Seismic Loss Assessment Research Articles

Probabilistic economic seismic loss estimation of steel braced frames incorporating emerging self-centering technologies

This paper presents a comprehensive economic seismic loss assessment of emerging steel frames incorporating different types of self-centering braces. Particular focus is on failure mechanism of the braces and accurate modelling of the possible failure modes, especially fracture of the PT tendons and failure of energy dissipation devices. Moreover, the damage state, component fragility, and repair cost of the considered braces are developed in a more rigorous manner, aided by professional judgment and market research with reduced subjective decision. System-level analysis shows that tendon fracture indeed happens in the braces with FRP tendons under the maximum considered earthquake (MCE), which compromises the self-centering capability of the structures. Shape memory alloy (SMA)-viscoelastic hybrid braces are shown to effectively reduce the deformation and floor acceleration demands, and leads to the lowest probability of collapse. By examining the vulnerability functions and expected losses of the structures, a single-core SCB configuration with FRP tendons leads to the worst economic performance due to the limited brace ductility. A dual-core configuration can significantly improve the brace ductility and hence reduce the economic loss. The SMA-viscoelastic hybrid brace results in the best economic performance with the lowest expected loss. A subsequent sensitivity analysis shows that the vulnerability curves of the structures exhibit mild sensitivity to the residual inter-story drift threshold, but the modelling assumption has a more remarkable influence on the economic loss estimation results. Employing idealized numerical models without considering brace failure in the analysis could underestimate the seismic loss of self-centering braced frames by more than 30%.

Seismic loss risk assessment of RC frame structures designed according to Chinese code

According to the PEER probabilistic seismic loss assessment methodology, a structure-level seismic risk assessment method was proposed and implemented for a set of RC frames designed according to Chinese seismic code. These frames were designed for fortification intensities of 6,7 and 8 and classified into 4,6 and 8 stories. Through incremental dynamic time history analysis (IDA), the statistical relationships of the maximum inter-story drift ratio with the seismic spectral acceleration were obtained and used to determine fragility curve for each damage states. The site seismic hazard model was established based on Chinese seismic code, and the probability distribution of each discrete intensity levels was derived. Using loss index from the Chinese standard and Hazus, the structure means annual frequency of collapse, the Expected Annual Financial Loss (EAL) and the Expected Annual Fatalities (EAF) were calculated. The variation trends of these performance metrics with seismic fortification intensities and structure heights were evaluated, and the weaknesses of the current seismic code of China were pointed out. It was concluded that the method proposed in this paper is simple and reliable for practical applications.

Seismic loss assessment of steel structures equipped with rotational friction dampers subjected to intensifying dynamic excitations

The expected seismic losses of structures with Rotational Friction Dampers (RFDs) are assessed by the Endurance Time (ET) method considering the optimal frictional moment of the devices. A practical method is proposed to obtain the optimal frictional moment of the dampers in multi-story structures at multiple seismic hazard levels. The ET method is used as the analytical tool in this research due to its ability to reduce the number of required analyses and providing good estimations of structural responses at various hazard levels. In order to investigate the effectiveness of the dampers, the life cycle costs of a weak steel structure equipped with optimal RFDs are compared with a standard structure with optimal RFDs and without RFDs. To this end, a comprehensive performance evaluation is performed on the structures based on FEMA P-58 methodology. The ET method is also used as a tool to assess the structural responses in the framework of this methodology. The probability of collapse, fatalities, and expected damage costs are estimated utilizing a Monte Carlo procedure considering uncertainties. Also, a cost-benefit analysis is performed to determine the payback period of investment for the additional cost of the rotational friction damping systems.

Examining the contribution of near real-time data for rapid seismic loss assessment of structures

This study proposes a probabilistic framework for near real-time seismic damage assessment that exploits heterogeneous sources of information about the seismic input and the structural response to the earthquake. A Bayesian network is built to describe the relationship between the various random variables that play a role in the seismic damage assessment, ranging from those describing the seismic source (magnitude and location) to those describing the structural performance (drifts and accelerations) as well as relevant damage and loss measures. The a priori estimate of the damage, based on information about the seismic source, is updated by performing Bayesian inference using the information from multiple data sources such as free-field seismic stations, global positioning system receivers and structure-mounted accelerometers. A bridge model is considered to illustrate the application of the framework, and the uncertainty reduction stemming from sensor data is demonstrated by comparing prior and posterior statistical distributions. Two measures are used to quantify the added value of information from the observations, based on the concepts of pre-posterior variance and relative entropy reduction. The results shed light on the effectiveness of the various sources of information for the evaluation of the response, damage and losses of the considered bridge and on the benefit of data fusion from all considered sources.

