Analysis of Traffic-Induced Vibrations in a Cable-Stayed Bridge. Part II: Numerical Modeling and Stochastic Simulation

This paper describes the development of a numerical model to simulate the dynamic response of the bridge–vehicle system of Salgueiro Maia cable-stayed bridge, using the results from an extensive experimental investigation to calibrate this model. Further, a set of stochastic Monte Carlo simulations of the bridge–vehicle dynamic response is also presented, with the purpose of evaluating dynamic amplification factors, taking into account the randomness of different factors associated to characteristics of the pavement, of the vehicles and of the traffic flow.     

Analysis of Traffic-Induced Vibrations in a Cable-Stayed Bridge. Part I: Experimental Assessment

This paper characterizes the experimental approach used for the evaluation of traffic-induced dynamic effects in Salgueiro Maia cable-stayed bridge. It presents the most significant results obtained both in terms of the static load tests developed at the commissioning phase, and of the dynamic tests under controlled heavy traffic. These tests were specifically conducted for the evaluation of dynamic amplification factors considering the passage of heavy trucks isolated or in groups, along several lanes and at different speeds. Furthermore, the experimental characterization of the random characteristics of the pavement roughness, using an appropriate spatial laser scanning measurement system, is referred.     

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.     

Neural Networks for Decentralized Control of Cable-Stayed Bridge

The system identification and vibration control of a cable-stayed bridge are considered difficult to achieve due to the bridge’s structural complexity and system uncertainties. In this paper, based on the concept of decentralized information structures, a decentralized, nonparametric identification and control algorithm with neural networks is proposed for the purpose of suppressing the vibration of a documented six-cable-stayed bridge model induced by earthquake excitations. The control strategy proposed here uses the stay cables as active tendons to provide control forces through appropriate actuators. Each individual actuator is controlled by a decentralized neurocontroller that only uses local information. The feature of decentralized control simplifies the implementation of the control algorithms and makes decentralized control easy to practice and cost effective. The effectiveness of the decentralized identification and control algorithm based on neural networks is evaluated through numerical simulations. And the adaptability of the decentralized neurocontrollers for different kinds of earthquake excitations and for a damaged cable-stayed bridge model is demonstrated via numerical simulations.     

Feasibility of a 1,400 m Span Steel Cable-Stayed Bridge

This paper describes the feasibility of 1,400 m steel cable-stayed bridges from both structural and economic viewpoints. Because the weight of a steel girder strongly affects the total cost of the bridge, the writers present a procedure to obtain a minimum weight for a girder that ensures safety against static and dynamic instabilities. For static instability, elastoplastic, finite-displacement analysis under in-plane load and elastic, finite-displacement analysis under displacement-dependent wind load are conducted; for dynamic instability, multimodal flutter analysis is carried out. It is shown that static critical wind velocity of lateral torsional buckling governs the dimension of the girder. Finally, the writers briefly compare a cable-stayed bridge with suspension bridge alternatives.     

Sliding Mode Control of Cable-Stayed Bridge Subjected to Seismic Excitation

The working group on bridge control within the ASCE Committee on Structural Control recently initiated a first-generation benchmark problem addressing the control of a cable-stayed bridge subjected to seismic excitation. Previous research examined the applicability of a LQG-based semiactive control system using magnetorheological (MR) dampers to reduce the structural response of the benchmark bridge and confirmed the capability of the MR damper-based system for seismic response reduction. In this paper, sliding mode control (SMC) is applied in lieu of the LQG formulation to the benchmark bridge problem. The performance and robustness of the SMC-based semiactive control system using MR dampers (SMC/MR) is investigated through a series of numerical simulations, and it is confirmed that SMC/MR can be very effectively applied to the benchmark cable-stayed bridge, subjected to a wide range of seismic loading conditions.     

Geometrically Nonlinear Buffeting Response of a Cable-Stayed Bridge

A geometrically nonlinear buffeting analysis of a cable-stayed bridge in the time domain is described. The bridge structure is modeled with three-dimensional thin-walled beam elements and three-dimensional elastic catenary cable elements. Spatially correlated wind velocity fluctuations are modeled and simulated using an algorithm for generating sample functions of a stationary, multivariate stochastic process according to its prescribed cross-spectral density matrix. Aerodynamic damping and aerodynamic stiffness are formulated based on experimentally determined flutter derivatives. The focus of this paper is on the effect of fluctuating components of the spatially correlated wind velocity on the geometrically nonlinear buffeting response for an 870 m cable-stayed bridge.     

