereby provided. Verification of safety against local mechanisms can also be carried
out using the kinematic approach. This procedure is based on evaluating the horizontal action needed
to activate out-of-plane collapse mechanisms. Based on a full-scale study (Sion Cathedral), this paper
evaluates the reliability of the “LV1-church” approach and of the kinematic approach through a
comparison with the results obtained with a complex 3D model using the Applied Element Method
Seismic displacement demand prediction in non-linear domain: Optimization of the N2 method
No full textIn Europe, computation of displacement demand for seismic assessment of existing buildings is essentially based on a simplified formulation of the N2 method as prescribed by Eurocode 8 (EC8). However, a lack of accuracy of the N2 method in certain conditions has been pointed out by several studies. This paper addresses the assessment of effectiveness of the N2 method in seismic displacement demand determination in non-linear domain. The objective of this work is to investigate the accuracy of the N2 method through comparison with displacement demands computed using non-linear time-history analysis (NLTHA). Results show that the original N2 method may lead to overestimation or underestimation of displacement demand predictions. This may affect results of mechanical model-based assessment of seismic vulnerability at an urban scale. Hence, the second part of this paper addresses an improvement of the N2 method formula by empirical evaluation of NLTHA results based on EC8 ground-classes. This task is formulated as a mathematical programming problem in which coefficients are obtained by minimizing the overall discrepancy between NLTHA and modified formula results. Various settings of the mathematical programming problem have been solved using a global optimization metaheuristic. An extensive comparison between the original N2 method formulation and optimized formulae highlights benefits of the strategy
Improved urban seismic vulnerability assessment using typological curves and accurate displacement demand prediction
No full textImpact of displacement demand reliability for seismic vulnerability assessment at an urban scale
Full text linkThis paper addresses seismic vulnerability assessment at an urban scale by focusing on the displacement demand determination for building damage prediction. The study is based on the comparison of urban seismic damage distributions obtained by the displacement demand computed using non-linear time-history analysis (NLTHA) with three simplified methods. These methods include the N2 method, the Lin & Miranda proposal and an optimized version of the N2 method. Comparing the different damage distributions from the three simplified methods with the one obtained by time-history analysis helps understanding the reliability of displacement demand determination. The study is carried out on Sion and Martigny, two typical Swiss cities. For the case of Sion, results clearly show that using N2 method may lead to significant overestimation of damage grade distribution. The use of Lin & Miranda method and optimized version of N2 improves the damage prediction in both cases. For the other studied case of Martigny, N2 method and Lin & Miranda proposal are not accurate. The optimized version of N2 method provides stable and reliable results
Improved urban seismic vulnerability assessment using typological curves and accurate displacement demand prediction
No full textThis article addresses seismic vulnerability assessment at an urban scale using mechanical methods, more specifically potential improvements by involving typological curves instead of standard capacity curves and by using accurate displacement demand determination for reliable building damage prediction. The impact in terms of damage grades is computed for two typical Swiss cities. In Europe, seismic-vulnerability assessment is usually performed using the Risk-UE methodology, which involves an empirical approach (LM1 method) and a mechanical approach (LM2 method). The LM2 method contains standard capacity curves of conventional building types for computation of the corresponding damage grades. These capacity curves have been developed for southern Europe and are not optimal for describing features of other building stocks. New specific refined capacity curves are developed for northern Europe. Eurocode 8 prescribes the computation of displacement-demand for seismic assessment of existing building through a process based on the N2 method. However, the inaccuracy of the N2 method in certain conditions has already been studied. Therefore, modifications of N2 method have been proposed to improve the reliability of displacement-demand determination. In this study, the impact of typological capacity curves and the modified N2 method are investigated independently. Results show that both refinements contribute to improve the damage-grade distribution assessment
Using data interpretation to enhance post-seismic decision making at urban scale
No full textRecent events around the globe are evidence that earthquake action is still a threat for many structures. Low replacement and retrofitting rates of urban housing mean that many buildings do not comply with seismic actions defined in present-day seismic codes and thus, important post-seismic assessment activities are still to be expected. City-scale resilience, which implies rapid recovery of building functionalities, is undermined by the slowness and qualitative nature of visual inspection (being current practice for post-seismic assessment). A methodology involving model-based interpretation of post-seismic data sources to assess residual capacity of damaged buildings is presented. Vibration measurements and visual inspection outcomes are combined to reduce the uncertainty related to residual capacity. Simplified behaviour models for recurrent building types are used to predict building behaviour during future events. A simulated scenario on a real building stock of a typical Swiss city subjected to moderate seismicity is used for illustration
Accuracy Assessment of Nonlinear Seismic Displacement Demand Predicted by Simplified Methods for the Plateau Range of Design Response Spectra
Full text linkThe non-linear seismic displacement demand prediction for low-period structures, i.e. with an initial fundamental period situated in the plateau of design response spectra is studied. In Eurocode 8, the computation of seismic displacement demands is essentially based on a simplified method called the N2 method. Alternative approaches using linear computation with increased damping ratio are common in other parts of the world. The accuracy of three methods for seismic displacement demand prediction is carefully examined for the plateau range of Type-1 soil class response spectra of Eurocode 8. The accuracy is assessed through comparing the displacement demand computed using non-linear time-history analysis (NLTHA) with predictions using simplified methods. The N2 method, a recently proposed optimization of the N2 method and the Lin&Miranda method are compared. Non-linear single-degree-of-freedom systems are subjected to several sets of recorded earthquakes that are modified to match design response spectra prescribed by Eurocode 8. The shape of Eurocode 8 response spectra after the plateau is defined by a constant pseudo-velocity range (1/T). However, the slope of this declining branch may be specified using precise spectral microzonation investigation. However, the N2 method has been found to be particularly inaccurate with certain microzonation response spectra that are characterized by a gently decreasing branch after the plateau. The present study investigates the impact of the slope of the decreasing branch after the plateau of response spectra on the accuracy of displacement demand predictions. The results show that the accuracy domain of the N2 method is restricted to strength reduction factor values around 3.5. Using the N2 method to predict displacement demands leads to significant overestimations for strength reduction factors smaller than 2.5 and to significant underestimations for strength reduction factors larger than 4. Fortunately, the optimized N2 method leads to accurate results for the whole range of strength reduction factors. For small values of strength reduction factors, up to 2.5, the optimized N2 method and the Lin&Miranda method both provide accurate displacement demand predictions. However, the accuracy of displacement demand prediction strongly depends on the shape of the response spectrum after the plateau. A gently decreasing branch after the plateau affects the accuracy of displacement demand predictions. A threshold value of 0.75 for the exponent of the decreasing branch (1/T^α) after the plateau is proposed. This issue should be considered for the ongoing developments of Eurocode 8.IMACThis article is licensed under a Creative Commons Attribution 4.0 International Licens
Impact of displacement demand reliability for seismic vulnerability assessment at an urban scale
No full textIMA
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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