Journal of Bridge Engineering

Using field monitoring and finite-element analysis (FEA), this paper presents the results of an investigation on stress behavior and fatigue life estimation of fatigue-prone details on an orthotropic steel deck (OSD) with the ultrahigh-performance concrete (UHPC)-deck plate composite system. The work was performed on the Fochen West Bridge in southern China, a three-span-continuous OSD girder structure with a UHPC-deck plate composite system. The results of the study showed that welded details connected to the deck plate experienced one stress cycle for each passing individual axle, while other details away from the deck plate experienced one stress cycle for each passing axle group. Due to the significant contribution of the UHPC-deck plate composite system to deck stiffness, welded details connected to the deck plate experienced low stress ranges under direct wheel loads. However, local load effects under concentrated wheel loading still existed, and the magnitudes of stresses at fatigue-prone details were sensitive to the transverse position of individual wheel loads. Comparisons between FEA and field measurements indicated that the AASHTO fatigue truck may have underestimated stress ranges for fatigue evaluation of this bridge. The study concluded that all fatigue-susceptible details investigated on the Fochen West Bridge had sufficient resistance against fatigue cracking under the current traffic flows per AASHTO fatigue provisions. Finally, suggested guidance for the design of OSD with the UHPC-deck plate composite system was provided.

A set of equations was developed to estimate the maximum mechanical elements and midspan deflections of plan-curved steel I-girder bridges. These formulas were obtained from a statistical correlation analysis based on the results of 54 tridimensional finite-element models corresponding to different 3-span continuous curved bridges. The parameters that varied from one model to another were curvature radius, span length, and number of girders (i.e., load lanes). Two different live-load models were studied separately: the HL-93 and the IMT 66.5. The proposed formulas estimate the maximum mechanical elements of girders, such as positive and negative bending moments around the major and minor axes of girders, vertical shear force, torsional moment, and deflection at the midspan of girders, as a function of the results corresponding to an equivalent straight bridge. Different formulas are proposed for interior, intermediate, and exterior girders in accordance with the bridge cross section and for central and extreme girders in accordance with the span where the girder is located. For each bridge model, the maximum mechanical elements and midspan deflections were normalized with respect to the corresponding results of an equivalent straight bridge with the same characteristics of the curved bridge (span lengths and number of girders), but with a curvature radius equal to ∞. The accuracy of the proposed formulas was tested for different bridge models considered in the correlation analysis, and the results show that they are accurate enough to be used for design purposes. In some cases, they were more accurate than current applicable formulas and procedures recommended in the literature. However, special care must be taken in the applicability of these expressions because they were obtained from models with particular characteristics.

Digital image correlation (DIC) and fiber optic strain sensors (FOSs) are two structural health monitoring (SHM) techniques that are reasonably well developed, but temperature effects remain a difficulty in interpreting the data. In this study, DIC and FOS were used to measure crack widths, deflections, and strains for eight large-scale RC beams tested under static and fatigue loading at room and low temperature. In addition, to evaluate the accuracy and precision of these technologies with temperature variations, calibration tests were conducted to measure the temperature-related strains induced in these systems. The results show that both DIC and FOS were affected by temperature changes, and thus their measurements need to be corrected for temperature when they are used for measuring strains. This study also shows that the DIC technique is capable of measuring crack widths and deflections with high accuracy, and external FOSs can measure strains in concrete in compression with reasonable accuracy. Based on the results of calibration tests, a methodology is proposed to determine the coefficient of thermal expansion (CTE) of the optical fibers to aid in interpreting fiber optic measurements under varying temperature conditions.