Lessons Learned from the Damaged Chi-Lu Cable-Stayed Bridge

A disastrous earthquake struck central Taiwan at 01:47 a.m. September 21, 1999 (Taiwan local time). The Seismology Center of the Central Weather Bureau (CWB) determined the magnitude of this earthquake to be ML 7.3 (CWB) and MW 7.7 (Harvard CMT). The earthquake caused heavy casualties and structural damage to bridges and buildings. In the damaged areas, the only cable-stayed bridge, the Chi-Lu, was in the final stages of completion at the time of the earthquake. This bridge connected Chi-Chi to the small town of Lu-Ku across the Juoshuei River. Viaducts ran from both banks of the river to the ends of the cable-stayed bridge. The bridge, designed by T. Y. Lin International, was supported on a single pylon, which was connected to the center of the roadway by two rows of cables. In this paper, the damage suffered by the Chi-Lu bridge is reported. Severe damage occurred in the deck on the southern side of the bridge. Additional damage occurred in the pylon. Below the roadway, the pylon showed evidence of only minor cracking. However, above the roadway there was severe spalling of the cover and a crack extended upward nearly to the level of the lowest cables. The seismic performance of the bridge was evaluated by computer modeling. The damage predicted by the computational results was compared to that sustained by the bridge. The lessons learned from this study are described.     

In-Service Evaluation of Cable-Stayed Bridges, Overview of Available Methods and Findings

This paper discusses advances in evaluation and health monitoring of cable-stayed bridges and available methods. Bridge engineers and highway administrators in the United States are gradually becoming more comfortable with cable-stayed bridges, and the past few years have seen a significant increase in construction of these elegant bridges in many parts of this great nation. In the last decade, several investigations have been directed to condition assessment of cable-stayed bridges and contributed extensively to advances in construction, design, and health monitoring of this type of structures. Results of these investigations have helped toward formation of a unified approach for in-service evaluation and problem solving of these aesthetic structures. This paper describes this approach with reference to sources for more detailed information. Additionally, discussed in this paper are a series of methods developed or tailored for evaluation of these unique structures. The paper also reviews the typical problems observed in the course of field evaluations for in-service cable-stayed bridges.     

Wavelet-Hybrid Feedback Linear Mean Squared Algorithm for Robust Control of Cable-Stayed Bridges

Cable-stayed bridges are flexible structures, and control of their vibrations is an important consideration and a challenging problem. In this paper, the wavelet-hybrid feedback least mean squared algorithm recently developed by the writers is used for vibration control of cable-stayed bridges under various seismic excitations. The effectiveness of the algorithm is investigated through numerical simulation using a benchmark control problem created based on an actual semifan-type cable-stayed bridge design. The performance of the algorithm is compared with that of a sample linear quadratic Gaussian (LQG) controller using three different earthquake records: the El Centro (California, 1940), Mexico City (Mexico, 1985), and Gebze (Turkey, 1999) earthquakes. Simulation results demonstrate that the new algorithm is consistently more effective than the sample LQG controller for all three earthquake records. Additional numerical simulations are performed to evaluate the sensitivity of the new control algorithm. It is concluded that the algorithm is robust against the uncertainties existing in modeling structures.     

Optimization of Cable Tensioning in Cable-Stayed Bridges

During the structural analysis of cable-stayed bridges, some specific problems arise that are not common in other types of bridges. One of these problem is the derivation of an optimal sequence for the tensioning of the stay cables. This paper describes a novel solution to this problem, the unit force method. The method takes into account all relevant effects for the design of cable-stayed bridges, including construction sequence, second-order theory, large displacements, cable sag and time-dependent effects, such as creep and shrinkage or relaxation of prestressing tendons. Information about the implementation of this method into a computer program is given, and an example of a practical application of this method concludes this paper. The method is not restricted to the design of cable-stayed bridges and may well be used for other structural applications in the future.     

Applicability of 4D CAD in Civil Engineering Construction: Case Study of a Cable-Stayed Bridge Project

Four-dimensional (4D) computer-aided design (CAD) has been credited with improving construction planning procedures. The integration of three-dimensional CAD with schedule information has enabled the effective detection of design and planning flaws in many construction projects. However, the benefit of 4D CAD has been centered on architectural constructions, as other areas such as civil infrastructure have seldom been the target of 4D CAD application. This paper presents a case study in which a cable-stayed bridge construction was analyzed and modeled using the 4D graphic simulation approach. The cable-stayed bridge was chosen for the case study because it suitably represents the complex nature of modern civil infrastructure. 4D CAD models were developed at three different levels of detail: activity, discrete operation, and continuous operation. The clear definitions of the three levels of detail of 4D CAD and their application results for the cable-stayed bridge are presented herein.     

Constructability Concepts in Kuala Selangor Cable-Stayed Bridge in Malaysia

The writers formulated a case study of the Kuala Selangor Cable Stayed Bridge to examine the application of the constructability concepts particularly during the conceptual planning and the design phases of the project. This paper presents the advantages of implementing the constructability concepts and the barriers that were encountered when applying these concepts during the planning and design phases of the cable stayed bridge project of Kuala Selangor in Malaysia. The writers concluded that barriers to constructability implementation that are related to the owner were the major impediments in the application of constructability concepts during the early conceptual planning phase. The opinion of the engineer was another factor behind nonapplication of some other concepts. At the same time, many others were implemented due to the awareness and opinion of the engineer and his ability to control their application.     

