Finite-Element Model Updating for the Kap Shui Mun Cable-Stayed Bridge

This paper presents the implementation of the finite-element model updating for the Kap Shui Mun Bridge, a 430 m main span double-deck cable-stayed bridge in Hong Kong. The dynamic characteristics of the bridge have been studied through both three-dimensional finite-element prediction and field vibration measurement previously. In this paper, the developed finite-element model is updated based on the field measured dynamic properties. A comprehensive sensitivity study to demonstrate the effects of various structural parameters (including the connections and boundary conditions) on the modes of concern is first performed, according to which a set of structural parameters are then selected for adjustment. The finite-element model is updated in an iterative fashion so as to minimize the differences between the predicted and the measured natural frequencies. The final updated finite-element model for the Kap Shui Mun Bridge is able to produce natural frequencies in good agreement with the measured ones, and can be helpful for a more precise dynamic response prediction.     

Dynamic Analysis of a Composite Cable-Stayed Bridge: Escaleritas Viaduct

This work describes some of the most important results of the experimental and numerical analyses of Escaleritas Viaduct, Spain. Before the inauguration of this composite cable-stayed bridge in 2006, the bridge authority required a dynamic load test identifying, for instance, the natural vibration modes, the dynamic magnification factor, and the maximum vertical acceleration. The dynamic test was accompanied by numerical simulation performed in two different three-dimensional finite-element models, one of them composed of 145,000 shell elements. The correlation of test and analysis data is good and allows several interesting general conclusions to be drawn. It is shown that Escaleritas Viaduct complies with the requirements on the dynamic structural behavior defined in the standards.     

Output-Only System Identification of Posttensioned Segmental Concrete Highway Bridges

This paper discusses the application of system identification of a highway bridge using finite-element method and ambient-vibration testing. The posttensioned Gülburnu Highway Bridge located on the Giresun-Espiye state highway was selected as a case study. A finite-element model of the bridge was developed using SAP2000 software, and dynamic characteristics were obtained analytically. During the test, sources of ambient excitations were provided by the traffic effects over the bridge. Ambient-vibration tests were applied to the bridge to identify dynamic characteristics. The selection of measurement time, frequency span, and effective mode number was considered from similar studies in the literature. Two output-only system identification methods, enhanced frequency domain decomposition and stochastic subspace identification, were used to estimate the dynamic characteristics of the bridge experimentally. The accuracy and efficiency of both methods were investigated and compared with finite-element results. Results suggest that ambient-vibration measurements are sufficient to identify structural modes with a low range of natural frequencies. In addition, the dynamic characteristics obtained from the finite-element model of the bridge have a good correlation with experimental frequencies and mode shapes.     

Model Updating of Semirigid Jointed Structure Using Generic Parameters

Semirigid connections are usually found in large-scale engineering structures, and the knowledge of the dynamic characteristics of these connections is important to the accurate definition of the dynamic characteristics of the engineering structure. Different models have been presented to define the connection, but most of them are not suitable for model improvement from dynamic measurements of the structure. This paper presents a hybrid finite-element model that consists of a beam element with two semirigid connections at the ends for updating the finite-element model of the jointed structure. The parameter selection strategy of the generic element is adopted, and the stiffnesses of the joint in three dimensions are selected as generic parameters to be updated simultaneously with other structural parameters of the structure. The proposed method is applied to the model updating of a 3D steel truss in the laboratory. Results show that the method could improve significantly not only those vibration modes used in the updating but also the higher modes with a maximum error of 6%.     