Prestressed steel-concrete composite girders constructed by postconnection have gained increasing attention in bridge engineering in recent years. By prestressing the concrete slabs before connecting them with the steel girders in the hogging regions subject to negative moments, this new construction method for steel-concrete composite girders is capable of mitigating the risk of concrete cracking in continuous girders to improve the safety and serviceability of bridges. To study the complex stress and strain distributions in the prestressed composite section as well as their nonlinear evolution with time, a three-dimensional (3D) viscoelastoplastic damage constitutive model is presented in this investigation. In this model, the instantaneous responses of concrete are described by an elastoplastic damage model, and the time-dependent concrete creep and shrinkage are approximated based on an improved rate-type formulation. Compared with the one-dimensional (1D) elastic analysis widely used in current practice, the proposed model provides detailed and realistic information of the stress and strain distributions within the entire composite section during construction and in service. In a case study of a real continuous girder, the coupled effects of concrete shrinkage, creep, and cracking on the long-term behavior of the composite section are estimated based on the proposed model. Furthermore, a parametric study on the curing duration shows that this new construction method can be further improved by controlling the concrete shrinkage.

The cyclic behavior of RC bridge columns with a square cross section was experimentally evaluated using two types of quasi-static cyclic deformations, a conventional loading protocol and a loading protocol designed to assess the behavior or capacity of deficient bridge columns under subduction-zone earthquakes. The specimens and the laboratory arrangement were chosen to represent full-scale typical bridge columns constructed in the 1950s to mid-1970s as part of a typical multicolumn bridge bent in the Pacific Northwest. These columns included lap splices of longitudinal bars in the plastic hinge region and lacked sufficient transverse reinforcement details, making them vulnerable to major seismic events. The experimental results showed that the specimens achieved moderate to high displacement ductilities despite the detailing deficiencies, which can be attributed to the flexure-dominated response. More importantly, however, the experimental results illustrated that these types of substandard RC columns can exhibit a shift in the mode of failure and exhibit less strength and displacement capacity under the subduction earthquake-based cyclic protocol compared with more conventional cyclic protocols. A numerical modeling approach was also adopted with the aim of characterizing the response of the specimens. The numerical results show that the model provided a reasonable approximation of the nonlinear behavior of the columns, including stiffness and strength degradation.

The spectral representation method (SRM) has been widely used to simulate the random wind field for engineering structures. In the modeling process, the Cholesky decomposition of the cross power spectral density (CPSD) matrix is a critical step in the simulation. However, the decomposition of the CPSD matrix is a time-consuming procedure and the required decomposition becomes a computational challenge as the number of points to be simulated as well as frequency segments becomes larger. Such requirements are often noted in buffeting analysis of long-span bridges because they cover a large expanse. This paper examines the efficacy of the interpolation-enhanced scheme (IES) in improving the computational efficiency of SRM by reducing the number of Cholesky decompositions in the random wind field simulation of long-span bridges. Although the interpolation technique has been used to reduce the computational efforts of SRM, there is no literature on the selection of appropriate parameters concerning the interpolation, which is a critical consideration in the context of modeling efficiency and accuracy in applications. Hence, three vital issues related to the selection of interpolation functions, distribution of interpolated points, and interpolation intervals are discussed via a parametric study. The results show that IES can significantly improve the modeling efficiency of SRM, and the improvement becomes increasingly noteworthy as the number of simulation points increase. Hermite and spline-based interpolations are two interpolation functions of choice that can reduce the computational efforts and minimize the attendant computational error. The exponential and quartic polynomial transform are recommended for making the distribution of interpolated points adapt to the low-frequency concentrated contents of each element in the H matrix. In addition, reasonable suggestions are also provided for the selection of interpolation intervals. A comparison between the IES and the POD-based approach as well the explicit decomposition method demonstrates the effectiveness of IES in terms of both the computational efficiency and accuracy.

