Journal of Bridge Engineering

Creep, shrinkage, and temperature drops will shorten the main girder and create additional internal forces in the piers of continuous rigid-frame bridges. Horizontal jacking forces can be applied at the ends of a closure segment before casting to improve the stress state in the piers. Multispan continuous rigid-frame bridges have several closure segments and usually have different jacking forces. In general, the determination of the optimal jacking forces is relatively difficult because of their compound effects on the bridge piers. In this study, multiobjective linear programming was used to calculate the jacking forces by selecting the stress in the piers as the objective function in the service stage and the stresses at the various construction stages as constraints. The minimum tensile stress in the piers was obtained by an iterative process that allowed for the creep effect of the jacking forces to be included in the calculations. The results obtained show that the proposed method is convenient for design, and the appropriate jacking forces can be determined to minimize detrimental long-term effects. Creep caused by jacking forces was found to affect pier stress significantly. In comparison, jacking forces were found to have a smaller effect on the internal stresses of the main girder. Calculation results show that if jacking force is not applied, the long-term effect of creep will generate large stress variations between the top and bottom of the piers and may cause cracking. However, when jacking force is applied, stresses in the piers in the service stage are relatively uniform.

This study reports on the assessment of the vibrational serviceability performance of a parallel cable-stayed bridge, which was subjected to a vortex-induced vibration (VIV) in 2011, by identifying modal damping ratios from the operational monitoring data that were obtained. The natural excitation technique (NExT) combined with the eigen realization algorithm (ERA) was applied for the output-only modal analysis. Parameters regarding the NExT and ERA procedures were determined from a sensitivity analysis of identified damping ratios. Because a multiple tuned mass damper (MTMD) was installed at the center of the main span to mitigate VIV, the modal damping ratios before and after the installation of the MTMD were also compared. Several sets of operational monitoring data that had been collected under various windy conditions were used to develop a relationship between the identified damping ratios and the corresponding VIV level of the bridge. On the basis of these findings, the performance of the bridge was enhanced regarding vibrational serviceability.

Monitoring data of civil structures mainly include load- and temperature-induced structural responses. Traditional damage-detection methods use vibration-based structure responses by eliminating temperature effects from the measured data. In this article, a new structural damage identification method using temperature-induced responses is proposed and applied to a long-span suspension bridge. The novelty of the method is that it derives the structural transfer function by taking temperature load variation and temperature-induced strains input–output data; thus, it is able to accurately reveal inherent structural characteristics, unlike traditional methods that use structural vibration responses from ambient testing. In the proposed method, the temperature-induced strain is separated from measured strain responses with ensemble empirical mode decomposition (EEMD) technology, and a Euclidean distance-based damage index is defined that uses temperature variations and temperature-induced strains for structural damage detection. Numerical analysis results successfully verify the feasibility of the proposed method, which was used to evaluate the condition of a long-span suspension bridge before and after a ship collision with the use of the monitoring data. The performance of the bridge under normal operating conditions was also evaluated through the proposed method with the use of long-term monitoring data, including temperatures and strains.

Fatigue damage of coastal slender bridges resulting from strong winds and high waves can accumulate during extreme hurricane or winter storm events and lead to possible catastrophic failures in a bridge’s lifecycle. With the transient, nonstationary features of extreme winds and strong waves, the interactions of winds, waves, and coastal slender bridges can be complicated because of the nonlinear nature of the structural system and fluid–structure interactions. For accurate coupled dynamic analysis, simulation of wind and wave fields around the structures under extreme weather conditions is necessary. This paper presents a numerical scheme to simulate the nonstationary wind and wave fields around a coastal slender bridge during hurricane events that also can be used in bridge–wind–wave (BWW) system dynamic analyses. In the present study, the wind was modeled as a time-varying mean component plus nonstationary fluctuation components, and the associated wave was modeled as a nonstationary random process. The near-surface (i.e., 10 m in height) time-varying mean wind speed was treated as a deterministic function, which was simulated by utilizing a parametric hurricane wind model composed of the storm vortex and environmental background flow. To consider the correlations of mean wind speeds at the near-surface and gradient levels, the vertical mean wind profile was adopted. Both the wind fluctuation and wave were characterized in terms of their evolutionary power spectral density (EPSD) functions. The nonstationary wind fluctuation was modeled as a uniformly modulated evolutionary vector stochastic process, and the EPSD for the nonstationary wave was obtained by direct extension from the current stationary wave spectrum based on the assumption of slow change in the large-scale structure of the hurricane. Finally, the proposed scheme was used to generate wind and wave fields for a coastal slender bridge, and a wavelet transform (WT) method was applied to check the similarity of the time frequency of the energy distribution for the target and estimated EPSDs.

