Journal of Bridge Engineering

The paper presents a new formulation of a beam finite element for the time-dependent analysis of self-anchored suspension bridges, considering the shear lag in a multicell concrete box girder. The beam kinematics are deduced using a displacement-based approach. Warping of the girder section is captured with a warping intensity function representing the warping magnitude along the girder axis and a series of segmental shape functions describing the warping shape of the asymmetrical multicell box section, which is deduced based on shear flow transmission. A three-dimensional 14 degree-of-freedom (dof) beam finite element employing hermitian polynomials to ensure consistent displacement interpolation is proposed. The proposed beam element is implemented in ANSYS as a user-defined element. The convergence test results and comparisons with the refined analyses using a solid finite-element model demonstrate the accuracy of the proposed element. Time-dependent behavior of concrete is calculated using the B3 prediction model and the age-adjusted elastic modulus method. The moment estimation method is adopted to conduct the random analysis, which yields the 95% confidence limits of the structural responses obeying approximately the normal distribution. Application to a full-scale bridge structure shows the efficiency and accuracy of the proposed method and its ability to describe the elastic and time-dependent behavior of a self-anchored suspension bridge with extra-wide concrete girders.

An objective, data-driven approach to evaluate the performance of bridges for developing a structural health monitoring system is introduced as bridge behavior. A method of identifying structural damage through the evaluation of response data from an instrumented bridge is proposed. Strains during operational traffic events at the Powder Mill Bridge in Barre, Massachusetts, are recorded at many locations on the bridge. Bridge behavior is defined as each sensor location’s range of expected peak strain during a traffic event based on all other sensor locations’ strains measured at that instance in time. Artificial neural networks (ANNs) are trained with operational bridge response data in a bootstrapping scheme to generate a probabilistic model of bridge behavior. When tested against new data, the ANN-learned model of predicted bridge behavior is proven effective and applicable to varying traffic events with unknown loading conditions. A method for long-term performance assessment using the expected bridge behavior is proposed. Structural damage can impact bridge behavior and thus bridge performance. The effects of structural damage are extracted from simulated HS20 design truck runs on a calibrated finite-element model (FEM) and are applied to operational strain data to assess the damage identification method. When assessed, the damage identification method is effective at detecting the presence of damage, with no Type I or Type II errors when using a Wilcoxon rank-sum test of an appropriate significance level. Damage is effectively localized for most types of simulated damage.

The center-to-center spacing, or pitch, between headed shear studs in composite bridge girders is currently limited to 0.61 m (24 in.). However, research into shear stud performance at larger spacings has indicated that an increase in the pitch limit from 0.61 m (24 in.) to 1.22 m (48 in.) may be justified. As shear stud pitch increases, and as studs are grouped into clusters, the applicability of existing shear demand equations (based on continuous shear flow assumptions) may no longer be valid. This paper investigates shear demands in embedded studs of composite bridge girders through a parametric finite-element study, examining the effect of shear stud pitch, girder depth, and girder span on resulting stud demands. A total of 24 detailed finite-element models were analyzed using the commercial software ABAQUS, and four different shear stud pitches, three different girder depths, and two different span lengths were considered. Results indicated that the current AASHTO shear flow estimations do not accurately capture demands on stud clusters having center-to-center spacing greater than 0.61 m (24 in.). In stud clusters spaced at 0.91 m (36 in.) and 1.22 m (48 in.), the AASHTO shear flow prediction equation consistently underpredicted forces found in the outermost rows of each stud cluster. A new design method and updated formulation for predicting stud demands at larger spacings is presented.

Experiments were conducted in a wind tunnel with scaled models to investigate the aerodynamic characteristics of a train on a steel truss girder. Simultaneous surface pressure measurements were conducted under two turbulent flow fields. The aerodynamic-force coefficients, aerodynamic-admittance functions, and spanwise correlation characteristics of buffeting forces on the train were examined. A mean pressure coefficient suction peak was observed at the windward roof corner, and a fairly uniform pressure distribution was observed on the leeward surface of the train. The variation of the wind angle of attack (–3° to 3°) and turbulent flow field had minimal effects on the spanwise correlation of buffeting forces, whereas the effects of the train position on the truss girder and spanwise distance were significant. The aerodynamic admittances of the train were found to be a function of the train position on the truss girder and turbulent flow field. The effect of the wind angle of attack (–3° to 3°) on the aerodynamic admittances of the lateral and lift forces was mainly in the low-frequency region. Finally, empirical expressions were proposed to facilitate engineering applications.

Residual drift of bridge columns is an important performance measure for structural damage and postearthquake repair decisions. Yet there are very limited models available for estimating the residual drifts accurately. This paper presents an innovative method to realistically predict the residual drifts (including their trend and upper bound) of bilinear bridge deck-column systems directly from their inelastic mechanical properties and ground motion characteristics. The proposed estimation originated from the rigorous dimensional analysis of nonlinear time-history responses of various bilinear bridge deck-column systems under near-fault ground motions. Under this framework, the peak inelastic drifts and residual drifts were presented in dimensionless forms and showed remarkable order and correlation with structure-to-pulse frequency and the dimensionless nonlinearity index that accounts for the preyielding strength, ground motion amplitude, and softening or hardening postyielding behavior. Regressive equations for maximum displacement and residual-drift demands were proposed and validated. The corresponding error of this approach was shown to be lower than those of the existing codified methods.

