Analytical Content Vulnerability Assessment Methodology for Earthquake Catastrophe Models

The scarcity of detailed claims data for building contents (Coverage C) from historical earthquake events poses a significant challenge for property insurance catastrophe models to reliably estimate the losses associated to building contents. To develop content vulnerability functions empirically, one would need to have access to data from a multitude of historical events; however, loss disaggregation by coverage is rarely reported even when claims data become available from recent significant events such as Maule (2010) and Tohoku (2011). While damage to the building structure (Coverage A) can be estimated analytically using simulation-based fragility functions to amend sparse historical observations, the adoption of analytical approaches for other coverages is limited in the current generation of catastrophe models. In the absence of analytical methods, content loss estimation often relies on a combination of expert opinion and abstract reasoning on top of precious-little available data which is often limited to residential properties. In this paper, the authors employ FEMA P-58’s component-based methodology to develop a framework for simulation-based derivation of content vulnerability functions. Following a review of published literature and the types of content components in FEMA P-58’s PACT library, the authors present the simulation-driven vulnerability function for a four-story office building in Los Angeles, and compare the results against respective functions for office buildings from commercial models. Moreover, this paper discusses the need for new content component types in offices and professional service occupancy. Through this study, the authors demonstrate the possibility of improving content loss estimates in catastrophe models by adopting approaches similar to those involved in the development of structural vulnerability functions

Development of Earthquake Vulnerability Functions and Risk Curves for Low and Mid-rise Hotel Buildings using a Performance-based Loss Estimation Framework

The concept of performance-based earthquake engineering has gained significant attentions in both the research and engineering communities. The development of a performance-based seismic loss assessment framework, known as the FEMA P-58 method, allows one to estimate the potential financial losses of a building using performance-based engineering method. This research employs a seismic loss estimation framework derived using the P-58 method to estimate the monetary loss of a mid-rise wood-frame hotel building which is assumed to be located in Napa Valley, California. A 3D structural model representative of the dynamic behavior of the wood-frame hotel was created and subjected to Incremental dynamic analysis (IDA). The structural demands (peak inter-story drifts, peak floor accelerations etc.) obtained from the IDA were utilized in the developed loss estimation framework to assess losses of structural and non-structural components as well as content damages. Preliminary results such as the cumulative loss functions for given intensities and annual risk curve (annual exceedance probability versus monetary loss) are presented and discussed

Influence of Irreparability Fragility on Seismic Vulnerability Assessment of Buildings

The probability that a building is sanctioned to demolition following an earthquake depends on several geotechnical, structural, strategic and financial decision variables. This paper explores the literature on post-earthquake reparability assessment of buildings focusing on structural characteristics and evaluates their approaches for four midrise code-compliant structural systems, namely, steel moment frame, reinforced concrete moment frame, light frame wood, and steel braced frame. The structural responses are estimated using incremental dynamics analysis (IDA) in accordance with FEMA P-695 provisions and the IDA results are relayed to a building-specific loss assessment framework to estimate their seismic vulnerability in terms of monetary losses. To estimate the impact of irreparability fragility, the loss assessment framework evaluates the vulnerability for each reference model at four levels of irreparability thresholds as well as for a case which excludes irreparability. The results show that the projected losses for these reference models are very sensitive to the assumptions for irreparability fragility. The impact of irreparability fragility on the final loss estimates, while varying by reference model, is relatively limited at lower levels of shaking intensity and tends to grow when incrementing toward higher levels of shaking. The paper also discusses a potential numerical issue with the framework to include irreparability in loss estimation, called ‘irreparability anomaly’, which arises from merely linking irreparability to peak residual drift. The observations emphasize the significance of the underlying assumptions for irreparability fragility in seismic vulnerability and loss assessment of building and call for further studies to establish more robust procedures

Seismic Vulnerability Assessment of Buildings Using a Statistical Method of Response Prediction