Finite-Element Analysis and Vibration Testing of a Two-Span Masonry Arch Bridge

This paper presents the analytical modeling, modal testing, and finite-element model updating for a two-span masonry arch bridge. An Ottoman masonry arch bridge built in the 19th century and located at Camlihemsin, Rize, Turkey is selected as an example. Analytical modal analysis is performed on the developed 3D finite-element model of the bridge to obtain dynamic characteristics. The ambient vibration tests are conducted under natural excitation such as human walking. The operational modal analysis is carried out using peak picking method in the frequency domain and stochastic subspace identification method in the time domain, and dynamic characteristics (natural frequencies, mode shapes, and damping ratios) are determined experimentally. Finite-element model of the bridge is updated to minimize the differences between analytically and experimentally estimated dynamic characteristics by changing boundary conditions. At the end of the study, maximum differences in the natural frequencies are reduced on average from 18 to 7% and a good agreement is found between analytical and experimental dynamic characteristics after finite-element model updating.     

Vibration Characteristics of K?mürhan Highway Bridge Constructed with Balanced Cantilever Method

K?mürhan Highway Bridge is a reinforced concrete box girder bridge located on the 51st km of Elaz??–Malatya Highway over the F?rat River. Because of the fact that the K?mürhan Bridge is the only bridge in this part of F?rat, it has major logistical importance. So, this paper aims to determine dynamic characteristics such as natural frequencies, mode shapes, and damping ratios of the bridge using experimental measurements and finite-element analyses to evaluate current behavior. The experimental measurements are carried out by ambient vibration tests under traffic loads. Due to the expansion joint in the middle of the bridge, special measurement points are selected and experimental test setups are constituted. Vibration data are gathered from the both box girder and bridge deck. Measurement time, frequency span, and effective mode number are determined by considering similar studies and literature. The peak picking method in the frequency domain is used for the output-only modal identification. An analytical modal analysis is performed on the developed two- and three-dimensional finite-element model of the bridge using SAP2000 software to provide the analytical frequencies and mode shapes. At the end of the study, dynamic characteristics of the Elaz?? and Malatya parts of the bridge obtained from the experimental measurements are compared with each other and transverse effects on the bridge are determined. Also, experimental and analytical dynamic characteristics are compared. Good agreement is found between dynamic characteristics in the all measurement test setups performed on the box girder and bridge deck and analytical modal analyses.     

Field Static Load Test on Kao-Ping-Hsi Cable-Stayed Bridge

Field load testing is an effective method for understanding the behavior and fundamental characteristics of a cable-stayed bridge. This paper presents the results of field static load tests on the Kao-Ping-Hsi cable-stayed bridge, the longest cable-stayed bridge in Taiwan, before it was open to traffic. A total of 40 loading cases, including the unit and distributed bending and torsion loading effects, were conducted to investigate the bridge behavior. The atmospheric temperature effect on the variations of the main girder deflections was also monitored. The results of static load testing include the main girder deflections, the flexural strains of the prestressed concrete girder, and the variations of the cable forces. A three-dimensional finite-element model was developed. The results show that the bridge under the planned load test conditions has linear superposition characteristics and the analytical model shows a very good agreement with the bridge responses. Further discussion of deflection and cable forces of the design specifications for a cable-stayed bridge is also presented.     

Field Load Tests and Numerical Analysis of Qingzhou Cable-Stayed Bridge

A field load test is an essential way to understand the behavior and fundamental characteristics of newly constructed bridges before they are allowed to go into service. The results of field static load tests and numerical analyses on the Qingzhou cable-stayed bridge (605?m central span length) over the Ming River, in Fuzhou, China are presented in the paper. The general test plan, tasks, and the responses measured are described. The level of test loading is about 80–95% of the code-specified serviceability load. The measured results include the deck profile, deck and tower displacements, and stresses of steel-concrete composite deck. A full three-dimensional finite-element model is developed and calibrated to match the measured elevations of the bridge deck. A good agreement is achieved between the experimental and analytical results. It is demonstrated that the initial equilibrium configuration of the bridge plays an important role in the finite-element calculations. Both experimental and analytical results have shown that the bridge is in the elastic state under the planned test loads, which indicates that the bridge has an adequate load-carrying capacity. The calibrated finite-element model that reflects the as-built conditions can be used as a baseline for health monitoring and future maintenance of the bridge.     

