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Seismic fragility analysis is an efficient method to evaluate the structural failure probability during earthquake events. Among the existing fragility analysis methods, the probabilistic seismic demand model (PSDM) and the joint probabilistic seismic demand model (JPSDM) are generally used to compute the component and system fragility, respectively. However, the statistical significance behind the parameters related to the current PSDM and JPSDM are not comparable. Aside from that, when calculating the system fragility, the Monte Carlo sampling (MCS) method is time-consuming. To solve the two flaws, in this paper, the logarithm piecewise functions were used to generate the PSDM and the JPSDM, and the MCS was replaced by the univariate conditioning approximation (UCA) method. The concepts and application procedures of the proposed fragility analysis methods were elaborated first. Then, the UCA method was illustrated in detail. Finally, fragility curves of a steel arch truss case study bridge were generated by the proposed method. The research results indicate the following: (1) the proposed methods unify the data sources and statistical significance of the parameters used in the PSDM and the JPSDM; (2) the logarithmic piecewise function-based PSDM sensitively reflects the changing trend of the component’s demand with the fluctuation of the seismic intensity measure; (3) under transverse seismic waves, major injuries happen on the side bearings of the bridge, while slight damage may occur on each pier, and as the seismic intensity measure increases, the side bearings are more likely to be damaged; (4) for the severe damage and the absolute damage of the studied bridge, the system fragility curves are closer to the upper failure bounds; and (5) compared with the MSC method, the accuracy of the UCA method can be guaranteed with less calculation time.

Relating the ground motion intensity measure (IM) and the structural engineering demand parameter is a crucial step in the performance-based earthquake engineering framework. This study investigates the selection of IM for development of probabilistic seismic demand model of urban shield tunnels subjected to earthquake ground motions in liquefiable and non-liquefiable soils. Nonlinear dynamic effective stress analyses are conducted to develop a database of the intensity measures and structural seismic responses exposed to ground shaking and soil liquefaction. Two advanced soil constitutive models (i.e., Pressure DependMultiYield03 and PressureIndependMultiYield for liquefiable and non-liquefiable soils, respectively) are employed to capture the nonlinear behavior. A suite of 23 ground motion intensity measures is selected and assessed based on the evaluation criteria of correlation, efficiency, practicality and proficiency. Eventually, the multi-level fuzzy comprehensive evaluation method is employed to comprehensively consider the four evaluation criteria and establish the optimal ground motion IM suitable for probabilistic seismic demand analysis of shield tunnel structures. The obtained results show that the sustained maximum acceleration is the optimal IM for evaluating the structural seismic response, followed by the peak ground acceleration in both liquefiable and non-liquefiable soils. Peak pseudo velocity spectrum, displacement square integral and Housner spectral intensity are found to be not suitable for the probabilistic seismic demand analysis of shield tunnel structures.

The focus of this study is the impact of the seismic excitation direction on the fragility of horizontally curved bridges. Nonlinear time history analyses are performed on a typical, curved concrete bridge in China using a set of real ground motions with different incident angles. To build reliable probabilistic seismic demand models, ten commonly used intensity measures (IMs) are assessed in terms of various metrics to determine the optimal IMs, which account for the influence of the seismic excitation directions. Subsequently, fragility surfaces with respect to both the optimal IM and incident angles are generated to qualify the fragility sensitivity for various components and the bridge system to the seismic excitation directions. Moreover, the rationality and applicability of the methods recommended by the Caltrans, Eurocode 8 and Chinese codes for determining the seismic excitation direction of curved bridges are evaluated. The results indicate that the excitation direction imposes a minor impact on the optimal IM rankings. Compared to structure-independent IMs, structure-dependent IMs are more appropriate for predicting the demands of horizontally curved concrete bridges. However, the seismic excitation direction significantly affects the component fragilities, and the level of the effect intensifies with increasing limit states. If the incident angle occurrence probability is not provided, the Chinese code method for the seismic excitation direction is more suitable for the horizontally curved concrete bridge fragility assessment, which has the advantages of computational efficiency when compared to the Caltrans code and relatively conservative results when compared to Eurocode 8.

