Journal of Bridge Engineering

The recent development in structural health monitoring (SHM) technology enables the buffeting responses of bridges to be evaluated in a more realistic manner. In this paper, the buffeting responses of the cable-stayed Sutong Bridge with a main span of 1,088 m is analyzed with the wind spectra used in the design phase and those obtained experimentally from a long-term SHM system to compare the actual buffeting response with design predictions. The autospectra of longitudinal and vertical fluctuating wind components are derived from the in situ strong wind data recorded by the monitoring system. The buffeting analysis is accomplished in the time domain with the aeroelastic effect included. Compared with the buffeting responses obtained from the measured spectrum, the girder responses from the design spectrum are larger in the horizontal direction and smaller in other directions, whereas the tower responses are larger and thus relatively conservative.

The effects of skew angle, cross-frame spacing, cross-frame layout, cross-frame stiffness, and load placement on the potential for distortion-induced fatigue damage in steel bridges was investigated by performing a suite of more than 1,000 analysis jobs of high-resolution three-dimensional finite-element models. Susceptibility to fatigue damage was quantified in terms of computed stress demand in the web gap region of the girders. Bridge configurations with three different cross-frame layouts were evaluated, including configurations with cross-frames placed parallel to skew angle (skewed-parallel) and perpendicular to the girder line, both staggered (skewed-staggered) and unstaggered (skewed-unstaggered). Skew angles of configurations evaluated ranged between 0 and 50°, and cross-frame spacing ranged from 2.29 to 9.14 m (7.50 to 30.0 ft). Influence and envelope surfaces were constructed to show the relationship between load placement, location of the maximum web gap stress, and the magnitude of the maximum web gap stress. It was found that maximum web gap stress always occurred when loads were positioned directly above the intersection of a cross-frame and girder web. The parametric study showed that cross-frame stiffness and spacing had a significant effect on the susceptibility to distortion-induced fatigue damage; greater cross-frame stiffness resulted in higher web gap stresses, and increased cross-frame spacing resulted in increased web gap stresses. It was also found that the bridge configuration was key to determining the location of the web gaps where damage is most likely to occur. In skewed-parallel and skewed-unstaggered layouts, maximum web gap stresses were identified in top web gaps, whereas in skewed-staggered configurations, maximum stresses occurred in bottom web gaps. It was found that in configurations with staggered cross-frames, maximum web gap stresses tended to occur in regions of support, where cross-frames are often placed back-to-back along the skewed alignment.

Laminated elastomeric bridge bearings are commonly used in areas with low-to-moderate seismicity, although the applications are typically intended for service-level considerations such as thermal movements of the bridge superstructure. These components provide a potential source of displacement capacity frequently neglected in seismic design. An experimental program was carried out to evaluate the behavioral characteristics and performance of steel-reinforced, laminated elastomeric bearings, which had not been designed for seismic demands, as the primary quasi-isolation components for seismic events by permitting slip at the interface of the bearing and substructure. The rubber at the top of the bearing is vulcanized to a steel plate, which is bolted to the test frame to simulate a connection to the superstructure. At the base of the bearing, the elastomer directly contacts concrete representing the substructure, with no restraint of horizontal motion other than friction. The elastomeric bearings investigated during the experimental program displayed an approximately linear elastic response before sliding, with an initial friction coefficient in the range of 0.25–0.5 (at a shear strain between 125 and 250%) depending on combinations of the contact surface roughness, applied load, and bearing velocity. The friction coefficient decreased as a nonlinear function of the imposed vertical load. The maximum elastomer shear strain prior to sliding exhibited nonlinear increases with vertical load, resulting from the influence of the variable friction coefficient. Linear shear moduli were primarily influenced by the maximum shear strain imposed on the bearing, and showed shear stiffness reductions of approximately 40–50% following multiple, large displacement slip cycles, compared with 15–25% after reaching 50% shear strain. Multiple cycles of large displacement demands resulted in noticeable degradation in the friction coefficient over the duration of the tests. However, the bearings possessed a high degree of resiliency, considering that the specimens retained load-carrying capacity through total cumulative slip travel demands in the range of 3.5–4.5 m (140–180 in.).

In the current study, wind tunnel tests and buffeting analyses were conducted for a catwalk structure of a suspension bridge under turbulent winds. From the wind tunnel tests, it was found that the Reynolds number effects on the aerostatic coefficients were negligible for the catwalk floor systems. Simple design formulas were proposed to estimate the aerostatic coefficients of catwalks with various solidity ratios and angles of attack. The buffeting analysis results revealed that tying the catwalk to an erecting main cable may be an effective structural countermeasure to reduce the lateral displacements of the catwalk. Stay ropes fastening the catwalk and bridge tower were also found to be effective at alleviating the lateral displacements.

In current practice, no special measures are applied for enhancing structural fire safety of steel bridge girders. Further, there is very limited information and research data in the literature on the fire resistance of structural members in bridges. In this paper, the fire response of a steel bridge girder under different conditions is evaluated using the FEM computer program ANSYS. In the analysis, the critical factors that influence fire resistance, namely, fire scenario, fire insulation, and composite action arising from steel-concrete interaction, are accounted for. Results from numerical studies show that the composite action arising from steel-girder–concrete-slab interaction significantly enhances the structural performance (and fire resistance) of a steel bridge girder under fire conditions. Other significant factors that influence fire resistance of steel bridge girders are fire insulation and type of fire scenario.

