Highway Overcrossings Research Articles

Exploring the Use of Orientation-Independent Inelastic Spectral Displacements in the Seismic Assessment of Bridges

ABSTRACT Seismic intensity measures (IMs) provide a link between the seismic hazard and the dynamic response of structures subjected to earthquake shaking. The spectral acceleration at the first and usually dominant vibration mode, Sa(T 1), is a popular choice for building structures. Meanwhile, the IM selection for bridges is non-trivial since they do not typically possess a single dominant mode. Even for ordinary bridges with a dominant mode, the behavior can change significantly in each principal direction through the activation, or yielding, of its different components. This study examines the performance of a novel IM that incorporates ground motion directionality and structure non-linearity in this context: the nn th percentile of all rotation angles of the inelastic spectral displacement, Sd i,RotDnn. This evaluation is carried out within the context of an ordinary bridge structure and is compared with other conventional IMs used in regional risk assessment of bridges. The case study bridge utilized is a highway overcrossing located in California with two spans and a continuous prestressed reinforced concrete box girder deck section. A large ground motion set was selected from the NGA-West2 database, and incremental dynamic analysis was carried out on the structure to assess the IM performance to characterize collapse. The results indicate that Sd i,RotDnn performs very well compared to other IMs for the bridge structure and could be a prudent choice to characterize inelastic response of bridges with several possible mechanisms in different principal directions. Also, using the RotD50 definition, typically used in ground motion models, showed a 17.3% increase in efficiency compared to RotD100 definition typically used in engineering practice.

Earthquake Response Control of Isolated Bridges Using Supplementary Passive Dampers

AbstractEarthquake response control of base-isolated bridges using supplementary passive dampers is presented. A benchmark highway overcrossing located in California is selected to indicate the eff...

Sensitivity of seismic demands and fragility estimates of a typical California highway bridge to uncertainties in its soil-structure interaction modeling

This study investigates the sensitivity of seismic demands and fragility estimates of a typical highway bridge in California to variation in its soil-structure interaction (SSI) modeling parameters. A rigorous p-y spring based modeling approach is developed and validated for an instrumented highway overcrossing that provides a dependable screening of each modeling parameter. Modifications are made to benchmark the overcrossing against typical bridge designs in California, including the consideration of diaphragm and seat abutments. Plausible variation in SSI modeling parameters is established using 18 random variables that cover different soil zones. Influential SSI parameters are identified for the seismic demands of bridge components through two regression techniques such as stepwise and LASSO regressions. Concurring results from both regressions indicate that bridge demand models tend to be sensitive to the modeling parameters associated with near-ground soils. Furthermore, the relative importance of the uncertainty in SSI modeling parameters is assessed with respect to the fragility estimates in both component and system levels. The study reveals that the bridge performance and fragility curves of bridge columns and decks are dominated by the uncertainty in the ground motion. However, the propagation of the potentially variable SSI parameters plays a significant role in the fragility estimates of bridge foundations and abutment components such as span unseating, bearings and shear keys. The results offer insights to guide future uncertainty treatment in SSI modeling and investment in refined soil parameter estimates through field testing or other measures.

Seismic protection of the benchmark highway bridge with passive hybrid control system

The present paper deals with the optimum performance of the passive hybrid control system for the benchmark highway bridge under the six earthquakes ground motion. The investigation is carried out on a simplified finite element model of the 91/5 highway overcrossing located in Southern California. A viscous fluid damper (known as VFD) or non-linear fluid viscous spring damper has been used as a passive supplement device associated with polynomial friction pendulum isolator (known as PFPI) to form a passive hybrid control system. A parametric study is considered to find out the optimum parameters of the PFPI system for the optimal response of the bridge. The effect of the velocity exponent of the VFD and non-linear FV spring damper on the response of the bridge is carried out by considering different values of velocity exponent. Further, the influences of damping coefficient and vibration period of the dampers are also examined on the response of the bridge. To study the effectiveness of the passive hybrid system on the response of the isolated bridge, it is compared with the corresponding PFPI isolated bridges. The investigation showed that passive supplement damper such as VFD or non-linear FV spring damper associated with PFPI system is significantly reducing the seismic response of the benchmark highway bridge. Further, it is also observed that non-linear FV spring damper hybrid system is a more promising strategy in reducing the response of the bridge compared to the VFD associated hybrid system.