Monitoring and Analysis of a Bridge with Partially Restrained Bearings

This paper reports on the monitoring and analysis of a two-span bridge in which the bearings were partially restrained. In an earlier experimental study, it was shown that the natural frequencies changed in colder weather, and it appeared that this was due to restraints in the end bearings. This research was conducted to verify this initial conclusion and to develop an analytical approach based on the finite-element method to model this change. Additional field measurements were made. The nonlinear dynamic finite-element analysis is based on a planar model that includes the influence of both the deck cracking and the eccentric axial forces, which develop when the bearings are restrained. Both the flexural and the torsional modes are evaluated. Although the changes in the bearings and the overall structural behavior were relatively small, the results show that it was nevertheless possible to verify the changes with a nonlinear dynamic finite-element analysis calibrated with field measurements.     

Dynamic Field Test, System Identification, and Modal Validation of an RC Minaret: Preprocessing and Postprocessing the Wind-Induced Ambient Vibration Data

The investigation of dynamic response for civil engineering structures largely depends on a detailed understanding of their dynamic characteristics, such as the natural frequencies, mode shapes, and modal damping ratios. Dynamic characteristics of structures may be obtained numerically and experimentally. The finite-element method is widely used to model structural systems numerically. However, there are some uncertainties in numerical models. Material properties and boundary conditions may not be modeled correctly. There may be some microcracks in the structures, and these cracks may directly affect the modeling parameters. Modal testing gives correct uncertain modeling parameters that lead to better predictions of the dynamic behavior of a target structure. Therefore, dynamic behavior of special structures, such as minarets, should be determined with ambient vibration tests. The vibration test results may be used to update numerical models and to detect microcracks distributed along the structure. The operational modal analysis procedure consists of several phases. First, vibration tests are carried out, spectral functions are produced from raw measured acceleration records, dynamic characteristics are determined by analyzing processed spectral functions, and finally analytical models are calibrated or updated depending on experimental analysis results. In this study, an ambient vibration test is conducted on the minaret under natural excitations, such as wind effects and human movement. The dynamic response of the minaret is measured through an array of four trixial force-balanced accelerometers deployed along the whole length of the minaret. The raw measured data obtained from ambient vibration testing are analyzed with the SignalCAD program, which was developed in MATLAB. The employed system identification procedures are based on output-only measurements because the forcing functions are not available during ambient vibration tests. The ModalCAD program developed in MATLAB is used for dynamic characteristic identification. A three-dimensional model of the minaret is constructed, and its modal analysis is performed to obtain analytical frequencies and mode shapes by using the ANSYS finite-element program. The obtained system identification results have very good agreement, thus providing a reliable set of identified modal properties (natural frequencies, damping ratios, and mode shapes) of the structure, which can be used to calibrate finite-element models and as a baseline in health monitoring studies.     

Dynamic Tests on Large Cable-Stayed Bridge

This paper describes the dynamic tests performed on a large cable-stayed bridge, Vasco da Gama Bridge, on the basis of a nonconventional testing system, comprehending several independent accelerographs conveniently synchronized by a laptop, as well as a laser interferometry system for noncontact dynamic measurements in stay cables. This system showed to be rather portable, efficient, and accurate, leading to the creation of a very large high quality database concerning the dynamic behavior of the bridge. Subsequent processing of the data permitted accurate identification of all the significant modal parameters of interest from the aerodynamic and seismic point of view and presented a very good correlation with the corresponding values provided by the 3D numerical finite-element model previously developed at the design stage.     