Design and Experimental Study of a Harp-Shaped Single Span Cable-Stayed Bridge

This paper presents issues in the design concept, analysis, and test results of a harp-shaped single span cable-stayed bridge, Hongshan Bridge, located in Changsha, Hunan Province, China. The bridge has a 206 m span, with a pylon inclined at 58° from the horizontal and 13 pairs of parallel cable stays without a back?stay. This paper discusses the design approach for the main components of the bridge. Emphasis will be put on the following three aspects. First, the weight of the pylon and all dead loads of the main girder in addition to part of the live loads must be in a balanced condition. Second, the main girder should be an orthotropic steel-concrete composite box girder because of the superior safety and weight reduction of this type of structure. Third, the cable?stays should be anchored at the neutral axis of the pylon to prevent the development of high secondary moments caused by other anchor approaches. Furthermore, based on results from tests carried out on three models, namely, scaled full model tests in a scale of 1:30, scaled section model tests in a scale of 1:6, and wind tunnel tests, the following four key issues were studied: (1) the local stability of orthotropic steel-concrete composite box girder subjected to combined bending and axial loads; (2) the characteristics under loads of 13-m-long cantilever beams; (3) the safety of the bridge under some other dangerous conditions; and (4) the characteristics of wind resistance and wind tunnel testing.     

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.     

Life-Cycle Cost Analysis using Deterministic and Stochastic Methods: Conflicting Results

Life-cycle cost analysis is an essential approach to differentiating alternative rehabilitation strategies for steel bridge paint systems. An economic analysis (EA), which is a deterministic method, and the Markov decision process (MDP), which is a stochastic method, were used to carry out the life-cycle cost analysis. These analyses were applied to data from two state Departments of Transportation. The deterioration curves for steel bridge paint condition rating against age were constructed. Different rehabilitation scenarios were proposed for steel bridge paint. The EA and the MDP were used to analyze and differentiate among the proposed rehabilitation scenarios. The results of the EA were different from those of MDP for the two data sets. MDP favored the “do nothing” scenario until the end of paint life and then a complete repainting. EA indicated that the scenario “do spot repairs at state 3 of the paint life” and repeat that until the end of the bridge life was superior. The results were analyzed to determine the reason for the conflict.     

Combined Damping Effect of Two Dampers on a Stay Cable

The combined effect of two dampers, either on the same end or opposite ends of a stay cable, is analytically studied in this paper. By considering small distances of the dampers from the anchorages, an asymptotic formula for the modal damping ratio of the cable is derived from which the total damping effect is presented in an explicit form. It is shown that when two dampers are installed at opposite ends of the cable, the total damping effect is asymptotically the sum of the contributions from single dampers. On the contrast, if two dampers are at the same end, there is no advantage of increasing the maximum modal damping in the cable over the use of a single damper.     

Reliability-Based Optimum Design of Glulam Cable-Stayed Footbridges

This work presents a procedure for finding the reliability-based optimum design of cable-stayed bridges. The minimization problem is stated as the minimization of stresses, displacements, reliability, and bridge cost. A finite-element approach is used for structural analysis. It includes a direct analytic sensitivity analysis module, which provides the structural behavior responses to changes in the design variables. An equivalent multicriteria approach is used to solve the nondifferential, nonlinear optimization problem, turning the original problem into sequential minimization of unconstrained convex scalar functions, from which a Pareto optimum is obtained. Examples are given illustrating the procedure.     

Dynamic Testing for Structural Identification of a Bridge

Structural identification via modal analysis in structural mechanics is gaining popularity in recent years, despite conceptual difficulties connected with its use. This paper is devoted to illustrating the advantages and also the indeterminacy characterizing structural identification problems for bridge structures, even in rather simple instances. In particular, an identification procedure based on modal analysis and finite-element model updating is presented for the characterization of a concrete bridge whose constructive typology is quite diffuse in the area of Friuli Venezia Giulia, Italy. Experience has suggested (so as to restrict the indeterminacy frequently affecting identification issues) resorting to all the a priori information on the system and mindfully selecting the parameters to be identified. The analysis pointed out some particularities in the modeling of bridge typology under study, otherwise not a priori detectable from an analytical point of view.     

Corrosion and Embrittlement in High-Strength Wires of Suspension Bridge Cables

An in-depth analysis of the deterioration mechanisms in high-strength wires of suspension bridge cables is presented. Accelerated cyclic corrosion tests were conducted to assess the relative effect of corrosion on galvanized and ungalvanized wires. Samples were corroded under various levels of sustained loads in a cabinet that cyclically applied an acidic salt spray, dry conditions, and 100% relative humidity at elevated temperature, and mass loss, hydrogen concentration, ultimate load, and elongation at failure were measured. Elongation measurements indicated a significant embrittlement of the wires that could not be explained solely by the presence of absorbed hydrogen (hydrogen embrittlement). The main cause of reduction of wire elongation was found to be the surface irregularities induced by the corrosion process. The experimental results were validated through a numerical analysis using a finite-element method model of the corroded steel wire and through a series of scanning electron microscope analyses of the fracture surfaces.