Probabilistic Seismic Assessment Research Articles

Seismic Collapse Assessment of a 20-Story Steel Moment-Resisting Frame Structure

The 2010 edition of the load standard in the United States (U.S.), ASCE 7-10, (Minimum Design Loads for Buildings and Other Structures) introduced risk-targeted spectral acceleration values for the estimation of seismic design loads. In this study, a 20-story steel moment resisting frame structure located in Century City, CA, USA was designed based on ASCE 7-10 and a probabilistic seismic collapse assessment was conducted. The main goals of this study are: (a) to evaluate whether the design of a typical steel moment-frame structure based on risk-targeted spectral accelerations fulfills the target design collapse level of 1% probability of collapse in 50 years; and (b) to quantify the collapse potential of a tall steel structure design based on the most current U.S. seismic code provisions. The probability of collapse was estimated for two sets of 104 and 224 recorded ground motions, respectively. An evaluation of the results demonstrated that for this specific structure the code-prescribed collapse performance target was reasonably met.

Probabilistic seismic response assessment of linear systems equipped with nonlinear viscous dampers

SUMMARYThe paper aims at evaluating the influence of damper properties on the probabilistic seismic response of structural systems equipped with nonlinear viscous dampers.For this purpose, a linear single‐degree‐of‐freedom system with an added linear or nonlinear viscous damper is considered, and the response statistics are evaluated for a set of natural records describing the ground motion uncertainty. A dimensional analysis of the seismic problem is carried out first to identify the minimum set of characteristic parameters describing the system and controlling the seismic response. An extensive parametric study is then performed to estimate the influence of the damper properties on the statistics of the main response quantities of interest (i.e. maximum displacements, accelerations and damper forces), for a wide range of values of the characteristic parameters. Finally, a set of case studies is investigated to show some interesting issues concerning the influence of the damper nonlinear behaviour on the evaluation of the system reliability and to highlight some limitations of current deterministic approaches neglecting the probabilistic properties of the response. Copyright © 2014 John Wiley & Sons, Ltd.

Construction of variance-based metamodels for probabilistic seismic analysis and fragility assessment

Finite element models used in industrial studies for seismic structural reliability analysis are in general very complex and computationally intensive. This is due to the important number of degrees of freedom as well as due to advanced damage models and failure modes that have to be simulated. In consequence, reliability studies are feasible only by means of simpler surrogate models able to represent essential physics. Then the choice of an accurate surrogate or metamodel is crucial for uncertainty propagation and sensitivity analysis. The construction of a pertinent metamodel is however a not simple task when random uncertainties, not explained by the model parameters, have to be accounted for. This is the case for transient seismic analysis where the ground motion, an intrinsically random phenomena, is modelled by a stochastic process that cannot be entirely described by a set of parameters. In this paper, we construct a versatile metamodel based on analysis of variance (ANOVA) decomposition. The ANOVA decomposition provides a convenient framework allowing both for parametric uncertainties and for stochastic variability introduced by seismic load. We then compute fragility curves and perform sensitivity analysis.

A probabilistic analytical seismic vulnerability assessment framework for substandard structures in developing countries

This paper presents a framework for analytical seismic vulnerability assessment of substandard reinforced concrete (RC) structures in developing countries. Amodified capacity-demand diagram method is used to predict the response of RC structures with degrading behaviour. A damage index based on period change is used to quantify the evolution of damage. To demonstrate the framework, a class of substandard RC buildings is examined. Abrupt accumulation of damage is observed due to the brittle failure modes and this is reflected in the developed vulnerability curves, which differ substantially from the curves of ductile structures.