Polynomial friction pendulum isolators (PFPIs) for seismic performance control of benchmark highway bridge

The seismic response of a benchmark highway bridge isolated with passive polynomial friction pendulum isolators (PFPIs) is investigated and subjected to six bidirectional ground motion records. The benchmark study is based on a lumped mass finite-element model of the 91/5 highway overcrossing located in Southern California. The PFPI system possesses two important parameters; one is horizontal flexibility and the other is energy absorbing capacity through friction. The evaluation criteria of the benchmark bridge are analyzed considering two parameters, time period of the isolator and coefficient of friction of the isolation surface. The results of the numerical study are compared with those obtained from the traditional friction pendulum system (FPS). Dual design performance of the PFPI system suppressed the displacement and acceleration response of the benchmark highway bridge. The dual design hysteresis loop of the PFPI system is the main advantage over the linear hysteresis loop of the FPS. The numerical result indicates that the seismic performance of the PFPI system is better than that of the traditional FPS isolated system. Further, it is observed that variations of the isolation time period and coefficient of friction of the FPS and PFPI systems have a significant effect on the peak responses of the benchmark highway bridge.

Seismic response control of benchmark highway bridge using non-linear FV spring damper

The benchmark structure used in this study is the lumped mass finite-element model of 91/5 highway overcrossing located at Southern California. The effectiveness of the non-linear fluid viscous (FV) spring damper on the benchmark highway bridge subjected to six bi-directional ground motion is investigated. A parametric study is carried out to find the optimum vibration period, the damping coefficient and the velocity exponent of the FV spring damper. The methodology of the technique is to achieve adequate energy dissipation by combining the stiffness and viscous damping effect in one system. Combination of a horizontal elliptical hysteresis loops of the non-linear viscous damper plus elastic stiffness of the spring produce a dynamic inclined hysteresis loop, which has no permanent displacement at the end of the excitation. Due to inclined hysteresis loop, non-linear FV spring damper has significantly reduced the responses, such as, base shear, mid-span displacement and especially abutment displacement of ...

Parametric time‐domain identification of multiple‐input systems using decoupled output signals

SUMMARYCivil engineering structures are often subjected to multidirectional actions such as earthquake ground motion, which lead to complex structural responses. The contributions from the latter multidirectional actions to the response are highly coupled, leading to a MIMO system identification problem. Compared with single‐input, multiple‐output (SIMO) system identification, MIMO problems are more computationally complex and error prone. In this paper, a new system identification strategy is proposed for civil engineering structures with multiple inputs that induce strong coupling in the response. The proposed solution comprises converting the MIMO problem into separate SIMO problems, decoupling the outputs by extracting the contribution from the respective input signals to the outputs. To this end, a QR factorization‐based decoupling method is employed, and its performance is examined. Three factors, which affect the accuracy of the decoupling result, including memory length, input correlation, and system damping, are investigated. Additionally, a system identification method that combines the autoregressive model with exogenous input (ARX) and the Eigensystem Realization Algorithm (ERA) is proposed. The associated extended modal amplitude coherence and modal phase collinearity are used to delineate the structural and noise modes in the fitted ARX model. The efficacy of the ARX‐ERA method is then demonstrated through identification of the modal properties of a highway overcrossing bridge. Copyright © 2013 John Wiley & Sons, Ltd.

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.

Response simulation and seismic assessment of highway overcrossings

AbstractInteraction of bridge structures with the adjacent embankment fills and pile foundations is generally responsible for response modification of the system to strong ground excitations, to a degree that depends on soil compliance, support conditions, and soil mass mobilized in dynamic response. This paper presents a general modeling and assessment procedure specifically targeted for simulation of the dynamic response of short bridges such as highway overcrossings, where the embankment soil–structure interaction is the most prevalent. From previous studies it has been shown that in this type of interaction, seismic displacement demands are magnified in the critical bridge components such as the central piers. This issue is of particular relevance not only in new design but also in the assessment of the existing infrastructure. Among a wide range of issues relevant to soil–structure interaction, typical highway overcrossings that have flexible abutments supported on earth embankments were investigated extensively in the paper. Simulation procedures are proposed for consideration of bridge‐embankment interaction effects in practical analysis of these structures for estimation of their seismic performance. Results are extrapolated after extensive parametric studies and are used to extract ready‐to‐use, general, and parameterized capacity curves for a wide range of possible material properties and geometric characteristics of the bridge‐embankment assembly. Using two instrumented highway overpasses as benchmark examples, the capacity curves estimated using the proposed practical procedures are correlated successfully with the results of explicit incremental dynamic analysis, verifying the applicability of the simple tools developed herein, in seismic assessment of existing short bridges. Copyright © 2009 John Wiley & Sons, Ltd.