The main objective of this study was to evaluate the effect of shear stud connections on the dynamic response of the fiber-reinforced polymer (FRP) deck system under moving loads. A FRP deck bridge in Pennsylvania was studied based on a field test and finite-element (FE) analysis. In the field test, the strain of each steel girder at the midspan was measured at three positions: top, midheight, and bottom. In the FE analysis, the connection between the steel girders and the FRP deck was simulated as fully and partially composite, separately. Static performance under a simplified truck load was investigated based on these two FE models, and the FE analysis results were compared with the field test results to validate the FE models. The FE results of the fully composite model and the partially composite model provide a lower bound and an upper bound for the real response of the FRP deck system. Next, the dynamic behavior of the FRP deck system under moving loads was studied based on the two verified FE models. The static or dynamic response in the partially composite model of the FRP deck bridge was greater than the corresponding static or dynamic response in the fully composite model. Also, it was shown that the dynamic response in the partially composite model lags behind that in the fully composite model. Additionally, the FE analysis revealed that the number of shear stud connections affected the dynamic deflection, slip, and separation. Finally, the dynamic response of the FRP deck system was compared with that of the commonly used RC system.

Corrosion of high-strength steel wires in a suspension bridge’s main cable has been attributed to the environment within the cable wrapping. A sensor network was developed to monitor and provide information in order to indirectly assess the environmental conditions and the deterioration of the interior of suspension bridge main cables. The overall functionality of both the individual sensors and the monitoring system was tested on a full-scale mock-up cable. The cable mock-up was covered in aluminum wrapping and an environmental chamber was built around it in order to subject the test specimen and sensor network to an aggressive corrosive environment created by cyclic temperature and humidity conditions. The temperature, relative humidity (RH), and corrosion rate levels were recorded by all sensors. The recorded data were analyzed in an attempt to determine general trends and correlations between the environmental variables themselves and their effects on corrosion rates. The recorded temperature fluctuations were highly dependent on the sensor depth within the cable; however, the RH levels were not. During cyclic testing, near-linear temperature increases and RH decreases were recorded close to the cable’s center. The baseline corrosion rate levels were affected by the RH levels, with significant increases in corrosion rates at RH levels greater than 50%. The temperature changes proved to impact the corrosion rates on a cyclic level, with high correlations between the temperature and corrosion rate readings recorded by linear polarization resistance corrosion rate sensors.

In this paper, a study about stay stressing procedures of concrete arch bridges built by cantilevering with temporary stays is presented. Particularly, the partial elastic scheme method is proposed to find the initial cable forces, and a forward procedure is implemented to follow the actual sequence of construction by extending a procedure already applied to concrete cable–stayed bridges. The theoretical treatment is followed by a numerical application on a case study of a concrete arch bridge, and a comparison between initial cable forces found by the partial elastic scheme method and classical backward analysis is presented here. Results show the effectiveness of the proposed procedure to achieve the requested design geometry of the arch and for limiting the variation of bending moments and stay forces in construction stages.

Current AASHTO LRFD Bridge Design Specifications Service I deflection limits are in place with the purpose to prevent deformation-induced structural damage and psychological user discomfort from excess bridge vibration. Previous research has shown that deflection criterion alone is insufficient in controlling excess bridge vibrations and structural deterioration of the concrete deck. Previous research shows that natural frequency criteria better controls excess vibration than deflection criteria alone. In addition, previous research shows no significant correlation between deflection and structural deformation of the concrete deck slab. To better control excess bridge vibrations and deformation-induced structural deterioration, two new separate criteria formulations are proposed. The first formulation consists of a natural frequency criteria transformed into deflection-type terms familiar to the typical bridge engineer. The second proposed formulation directly controls the acting flexural strain in the concrete deck to control deformation-induced structural damage. The proposed serviceability criteria are applied to a database of 185 steel girder bridges. Both the as-built behavior and the design optimized behavior are examined and compared with current AASHTO serviceability criteria. The proposed user comfort and deformation-induced damage serviceability formulations are intended to be incorporated into ongoing Federal Highway Administration and bridge industry long-term bridge performance research where serviceability criteria is an important component.

Bridge structures are valuable national assets for transportation and economy that should be maintained properly for continuous stable operation. Corrosion is common in steel bridges; severe corrosion may result in significant economic impact and long downtime for retrofit. To date, various corrosion evaluation technologies have been developed such as nondestructive evaluation techniques and analytical model updating strategies. Among them, nondestructive evaluation is costly and time consuming for scanning entire bridges. For model updating, few examples on full-scale bridges with severe corrosion have been reported. In this paper, the corrosion level in a historic steel-truss bridge is estimated using model updating. Dynamic characteristics of the bridge are identified via a series of short-term full-scale experiments. An initial finite-element model of this bridge is then updated to match the field corrosion estimation results. The corrosion levels predicted by the proposed approach were consistent with the results of a visual inspection of this bridge. The results of the model updating routine could be used to monitor the overall corrosion levels in the structure with periodic inspection over time.

This paper presents the field evaluation of a damaged noncomposite steel girder bridge that is part of the interstate highway system in Vermont. This bridge is typical of late 1960s construction and spans over a two-lane state highway near the town of Weathersfield, Vermont. The superstructure contains three-span continuous girders supported on abutments at the ends and on RC multicolumn interior bents. Strains were measured during live-load testing that was conducted to better understand the bridge behavior. The field results were compared with results from finite-element models created using common engineering assumptions. In addition, the load-distribution characteristics of girders that were damaged by an overheight truck traveling on the state highway under the bridge were evaluated. The results indicate that alternate load paths were developed within the bridge superstructure as a result of damage from the truck impact. For the loading magnitude applied during the load tests, evidence of composite action was observed and participation of curbs on the response of the bridge was noticed. Bridge skew and partial restraint generated at the supports also contributed to differences in the observed and calculated responses. These nondestructive load testing results were used to provide confidence on the load-carrying capacity of the bridge and to avoid costly bridge closures and detours.