Probabilistic seismic assessment of multistory precast concrete frames exposed to corrosion

Seismic design of concrete structures is currently based on time-invariant capacity design criteria which do not account for environmental hazards. The significant progressive decay of strength and ductility of concrete structures exposed to damage, in particular due to reinforcing steel corrosion, shows that this approach should be revised to consider the deterioration over time of the seismic performance. This is important also for precast systems, for which most of structural members are often directly exposed to the atmosphere and environmental aggressiveness. This paper presents a probabilistic approach for the lifetime assessment of seismic performance of concrete structures considering the interaction of seismic and environmental hazards. The effectiveness of the proposed approach is shown by its application to multistory precast buildings exposed to corrosion. The results show that structures designed for the same seismic action could have different lifetime seismic performance depending on the environmental exposure. These results emphasize the importance of a life-cycle approach to both seismic assessment of existing buildings and seismic design of new structures, and indicate that capacity design criteria need to be properly revised to consider the severity of the environmental exposure.

Seismic assessment of R/C residential buildings with infill walls in Turkey

In 1999 Marmara and 2011 Van earthquakes in Turkey, majority of the existing buildings either sustained severe damage or collapsed. These buildings include masonry infill walls in both the interior and exterior R/C frames. The material of the masonry infill is the main variant, ranging from natural stones to bricks and blocks. It is demanding to design these buildings for satisfactory structural behavior. In general, masonry infill walls are considered by its weights not by interaction between walls and frames. In this study, R/C buildings with infill walls are considered in terms of structural behavior. Therefore, 5 and 8-story R/C buildings are regarded as the representative models in the analyses. The R/C representative buildings, both with and without infill walls were analyzed to determine the effects of structural behavior change. The differences in earthquake behavior of these representative buildings were investigated to determine the effects of infill walls leading structural capacity. First, pushover curves of the representative buildings were sketched. Aftermath, time history analyses were carried out to define the displacement demands. Finally, fragility analyses were performed. Throughout the fragility analyses, probabilistic seismic assessment for R/C building structures both with and without infill walls were provided. In this study, besides the deterministic assessment methodology, a probabilistic approach was followed to define structural effect of infill walls under seismic loads.

A new bracing system for improvement of seismic performance of steel jacket type offshore platforms with float-over-deck

In this paper, the seismic response of a newly designed steel jacket offshore platform with a float over deck (FOD) system in the Persian Gulf was investigated through incremental dynamic analysis. Comparison of incremental dynamic analysis results for both directions of the platform shows that the lateral strength of the platform in the float over direction is less than its lateral strength in other direction. Dynamic characteristics measurement of a scale model of platform was also performed using forced vibration tests. From experimental measurement of the scaled model, it was observed that dynamic characteristic of the platform is different in the float over direction compared to the other direction. Therefore, a new offshore installed bracing system for the float over direction was proposed for improvement of seismic performance of this type of platform. Finally, the structure with the modified system was assessed using the probabilistic seismic assessment method as well as experimental measurement of its dynamic characteristics. It was observed that the proposed offshore installed bracing system improves the performance of platforms subjected to strong ground motion.

Seismic insurance model for the Italian residential building stock

ABSTRACT The expected life-cycle cost can be regarded as a benchmark variable in decision making problems involving insurance policy making for existing structures in seismic risk prone areas. The present study is a preliminary study aiming to calculate the expected insurance premium for Italian building stock subjected to seismic action in its service lifetime based on probabilistic seismic loss assessment. The proposed methodology leads to probabilistic assessment of the structural performance, expressed in terms of the discrete structural limit state exceedance probabilities, and the life cycle cost taking into account the Italian seismic zonation and the seismic vulnerability of the existing life stock. The expected insurance premium can then be evaluated based on the probabilities that the structure exceeds a set of discrete limit state thresholds and the average costs associated to them. The methodology is implemented in an illustrative numerical example which considers the Italian residential building stock discretized in 5 structural typologies and in 8088 areas, corresponding to the Italian municipalities. A monopoly market-based insurance model is built, assuming risk aversion of the property owners and risk neutrality of the insurance companies. The expected insurance premium is evaluated for each structural typology in each Italian municipality, taking into account also the maximum coverage and the insurance excess systems. Results are aggregated to compute the total annual expected loss for the entire Italian building stock, and the total income and profit margin for the insurance company assuming an insurance contract for all the property owners.