Finite-Element Model Tuning of Global Modes of a Grandstand Structure Using Ambient Vibration Testing

This paper describes the experimental and analytical modal analysis of a full-scale cantilevered grandstand. A 3D finite-element model was successfully updated manually based on the global modes identified from ambient vibration measurements. The ambient vibration testing was effective in capturing the global modes of the large grandstand. A number of global vibration modes of the entire grandstand were reliably identified in the frequency range 0–3.1 Hz, in addition to modes in the same frequency range that engaged primarily the cantilever roof structure. Following a two-stage manual FE model updating process, the correlation between the experimental and analytical results showed good agreement, with physically meaningful updated parameters. It was clearly illustrated that both the roof system and the nonstructural elements contributed significantly to the stiffness and mass of the global modes. Useful and novel lessons are highlighted for efficient and reliable future finite-element modeling of global modes of similar grandstand structures.     

Roebling Suspension Bridge. I: Finite-Element Model and Free Vibration Response

This first part of a two-part paper on the John A. Roebling suspension bridge (1867) across the Ohio River is an analytical investigation, whereas Part II focuses on the experimental investigation of the bridge. The primary objectives of the investigation are to assess the bridge’s load-carrying capacity and compare this capacity with current standards of safety. Dynamics-based evaluation is used, which requires combining finite-element bridge analysis and field testing. A 3D finite-element model is developed to represent the bridge and to establish its deformed equilibrium configuration due to dead loading. Starting from the deformed configuration, a modal analysis is performed to provide the frequencies and mode shapes. Transverse vibration modes dominate the low-frequency response. It is demonstrated that cable stress stiffening plays an important role in both the static and dynamic responses of the bridge. Inclusion of large deflection behavior is shown to have a limited effect on the member forces and bridge deflections. Parametric studies are performed using the developed finite-element model. The outcome of the investigation is to provide structural information that will assist in the preservation of the historic John A. Roebling suspension bridge, though the developed methodology could be applied to a wide range of cable-supported bridges.     

Control of Seismically Excited Cable-Stayed Bridge Using Resetting Semiactive Stiffness Dampers

Cable-stayed bridges are prone to exhibit large amplitude oscillations because of their large flexibility, small mass, and small inherent damping. Hence, the reduction of seismic or wind-induced vibration of cable-stayed bridges is vital for their safety and serviceability. In this paper, a resetting semiactive stiffness damper (RSASD) is used to control the peak dynamic response of a recently developed benchmark problem on a cable-stayed bridge subject to earthquakes. The model of the benchmark cable-stayed bridge is based on the actual cable-stayed bridge that is under construction on Cape Girardeau, Mo. The prime aim of this study is to investigate the application of protective devices, such as semiactive and passive dampers, in reducing the displacement of the deck as well as base shear and moments at the base of the towers. In this research, the applications of the RSASD as well as passive viscous and fluid dampers to the benchmark bridge problem have been investigated. Numerical simulations are conducted by installing RSASD devices as well as passive viscous and friction dampers between the pier and the deck of the bridge. Numerical results clearly indicate that the displacement of the deck, and shear and moments at the base of the towers, are reduced substantially by installing these protective devices. In particular, energy dissipating capabilities and performance of the RSASD are quite remarkable. It is shown that the RSASD is quite effective in reducing peak response quantities of the bridge to a level similar to that of the sample active controller. A further reduction in response quantities can be achieved by using the RSASD in a combination of passive viscous dampers.     

Refined Stick Model for Dynamic Analysis of Skew Highway Bridges

Stick models are widely employed in the dynamic analysis of bridges when only approximate results are desired or when detailed models are difficult or time-consuming to construct. Although the use of stick models for regular bridges has been validated by various researchers, the application of such models to skew highway bridges continues to present challenges. The conventional single-beam stick model used to represent the bridge deck often fails to capture certain predominant vibration modes that are important in obtaining the true dynamic response of the bridge. In this paper, a refined stick model is proposed for the preliminary dynamic analysis of skew bridges. The model utilizes a dual-beam stick representation of the bridge deck. The validity of the model is established by comparing results obtained from the proposed model with numerical solutions obtained for skew plates and a skew bridge. It is shown that this dual-beam stick model is superior to the conventional single-beam model in estimating the natural vibration frequencies and in predicting the predominant vibration modes of the bridge. Because of its simplicity and relative accuracy, this model is recommended for the preliminary dynamic analysis of skew highway bridges.     

