Dynamics of structures

This paper presents recommended methodologies for the quantitative analysis of landslide hazard, vulnerability and risk at different spatial scales (site-specific, local, regional and national), as well as for the verification and validation of the results. The methodologies described focus on the evaluation of the probabilities of occurrence of different landslide types with certain characteristics. Methods used to determine the spatial distribution of landslide intensity, the characterisation of the elements at risk, the assessment of the potential degree of damage and the quantification of the vulnerability of the elements at risk, and those used to perform the quantitative risk analysis are also described. The paper is intended for use by scientists and practising engineers, geologists and other landslide experts.

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Recommendations for the quantitative analysis of landslide risk

Probabilistic seismic demand models are a common and often essential step in generating analytical fragility curves for highway bridges. With these probabilistic models being traditionally conditioned on a single seismic intensity measure (IM), the degree of uncertainty in the models is dependent on the IM used. Selection of an optimal IM for conditioning these demand models is not a trivial matter and has been the focus of numerous studies. Unlike previous studies that consider a single structure for IM selection, this study evaluates optimal IMs for use when generating probabilistic seismic demand models for bridge portfolios such as would be found in HAZUS-MH. Selection criteria such as efficiency, practicality, sufficiency, and hazard computability are considered in the selection process. A case study is performed considering the multi-span simply supported steel girder bridge class. Probabilistic seismic demand models are generated considering variability in the geometric configurations and material properties, using two suites of ground motions-one synthetic and one recorded motion suite. Results show that of the 10 IMs considered, peak ground acceleration (PGA) and spectral acceleration at the fundamental period are the most optimal for the synthetic motions, and that cumulative absolute velocity is also a close contender when using recorded motions. However, when hazard computability is considered, PGA is selected as the IM of choice. Previous studies have shown that spectrally based quantities perform better than PGA for a given structure, but the findings of this study indicate that when a portfolio of bridges is considered, PGA should be used.

Selection of optimal intensity measures in probabilistic seismic demand models of highway bridge portfolios

Bridge fragility curves, which express the probability of a bridge reaching a certain damage state for a given ground motion parameter, play an important role in the overall seismic risk assessment of a transportation network. Current analytical methodologies for generating bridge fragility curves do not adequately account for all major contributing bridge components. Studies have shown that for some bridge types, neglecting to account for all of these components can lead to a misrepresentation of the bridges' overall fragilities.

In this study, an expanded methodology for the generation of analytical fragility curves for highway bridges is presented. This methodology considers the contribution of the major components of the bridge, such as the columns, bearings and abutments, to its overall bridge system fragility. In particular, this methodology utilizes probability tools to directly estimate the bridge system fragility from the individual component fragilities. This is illustrated using a bridge whose construction and configuration are typical to the Central and Southeastern United States and the results are presented and discussed herein. This study shows that the bridge as a system is more fragile than any one of the individual components. Assuming that the columns represent the entire bridge system can result in errors as large as 50% at higher damage states. This provides support to the assertion that multiple bridge components should be considered in the development of bridge fragility curves. The findings also show that estimation of the bridge fragilities by their first-order bounds could result in errors of up to 40%. Copyright © 2006 John Wiley & Sons, Ltd.

Seismic fragility methodology for highway bridges using a component level approach

Seismic fragility curves for classes of highway bridges are essential for risk assessment of highway transportation networks exposed to seismic hazards. This study develops seismic fragility curves for nine classes of bridges (common three-span, zero-skew bridges with non-integral abutments) common to the central and southeastern United States. The methodology adopted uses 3-D analytical models and nonlinear time-history analyses. An important aspect of the selected methodology is that it considers the contribution of multiple bridge components. The results show that multispan steel girder bridges are the most vulnerable of the considered bridge classes while single-span bridges tend to be the least vulnerable. A comparison of the proposed fragility curves with those currently found in HAZUS-MH shows a strong agreement for the multispan simply supported steel girder bridge class. However, for other simply supported bridge classes (concrete girder, slab), the proposed fragility curves suggest a lower vulnerability level than presented in HAZUS-MH. DOI: 10.1193/1.2756815

Bryant G. Nielson

Papers

Seismic fragility of typical bridges in moderate seismic zones

Selection of optimal intensity measures in probabilistic seismic demand models of highway bridge portfolios

Seismic fragility methodology for highway bridges using a component level approach

Analytical Seismic Fragility Curves for Typical Bridges in the Central and Southeastern United States

Analytical Fragility Curves for Highway Bridges in Moderate Seismic Zones