Options for the Treatment of Uncertainty in Seismic Safety Assessment of Nuclear Power Plants

This paper proposes options for improving seismic safety analysis for nuclear power plants. Cumulative absolute velocity (CAV) has been considered and analyzed for describing different load-cycle-dependent phenomena, e.g., fatigue failure and soil liquefaction. Fatigue damage estimation is based on load-cycle counting, which can be performed by counting zero or level crossings if power spectral density (PSD) of load time history is known. Correlation between CAV and moments of PSD of load time history is derived in this paper. A fatigue failure criterion is developed in terms of CAV. P-box theory is proposed for improving uncertainty modeling of probabilistic seismic safety assessment. P-boxes are represent upper and lower bounds of the distribution function specified by left side and right side distribution functions. The utilization of the p-box method has an advantage if the conditional probability of a particular failure mode of a component is known approximately only, and the sample size of damage histories is small or inconsistent or modeling of component failure is uncertain.

Fragility Analysis of Skewed Single-Frame Concrete Box-Girder Bridges

Damage to skewed bridges in recent earthquakes has reinforced the potential vulnerability of these structures. The effect of skew angleonabridge's fragility couldvary for different bridge types, ages, or geometric configurations. This paperconducts a probabilistic seismic assessment of skewed bridge performance, focusing on single-frame concrete box-girder bridge subclasses. The effect of skew angle on bridge seismicfragilityisinvestigatedforbridgeswithsingle-ortwo-columnbents,integralorseat-typeabutments,andminimalorsignificantlevelsof seismic design. Component and system-level damage states consistent with HAZUS-MHdefinitions are also explored in this study. The results reveal that older bridges, which are more likely to experience higher damage states, are particularly susceptible to column damage and are not sensitivetoskew.Similarly,thepresenceofintegralabutmentsinnewerbridgessignificantlyreducesthevulnerabilityandminimizestheimpact oftheskewangleonbridgefragility.Fornewbridgeswithseat-typeabutments,thebridgeskewanglehasasignificanteffectoncomponentand system fragility for both single- and two-column bent bridges. Forthese subclasses,HAZUS-MHskew factors are foundto reasonably estimate theshiftinmedianvaluefragilityfromtheirstraightcounterparts.DOI:10.1061/(ASCE)CF.1943-5509.0000435.©2014AmericanSocietyof

Generalized Fragility Relationships with Local Site Conditions for Probabilistic Performance-based Seismic Risk Assessment of Bridge Inventories

The current practice of detailed seismic risk assessment cannot be easily applied to all the bridges in a large transportation networks due to limited resources. This paper presents a new approach for seismic risk assessment of large bridge inventories in a city or national bridge network based on the framework of probabilistic performance based seismic risk assessment. To account for the influences of local site effects, a procedure to generate site-specific hazard curves that includes seismic hazard microzonation information has been developed for seismic risk assessment of bridge inventories. Simulated ground motions compatible with the site specific seismic hazard are used as input excitations in nonlinear time history analysis of representative bridges for calibration. A normalizing procedure to obtain generalized fragility relationships in terms of structural characteristic parameters of bridge span and size and longitudinal and transverse reinforcement ratios is presented. The seismic risk of bridges in a large inventory can then be easily evaluated using the normalized fragility relationships without the requirement of carrying out detailed nonlinear time history analysis.

Toward a rapid probabilistic seismic vulnerability assessment using satellite and ground-based remote sensing

Natural hazards such as earthquakes threaten millions of people all around the world. In a few decades, most of these people will live in fast-growing, inter-connected urban environments. Assessing risk will, therefore, be an increasingly difficult task that will require new, multidisciplinary approaches to be tackled properly. We propose a novel approach based on different imaging technologies and a Bayesian information integration scheme to characterize exposure and vulnerability models, which are among the key components of seismic risk assessment.