To accurately calculate stress responses and evaluate fatigue damage of the critical structural members/joints of a long-span cable-stayed bridge, a multiscale finite-element (FE) model of the bridge has been developed by using shell/plate elements to simulate the critical structural components (local models) and by using beam/truss elements to simulate the rest part of the bridge (global model). Nevertheless, the multiscale FE model will be updated to best represent the real bridge, and accordingly the multiscale model updating method is required. This paper presents a novel multiscale model updating method for long-span cable-stayed bridges. The many-objective optimization problem with four or more conflicting objective functions is first formulated because global model and local models will be updated simultaneously. The metamodel-assisted multiobjective optimization evolutionary algorithm (MOEA) is then developed by a combination of R2 indicator-based MOEA, kriging metamodel, and evolution control strategy for the multiscale model of the bridge, which is large in size and complex in system. The R2 indicator-based MOEA is used because of its high performance in solving the many-objective optimization problem. The kriging metamodel is used to improve the computational efficiency of the optimization. The evolutionary control strategy is developed to prevent the R2-MOEA from finding false optimal solutions or losing some of the optimal solutions. Finally, the developed method is applied to a long-span cable-stayed bridge in Hong Kong to demonstrate its feasibility and accuracy. The modal frequencies, displacement, and stress influence lines measured by the structural health monitoring (SHM) system installed in the bridge are used to define the multiple objective functions. The updated results show that the proposed updating method is feasible and can improve the accuracy of the multiscale model in global and local structural responses.

An improved method for calculating the vortex-induced vibration (VIV) of bridges is proposed in this article. In this method, the nonlinear characteristics of the additional aeroelastic effects during VIV versus structural amplitude are first identified through an instantaneous identification method and polynomial fitting. The expression for the aeroelastic effects as a function of structural amplitude is then transformed to the function of structural velocity and/or displacement to calculate the limit-cycle oscillation of the deck. The proposed method was validated through an experiment with different mass-damping conditions. The results indicate that the generalized polynomial model with parameters identified on one particular mass-damping condition can be used to calculate the VIV response of the deck within a certain range of mass-damping values. Based on this method, the VIV performance of a real bridge was calculated by considering the influences of modal shape and spatial coherence of VIV forces. Compared with the traditional method, the applicability of which is limited to a particular mass-damping condition for which the model parameters were estimated, the proposed method will significantly reduce the uncertainty in the prediction of the VIV performance of a real bridge.

The effectiveness of a novel negative stiffness device (NSD) and damper system for reduction of the seismic response of highway bridges was investigated in this study. To this end, a Phase II benchmark highway bridge was employed for the numerical evaluation. By engaging the NSD at an appropriate apparent yield displacement, the combination of isolation system and NSD device behaves like a softening system, resulting in an increase in the combined system displacement response. The increased deformation of the combined system is reduced by additional passive damping in parallel with the NSD. An analytical model for the NSD was developed. Experimental results are presented to verify the analytical model of the NSD. The effectiveness of the proposed NSD in response control was evaluated by numerical simulation of the benchmark highway bridge, and the results demonstrate that the proposed passive NSD and damper system is beneficial in controlling the seismic response of base-isolated bridges and provides performance comparable to the sample semiactive control but by passive means.

Large-span prestressed concrete (PC) box-girder bridges suffer excessive vertical deflections and cracking. Recent serviceability failures in China show that the current Chinese standard modeling approach fails to accurately predict long-term deformations of large box-girder bridges. This hinders the efforts of inspectors to conduct satisfactory structural assessments and make decisions on potential repair and strengthening. This study presents a model-updating approach that aims to assess the models used in the current Chinese standard and improve the accuracy of numerical modeling of the long-term behavior of box-girder bridges, calibrated against data obtained from a bridge in service. A three-dimensional finite-element model representing the long-term behavior of box-girder sections is initially established. Parametric studies are then conducted to determine the relevant influencing parameters and to quantify the relationships between those and the behavior of box-girder bridges. Genetic algorithm optimization, based on the response-surface method (RSM), is used to determine realistic creep and shrinkage levels and prestress losses. The modeling results correspond well with the measured historic deflections and the observed cracks. This approach can lead to more accurate bridge assessments, which result in safer strengthening and more economic maintenance plans.