An experimental study was conducted at the University of Nevada, Reno, on the seismic performance of horizontally curved steel plate girder bridges. A two-fifth scale, three-span highly curved bridge was constructed on four shake tables and subjected to earthquake motions. Bridge footings were free to uplift during seismic loading, and neoprene pads were placed underneath the footings to simulate soil effects. Prior studies on the effect of rocking foundation systems concluded that rocking has the ability to reduce the damage in bridge columns in addition to being a good source of damping through the soil inelastic behavior. This paper describes the results from the experiment on a complete bridge system designed with rocking foundations. The rocking behavior was able to considerably limit the damage in the columns and the residual displacement of the bridge under earthquake motions equivalent to 2.5 times the earthquake intensity for which the bridge was designed. For high earthquake intensities, instead of experiencing overturning, the effect of rocking decreased, causing damage in the plastic hinge regions similar to a fixed-base column behavior. However, the overall damage was still less than in a fixed-base column.

Recently, a steel plate concrete composite technique has been developed for the shear strengthening of RC bridges. The steel plate shear-strengthened (SPSS) beam is composed of an old RC beam, new concrete, and steel web. To investigate the shear behavior of SPSS beams strengthened in the shear span, six SPSS beams and four RC beams were tested. The test results showed that the failure mode of the SPSS beams was peeling failure at the interface between the old concrete and new concrete. The proposed technique showed a significantly enhanced shear capacity even when the tensile strength of the interface between the old and new concrete was relatively low. The initial interface failure appeared at the loading point, support, and corner of the new concrete and then expanded to the entire shear span. A finite-element (FE) model of the SPSS beam was established with the use of the FE software MSC.Marc, and the cohesive element was used to model the interface between the old and new concrete. The modeling scheme, material constitutive law, and material parameters are illustrated in this article. The results of the proposed FE model were found to agree fairly well with the test results in terms of the overall load-displacement curve, ultimate shear capacity, and interface failure pattern. Based on the FE model, the shear force contribution of the old concrete, new concrete, and steel web were decomposed with sufficient accuracy. The effects of the ratio of shear span to depth, material strength, and interface strength were investigated by an FE parametric analysis, and the interface strength between the old and new concrete was found to be the most important parameter. The shear contribution of the steel web was mainly affected by the interface strength. Finally, 1,296 elaborate FE models of SPSS beams were established with the use of MSC.Marc, and a practical design formula considering peeling failure with a reasonable level of accuracy was developed.

Overloading, corrosion, and material aging deteriorate the structural performance of prestressed concrete (PC) bridges. Strengthening techniques are needed to improve the serviceability and extend the life of these deteriorating bridges. This study examined a strengthening technique with double-layer prestressed steel wire ropes (PSWRs) to enhance the serviceability of an existing post-tensioned concrete box beam for the first time. The tested box beam was removed from a demolished 20-year-old bridge. The service-level behavior of the beam, before and after strengthening, was evaluated using four-point flexural loading. The enhancement effects of the double-layer PSWR on the service-level behavior of the beam are discussed, including details on deflection, crack width, and reinforcing steel stress. Results show that PSWR strengthening is a feasible method for improving the serviceability of post-tensioned concrete box beams. The restraining effect of PSWR on crack development is more significant than the effect on deflection and reinforcing steel stress. Crack width, deflection, and reinforcing steel stress under the code-specified service load decreased by 50, 23, and 21%, respectively, after strengthening.

The suspender is one of the most critical members for suspension bridges. Corrosion is the greatest degradation mechanism for suspenders during their service lives. Practices in North America have shown that the average time for the replacement of suspenders is between approximately 60 and 75 years. In this case study, three pairs of representative suspender ropes were removed and replaced on the Bronx–Whitestone Bridge, which was opened to traffic in 1939. The detailed suspender replacement procedure is presented. A refined three-dimensional (3D) finite-element (FE) model of the suspension bridge was developed to determine the jacking forces during replacement. To ensure that the new suspender tension reached a desirable value, an advanced vision-based sensor was adopted for noncontact force measurement, which eliminated the need for direct access to the suspender ropes to install conventional sensors. Subsequently, the existing suspenders that were removed were inspected visually. Three typical locations along suspenders, where dirt and water easily accumulate, were found to be especially vulnerable to corrosion: directly above the sockets, the section over the cable band, and at the suspender clamps. Finally, testing procedures are described to explain the estimation of the remaining ultimate strength of the removed existing ropes. The overall practices presented in this case study can help guide future suspender-rope replacements and investigations.