Comparison between the Seismic Performance of Integral and Jointed Concrete Bridges

This article presents a probabilistic fragility analysis for two groups of integral and jointed concrete bridges, with varying length and column height. The results show that the integral bridges perform consistently better from a seismic perspective than the jointed bridges. Comparisons are also drawn between the seismic fragility of different geometric configurations. The results show that for integral bridges, the seismic vulnerability increases with an increase in bridge length and decreases with an increase in column height. For the jointed bridge, it was found that geometric variation in column height and bridge length does not significantly affect its seismic vulnerability.     

Analytical Fragility Curves for a Class of Horizontally Curved Box-Girder Bridges

Analytical fragility curves were developed for curved single-frame concrete box-girder bridges with seat-type abutments. The bridges incorporated the current seismic design considerations and modern details that were recently adopted by CALTRANS. Fragility curves demonstrated that columns were the most vulnerable components, while the modern seismic details successfully protected the abutment piles from damage during large earthquakes. Increasing the subtended angle affected the seismic vulnerability at both the component and system levels. Functional relationships were proposed to evaluate the seismic vulnerability of curved bridges. Moreover, fragility curve parameters were shown to depend on soil condition and spectral characteristics of ground motions.     

Seismic Fragility Evaluation of Lightly Reinforced Concrete Beam-Column Joints

Fragility functions play an essential role in evaluating the seismic vulnerability of structures. To establish the seismic fragility functions of lightly Reinforced Concrete (RC) beam-column joints, the Park-Ang Damage model has been amended to quantify the damage states and the modified Bouc-Wen-Baber-Noori model has been employed and implemented in ABAQUS to predict the structural hysteresis behavior. Following successful calibration of the numerical results of a RC test frame from literature, the proposed model has been utilized to assess the seismic fragility curves of low to mid-rise RC frames in Singapore for 30 scaled ground motions using incremental dynamic analysis approach.     

Bayesian Updating of Seismic Demand Models and Fragility Estimates for Reinforced Concrete Bridges with Two-Column Bents

Probabilistic models have been developed in a previous study by the authors to estimate the seismic deformation demands on structural components of reinforced concrete (RC) bridges with two-column bents. However, such models should be updated to reflect the latest laboratory of field data. Using a Bayesian approach, this article updates a currently available probabilistic model for the deformation demands of columns in bridges with two-column RC bents. The updated model incorporates information from newly available experimental data from shake table tests conducted based on a record of the 1994 Northridge Earthquake for a structural system with three bents with two columns per bent. The updated model is more accurate than the previous one in predicting the deformation demand of bridges with two-column RC bents and reduces the statistical uncertainty due to the addition of new data. As an application, fragility estimates for an example bridge are computed using the updated model both at the component (column) and system (bridge) levels.     

Critical Assessment of Intensity Measures for Seismic Response of Italian RC Bridge Portfolios

The seismic assessment of a road network depends largely on the characterization of the fragility of its bridge components. The accuracy of bridge seismic demand estimates and the use of proper intensity measures (IM) will significantly influence such task. The available literature has mainly focused on buildings or a limited number of bridge configurations and IMs, which may not be representative for bridge portfolio assessment studies. In this paper, the correlation quality between a larger pool of traditional and innovative IMs and the nonlinear dynamic response of typical Italian RC bridges is investigated to identify the best-performing IMs.     

The Impact of Flood-Induced Scour on Seismic Fragility Characteristics of Bridges

Earthquake in the presence of flood-induced scour is a critical multihazard scenario for bridges located in seismically-active, flood-prone regions. The present article evaluates seismic performance of four example reinforced concrete bridges when they are pre-exposed to regional flood hazards. Nonlinear time history analyses of the example bridges are performed for a suite of ground motion time histories in the presence and absence of scour expected from different intensity flood events. Fragility analysis is performed to develop seismic fragility curves of the example bridges for various scour depths. Results show nonlinear increase in bridge seismic fragility with increase in scour depth.     