Three-Dimensional Analyses of Wave Barriers for Reduction of Train-Induced Vibrations

This paper explores the use of a three-dimensional finite-element analysis to model soil vibrations due to high-speed trains on bridges. Finite-element meshes include the bridge superstructure, bridge foundations, nearby building foundations, and piles. Wheel elements represented by appropriate mass, damping and stiffness factors were used to simulate a moving high-speed train. Along the mesh boundaries, absorbing boundary conditions were employed to avoid fictitious wave reflections. Isolation methods to reduce soil vibrations were investigated including construction of open and infilled trenches and soil improvement. Vibration isolation effects due to building foundations and piles were also studied. The finite-element results indicate that suitable axial stiffness between two simple beams can reduce vibration significantly, especially at a near-resonance condition. Operating with an appropriate train velocity to avoid resonance can be another way to reduce vibrations. Suitable mat foundations can significantly reduce soil horizontal vibration, but cannot isolate vertical vibration. Soil improvements near the bridge do not effectively attenuate low-frequency vibrations. Infilled and open trenches can isolate soil vertical vibration; however, their efficiency seems disproportionate to their cost.     

Challenges in the Application of Stochastic Modal Identification Methods to a Cable-Stayed Bridge

This paper presents an analysis of the data collected in the ambient vibration test of the International Guadiana cable-stayed Bridge, which links Portugal and Spain, based on different output-only identification techniques: peak-picking, frequency domain decomposition, covariance-driven stochastic subspace identification, and data-driven stochastic subspace identification. The purpose of the analysis is to compare the performance of the four techniques and evaluate their efficiency in dealing with specific challenges involved in the modal identification of the tested cable-stayed bridge, namely the existence of closely spaced modes, the perturbation produced by the local vibration of stay-cables, and the variation of modal damping coefficients with wind velocity. The identified natural frequencies and mode shapes are compared with the corresponding modal parameters provided by a previously developed numerical model. Additionally, the variability of some modal damping coefficients is related with the variation of the wind characteristics and associated with a component of aerodynamic damping.     

Evaluation of Viscous Dampers for Stay-Cable Vibration Mitigation

Many cable-stayed bridges around the world have displayed excessive and unanticipated vibrations of the main stays, often associated with the simultaneous occurrence of wind and rain, and mitigation of these vibrations has become a significant concern in cable-stayed bridge design and retrofit. Much of the previous research on this problem has been conducted using wind tunnels, and there have been relatively few opportunities to measure the vibrations at full-scale. This paper presents results from long-term field measurements of cable vibrations on a cable-stayed bridge in the United States. Characteristics of different types of measured vibrations are summarized, and the effectiveness of passive linear dampers in vibration suppression is evaluated by comparing response statistics from two stays before and after installation of dampers and by investigating in detail the damper performance in a few selected records corresponding to different types of excitation. The dampers are observed to be quite effective, but a fundamental limitation of mode-dependence in linear damper performance is emphasized, and some potential advantages offered by a nonlinear damper are discussed.     

Influence of Deck Material on Response of Cable-Stayed Bridges to Live Loads

During the last three decades, cable-stayed bridges have proven to be first-class structures providing vital transport links. Together with the construction process, erection procedure, and site conditions, the choice of material for the deck is a principal factor in the overall cost of construction. The effects of variable long-span bridge loads on the design of steel, composite, and concrete decks are investigated. Recent American and British long-span bridge loads have been used that are based on direct observations of modern traffic conditions. The three-dimensional finite-element models prepared for the study are based on the geometric and material properties of the Quincy Bayview cable-stayed bridge. Many cable arrangements are considered for the studied concrete, composite, and steel decks. A nonlinear analysis of the cable-stayed bridge models is carried out. The results of the different deck materials are compared. It is shown that the choice of material for the deck can be greatly affected by the distribution of stays and by the intensity of the live load adopted.