Fragility Methodology Research Articles

Stochastic Excitation-Incorporated Seismic Fragility Assessment Using Monte Carlo Simulations

Structures are susceptible to damage from natural disasters like tornadoes, floods, and seismic events. A resilient structure can withstand such damage and ensure cost-effectiveness. Therefore, accurately assessing the probability of structural failure is imperative for structural designers. This study employs an innovative fragility methodology to assess seismic damage in structures. In comparison to conventional fragility approaches, this method is cost-effective, universally applicable across various seismic sources, and highly precise. Specifically, this method involves the generation of artificial seismic records using the point-source stochastic seismological model and Monte Carlo simulation method. These synthetic seismic records offer distinct advantages when compared to the seismic data collected from real earthquakes at recording stations, such as the ability to adjust the epicentral distance of the synthetic waves as needed. Therefore, this approach enables a comprehensive analysis of structural responses under seismic waves characterized by different attributes. For example, the influence of different seismological parameters such as wave magnitude and epicentral distance are well studied and compared. The advanced finite element software, OpenSees, serves as the computational platform for examining how structures react to diverse seismic waves. The research findings suggest that, compared to traditional methods, utilizing OpenSees can significantly enhance computational efficiency. Furthermore, the methods employed introduce a novel technique for factoring in wave magnitudes and distances during the calculation of structural seismological responses/fragility. This innovation holds significance for the development of next-generation structural resilience designs.

Seismic fragility analysis of LRB-isolated bridges considering the uncertainty of regional temperatures using BP neural networks

Lead rubber bearings (LRBs) have been widely used as seismic isolators for bridges, owing to their outstanding working performance and wide applicability. However, the mechanical behavior of the main constituents of LRBs (rubber and lead) is sensitive to temperature variations. The objective of this study is to investigate the influence of regional temperature uncertainty on the seismic fragility of LRB-isolated bridges by combining joint seismic fragility and a (back propagation) BP neural network. In this study, a typical continuous beam bridge that is seismically isolated and uses LRBs is assumed to be located in three regions at different latitudes in China. Using the finite elements models of the bridge and incorporating the thermal–mechanical behavior of LRBs, concrete, and steel at different temperatures, the seismic responses of the piers and the bearings are derived by nonlinear dynamic analysis that is used to develop the statistical relationship between the regional temperature and the bridge’s seismic demand via a BP neural network. Then, the well-trained networks are applied to predict the seismic responses of the piers and the bearings at different temperatures in the three selected regions. Finally, the joint seismic fragility methodology is used to establish and compare the seismic fragility at component level and that at bridge system level in the considered regions. Analysis results show that regional temperature variations may have a notable effect on the component-level fragility as well as the bridge-level fragility.

Performance Assessment of Interaction Soil Pile Structure Using the Fragility Methodology

This study aimed to investigate whether the seismic fragility and performance of interaction soil-pile-structure (ISPS) were affected by different parameters: axial load, a section of the pile, and the longitudinal steel ratio of the pile were implanted in different type of sand (loose, medium, dense). In order to better understand the ISPS phenomena, a series of nonlinear static analysis have been conducted for two different cases, namely: (i) fixed system and (ii) ISPS system, to get the curves of the capacity of every parameter for developing the fragility curve. After a comparison of the numerical results of pushover analysis and fragility curves, the results indicate that these parameters are significantly influenced on lateral capacity, ductility and seismic fragility on the ISPS. The increasing in the axial load exhibit high probabilities of exceeding the damage state. The increase in pile section and longitudinal steel ratio, the effect of probability damage (low and high) are not only related to the propriety geometrically, but also related to the values of ductility and lateral capacity of the system. Doi: 10.28991/cej-2021-03091660 Full Text: PDF

Multihazard fragility assessment of steel‐concrete composite frame structures with buckling‐restrained braces subjected to combined earthquake and wind

SummaryEngineering structures may inevitably be subjected to multiple natural hazards (such as earthquakes and winds) during their life cycles. This paper presents an efficient multihazard fragility methodology based on the structural demand models. The approach is applied to two steel‐concrete composite frame structures (SCCFSs), with and without buckling‐restrained braces (BRBs), aiming to evaluate the effect of BRBs on controlling the structural responses and fragilities under the combined earthquake and wind loads. In total, 120 earthquake records are selected, and 120 sets of wind drag force time histories are simulated by considering the spatial variation along the height of the exemplar building. The combined “earthquake–wind” events are stochastically assembled, in which the intensities of these two hazards are modeled using the Monte Carlo simulation. The OpenSees platform is employed to calculate the dynamic responses of the SCCFSs with and without BRBs under simultaneous earthquake and wind loads. The goodness of fits of the first‐, second‐, and third‐order polynomial in predicting the structural demand are evaluated, and the optimal polynomial is employed to generate the multihazard fragility surfaces at different damage states. The numerical results indicate that the structural responses and fragilities under the combined earthquake and wind are higher than those under an individual hazard, while the influencing extent varies with the relative intensities of these two hazards. The impact of multiple hazards and the control effect of BRBs on the structural responses and fragilities are systematically quantified and discussed in details.