Natural Frequency of Single Pier Bridges Considering Soil-Structure Interaction

Because of the crucial role of free vibration frequency of a structure (e.g., a bridge) in design procedure, more realistic estimation of the frequency ends up in safer and more optimized design. As obtaining the free vibration frequencies of a bridge, considering soil-pile group-structure interaction, provide more realistic values, development of an analytical model to obtain such free vibration frequencies is studied in this research work. Most researchers have studied models with a single pile foundation. The purpose of this study is to assess soil-structure interaction (SSI) effects on dynamic performance of pile group supported bridges. A new analytical model is proposed to predict seismic analysis of these bridges. Applying the dynamic equations of motion for the system, SSI effects have been estimated. Based on the suggested analytical model, a new approximate equation is proposed for calculating natural frequency of pile group supported bridges. Equation accuracy has been investigated by comparing the results with those achieved by previous studies. Most periods calculated by the approximate equation are similar to those given for other case studies, indicating that the model could be applicable to other projects. Since the proposed model is very similar to real soil-pile-pier systems, this approximate equation can be used in preliminary seismic design of bridges.     

SEISMIC RISK ASSESSMENT OF RC STRUCTURES WITH THE “2000 SAC/FEMA” METHOD

The applicability of a new, fully probabilistic approach to seismic design and assessment of reinforced concrete (RC) structures is investigated. Fundamental advantages of the method are mathematical simplicity and comparatively light computational effort. The original formulation, which was developed for steel structures, is first illustrated; ah extension which allows consideration of multiple failure mechanisms, typical of RC structures, is then proposed. The applicability of the method is demonstrated through an example: the seismic risk of a four storey RC building that was not designed for seismic resistance is evaluated. Three failure mechanisms are considered: joint failure, column shear failure and drift failure.     

Regional Seismic Risk Assessment of Bridge Network in Charleston,South Carolina

This article presents the results of a seismic risk assessment of the bridge network in Charleston, South Carolina and the surrounding counties to support emergency planning efforts, and for prioritization of bridge retrofit. This study includes an inventory analysis of the approximately 375 bridges in the Charleston area, and convolution of the seismic hazard with fragility curves analytically derived for classes of bridges common to this part of the country. State-of-the-art bridge fragility curves and replacement cost estimates based on region-specific data are used to obtain economic loss estimates. The distribution of potential bridge damage and economic losses are evaluated for several scenario events in order to aid in the identification of emergency routes and assess areas for investment in retrofit. This article also evaluates the effect of uncertainty on the resulting predicted economic losses. The findings reveal that while the risk assessment is very sensitive to both the assumed fragility curves and damage ratios, the estimate of total expected economic losses is more sensitive to the vast differences in damage ratio models considered.     

Shake Table Test and Numerical Analysis of a Bridge Model Supported on Elastomeric Pad Bearings

Elastomeric pad bearings are widely applied in short- to medium-span girder bridges in China, with the superstructure restrained by reinforced concrete (RC) shear keys in the transverse direction. Field investigations after the 2008 Wenchuan earthquake reveal that bearing systems had suffered the most serious damage, such as span falling, bearing displaced, and shear key failure, while the piers and foundations underwent minor damage. As part of a major study on damage mechanism and displacement control method for short- to medium-span bridges suffered in Wenchuan earthquake, a 1:4 scale, two-span bridge model supported on elastomeric pad bearings were recently tested on shake tables at Tongji University, Shanghai. The bridge model was subjected to increasing levels of four seismic excitations possessing different spectral characteristics. Two restraint systems with and without the restraint of RC shear keys were tested. A comprehensive analytical modeling of the test systems was also performed using OpenSees. The experimental results confirmed that for the typical bridges on elastomeric pad bearings without RC shear keys, the sliding effect of the elastomeric pad bearings plays an important role in isolation of ground motions and, however, lead to lager bearing displacement that consequently increases the seismic risk of fall of span, especially under earthquakes that contain significant mid-period contents or velocity pulse components. It is suggested from the test results that RC shear keys should be elaborately designed in order to achieve a balance between isolation efficiency and bearing displacement. Good correlation between the analytical and the experimental data indicates that the analytical models for the bearing and RC shear key as well as other modeling assumptions were appropriate.     