Empirical fragility curves of engineered steel and RC residential buildings after Mw 7.3 2017 Sarpol-e-zahab earthquake

This study investigates the damage data after November 12, 2017, Iran earthquake (Mw 7.3), collected on 440 steel and reinforced concrete residential buildings. Structures have low-to-medium height and are located in Sarpol-e-zahab city, as well as in the west and northwest parts of Kermanshah province, Iran. The peak ground acceleration demands are determined according to data of the micro-shakemap of Sarpol-e-zahab city and the shakemap of Kermanshah province, while the mean values of intensities are determined from the existing empirical relationship between PGA and intensity. The investigated buildings are engineered steel and RC structures nominally erected according to the second and third editions of the Iranian code for earthquake-resistant buildings, but mostly under careless supervision and with low-quality materials. Damage probability matrix, vulnerability index and empirical fragility curves are presented for three subgroups of steel and RC structures on the basis of (i) structural materials and seismic resistant systems (i.e. braced, moment and combination of braced and moment steel frames, as well as moment and combination of moment and shear wall RC frames), without considering the height of structures; (ii) structural materials and height of structures, without considering the seismic resistant systems (i.e. low and medium-height steel and RC structures); (iii) structural materials, without considering the seismic resistant systems and height of structures (i.e. total data for steel and RC frames). The proposed fragility curves are compared with other fragility curves for steel and RC buildings from previous studies. Finally, since this earthquake was the first seismic event in Iran affecting a considerable number of steel and RC engineered buildings, the proposed empirical fragility curves are definitely unique and crucial for realistic damage and vulnerability assessment of similar buildings in future earthquake scenarios, as well as for developing rapid seismic loss assessment after damaging earthquakes.

A Simplified Approach for the Seismic Loss Assessment of RC Buildings at Urban Scale: The Case Study of Potenza (Italy)

Comprehensive methodologies based on a fully probabilistic approach (i.e., the performance-based earthquake engineering approach, PBEE), represent a refined and accurate tool for the seismic performance assessment of structures. However, those procedures are suitable for building-specific evaluations, appearing extremely time-consuming if applied at the urban scale. In the proposed contribution, simplified loss assessment procedure will be applied at the urban scale with reference to the residential building stock of the center of Potenza. After the identification of the main reinforced concrete (RC) structural typologies and the definition of specific archetype building numerical models, the direct estimation of expected annual loss (DEAL) methodology will be applied to derive the EAL (i.e., expected annual loss) of RC buildings, deriving information on the effectively seismic quality (or seismic resilience) of the aforementioned built heritage at urban scale. Similarly, the monetary losses associated with downtime are evaluated. Preliminary considerations on the socio-economic effects of seismic scenarios on the territorial scale are also proposed.

A Region-Specific Ground-Motion Model for Inelastic Spectral Displacement in Northern Italy Considering Spatial Correlation Properties

Abstract The peak inelastic displacement of single-degree-of-freedom bilinear systems (Sdi) is an effective intensity measure linking ground-motion features to the inelastic response and subsequent structural and nonstructural damage of engineered systems. This study develops a region-specific ground-motion model for Sdi considering source, path, and site effects and explicitly accounting for the spatial correlation between intraevent residuals when the model parameters are estimated. The model is developed based on 2427 two-component horizontal ground-motion records from 85 events in northern Italy with magnitudes ranging from 4.0 to 6.4 and source-to-site distances less than 200 km. An exponential stationary and isotropic model is considered to represent the spatial correlation properties of Sdi (after scrutinizing the appropriateness of the underlying assumptions for such a model). Comparisons are performed with existing models in the literature in terms of Sdi estimates, as well as the (spatial correlation) effective range parameter. Two practical applications of the developed model are presented: one on estimating the spatial distribution of Sdi (as an essential ingredient for seismic loss assessments) and one on the engineering validation of region-specific ground-motion simulations. Challenges regarding such validations are also discussed.

State of the art of seismic risk and loss assessment in structures

Earthquakes are known as one of the disasters that have fatal consequences for human safety. However, inevitably, the earthquake itself is not the leading cause of the losses suffered by humans, both material and soul. The most powerful thing in human safety is infrastructure such as buildings, bridges, and houses. Therefore, an in-depth analysis of the risk factors that the infrastructure will experience in a natural disaster is needed. There is a variable seismic hazard in the Southeast Asia region, ranging from high seismic hazard allied with the underneath of the Indonesian and Philippine archipelagos to moderate and low seismic tremors associated with a sizeable stable region on the Sunda Shelf. This paper describes the history of seismic risk and loss assessment of infrastructures. The method used is by doing literature reviews of the most recent research relating to seismic risk and assessment around the world. More than fifteen research results are studied and discussed to get a deep knowledge about seismic risk and the assessment of loss due to seismic disaster.

