Real-time life-cycle seismic fragility assessment of coastal bridges: a novel approach using deep temporal neural networks

Seismic response prediction and fragility assessment of high-speed railway bridges using machine learning technology

A procedure for the seismic fragility assessment of nuclear power plants by applying ground motions compatible with the conditional probability distribution of a conditional spectrum (CS) is presented with a case study of a containment building. Three CSs were constructed using different control frequencies to investigate the influence of the control frequency. Horizontal component-to-component directional variability was introduced by randomly rotating the horizontal axes of the recorded ground motions. Nonlinear lumped mass stick models were constructed using variables distributed by Latin hypercube sampling to model the uncertainty. An incremental dynamic analysis was performed, and seismic fragility curves were calculated. In addition, a seismic input based on a uniform hazard response spectrum (UHRS) was applied to the seismic fragility assessment for comparison. By selecting a control frequency dominating the seismic response, the CS-based seismic input produces an enhanced ‘high confidence of low probability of failure’ capacity and lower seismic risk than the UHRS-based seismic input.

It is a key step to determine the structural capacity at different limit states for a seismic fragility assessment. However, limit state definition is highly dependent on engineering practices, which includes strong fuzziness. Therefore, it is necessary to conduct a comprehensive study on the influence of fuzziness at limit states in a seismic fragility assessment. This study performs a seismic fragility assessment by considering fuzziness at limit states, where ten types of membership functions are considered with varying fuzziness levels. Four reinforced concrete frame structures with varying heights and fortification levels are taken as the study cases. The fuzziness-probability integration is adopted to derive seismic fragility functions corresponding to different types of membership functions. The seismic fragility results with and without considering fuzziness at limit states are compared to extract the effect of limit state fuzziness with considering varying membership functions and different fuzziness levels. Moreover, the modified seismic fragility function considering limit state fuzziness is derived. The analysis results show that different membership functions show a significant effect on seismic fragility results considering limit state fuzziness. As the promotion of fuzziness level, the difference in seismic fragility results considering limit state fuzziness is growing accordingly. The proposed modified fragility function considering limit state fuzziness can well represent the effect of fuzziness at limit states on the seismic fragility analysis.

Machine learning-based seismic fragility and seismic vulnerability assessment of reinforced concrete structures

Bridges are the most vulnerable elements in regional transportation networks. Seismic fragility assessment has significant implications regarding the potential damage of regional bridges and their seismic maintenance operations. Unlike individual bridges, assessing bridges at the regional scale involves greater diversity and distinct ground motions. This paper proposes a Bayesian parameter estimation methodology to assess the seismic fragilities of regional beam bridges and schedule their maintenances. The proposed multi-parameter models contain several structural parameters and intensity measures to comprehensively consider the regional diversity. The selected intensity measures represent the diversity of regional ground motions at the peak effect, spectrum intensity, and the duration of strong motion. To demonstrate the applicability of the proposed methods, this paper analyzes the seismic damage results of 13,500 bridge-ground motion pairs generated to train the fragility models. Results of the proposed models are similar to the seismic fragility probability derived from Monte-Carlo simulation results. This study proposes a two-level strategy to effectively manage regional bridge maintenance. These priority maintenance and secondary maintenance levels are determined based on the results of regional seismic fragility analysis. Additionally, significant sequences of structural parameters and intensity measures are identified using the leave-one-attribute-out analysis method. This process helps bridge designers and managers better understand the sensitive parameters pertaining to different components. This study also tests the proposed models on a virtual transportation network to assess the seismic fragility of its associated regional bridges, resulting in a two-level regional maintenance plan for that specific system.