Discussion of “Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings” by Sashi K. Kunnath, Emrah Erduran, Y. H. Chai, and Mark Yashinsky

Discussion of “Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings” by Sashi K. Kunnath, Emrah Erduran, Y. H. Chai, and Mark Yashinsky

Closure to “Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings” by Sashi K. Kunnath, Emrah Erduran, Y. H. Chai, and Mark Yashinsky

Closure to “Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings” by Sashi K. Kunnath, Emrah Erduran, Y. H. Chai, and Mark Yashinsky

Benchmark structural control problem for a seismically excited highway bridge-Part I: Phase I Problem definition

This paper presents the problem definition of the benchmark structural control problem for the seismically excited highway bridge. The benchmark problem is based on the newly constructed 91/5 highway over-crossing in southern California. The goal of this benchmark effort is to develop a standardized model of a highway bridge using which competing control strategies, including devices, algorithms and sensors, can be evaluated comparatively. To achieve this goal, a 3D finite-element model is developed in MATLAB to represent the complex behavior of the full-scale highway over-crossing. The nonlinear behavior of center columns and isolation bearings is considered in formulating the bilinear force–deformation relationship. The effect of soil–structure interaction is considered by modeling the interaction by equivalent spring and dashpot. The ground motions are considered to be applied simultaneously in two directions. A MATLAB-based nonlinear structural analysis tool has been developed and made available for nonlinear dynamic analysis. Control devices are assumed to be installed between the deck and the end abutments of the bridge. Evaluation criteria and control constraints are specified for the design of controllers. Passive, semi-active and active devices and algorithms can be used to study the benchmark model. The participants in this benchmark study are required to define their control devices, sensors and control algorithms, evaluate and report the results of their proposed control strategies. Copyright © 2009 John Wiley & Sons, Ltd.

Assessment and modeling of embankment participation in the seismic response of integral abutment bridges

The dynamic response and seismic performance of bridges may be appreciably affected by numerous contributing factors, with soil–structure interaction being the dominant exogenous influence. The most familiar form is the so-called soil–pile interaction, but embankment–abutment interaction is also documented through field observations and analytical investigations, particularly evident in integral R.C. bridges. Recent studies have shown that this form of interaction may significantly alter the bridge response and should be taken into account during design and assessment, especially in the case of typical highway overcrossings that have abutments supported on earth embankments. In light of this emerging problem and in order to facilitate quantitative estimates of the interaction effects, the question of appropriate modeling and seismic assessment of R.C. integral bridges is the main object of the present paper. Based on already established procedures to account for soil–structure interaction, a new approach is proposed to model the contribution of the embankment, the bent and the abutments to the overall bridge response. Furthermore, the capacity curve of the entire bridge system is evaluated through the implementation of Incremental Dynamic Analysis (IDA), therefore allowing for seismic assessment of the complex superstructure–foundation system with well established displacement based procedures. Using as a benchmark case two typical instrumented U.S. highway bridges located in California, the proposed method is implemented and provided results from this analysis are correlated successfully with available field data. Results obtained from the analysis indicate excessive displacement demands for the entire bridge–embankment system owing to the embankment contribution and the soil degradation under increasing shear strains. Furthermore, seismic performance is strongly related to the central bent deformation capacity, with soil–pile interaction effects being of critical importance.

Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings

Results of comprehensive nonlinear response history analyses on a range of configurations representing typical highway overcrossings subjected to combined effects of vertical and horizontal components of near-fault ground motions are reported. Current seismic design guidelines in California neglect the vertical components of ground motions for peak ground accelerations less than 0.6 g and provide rather simplistic measures to account for vertical effects when they need to be incorporated in the design. Results from the numerical simulations show that the vertical components of ground motions cause significant amplification in the axial force demand in the columns and moment demands in the girder at both the midspan and at the face of the bent cap. Axial capacity of the columns and moment capacity of the girder at the face of the bent cap were generally found to be sufficient to resist the amplification in the respective demands due to vertical effects. However, midspan moments in negative bending due to vertical motions are found to exceed the capacity of the girder. The amplified midspan moments lead to yielding of the top reinforcement resulting in average peak strains on the order of 1%. It is concluded that seismic demand analysis of ordinary highway bridges in general and overcrossings in particular should incorporate provisions for considering the adverse vertical effects of near-fault ground motions.

Seismic Analysis of Meloland Road Overcrossing Using Multiplatform Simulation Software Including SSI

A multiplatform simulation of a highway overcrossing bridge is introduced where the embankments, abutments, and pile groups are modeled in a powerful finite-element (FE) package with nonlinear soil material model while the bridge is modeled in another FE package that excels in fiber-based frame analysis. The Meloland Road Overcrossing Bridge, which is heavily instrumented, is selected as a reference analysis model due to the existence of measured data. The components as well as the integrated system are verified through comparison with previous studies and measured data. The stiffness of abutments and pile foundations are evaluated by three-dimensional finite-element analysis and compared with those from previous investigations. The analytical models of abutments and foundations are combined with the structural model using the multiplatform analysis framework, UI-SimCor. The dynamic properties of the model for multiplatform analysis are compared with those evaluated from system identification techniques using recorded ground motion. Finally, response history analyses are conducted with recorded free-field ground motion. The analysis results are in very good agreement with measured response showing the promising potential of multiplatform dynamic simulation.