Hurricane Surge-Wave Building Fragility Methodology for Use in Damage, Loss, and Resilience Analysis

AbstractPhysics-based fragilities for damage, loss, and resilience analysis are needed to model a community to earthquakes, hurricane winds, tornados, or floods. Currently, most building flood frag...

Artificial neural network based multi-dimensional fragility development of skewed concrete bridge classes

Recent researches are directed towards the regional seismic risk assessment of structures based on a bridge inventory analysis. The framework for traditional regional risk assessments consists of grouping the bridge classes and generating fragility relationships for each bridge class. However, identifying the bridge attributes that dictate the statistically different performances of bridges is often challenging. These attributes also vary depending on the demand parameter under consideration. This paper suggests a multi-parameter fragility methodology using artificial neural network to generate bridge-specific fragility curves without grouping the bridge classes. The proposed methodology helps identify the relative importance of each uncertain parameter on the fragility curves. Results from the case study of skewed box-girder bridges reveal that the ground motion intensity measure, span length, and column longitudinal reinforcement ratio have a significant influence on the seismic fragility of this bridge class.

Critical uncertainty parameters influencing seismic performance of bridges using Lasso regression

SummaryRecent efforts of regional risk assessment of structures often pose a challenge in dealing with the potentially variable uncertain input parameters. The source of uncertainties can be either epistemic or aleatoric. This article identifies uncertain variables exhibiting strongest influences on the seismic demand of bridge components through various regression techniques such as linear, stepwise, Ridge, Lasso, and elastic net regressions. The statistical results indicate that Lasso regression is the most effective one in predicting the demand model as it has the lowest mean square error and absolute error. As the sensitivity study identifies more than 1 significant variable, a multiparameter fragility model using Lasso regression is suggested in this paper. The proposed fragility methodology is able to identify the relative impact of each uncertain input variable and level of treatment needed for these variables in the estimation of seismic demand models and fragility curves. Thus, the proposed approach helps bridge owners to spend their resources judiciously (e.g., data collection, field investigations, and censoring) in the generation of a more reliable database for regional risk assessment. This proposed approach can be applicable to other structures.

Tornado fragility and risk assessment of an archetype masonry school building

Tornadoes are a low-occurrence high-consequence hazard and not only threaten the life safety of building occupants but have recently resulted in billions of dollars in direct and indirect damages for single events. Design codes do not consider tornado loads for building and other structures (with the exception of nuclear facilities) because the occurrence rate has historically been considered too low. The advent of performance-based seismic design has revolutionized the engineering thought process and as a result building owners can consider performance objectives that enable a building to perform better in an extreme hazard than observed with current design code. In this paper, the performance of a masonry school building subjected to tornado wind loads is investigated using a fragility methodology. The tornado fragility assessment methodology is described along with proposed damage states for consideration in loss estimation. An array of masonry material types are considered based on the Masonry Standards Joint Committee (MSJC) code to enable applicability of the fragilities developed herein for a range of designs throughout the United States.

Evaluation of Seismic Fragility of Weir Structures in South Korea

In order to reduce earthquake damage of multifunctional weir systems similar to a dam structure, this study focused on probabilistic seismic risk assessment of the weir structure using the fragility methodology based on Monte Carlo simulation (MCS), with emphasis on the uncertainties of the seismic ground motions in terms of near field induced pulse-like motions and far field faults. The 2D simple linear elastic plain strain finite element (FE) model including soil structure foundations using tie connection method in ABAQUS was developed to incorporate the uncertainty. In addition, five different limit states as safety criteria were defined for the seismic vulnerability of the weir system. As a consequence, the results obtained from multiple linear time history analyses revealed that the weir structure was more vulnerable to the tensile stress of the mass concrete in both near and far field ground motions specified earthquake hazard levels. In addition, the system subjected to near field motions was primarily more fragile than that under far field ground motions. On the other hand, the probability of failure due to the tensile stress at weir sill and stilling basin showed the similar trend in the overall peak ground acceleration levels.