During detailed visual inspections, inspectors on the Varina-Enon Bridge noticed a significant flexural crack opening, visually estimated at 1.5 mm under traffic, on the last span of the approach structure among other significant cracks on June 29, 2012. To investigate the causes of the observed cracking, live-load testing, long-term monitoring, and structural analysis were used including 77 total strain, crack displacement, deflection, and temperature sensors. The live-load test produced a crack opening of approximately 0.5 mm when under a less-severe thermal gradient. The collected data indicated the crack opening was greatly influenced by interaction of vehicular loads and thermal gradient magnitude. There were 389 crack openings larger than 0.0625 mm over the 17 months of the long-term monitoring, with a maximum measured crack opening of approximately 0.76 mm. Maximum measured thermal gradients were found to be in excess of the as-built design thermal gradient but similar to the current design thermal gradient. This may indicate potential underestimation of the maximum design thermal gradient, but would require a more robust study.

In recent years, several similar bridge overturning and collapse accidents have occurred in China. All of them occurred on bridges with continuous monolithic box girders and single-column piers that were eccentrically overloaded by heavy vehicles. In this study, an explicit nonlinear dynamic finite element method is used to analyze an accident occurred on an expressway exit ramp bridge. The entire overturning and collapse process is simulated. The results show a girder revolving around the overturning axis, which is a straight line between two supports for a bridge eccentrically loaded by heavy vehicles. When the rotation of the main girder is larger than the friction limit rotation, the sliding force is greater than the friction force between the girder and the support. This causes the main girder to slide obliquely, which can induce a horizontal reaction force, pushing the piers down and collapsing the whole bridge. This underestimates the anti-overturning ability of a bridge, based on the criterion that no support disengagement occurs under overloading conditions. Second-order effects due to girder rotation (including the increase of the overturning moment arm) must be taken into account when calculating an anti-overturning stability factor based on the overturning axis between two supports.

This study investigates the structural characteristics of midtowers in three-tower suspension bridges and proposes a direct approach to determining feasible midtower stiffness for preliminary designs. The lateral stiffness analysis of bridges demonstrates the feasible midtower stiffness is located in a range that can be obtained using a simplified multispan suspension bridge model. This study also defines dimensionless midtower stiffness, and a parametric analysis is carried out in it to examine the effects of different parameters, including the sag-to-span ratio, side-to-main span ratio, dead-to-live load ratio, span length, and traffic load, on the range of dimensionless midtower stiffness. The results illustrate that the range of dimensionless midtower stiffness relies mainly on the dead-to-live load ratio and the sag-to-span ratio. The dimensionless stiffness chart derived from the study is generic and provides an estimate of the feasible midtower stiffness of three-tower suspension bridges with different design parameters.

In recent years, northeast extreme tee (NEXT) beam bridges have gained increased attention in the bridge industry for their ease of construction. When designing a NEXT beam bridge, the actual live load moment in a beam stem can exceed the design stem moment (i.e., half of the design beam moment) because of the uneven stem spacing. Current guidelines conservatively use the average stem spacing to compute the live load distribution factor (LLDFs) per lane for moment for each stem, which is doubled to calculate the LLDFs for the entire NEXT beam. In this regard, this study aimed to evaluate the applicability of the current LRFD method for LLDFs per lane for moment to the NEXT beam bridges by employing validated finite-element (FE) simulations. Parametric studies were carried out by both simplified and detailed FE modeling of various bridges with minimum- and maximum-width NEXT beams to compute the FE LLDFs. By using the beam spacing and the properties of an entire NEXT beam section, the LRFD LLDFs for NEXT beam bridges were computed as LRFD types i, k, and h sections. The results of FE and LRFD LLDFs were compared, and results showed that LRFD LLDFs governed the FE LLDFs by at least 12%. In addition, it was observed that the LRFD types i and k sections were more applicable for NEXT beam bridges compared with the LRFD type h section.