Seismic Fragility Assessment of Lightly Reinforced Concrete Structural Walls

Development of fragility functions is a pertinent stage in seismic performance assessment of structures. A database of lightly Reinforced Concrete (RC) walls under simulated seismic loading is compiled from the literature to establish the drift-based seismic fragility functions. To classify the damage states experienced by RC walls, the Park-Ang Damage model is amended in this research. Then, the modified Bouc-Wen-Baber-Noori hysteresis model is implemented in ABAQUS to predict the hysteresis behavior of RC walls. Thereafter, the proposed hysteresis model is employed to develop the seismic fragility curves of low to mid-rise RC walls in Singapore using incremental dynamic analysis approach.     

Seismic Reliability Assessment of a High-Voltage Disconnect Switch Using an Effective Fragility Analysis

This article deals with evaluation of the seismic vulnerability of a high-voltage vertical disconnect switch, one of the most vulnerable elements of electric substations. The main objective of the research is to evaluate the seismic fragility of the apparatus using a new effective method. By combining standard reliability methods for time-invariant problems with the response surface technique, this original procedure called “EFA” (Effective Fragility Analysis) permits the evaluation of fragility curves using a very limited number of numerical simulations. On the basis of experimental tests, to determine the mechanical characteristics of the disconnect switch components (ceramic, joints, etc.) the fragility curves of the equipment analyzed are carried out. The results are discussed and compared with the results of Monte Carlo simulations, which confirm the reliability of the procedure.     

A Simplified Drift-Based Assessment Procedure for Regular Confined Masonry Buildings in Seismic Regions

This article presents a simplified procedure for assessing the seismic performance of existing low-to-medium rise confined masonry (CM) buildings, which are a typical construction type in Latin-America. The procedure consists of the estimation of the peak roof and first-story inelastic drift demand of CM buildings. The expected peak inelastic displacement demand is related to drift-based fragility curves, which express the probability of being or exceeding two key damage states in the masonry panels, developed from a relatively large experimental database. The proposed procedure could be very useful for obtaining rapid estimates of expected performance during future earthquake events and for assessing the seismic vulnerability of regular confined masonry structures.     

Seismic Evaluation of Tall Buildings Using a Simplified but Accurate Analysis Procedure

A simplified analysis procedure for evaluating the nonlinear seismic responses of tall reinforced concrete (RC) buildings is examined in this study. It is called the Uncoupled Modal Response History Analysis (UMRHA) procedure. It can be viewed as an extended version of the classical modal analysis procedure, where the nonlinear response of each vibration mode is first computed, and they are later on combined into the total response of the structure. The procedure requires the knowledge of the modal hysteretic behavior, which can be obtained from a cyclic modal pushover analysis. The responses of four tall buildings in Bangkok to distant large earthquakes are computed by this procedure and compared with those obtained from the Nonlinear Response History Analysis (NLRHA) procedure. These four buildings have different heights—varying from 20 to 44 stories, different configurations of floor plan, and different arrangement of RC walls. The comparison shows that the UMRHA procedure is able to accurately compute the story shears and story overturning moments, floor accelerations, and inter-story drifts of all these tall buildings. The required computational effort is also extremely low compared to that of the NLRHA procedure. Moreover, since the UMRHA procedure computes the response of each individual vibration mode, it provides more understanding and insight into the complex nonlinear seismic responses of these tall buildings.     

Experimental Study on the Seismic Performance of Superimposed RC Shear Walls with Enhanced Horizontal Joints

The seismic performance of superimposed reinforced concrete (RC) shear walls is decreased by rocking behavior and damage concentration at the horizontal joint. An enhanced horizontal joint method is proposed to improve the corresponding seismic performance. To validate the reliability of the proposed method, three full-scale superimposed walls and a cast-in-place shear wall (for comparison) are designed and tested under the quasi-static load. The test results indicate that the rocking phenomenon can be prevented using the proposed method, and the seismic performance of superimposed RC shear walls with enhanced horizontal joints is comparable to that of the cast-in-place RC shear walls.     