Restrainers, being of relatively low cost and easy to install, are often used to prevent unseating of bridge spans. The potential of using superelastic shape memory alloy (SMA) restrainers in preventing such failure has been discussed in the literature; however, the impact of such smart restrainers with optimized configurations in reducing the failure probability of bridge components and system as well as the long-term economic losses given different earthquake scenarios has not been investigated yet. This study presents a probabilistic seismic fragility and long-term performance assessment on isolated multi-span simply-supported bridges retrofitted with optimized SMA restrainers. First, SMA restrainers are designed following the displacement-based approach and their configuration is optimized. Then, seismic fragility assessment is conducted for the bridge retrofitted with optimized SMA restrainers and compared with those of the original bridge and the bridges with elastic restrainers (steel and CFRP). Finally, long-term seismic loss (both direct and indirect) are evaluated to assess the performance of the retrofitted bridges in a life-cycle context. Results showed that among three considered restrainers, SMA restrainers make the bridge less fragile and help the system lower long-term seismic loss. The design event (DE, 2475-year return period) specified in Canadian Highway Bridge Design Code (CHBDC, CSA S6-14 2014) may underestimate the long-term seismic losses of the highway bridges. Under DE, the damage probability of the bridge retrofitted with optimized SMA restrainers experiencing collapse damage is only 0.7%. Under the same situation, its expected long-term loss is approximate 17.6% of that with respect to the unretrofitted bridge.

Quantitatively modeling and propagating all sources of uncertainty stand at the core of seismic fragility assessment of structures. This paper investigates the effects of various sources of uncertainty on seismic responses and seismic fragility estimates of single-layer reticulated domes. Sensitivity analyses are performed to examine the sensitivity of typical seismic responses to uncertainties in structural modeling parameters, and the results suggest that the variability in structural damping, yielding strength, steel ultimate strain, dead load and snow load has significant effects on the seismic responses, and these five parameters should be taken as random variables in the seismic fragility assessment. Based on this, fragility estimates and fragility curves incorporating different levels of uncertainty are obtained on the basis of the results of incremental dynamic analyses on the corresponding set of 40 sample models generated by Latin Hypercube Sampling method. The comparisons of these fragility curves illustrate that, the inclusion of only ground motion uncertainty is inappropriate and inadequate, and the appropriate way is incorporating the variability in the five identified structural modeling parameters as well into the seismic fragility assessment of single-layer reticulated domes.

Geometric parameters affecting seismic fragilities of curved multi-frame concrete box-girder bridges with integral abutments

Utilizing shape memory alloy (SMA) cables to constrain frictional isolated bridges is considered an efficient approach to limit bearing displacement and prevent serious earthquake damage. Accurate seismic fragility assessments of this kind of structure are crucial for aseismic decision making. However, traditional assessment methods cannot quantitatively describe the impact of the pulse effect on pulse-type seismic motions, which may lead to inaccurate assessment results. Therefore, this study deduced a novel equation for seismic fragility assessment that considers the pulse effect. Firstly, the impact of the pulse effect is quantified. Then, a multivariable probabilistic seismic demand model (MV-PSDM) is developed that is conditioned on the pulse period, peak ground velocity, structural period, maximum friction coefficient and SMA consumption. Based on the MV-PSDM, an effective approach for predicting structural seismic vulnerability is recommended, which does not require finite element modeling or nonlinear time-history analysis. Finally, a novel equation for calculating the intensity measure corresponding to 50% damage probability is deduced. The results indicate that increased friction coefficients and SMA consumption can enhance structural seismic safety under pulse-type ground motions. However, when the ratio of pulse period to structural period is too small, increased friction coefficients or SMA consumption have no meaningful effect on the seismic fragility of the structure.