The seismic vulnerability functions for portfolio-level loss estimation are typically developed for general classes of buildings which may not be suitable to assess building-specific risks. Performance-based earthquake engineering (PBEE) provides the means to conduct building-specific seismic risk assessments. However, such assessments often rely on computationally-intensive analytical frameworks such as incremental dynamics analysis (IDA) which poses a challenge for many types of risk assessment projects. To expand its accessibility, FEMA P-58 outlines a simplified method to predict the nonlinear responses of buildings in which the scope is limited to lower levels of inter-story drifts (less than 4%). This limitation restricts its application to ductile structures, particularly when predicting the vulnerability of modern special moment frame systems. To overcome this shortcoming, this paper proposes an enhanced methodology by which the nonlinear responses of some common structural systems can be predicted by interpolating from a structural response database, itself developed by IDA. The database adopted in the current study consists of structural responses of 61 distinct modern buildings with variety of heights (number of stories), construction material, and lateral load resisting systems. Two building reference models, light-wood frame and special reinforced concrete moment frame with varying heights, are selected to validate the performance of the proposed statistical method. The predicted structural responses for these buildings are benchmarked against the corresponding IDA results. The estimated vulnerability of buildings based on the enhanced simplified method is in good agreement with IDA results. The proposed framework can be used in expedited seismic risk evaluations to estimate the losses of buildings in a large portfolio of diverse structures

Ground Motion Duration Effects on the Seismic Risk Assessment of Wood Light-Frame Buildings

Wood construction comprises a large portion of building stocks of several countries across the globe with high preparedness for earthquakes including Japan, Canada, and the United States. Built environments of these countries are prone to long-duration ground shakings due largely to the proximity of subduction faulting systems. However, the current seismic design requirements do not adequately emphasize this key feature of ground motions. This study evaluates the impact of long-duration ground motions on seismic risk characteristics of code-conforming wood lightframe buildings. To this end, a study matrix of wood light-frame buildings is developed incorporating with two different heights (i.e., 1-story and 4-story) and two distinct occupancies (i.e., multi-family and commercial) designed for a very high seismic region according to the latest pertinent design requirements of the United States. The seismic performance of these buildings is assessed through incremental dynamic analysis (IDA) in accordance with FEMA P-695 recommendations. Each building is analyzed using three sets of ground motions, i.e., far-field FEMA P-695 ground motions ensemble, an ensemble of short-duration ground motions, and an ensemble of long-duration ground motions. For each building, structural responses are obtained, and collapse fragility for these three sets of ground motions are derived. Next, the structural analysis results are relayed to a component-based loss assessment framework developed based on performance-based earthquake engineering principles in order to predict the seismic risk characteristics of the adopted buildings including the vulnerability function, risk curve, and average annual loss (AAL). The loss assessment is conducted separately for the structural and nonstructural components as well as the content of the buildings. The study reveals the considerable effect of ground motion duration on the seismic vulnerability of light-frame wood buildings, specifically in the case of 4-story wood light-frame building which reveals approximately a mean increase of 140.0% in the predicted losses

A Probabilistic Casualty Model to Include Injury Severity Levels in Seismic Risk Assessment

Despite the increasing adoption of Performance-Based Earthquake Engineering (PBEE) in seismic risk assessment and design of buildings, earthquakes resulted in around 1.8 million injuries (three times the number of fatalities) over the past two decades. Several existing PBEE-based methodologies use rudimentary models that may not accurately estimate earthquake-induced casualties. Even when models are suitable for predicting the total number of fatalities and critical injuries, they may fail to adequately differentiate between different levels of injury severity. This paper draws attention to the importance of extending the seismic casualty assessment method by broadening the perspective on injury severity. To this cause, a probabilistic model is developed to predict fatalities and injuries due to earthquakes. The proposed model adopts the FEMA P-58 framework for risk assessment and considers six injury severity levels (minor, moderate, serious, severe, critical and fatal), in accordance with the Abbreviated Injury Scale (AIS). The aforementioned framework evaluates the casualty risk with five modules: seismic hazard analysis, structural analysis and response evaluation (using incremental dynamic analysis), building collapse simulation, detailed casualty assessment caused by structural, nonstructural, and content components of the building, and injury severity assessment. The injury severity assessment module assumes two modes of injury: occupants falling on the floor resulting in injury and injuries caused by unstable building contents hitting occupants as a result of sliding or overturning. The framework uses an occupant-time location model to predict the number of injuries and a set of building content fragility curves for sliding and overturning failure modes, developed by the incremental dynamic analyses. The proposed model was applied to a case study of a reinforced concrete, moment-frame office building furnished with 21 different content objects. The results show that the frequency of injuries resulting in hospitalization can be up to 30 times more than that of the fatal injuries at low shaking intensity levels and may amplify by 20 times at high intensity shaking

Seismic Vulnerability Assessment of Anchored Block Type Contents Due to Sliding and Overturning