Probabilistic seismic demand assessment of steel moment frames with side-plate connections

Seismic performance of Steel Moment-Resisting Frames (SMRFs) with side-plate connections has been investigated, incorporating record-to-record uncertainties. Based on experimental and finite element results, a connection model was proposed and calibrated to represent the side-plate connection behavior. Three code-conforming special SMRFs, varying in height, were designed and were modeled using fully nonlinear assumptions and incorporating the connection model calibrated in the previous step. Subsequently, more than 1500 Nonlinear Dynamic Analyses (NDAs) were performed within the Incremental Dynamic Analysis (IDA) procedure and were used as input to the Performance-Based Earthquake Engineering (PBEE) methodology. The structures performance was then quantitatively assessed in terms of Limit State (LS) frequency and “seismic demand hazard curves”. The effect of neglecting some level of accuracy in the structural modeling process on the predicted performances was also assessed disregarding calibrated connection behavior and employing two alternate sets of building representatives. The performances predicted by inaccurate conventional models, through about 3500 additional NDAs, were then assessed qualitatively, and the significance of incorporating accurate structural models in the performance evaluation process was highlighted with reference to the obtained comparative results.

Seismic demand models for probabilistic risk analysis of near fault vertical ground motion effects on ordinary highway bridges

SUMMARYThe influence of vertical ground motions on the seismic response of highway bridges is not very well understood. Recent studies suggest that vertical ground motions can substantially increase force and moment demands on bridge columns and girders and cannot be overlooked in seismic design of bridge structures. For an evaluation of vertical ground motion effects on the response of single‐bent two‐span highway bridges, a systematic study combining the critical engineering demand parameters (EDPs) and ground motion intensity measures (IMs) is required. Results of a parametric study examining a range of highway bridge configurations subjected to selected sets of horizontal and vertical ground motions are used to determine the structural parameters that are significantly amplified by the vertical excitations. The amplification in these parameters is modeled using simple equations that are functions of horizontal and vertical spectral accelerations at the corresponding horizontal and vertical fundamental periods of the bridge. This paper describes the derivation of seismic demand models developed for typical highway overcrossings by incorporating critical EDPs and combined effects of horizontal and vertical ground motion IMs depending on the type of the parameter and the period of the structure. These models may be used individually as risk‐based design tools to determine the probability of exceeding the critical levels of EDP for pre‐determined levels of ground shaking or may be included explicitly in probabilistic seismic risk assessments. Copyright © 2011 John Wiley & Sons, Ltd.

Assessment of the Statistical Distributions of Structural Demand Under Earthquake Loading

Many existing probabilistic seismic safety assessment studies assume that structural demand conditional to a seismic intensity follows a lognormal distribution. Based on the analysis of five reinforced concrete structures subjected to real earthquake records scaled to several intensities, an in-depth analysis of this assumption is performed using adequate statistical methods. The considered demand parameters are the chord rotation, curvature, shear force, and inter-story drift. The results found indicate that the lognormal distribution is suitable for the probabilistic modeling of the considered demand parameters. In addition, the normal distribution was also found suitable for the shear force demand.

A probabilistic method for the seismic assessment of existing concrete gravity dams

This work presents a probabilistic seismic assessment method able to manage the physical complexity of the dam–foundation–reservoir system and the uncertainties regarding structural data and external actions. The seismic response of the structure is estimated from a reduced number of dynamic time-history analyses, performed employing a finite element discretisation of dam body, reservoir water and foundation rock mass. The system fragility curves are then obtained via a standard Monte Carlo simulation procedure. The methodology has been applied to the case of Kasho Dam, a concrete gravity dam located in Japan, which experienced in 2000 the Western Tottori earthquake with no damage at dam body. The assessment has been carried out with respect to an operational limit state, for which several ‘critical’ failure mechanisms have been identified and numerically evaluated, both in terms of demand definition and capacity evaluation.