Connections for steel–concrete composite trusses (SCCTs) for bridge applications were investigated. Eight specimens on a scale of 1/3 of the actual bridge were tested under static loading using connections with different gusset plates, including rectangular (RGP), π shape (PSGP), and J shape (JSGP). A detailed account of the design considerations, loading procedure, and experimental parameters is provided. A three-dimensional (3D) finite-element (FE) model was developed to analyze the mechanical behavior of these three composite truss connections. The results of the FE analysis were in good agreement with the experimental results. Both indicated excellent mechanical behavior for the investigated composite truss connections, with sufficient safety factors. The minimum yielding, cracking, and ultimate loads obtained from specimens were 2.65, 2.21, and 3.87 times the design load (907 kN), respectively. All specimens underwent considerable deformation, thereby suggesting satisfactory ductility. The presented overall investigation may provide a reference for the design and construction of composite joints in composite truss bridges.

Using seismic isolation systems for highway bridges modifies the structure’s principal vibration modes and effectively reduces the seismic base shear conveyed from the superstructure to the substructure. However, for some low-damping rubber isolation bearings, large displacements can be a problem. Supplemental hysteretic dampers can be introduced into the base-isolated bridge, which might nevertheless increase the structure base shear, and the merit of adding dampers has to be evaluated properly. In this paper, a simplified method was implemented for the design of a low-cost hysteretic damper, and the resulting isolator-damper system was tested experimentally. The design method used is based on an equivalent linearization approach. A full-scale elastomeric isolation bearing was characterized and used in the design of a hysteretic damper. Both the isolator and the damper went through cyclic testing and real-time dynamic substructuring (RTDS) methods to verify the capacity of the method to design base isolation-damping systems. The study was further extended to extreme seismic loading by nonlinear time-history analysis. The results reveal that the simplified method is adequate for use in the performance optimization of isolated-damped bridges.

This paper evaluates the seismic responses of a super-span cable-stayed bridge subjected to near-fault ground motions. A new method, record-decomposition incorporation (RDI), is proposed to synthesize the artificial near-fault pulse-type ground motions by combining the high-frequency background record (BGR) with simple equivalent pulses. The effects of forward-directivity pulses and fling-step pulses on the responses are assessed for the Sutong cable-stayed bridge (with a main span of 1,088 m) in China. The results show that the near-fault pulse-type ground motions generate larger displacement and internal force to the bridge compared with the nonpulse ground motions, and the fling-step ground motions are more damaging to the bridge than those of the forward-directivity ground motions. The high-frequency components of near-fault records have a significant effect on the responses of the bridge. Subsequently, the longitudinal displacement and bending moment of the tower induced by artificial ground motions with different pulse parameters (i.e., pulse period, velocity amplitude, and numbers of pulselike wave peaks) are analyzed. Last, the effects of artificial ground motions incorporating actual records originally exhibiting fling-step effects with a forward-directivity pulse model on the responses of the tower are assessed. The arrival time of the peak has notable effects on the responses of the tower.

This study investigates the effectiveness and optimal design of protective devices for the seismic protection of highway bridges. The Painter Street Overcrossing is seismically redesigned with protective devices. Component-level fragility functions are first derived by probabilistic seismic demand analysis using nonlinear time history analyses that include soil–structure interaction effects and ground motion uncertainties. The bridge repair cost ratios are then derived using a performance-based methodology and the associated component failure probability. Results of the comparison of two initial protection designs show that the bridge repair cost ratios provided an efficient evaluation of the protective devices. Subsequently, a multiobjective genetic optimization method utilizing the Pareto optimal concept is employed to identify the optimal design parameters of protective devices for six design cases with various combinations of isolation bearings and fluid dampers. Finally, the repair cost ratios of the bridge with optimally designed protective devices are evaluated. The results show that these optimal devices are able to minimize the overall damaging potential of the bridge, hence validating the optimal design procedure as a practical method for selecting protective devices.