Application of smart passive damping system using MR damper to highway bridge structure

Magnetorheological (i.e., MR) dampers are one of the most prospective semiactive control devices for civil engineering applications to earthquake hazard mitigation, because they have many advantages such as small power requirement, reliability, and low price to manufacture. A smart passive system based on an MR damper system without including a power supply, controller, and sensors consists of an MR damper and an electromagnetic induction (i.e., EMI) system that uses a permanent magnet and a coil. The electromotive force induced by movement of a structure can control MR damper effectively without any external power supply and control algorithm. This smart passive control system is implemented to verify the effectiveness for seismic protection of benchmark structural control problem for the seismically excited highway bridge, which is based on the newly constructed 91/5 highway over-crossing in Southern California. The results of the numerical simulations show that the presented control system can be beneficial in reducing seismic responses of benchmark bridge structure.

Structural Characterization of Modern Highway Overcrossings—Case Study

This paper revisits the mechanical characterization of the main substructure elements of highway overcrossings in an effort to build a more balanced methodology to compute the earthquake response of seismically protected bridges accounting for the effects of soil–structure interaction. Various macroscopic constitutive laws that are well known in literature are summarized and synthesized in a way that can be incorporated in reduced-order stick models used in practice. Here, we discuss the required sophistication level of the proposed macroscopic constitutive laws in order to capture the leading mechanical behavior of each substructural element without adding unnecessary complications when incorporated in a stick model idealization of the bridge.

Seismic Response Analysis of a Highway Overcrossing Equipped with Elastomeric Bearings and Fluid Dampers

This paper presents a case study on the seismic response of a recently constructed freeway overcrossing located in southern California, which is equipped with elastomeric bearings and fluid dampers at its end abutments. The analysis employs the substructure method and a reduced order stick model. The macroscopic constitutive laws of the springs and dashpots that approximate the mechanical behavior of approach embankments, pile foundations, center bent, abutments, elastomeric bearings, and fluid dampers are established in the companion paper. The paper presents an in-depth analysis of the seismic response of the bridge equipped with the response modification devices accounting for the effects of soil–structure interaction. The various response quantities presented are compared with the corresponding response quantities of a hypothetical bridge with integral abutments. Advantages and challenges in the two design configurations are identified and discussed.

Seismic response analysis of highway overcrossings including soil–structure interaction

AbstractThis paper presents a systematic procedure for the seismic response analysis of highway overcrossings. The study employs an elementary stick model and a more sophisticated finite element formulation to compute response quantities. All dynamic stiffnesses of approach embankments and pile groups are approximated with frequency‐independent springs and dashpots that have been established elsewhere. A real eigenvalue analysis confirms the one‐to‐one correspondence between modal characteristics obtained with the three‐dimensional finite element solutions and the result of the simpler stick‐model idealization. A complex eigenvalue analysis yields modal damping values in the first six modes of interest and shows that modal damping ratios assume values much higher than those used by Caltrans. The validity of the proposed method is examined by comparing the computed time response quantities with records from the Meloland Road and Painter Street overcrossings located in southern and northern California, respectively. The proposed procedure allows for inexpensive parametric analysis that examines the importance of considering soil–structure interaction at the end abutments and centre bent. Results and recommendations presented by past investigations are revisited and integrated in comprehensive tables that improve our understanding of the dynamic characteristics and behaviour of freeway overcrossings. The study concludes with a step‐by‐step methodology that allows for a simple, yet dependable dynamic analysis of freeway overcrossings, that involves a stick model and frequency‐independent springs and dashpots. Copyright © 2002 John Wiley & Sons, Ltd.

Kinematic response functions and dynamic stiffnesses of bridge embankments

AbstractRecognizing that soil–structure interaction affects appreciably the earthquake response of highway overcrossings, this paper compares approximate analytical solutions and finite element results to conclude on a simple procedure that allows for the estimation of the kinematic response functions and dynamic stiffnesses of approach embankments. It is shown that the shear‐wedge model yields realistic estimates for the amplification functions of typical embankments and reveals the appropriate levels of dynamic strains which are subsequently used to estimate the stiffness and damping coefficients of embankments. The shear‐wedge model is extended to a two‐dimensional model in order to calculate the transverse static stiffness of an approach embankment loaded at one end. The formulation leads to a sound closed‐form expression for the critical length, Lc, that is the ratio of the transverse static stiffness of an approach embankment and the transverse static stiffness of a unit‐width wedge. It is shown through two case studies that the transverse dynamic stiffness (‘spring’ and ‘dashpot’) of the approach embankment can be estimated with confidence by multiplying the dynamic stiffness of the unit‐width wedge with the critical length, Lc. The paper concludes that the values obtained for the transverse kinematic response function and dynamic stiffness can also be used with confidence to represent the longitudinal kinematic response function and dynamic stiffness, respectively. Copyright © 2002 John Wiley & Sons, Ltd.