Extension of displacement‐based simplified procedures to the seismic loss assessment of multi‐span RC bridges

AbstractSimplified seismic assessment procedures relying on displacement‐based formulations have recently been implemented for the evaluation of the seismic performance in buildings and bridges. For bridges, displacement‐based assessment procedures have been formulated to predict the displacement response at several performance levels defined based on the expected damage on the structural elements. These displacement profiles have been subsequently used to estimate the performance level achieved under a given seismic hazard intensity and to develop damage fragility curves. For buildings, these concepts have been extended to compute economic losses in agreement with current performance‐based earthquake engineering procedures. In this study, existing displacement‐based formulations for the approximate seismic assessment of single‐column multi‐span continuous RC bridges, with non‐sacrificial shear keys for the pier‐to‐deck connections, are extended for the computation of expected annual losses under transverse direction excitation. Additionally, an iterative response spectrum analysis procedure, which directly considers higher mode effects, is proposed for computing the displacement response, and these results are also used to estimate direct expected annual losses. Results show that both procedures tend to compute higher losses when compared with those obtained with a fully probabilistic loss assessment framework, using demand estimations computed with nonlinear response history analysis. Results also show that the simplified loss assessment procedure is highly sensitive to the definition of the collapse fragility curve.

Performance-based decision-making of buildings under seismic hazard considering long-term loss, sustainability, and resilience

It is of vital importance to incorporate sustainability and resilience in the performance-based decision-making of civil infrastructure under seismic hazard. However, a performance-based engineering framework utilizing component-level approach, integrating seismic loss, sustainability, and resilience in a multi-criteria decision-making (MCDM) is not yet extensively developed particularly for retrofit selection in a long-term perspective. This paper introduces a framework utilizing performance-based approach to couple seismic loss, sustainability, and resilience in decision-making framework for selection of different retrofit alternatives. A component-based probabilistic approach is developed for the seismic loss, sustainability, and resilience assessment in a long-term perspective. The resulting social, economic, and environmental consequences are converted to expected annual consequences (EACs) by considering the full range of seismic hazards, and are utilized as a multi-criterion in the technique for order preference by similarity to ideal solution (TOPSIS). The proposed long-term performance-based multi-criteria decision-making (PB-MCDM) framework considers five consequences, which include cost, casualties, equivalent carbon emissions, embodied energy, and repair time. Based on the illustrative example, it may be concluded that incorporating seismic sustainability and resilience in PB-MCDM approach in a long-term perspective can provide ideal solutions and better decision-making against retrofit alternatives.

Simplified seismic loss assessment for optimal structural retrofit of RC buildings

This study deals with selecting optimal seismic retrofit solutions for reinforced concrete (RC) buildings. To this aim, multi-criteria decision-making (MCDM) is implemented explicitly considering earthquake-induced economic loss as a decision criterion. Fragility (i.e. likelihood of damage levels vs intensity measure ( IM) levels) and vulnerability (i.e. likelihood of loss levels vs IM levels) relationships are derived by using three increasingly refined analysis methods: Simple Lateral Mechanism Analysis; numerical pushover; time-history analysis. A seismically deficient RC school index building, with construction details typical of developing countries, is used for illustrative purposes. Concrete jacketing, addition of concrete walls, and addition of steel braces are the considered retrofit alternatives. Intensity-based expected loss and expected annual loss are adopted in the MCDM, among other criteria, independently derived with the three analysis methods. It is shown that, given the adopted loss-analysis methodology, the ranking of the retrofit alternatives is insensitive to both analysis methods and loss metrics, even when the weight for the seismic loss criterion is high. These findings suggest that simplified methods can be effectively employed in the conceptual/preliminary design of retrofit alternatives.