A method for structural health monitoring of cable-stayed bridges based on the dynamic distributed sensing of bridge deck strains is introduced in this article. The objective is to detect the location and the magnitude of the cables that have totally or partially lost their tensile load-carrying capacities. Dynamic sensing provides a realistic approach for condition assessment of the bridge under operational conditions. A Brillouin scattering optical time domain analysis (BOTDA) fiber-optic sensor was used to monitor the distributed strain in the deck of a scaled model cable-stayed bridge in the laboratory. The formulations developed in the present study take advantage of the dynamic distributed sensing capability of the BOTDA in amplitude transfer (AT) mode for the establishment of a relationship between the redistribution of deck strains and the tension loss in the individual cables of cable-stayed bridges. The experimental program involved single cable and multicable damage scenarios. The applicability of the method was independently evaluated by the direct measurement of cable forces and nonlinear finite-element analysis of the bridge.

Horizontal-ellipse culverts have been used for many years as a substitute for more conventional short-span bridges; however, their performance has never been evaluated experimentally. This paper describes an experimental program to understand the behavior of a horizontal-ellipse culvert during backfilling, when subjected to simulated service loading at the ground surface, and during an ultimate limit states test. The backfill response of the specimen was similar to circular culverts except that, as expected, the specimen exhibited lower vertical stiffness than horizontal stiffness due to its shape. Contrary to current design conventions, the response of the culvert to surface loading was influenced by the cover depth. At 0.9 m of cover, the load-carrying mechanism was ring compression, whereas at 0.45 m, significant bending stresses developed in the top of the pipe. At 0.45 m of cover, the ultimate capacity of the culvert was measured as a tandem axle load of 1,324 kN. Although this is approximately twice the fully factored design load, the culvert failed after the development of a plastic hinge mechanism instead of the wall compression considered in American and Canadian design codes, although the structure still had reserve capacity.

Adjacent prestressed concrete box beam bridges are one of the most popular bridges in the United States for short to medium spans. Recently, there has been concern about the structural capacity of these bridges as they age and show signs of deterioration. Unfortunately, limited research has been performed on the transverse ties because they are typically used for pulling the adjacent beam together during construction. Therefore, they are typically neglected in the overall performance of the bridge. Little, if any, information is known of the behavior and contribution of the transverse ties to load transfer and the ultimate capacity after failure of the longitudinal shear key joints. Instrumenting installed transverse tie rods has not been done in the past due to difficultly in accessing the rods, and no technique has been established to perform the installation of a sensor in the tie rods. In addition, instrumenting a tie rod that has already been installed from the fascia beam would only allow the monitoring of the rod at the outer edge of the bridge. In this study, a 50-year-old adjacent box beam bridge was instrumented and monitored under truck loading. A finite-element model was also created and verified with the field measurements. The results showed that the bridge behaved satisfactorily in transferring the load in spite of the corrosion at the exterior beams, and the tie rods did not exhibit high strain.

This paper describes a linear redundancy analysis procedure to identify fracture critical members in steel truss bridges by considering progressive collapse analysis that propagates damage from the initially fractured member to other members. The conventional linear approach assesses structural robustness by checking the strength of every single member through linear equations of member strength for all types of cross sections. However, results are more accurate if member strength is assessed with a nonlinear curve rather than a single linear equation. This paper presents a new linear redundancy analysis method that uses a more accurate nonlinear equation for member strength that accounts for the effect of the plastic region before the cross section has completely yielded. The proposed method can be applied to steel truss bridges with typical sections, such as I-shaped, H-shaped, and box-shaped cross sections. A nonlinear redundancy analysis of a typical steel truss bridge was conducted to validate the proposed criteria. The results of the proposed method were found to be consistent with the results of the nonlinear redundancy method, which is well known as a highly accurate approach.

Sliding resistance of the main cable is of the biggest concern when designing multispan suspension bridges. This paper presents a study on the layout form and sliding-resistance stability of the main cable in a double-cable multispan suspension bridge. It proposes a “top cable to bottom cable” layout, based on which analytical formulas for calculating the sliding-resistance coefficient of the double-cable have been derived. The formulas were verified by finite-element models (FEMs), and the results showed good agreement. The effects of major design parameters on the sliding resistance of the main cable were studied. Analysis shows that the top cable to bottom cable layout can effectively improve the sliding resistance of the main cable, and the bottom cable of the loaded span and the top cable of the unloaded span control the antisliding design of double cable; the sliding resistance of the main cable decreases along with an increase in the ratio of tower stiffness to cable stiffness; the influence of the sag-to-span ratio on the sliding resistance of the main cable is related to the tower stiffness; and the sliding resistance of the main cable increases with an increase in the ratio of dead load to live load.