Seismic fragility was assessed for non-seismic reinforced concrete shear walls in Korean high-rise apartment buildings in order to implement an earthquake damage prediction system. Seismic hazard was defined with an earthquake scenario, in which ground motion intensity was varied with respect to prescribed seismic center distances given an earthquake magnitude. Ground motion response spectra were computed using Korean ground motion attenuation equations to match accelerograms. Seismic fragility functions were developed using nonlinear static and dynamic analysis for comparison. Differences in seismic fragility between damage state criteria including inter-story drifts and the performance of individual structural members were investigated. The analyzed building had an exceptionally long period for the fundamental mode in the longitudinal direction and corresponding contribution of higher modes because of a prominently insufficient wall quantity in such direction. The results showed that nonlinear static analyses based on a single mode tend to underestimate structural damage. Moreover, detailed assessments of structural members are recommended for seismic fragility assessment of a relatively low performance level such as collapse prevention. On the other hand, inter-story drift is a more appropriate criterion for a relatively high performance level such as immediate occupancy.

Gaussian process regression driven rapid life-cycle based seismic fragility and risk assessment of laminated rubber bearings supported highway bridges subjected to multiple uncertainty sources

New regulatory requirements in Japan have strengthened the mitigation of damage caused by natural hazards, such as earthquakes, and the operational guide for safety improvement evaluation recommends the use of a probabilistic risk assessment (PRA) as the evaluation method in Japan. In the PRA of an earthquake, also known as the seismic PRA, one of the most important issues is the realistic assessment of the structural seismic response and the conditional damage probability (fragility) assessment using a realistic response assessment of nuclear buildings and equipment. Accordingly, we conducted this study both on the analysis methods used for realistic seismic response and assessment methods of seismic fragility to ensure the seismic safety of nuclear buildings and equipment. In this study, we use a three-dimensional (3D) structural model of a reactor building to conduct a nonlinear seismic response analysis for input ground motions beyond a design basis. In addition, we identify the failure mode of the structural components of the reactor building associated with the equipment and assess the seismic fragility based on the 3D behavior of the reactor building. The local response and detailed damage progress of the reactor building obtained through seismic response analysis are reported, along with the results of the seismic fragility assessment.

The analytical formulations of two types of seismic fragility functions, namely seismic demand fragility and seismic damage fragility, are derived from the general definition of fragility function and usually adopted assumptions in seismic risk assessment. Using suitable intensity measure (IM) and damage measure (DM), the well-known Cornell's IM- and displacement-based formulations for seismic risk are revisited from the viewpoint of the analytical fragility functions. It is found that the recently widely used formulations using engineering demand parameters (EDPs) as well as DM-based approaches are two specific cases of the general IM-based risk equation, depending on the chosen fragility parameters. To apply Cornell's formulations to assess the seismic performance of Chinese code-conforming buildings and to investigate the effects of the derived fragility parameters on the seismic performance, a five-storey reinforced concrete (RC) frame designed according to the Chinese codes has been used as a case study. The results of this example study demonstrate that the capacity randomness and the selection of earthquake IMs all have obvious influences on seismic fragility and risk. It is also found that the computed failure probabilities for different limit states in 50 years for the example frame all satisfy the probabilistic safety requirements by the Chinese code for seismic design of reinforced concrete buildings.

Seismic fragility and resilience assessment of bridge columns with dual-replaceable composite link beam under near-fault GMs

Earthquakes can cause serious damage to traffic infrastructures, among which the impact on bridge structure is the most important. Therefore, in order to assess bridges serviceability, it is important to master their damage mechanism and to analyze its probability of occurrence under a given seismic action. Various uncertainties, like the location of epicentre of future earthquakes and their magnitudes, make this task quite challenging. We are also required to consider different earthquake scenarios and the damaged states of bridge components associated with those earthquakes. To suppress these difficulties, this study proposed a new method of performance‐based seismic fragility and risk assessment for bridges. The proposed method included three steps: (1) performance‐based seismic fragility estimation of a five‐span continuous rigid frame bridge, (2) seismic hazard analysis for locations of the bridge, and (3) seismic risk analysis of the bridge. The proposed method that considered the performance of the bridge and the uncertainty in the location of the earthquake epicentre and magnitudes can provide valuable references for seismic‐resistant design of multispan continuous rigid frame bridges in the future.