Probabilistic seismic loss estimation of aging highway bridges subjected to multiple earthquake events

This study investigates the seismic life-cycle cost of aging highway bridges under chloride exposure when subjected to multiple main shock earthquake events along the design lifetime of the structure. While chloride induced corrosion manifests as a continuous deterioration process, earthquake occurrences are typically intermittent. Although relatively weak seismic events that induce none-to-minor bridge damage may not instigate immediate intervention and repair, resulting structural cracks may further accelerate the corrosion process. This study presents a novel Monte Carlo based methodology that explicitly considers potentially altered deterioration pattern between seismic shocks as well as uncertainty in earthquake occurrences, record-to-record variability, repair decisions and repair processes for seismic life-cycle cost computations. The proposed framework also eliminates the need for the often improbable assumption in past literature on seismic life-cycle cost assessment that necessitates structural rehabilitation to pre-hazard states regardless of the seismic damage level. Case-study application of the proposed framework is demonstrated on a single column integral bridge located in the marine splash zone in California, United States. Results from multiple main shock analysis of both non-deteriorating and aging case-study bridge reveals a significant contribution of cumulative damage from corrosion deterioration and shock sequences towards seismic loss and life-cycle cost assessment.

Brace-to-frame connection modelling effects on seismic loss assessment of steel concentrically-braced frames

The main objective of this study is to investigate the implications of the explicit brace-to-frame gusset connection modelling on the seismic performance assessment of steel concentrically-braced frames (CBFs). Two key modelling alternatives are considered, namely through the simulation of CBFs with: i) a benchmark experimentally-validated model, in which the gusset plates are explicitly designed and simulated; and ii) a more simplified option, whereby diagonals are simulated through a centreline-to-centreline approach with fully-pinned boundary conditions. Anticipating the consequences of a less refined modelling approach, a simplified regression-based design process to Eurocode 8 for these gusset connections is proposed, therefore avoiding the need for an explicit connection design for seismic assessment purposes. A third modelling option, an identical approach to the benchmark but with the gusset dimensions being determined through the aforementioned regression-based design process, is also considered. The importance of the explicit modelling of the gusset plate connections to obtain reliable estimates of seismic performance is shown through the comparison of the seismic performance of various building archetypes, considering different metrics (e.g. lateral deformations, earthquake-induced collapse risk and economic losses). Furthermore, the validity of the proposed gusset-design methodology is discussed, by comparing the resulting gusset dimensions against those associated with a rigorous seismic design process, as well as by comparing the seismic performance assessed with numerical models incorporating explicitly-designed or simplified-designed gusset geometries.

Displacement-Based Simplified Seismic Loss Assessment of Italian Precast Buildings

ABSTRACT Economic losses associated with the structural and non-structural damage occurring after an earthquake are of particular importance in the case of industrial buildings due to the consequences of such losses on the local economy and employment level. The seismic sequences that hit the industrial area of Emilia-Romagna region of Italy in 2012 represent an emblematic example. In this earthquake event, major damage on poorly performing precast structures was recorded: many buildings were severely damaged and experienced partial or full collapse. The level of the recorded damage was related to a design lacking modern seismic detailing and to a non-up-to-date evaluation of the seismic hazard: in fact, several industrial buildings, typically one storey precast reinforced concrete (RC) structures, were designed to transfer horizontal loads (i.e. between roof elements and supporting beam or main girder and supporting columns) through either friction or under-designed mechanical connections. The aim of this paper is to provide insights on the evaluation of direct losses in the case of precast RC structures typical of the Italian industrial sector, particularly for buildings built before the enforcement of modern seismic codes. A simplified displacement-based seismic loss assessment procedure is proposed and applied to a selected case study and comparisons are made with the results obtained from non-linear time history analyses on simplified (i.e. single column models) and complete three-dimensional models. Retrofit solutions are proposed and their influence on the collapse probability of the structural elements and on the economic losses is evaluated.

Displacement-Based Simplified Seismic Loss Assessment of Masonry Buildings

ABSTRACT In the framework of the evaluation of the consequences of an earthquake, the paper provides a procedure for the economic loss assessment in unreinforced masonry (URM) buildings, proposing an analytical approach based on a cost function directly dependent on the damage level associated to different structural elements and identified by specific engineering demand parameters. The procedure follows a component-based approach, to be implemented within modern probabilistic seismic risk analyses, and it includes both the in-plane and out-of-plane damage modes that can be activated in a URM structure. It is applied to a three-storey building, examined varying some configurations of structural details, aimed to simulate two different in-plane collapse mechanisms (with damage concentrated mostly on piers or also in spandrels), or to allow, in one case, also the activation of local out-of-plane mechanisms.