경량 목구조 지붕 쉬딩 시스템에 대한 강풍 취약도 평가기법 개발

This paper presents a fragility assessment for roof sheathing in light-frame wood constructions built in high wind regions. A fragility methodology is developed to assess the performance of roof sheathing subjected to wind-induced building pressures. The goal of this study is to develop a fragility model for roof sheathing system using available resistance test data, recently developed wind load statistics and building code. A typical baseline building considering different geographic locations is investigated using a Mote Carlo simulation method. Fragilities of the baseline building considering three different levels of damages are developed as a function of 3 second gust wind speed. The fragility methodology described in this paper can be used to estimate physical vulnerability and financial loss of light-frame wood construction in high wind regions.

Systematic Study of the Failure of a Light-Frame Wood Roof in a Tornado

Tornadoes are a particularly devastating natural hazard that affect communities across the United States, particularly the Midwest and South. They are unique from an engineering point-of-view due to their very low probability of occurrence but often highly destructive consequences. The 2011 season was particularly devastating to the Southeastern portion of the U.S. This paper presents a single case study of a 2012 tornado that struck a single large rural light-frame wood house with an unconventional roof system. A fragility methodology was used as a tool to probabilistically study the loss of the roof system, and bound an Enhanced Fujita (EF) scale rating of the tornado. The tornado was initially rated as an EF3 tornado by the U.S. National Weather Service. However, following a detailed site inspection verified with numerical structural models, the tornado was downgraded to an EF2 tornado. As expected, the use of nail connections in a roof-to-wall connection resulted in a weaker link compared to a hurricane clip. The approach presented in this paper can be used as a supplement to the EF rating provided by U.S. National Weather Service meteorologists when unusual conditions in either the structure or surroundings exists.

Environmental fragility and susceptibility mapping using geographic information systems: applications on Ribeirão do Pinhal watershed (Limeira, State of São Paulo)

This paper presents the results of integrated environmental analysis of the Ribeirão do Pinhal drainage basin, undertaken with geographic information systems and spatial analysis techniques. The empirical analysis of environmental fragility methodology was used to identify areas that require more attention for improving environmental conditions. Because more than 60% of the study area has weak or very weak potential fragility grades, the natural characteristics of the basin may be considered appropriate. Regarding the environmental fragility, i.e. taking into account human actions, the basin has more than 50% of its area with weak or very weak grades. However, more than 40% of the study area has environmental fragility above their potential fragility grades. This situation indicates the presence of intensive land uses beyond natural landscape restoration processes. These sectors require that stricter territory management policies be implemented.

A Simplified Fragility Methodology for Regular Steel MRFs

During the last decade, significant progress has been made toward the development of probabilistic methods for the seismic assessment of structures. However, the use of existing analytical fragility methodologies for practical applications related to structures of moderate to low importance remains prohibitive, in part due to substantial computational demands. This paper explores, through a case study, the robustness of a simplified methodology for fragility assessment of regular steel Moment Resisting Frames (MRFs). Through comparisons with a more accurate but computationally demanding methodology, it was confirmed that the “2000 SAC/FEMA” procedure gives robust fragility estimates. Moreover, it was found that a closed-form fragility assessment, where the structural response is evaluated by means of an Equivalent Single Degree Of Freedom (ESDOF) oscillator, can yield sufficiently accurate results for regular steel MRF structures, providing acceptable construction quality has been achieved in the connections.

Seismic fragility methodology for highway bridges using a component level approach

AbstractBridge 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.

Fragility assessment for roof sheathing failure in high wind regions

This paper presents a fragility assessment for roof sheathing in light frame constructions built in high wind regions. A fragility methodology is developed to assess the performance of roof sheathing subjected to uplift (suction) pressures. The majority of single-family housing in the United States is woodframe construction. A review of the performance of woodframe buildings after recent hurricanes has shown that the majority of wind damage (insured losses) was the result of a breach in the building envelope. Loss of roof sheathing and broken windows result in water penetration causing extensive interior damage and associated property and contents losses. The aim of this study was to develop a fragility model for roof sheathing uplift using available fastener test data, recently developed wind load statistics, and a code-based approach for evaluating pressures. Five baseline structures considering different roof shapes, geographic locations, nail types, and enclosure conditions were investigated using simulation and system reliability concepts. Fragilities and complementary fragilities (or survivorship curves) of roof sheathing removal considering different levels of damage are developed as a function of basic wind speed (3 s gust wind speed at 33 ft (10 m) above the ground in open terrain). The fragility models presented in this paper can be used to develop performance-based design guidelines for woodframe structures as well as tools for condition assessment and loss estimation for use with the existing building inventory.