This paper presents the probabilistic seismic demand and fragility analyses of a novel mid-rise large-span cassette structure. A newly designed nine-storey office building in Hunan, China, is selected, and its two different design schemes, namely, a traditional frame structure and a novel cassette structure, are examined using numerical models established on the basis of a shake table test. Based on probabilistic seismic theory, the appropriate intensity measures are firstly studied based on a set of 110 seismic records; and PGV and GeoSaavg, which consider the 3D characteristics of the structure, are selected. In addition, the uncertainty of earthquakes, including spectral characteristics, fault distance and input direction, are considered, and 25 seismic records recommended by the Federal Emergency Management Agency are selected. An incident angle interval of 22.5° is selected to consider the uncertainty in the input directions of real earthquakes. Incremental dynamic analyses are conducted, and the structural responses in every individual input direction as well as in all the directions are studied. Finally, probabilistic seismic fragility analysis is conducted, and the probabilities of exceeding different limit states of the frame and cassette structures is presented. Amongst the studies, the novel cassette design can not only achieve much larger span, but also shows a better, more stable seismic performance. Therefore, the cassette structure may be a better alternative in seismic design.

Reconnaissance of structural damage under earthquakes has indicated that though current design philosophy can reduce structural collapse probability, it results in a significant reduction of functionality following earthquakes considering residual drift and numerous bridges had to be demolished. To protect bridges against earthquakes and reduce the residual drift, shape memory alloy (SMA) is studied and incorporated in the plastic hinge region of reinforced concrete (RC) piers to increase the resilience of bridges. The performance-based engineering (PBE) of SMA bar reinforced RC bridges considering residual drift ratio and maximum displacement is assessed by taking advantages of self-centering and energy dissipation features of SMA, specifically under extensively large seismic events. Additionally, the PBE is conducted within the lifetime of bridges considering the corresponding economic impacts. The proposed approach is illustrated within highway bridges with and without using SMA bars in the piers.

Assessing the fragility of intake towers using a single damage index does not allow for accurate evaluation of the potential for structural damage under seismic conditions. In this study, based on the probabilistic seismic demand analysis method, the effects of ground motion intensity on maximum displacement, local damage index, and global damage index are considered, and the seismic fragility of an intake tower structure is analyzed. First, 10 natural ground motion records were selected from the ground motion database (PEER) and 2 artificial seismic waves were synthesized. These seismic waves were amplitude-modulated for incremental dynamic analysis (IDA). The trends of the IDA curves were analyzed to divide the performance levels of the intake tower structure. Furthermore, a two-dimensional fragility curve for the intake tower structure was plotted in this study. The maximum displacement in the direction of parallel flow and the damage index were taken into account in the two-dimensional fragility curve. The results show that, under the designed seismic acceleration, the two-dimensional fragility curve for the intake tower structure was lower than the one-dimensional curve. This indicates that the seismic design based on the one-dimensional performance index was unstable. This provides a theoretical reference for seismic optimization design and the strengthening of intake towers. Therefore, it is recommended to use multidimensional fragility analysis to study the seismic performance of intake tower structures in seismic design.

Flexible pipelines are often used to connect hard pipes from a foundation to a superstructure to accommodate large deformation in the base isolation layer during an earthquake. Although Chinese seismic design guidelines suggest several configurations, they are different from the designs that have been proven in practice, e.g., Japanese styles, and extensive experimental investigation into their seismic performance is required. Three types of seals, rubber-, metal- and asbestine-based, were tested quasi-statically with infilled pressurized water at 2.5 MPa. The asbestine-based seal leaked at a smaller deformation than the other two types of seals. Based on the test results, three damage states were defined and the deformation capacity was estimated. To evaluate their performance, a three-dimensional model of a base-isolated medical building was developed using OpenSees, with the flexible pipelines simulated by a mechanical model calibrated from the experimental data. A probabilistic seismic demand model and the fragility function of the flexible pipelines were then developed to evaluate the seismic performance.