Displacement-Based Framework for Simplified Seismic Loss Assessment

ABSTRACT Loss assessment methodologies have been introduced to assess the seismic performance of buildings using more meaningful metrics like direct monetary losses. Different approaches exist, each with varying degrees of complexity and requiring different levels of detail, regarding structural behaviour characterisation or damage and loss estimation, for example. With these developments, loss assessment is increasingly becoming a more commonplace instrument in the seismic evaluation and retrofitting of existing buildings. Despite these developments, there is arguably still a need to provide practising engineers with simplified tools with which to conduct building-specific loss assessment. Displacement-based methodologies have been developed over the past number of years with a particular focus on design. The extension of this approach to loss assessment via displacement-based assessment (DBA) is the subject of this article, where a general framework for its implementation to different structural typologies is outlined and illustrated. This forms a general overview of a recently-concluded 5-year research project on the topic in Italy, where different research groups from various universities focused on specific building typologies as part of a coordinated effort to develop DBA for simplified loss assessment. An overview of the DBA method employed is presented here in addition to an overall description of the results of each working group. A summary of the developments for each typology examined is presented along with an illustration of the potential benefits of different retrofitting techniques in reducing monetary losses, whose details are found in the different typology-specific contributions to the special issue in which this paper is presented. To conclude, a comparative implementation of these simplified methodologies is described for three school buildings in Italy.

Displacement-Based Simplified Seismic Loss Assessment of Post-70s RC Buildings

ABSTRACT To help facilitate performance-based earthquake engineering (PBEE) in Italy, this study examines an existing reinforced concrete frame building damaged during the 2009 L’Aquila earthquake and compares direct monetary loss estimates computed via a simplified Displacement-Based Assessment (DDBA) method with those obtained using the refined PEER-PBEE approach. The considered case study is representative of a category of buildings that has undergone some level of seismic design, typical of post-70s construction in Italy, where previous buildings were largely designed for gravity loads only. The research finds that the expected annual loss predicted using the two approaches are comparable and thus DDBD could aid loss-assessment and hence reparability evaluations. Different retrofit options are examined and it is concluded that the DDBA approach could provide useful indications of the impact that retrofit can have on expected annual losses.

Displacement-Based Simplified Seismic Loss Assessment of Pre-70S RC Buildings

ABSTRACT A Displacement-Based framework for the Simplified Seismic Loss Assessment of pre-70 RC buildings is presented. The attention is focused on the calculation of the Expected Annual Loss using results of traditional structural analyses within a closed-form expression. Comparisons with conventional approach proposed in the Italian guidelines for seismic classification, and rigorous probabilistic seismic performance assessment presented in FEMA-P85 are made for a number of case-studies. Results show that the proposed method performs better than the conventional approach and is aligned with the rigorous method, with errors less than 20%. Finally, preliminary considerations on how to incorporate indirect losses are made.

Displacement-Based Simplified Seismic Loss Assessment of Steel Buildings

ABSTRACT Evaluating losses consequent to damages induced by earthquakes has become one main paradigm in seismic performance assessment. Within this context, this paper explores a simplified seismic loss assessment methodology for steel structures that utilises displacement-based assessment in place of non-linear dynamic analyses. To this end, two case studies have been considered: (i) an archetype existing single-storey non-residential building, (ii) a prototype new multi-story residential building. Comparing results obtained using the fully probabilistic and the simplified displacement-based assessment methodologies allows the benefits of the simplified method to be highlighted. Possible difficulties encountered in applying the simplified method are also identified.

Seismic loss and resilience assessment of single-column rocking bridges

This study focuses on structural systems, which are particularly attractive for bridge design. Specifically, it investigates the seismic performance of single-column bridges, which are either conventionally designed, with the column monolithically connected with the ground (i.e. fixed-base), or designed with the column-footing system able to uplift and exhibit planar rocking motion during an earthquake. Although various researchers have studied the examined structures in terms of their seismic fragility, their seismic losses, post-earthquake functionality and resilience have received less attention. This paper redirects our attention to the main benefits of rocking design over the conventional (fixed-base) design in the aftermath of severe seismic hazard scenarios. The analysis reveals the considerably mitigated (short-term and long-term) seismic losses of the rocking structure compared to the pertinent losses of the fixed-base structure. In addition, the results show the remarkable functionality and resilience of the rocking structure after all the examined seismic hazard scenarios. Importantly, this work unveils that the post-earthquake financial benefits of the rocking structure can be further increased when the structure is carefully designed. In particular, even a small modification of its slenderness can lead to a substantial enhancement of its post-earthquake performance. The above findings illustrate the potential of the rocking structural system as an alternative seismic design paradigm for bridges and serve as the basis for a more rational and holistic seismic assessment framework of single-column rocking bridges.