Probabilistic seismic loss assessment of aging bridges using a component‐level cost estimation approach

AbstractDeteriorating highway bridges in the United States and worldwide have demonstrated susceptibility to damage in earthquake events, with considerable economic consequences due to repair or replacement. Current seismic loss assessment approaches for these critical elements of the transportation network neglect the effects of aging and degradation on the loss estimate. However, the continued aging and deterioration of bridge infrastructure could not only increase susceptibility to seismic damage, but also have a significant impact on these economic losses. Furthermore, the contribution of individual aging components to system‐level losses, correlations between these components, and uncertainty modeling in the risk assessment and repair modeling are all crucial considerations to enhance the accuracy and confidence in bridge loss estimates. In this paper, a new methodology for seismic loss assessment of aging bridges is introduced based on the non‐homogeneous Poisson process. Statistical moments of seismic losses can be efficiently estimated, such as the expected value and variance. The approach is unique in its account for time‐varying seismic vulnerability, uncertainty in component repair, and the contribution of multiple correlated aging components. A representative case study is presented with two fundamentally distinct highway bridges to demonstrate the effects of corrosion deterioration of different bridge components on the seismic losses. Using the proposed model, a sensitivity study is also conducted to assess the effect of parameter variations on the expected seismic losses. The results reveal that the seismic losses estimated by explicitly considering the effects of deterioration of bridge components is significantly higher than that found by assuming time‐invariant structural reliability. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of Frequency Content of Earthquake Ground Motions on Probabilistic Seismic Demand Assessment of Long-Span Bridge Structures

Earthquake ground motions were reasonally selected for the nonlinear dynamic time-history analysis conducted for a two-tower long-span cable-stayed bridge. The correlation between frequency content of earthquake ground motions and probabilistic seismic demands reveals that the geometric mean and dispersion of response spectra from earthquake ground motions have significant effects on probabilistic seismic demand assessment of long-span bridge stuctures and these effects are related to the difference of the shape of geometric mean spectra in the important period ranges where cumulative modal mass participation is significant. Response spectra of selected earthquake ground motions should match well with target spectra in the important period ranges. If input ground motions are reasonally selected, analytic results can be obtained more precisely and effectively and more amplitude parameters can be selected as intensity measures.

Probabilistic seismic risk assessment of hall buildings in Turkey

SUMMARYSteel space framed hall buildings are dedicated as shelters for people suffering from earthquakes. In general construction, steel space frames are built on reinforced concrete (R/C) frames or wall structures above the bottom side. For this reason, the bottom side has higher rigidity comparing with the upper side. In Turkey, where there is a very high earthquake risk, earthquake‐resistant steel space framed structures is an important issue. In this current research, hall buildings in Turkey, involving two different rigidity parts as R/C and steel, are taken into consideration regarding earthquake effect. In this study, three different hall structures were modeled with different elastic moduli for the analysis part. Nonlinear time history analyses were applied with 25 different earthquake data for performance estimation. After the time history analyses, probabilistic seismic assessment was carried out for the model buildings through fragility analyses. For each model, analysis results were evaluated and compared. As a result, the hall buildings were found to be vulnerable to damage during expected future earthquakes. Moreover, elastic moduli have significant effect on the structural response. Copyright © 2011 John Wiley & Sons, Ltd.

Seismic risk assessment of storage tanks in Turkish industrial facilities

In 1999, two earthquakes in northwest Turkey caused heavy damage to a large number of industrial facilities. This region is the most industrialized in the country, and heavy damage has a significant economic influence. Industrial storage tanks, ruptured by earthquakes, exascerbate damage through the spread of fire. Storage tanks are uniquely structured, tall cylindrical vessels, some supported by relatively short reinforced concrete columns. The main aim of this study is to evaluate the earthquake performance of Turkish industrial facilities, especially storage tanks in terms of earthquake resistance. Modeling a typical storage tank of an industrial facility helps to understand the structure’s seismic response. A model tank structure was modelled as a solid with lumped mass and spring systems. Performance estimation was done with 40 different earthquake data through nonlinear time history analyses. After the time history analyses, fragility analyses produced probabilistic seismic assessment for the tank model. For the model structure, analysis results were evaluated and compared. In the study, vulnerability of storage tanks in Turkey was determined and the probabilistic risk was defined with the results of the analysis.