For medium- and small-span bridges, the weight of the superstructure in steel–concrete composite girder bridges is lighter than that of a reinforced concrete girder bridge. However, it is still uncertain whether steel–concrete composite girder bridges exhibit superior seismic performance compared to reinforced concrete girder bridges. This study quantitatively compared the seismic performance of the two types of bridges. Using the theory of probabilistic seismic demand analysis, the seismic vulnerability curves of bridges were derived. To conduct seismic demand analysis for probabilistic analysis on the OpenSEES platform, bridge samples were generated using the Latin hypercube stratified sampling method, which considers the uncertainties associated with the two types of bridges. The vulnerability curves of the piers, bearings, abutments, and the system of the two bridges were established using probabilistic analysis of the time history analyses. The results showed that the seismic vulnerabilities of components and the overall system of the steel–concrete composite girder bridge were both lower than those of the reinforced concrete girder bridge. When the peak ground acceleration (PGA) of the ground motion was 0.3 g, the moderate and serious damage probabilities of the piers in the steel–concrete composite bridge were only 54.61% and 60.89%, respectively, of those of the reinforced concrete bridge. Consequently, replacing the upper reinforced concrete girders with steel–concrete composite girders can significantly improve the seismic performance of a large number of existing bridges.

Non-structural elements play a crucial role in the overall seismic performance of buildings, as has been largely demonstrated in recent earthquakes that have stuck densely populated regions. Therefore, the development of performance-based seismic design and assessment methodologies for non-structural elements is becoming an important research topic within earthquake engineering. A crucial aspect in such methodologies is the accurate prediction of the seismic demands acting on non-structural elements in terms of consistent absolute acceleration and relative displacement floor response spectra for the most common types of structural seismic force resisting systems. Masonry-infilled reinforced concrete frames are one of the most common building typologies in high seismicity regions, such as the Mediterranean region. This study proposes a simplified procedure to estimate consistent absolute acceleration and relative displacement floor response spectra in masonry-infilled reinforced concrete frames based on an existing methodology to estimate consistent floor response spectra in bare reinforced concrete frames. Nine archetype masonry-infilled reinforced concrete buildings with different numbers of storeys and arranged with three masonry infill typologies were considered as case-study archetypes, and were used to validate the proposed methodology using nonlinear time history analyses. The proposed procedure can accurately estimate consistent absolute acceleration and relative displacement floor response spectra for masonry-infilled reinforced concrete buildings that respond both in the elastic and nonlinear ranges for all the non-structural period range. The estimates of floor response spectra given by the proposed procedure are fully consistent with the well-known pseudo-spectral relationship for the entire non-structural period range.

A quick and accurate estimate of the seismic demand of tall buildings is one of the important issues in the seismic evaluation of buildings. Nonlinear response time history analysis method (NLRHA) is considered as the most accurate and rigorous method, but the computation requirement of NLRHA for tall buildings can be complex and very time-consuming. Whereas the conventional pushover procedure is not capable of reasonably estimating seismic demand of mid and high rise-buildings, due to the oversimplification of conventional pushover approaches and the complexity of seismic performance of buildings. In this paper, a quick, yet effective, method of analysis, named as a spectrum-based pushover analysis (SPA) method, is proposed to estimate the seismic demand of tall buildings. In the SPA procedure, the very complex and complicated dynamic coupling effect of modes of the nonlinear seismic performance of a building is simplified, and the consecutive pushover technique is adopted to consider the simplified coupling effect. Comparison of the results obtained from NLRHA, the modal pushover analysis method, the consecutive modal pushover analysis method and the proposed SPA method is made. It is seen that the SPA method predicted the seismic demand of buildings well, including the inter-storey drift ratio and hinge plastic rotation, which are very close to those of NLRHA. Owing to its accuracy, effectiveness, and spectrum-based calculation procedure, the proposed SPA procedure is considered to be a very promising tool for predicting the seismic demand of tall buildings.