Damage to contents and nonstructural components is often the main driver of property losses against smaller earthquakes as evidenced by empirical evidence from past events. In the 2014 South Napa earthquake in California, for example, 56% of the affected buildings reported content damage. The primary modes of content damage include sliding, rocking, and overturning. The FEMA P-58 document provides seismic fragility functions for sliding and overturning of unanchored block content types, but no data is provided for anchored components. The ASCE/SEI 7-16 provides stability guidelines for different types of nonstructural components, but falls short of providing recommendations for the contents and furniture. This study investigates the behavior of anchored contents in commercial buildings and explores the impact of anchorage on the economic losses caused by content damage due to earthquake shaking. Anchored contents are generally represented here by rigid blocks with post-tensioned cables. The presented methodology adopts two engineering demand parameters (EDPs), the sliding displacement and the rotation angle of the rigid block, which are estimated by analytically modeling sliding and overturning responses due to ground motions. Their respective fragility functions are subsequently used to quantify the content seismic vulnerability by taking the maximum losses from sliding and overturning failure modes. The vulnerability functions of anchored versus unanchored contents are compared for commercial buildings of two different structural systems: steel and reinforced concrete moment resisting frames. Comparing the anchored and unanchored vulnerability functions reveals that the unanchored contents are more susceptible to damage and losses than the anchored ones. Moreover, numerical simulations show the extent of reduction in vulnerability, in terms of financial losses, for each level of spectral acceleration as the result of anchorage

Probabilistic Methodology for Terrorism Blast Risk Assessment

In this study, a probabilistic methodology has been developed to quantify terrorism blast risk for buildings. Concept of protection zones, which are zones in building with varying level of security, has been introduced based on the principle - as security increases the probable size of bomb should decrease. Probable bombs are uniformly placed at each protection zone to create many possible scenarios of terrorism event. Blast parameters (pressure and impulse) are estimated at many locations in 3D model of building for each scenario using a modified Kingery and Bulmash (KB) blast model called KB beta model. The United States Department of Defenses Pressure - Impulse damage curves are used to convert blast parameters to damage. The average damage to the building is estimated based on aggregation of damages to the building components. The methodology is applied to investigate the recent Brussels airport attack incident and the results are compared with actual Brussels Airport Attack. The terrorism-blast risk assessment shows that the attack could have been worse

Selection of ground motion prediction equations for the global earthquake model

Ground motion prediction equations (GMPEs) relate ground motion intensity measures to variables describing earthquake source, path, and site effects. From many available GMPEs, we select those models recommended for use in seismic hazard assessments in the Global Earthquake Model. We present a GMPE selection procedure that evaluates multidimensional ground motion trends (e.g., with respect to magnitude, distance, and structural period), examines functional forms, and evaluates published quantitative tests of GMPE performance against independent data. Our recommendations include: four models, based principally on simulations, for stable continental regions; three empirical models for interface and in-slab subduction zone events; and three empirical models for active shallow crustal regions. To approximately incorporate epistemic uncertainties, the selection process accounts for alternate representations of key GMPE attributes, such as the rate of distance attenuation, which are defensible from available data. Recommended models for each domain will change over time as additional GMPEs are developed

A comprehensive framework for seismic risk assessment of urban water transmission networks

Earthquakes are natural disasters which human beings cannot control, causing significant damage to the economy and society as a whole. In particular, earthquakes affect not only buildings but also lifeline structures such as water distribution, electric power, transportation, and telecommunication networks. The interruption of these networks is critical because it can directly damage the facilities and, at the same time, cause long-term loss of the overall system for society. In recent years, there has been increasing interest in the uncertainties of ground motion, deterioration of pipelines, and interdependency of lifelines. Therefore, it is essential to predict the damage through possible earthquake scenarios and accounting for factors affecting lifeline structures. This study proposes a comprehensive framework to quantify the impact of earthquakes on the connectivity of urban water transmissions. The framework proposes the following steps to predict damage from earthquakes: (1) estimate the ground motion considering the spatial correlation, (2) propose a modified failure probability of buried pipelines considering deterioration, and (3) evaluate the seismic fragility curves of network components and the interdependency among water treatment plants, pumping plants, and substations. For numerical simulations, an actual water network system in South Korea was constructed using graph theory, and the magnitudes and locations of the epicenters were determined based on historical earthquake data. Finally, the reliability performance indicators (e.g., connectivity loss and serviceability ratio) were measured when earthquakes of various magnitudes occurred in the urban area. This framework will enable the prediction of damage from earthquakes and enhance decision making to minimize the extent of damage