Seismic Displacement Demands on Skewed Bridge Decks Supported on Elastomeric Bearings

The unseating of decks is one of the most prevalent failure modes of bridges after earthquake events, as observed in the 2010 Chile Earthquake. Damaged bridges in Chile often had skew angles and were supported on elastomeric bearings. Similar bridge construction practices with decks supported on elastomeric bearings are also common in the central and eastern U.S. (CEUS). The seismic displacement demands on skewed bridges are more complicated than those on bridges without skew angles due to the coupling of translational modes with the rotational mode of vibration. The study presented in this article seeks to understand the seismic response of skewed bridge decks supported on elastomeric bearings. The scope of the study is limited to one- and two-span bridges, which constitute a large portion of bridge inventory in the CEUS. The vibration modes of skewed bridge decks are derived in closed form and the modes are compared when the gaps between the bridge deck and the abutment are open and when one of the gaps is closed due to seismic excitation. Nonlinear response history analyses are carried out to understand the effects of vertical ground motion, skew angles, aspect ratios, and different ground motion types on the seismic displacement demand in these cases. Amplification factors that approximate the increase in the displacement demand due to the skew angle are proposed.     

Simplification and Assessment of Modal-Based Story Damage Index for Reinforced Concrete Frames Subjected to Seismic Excitations

Different relations have been represented for the local damage index of structures to date, while the same application is defined for them as can be an indicator of relative sustained damage by the components or stories. Since different force-resisting systems subjected to the ground motions can behave differently, some well-known story damage indices are evaluated for the reinforced concrete frames with regards to their operation during nonlinear time history analysis. Two general concepts of story damage determination are selected for this purpose. SDI is a modal-based story damage index, which is calculated by the modal frequency and mode shapes. The behavior of this local index is evaluated during the seismic excitations. The results were compared with Park-Ang and modal flexibility story damage indices. Based on analytical study on seismic responses of some RC frames subjected to a suit of earthquake records a new story damage index has been developed. It has been derived from a simple global damage equation (softening index) using a normalized ratio of inelastic story shear to its drift. A procedure is recommended to use the proposed equation without any requirement to perform nonlinear dynamic analysis, which can significantly reduce the computational efforts. Distribution of the new represented SDI along the structural height shows a good agreement with damaged state of the RC frames after seismic excitations.     

Numerical Investigation of Residual Strength and Energy Dissipation Capacities of Corroded Bridge Members Under Earthquake Loading

Recent damage examples of aged steel bridge infrastructures around the world are so alarming. They intensified the importance of careful evaluation of existing structures for the feasibility of current usage and to ensure public safety. Corrosion and fatigue cracking may be the two most important types of damages in aging structures. Furthermore, recent earthquakes demonstrated potential seismic vulnerability of some types of steel bridges. Corrosion and its effects can trigger the damages caused by earthquakes, and it will be vital to understand the behavior of existing steel bridges which are corroding for decades in future severe seismic events as well. This article comprises the results of nonlinear FEM analysis of many actual corroded plates with different corrosion conditions and proposes a simple and reliable methodology to estimate remaining seismic strength and energy dissipation capacities by measuring only the minimum thickness of a corroded surface, which can be used to make rational decisions about the maintenance management plan of steel infrastructures.     

Long-Period Ground Motion Simulation and its Impact on Seismic Response of High-Rise Buildings

This paper first critically reviews a seismological model and then a three-segment curve model (in log-log space) to model the Q-f relationship is proposed to overcome the potential biased estimation in the long-period range by the “coda wave” method. The optimal curve-fitting process is performed to determine the Q-f relationship for the Hong Kong region. The calibrated seismological factors are incorporated with the stochastic simulation procedure to generate synthetic ground motions, which are validated through comparison with seismic records. The impact of long-period ground motions on the seismic response of high-rise buildings is finally manifested through a numerical study.