Journal of Bridge Engineering

Parallel seven-wire steel prestressing strands are the dominant form of the main tension elements (MTE) used in stay cables. In this paper, probabilistic models for fatigue resistance of seven-wire prestressing strands that are not embedded in concrete and are subjected to axial stresses are developed. Available test data from seven-wire strand fatigue tests were collected and analyzed to develop probabilistic models and nonlinear S–N curves using survival analysis techniques. Results indicate that the fatigue resistance of classic stress-relieved strands produced before early 1980s is higher than the modern low-relaxation strands that have been manufactured since then. Neither the conventional classic nor the modern strands have a good chance of passing the fatigue qualification tests required by the latest design standards for use in stay cables. Only the cable-quality (CQ) strands can pass the latest fatigue qualification tests with a less than 2.5% probability of failure. Nonlinear S–N equations for all three strand types and stay cables made with CQ strands are proposed using a log-logistic parametric survival model.

Hybrid sliding-rocking (HSR) bridge columns are among the resilient column designs recently developed to allow accelerated bridge construction for bridge substructures in seismic areas. HSR columns are precast concrete segmental columns with unbonded posttensioning, end rocking joints, and intermediate sliding joints. This design provides significant energy dissipation and partial self-centering capabilities. This paper describes Second-Generation HSR columns and assesses their seismic performance through experimental testing. The Second-Generation HSR columns have fewer sliding joints than the original HSR columns, employ high-performance materials at their sliding joints to better control their frictional properties, and are designed to minimize the columns' seismic damage at target hazard levels through large joint sliding and relatively small end joint rocking. The experimental results discussed herein are from 15 selected tests performed on two half-scale identical column specimens tested under cantilever and fixed–fixed conditions. Both column specimens were tested under reversed lateral loading, including a variety of cyclic and arbitrary loading protocols with various loading rates, representing quasi-static and quasi-dynamic conditions. Satisfying their performance objectives, the damage sustained by both columns under the peak drift ratios representing 975- and 2475-year ground motions representative of Los Angeles, California, was minimal. Under those peak drift ratios, the residual drift ratios remained below 1.1% and 0.7% for the cantilever and fixed–fixed columns, respectively, and more than 90% of those residual drifts were from joint sliding and, thus, recoverable. The damage observed under even more rare ground motion demands included concrete spalling near the rocking joints and strand wire fractures in both the cantilever and fixed–fixed column specimens, as well as concrete cone failures near the sliding joints in the fixed–fixed specimen.

Proper inspection and maintenance schedules are integral to bridge functionality and safety; however, they also pose challenges in light of budget and resource limitations. As such, bridge management systems (BMSs) are always concerned with finding the best deterioration and maintenance models to optimize scheduling. The current work proposes parameterized logistic models that can capture bridge deterioration and the effect of maintenance interventions. Given a handful of easy-to-track bridge parameters, such as age, time since last major maintenance, and location, the proposed models predict the probability of a bridge (or group of bridges) to need repair throughout its service life. Combined with the appropriate probability threshold, obtained from life-cycle cost analysis, this allows for the optimization of inspection frequency and helps in maintenance planning. The results indicate that the proposed models predict the bridge condition more accurately compared to the Markov Chains models adopted by many North American BMSs. Finally, the application of the parameterized logistic models is demonstrated through a case study.

Eliminating the bridge modal variability induced by temperature interference is crucial in vibration-based damage detection. In this paper, a novel localized thermal–frequency correlation model is proposed to remove the masking effect. Motivated by the modal frequencies may be generated and affected by different temperature mechanisms and nonlinear dependence exists between them, a Gaussian mixture model was introduced to cluster the temperature and frequency data into different subsets. Then, a new representative temperature of bridge temperature field was deduced through partial least squares, which is sensitive to modal frequency. After that, the more accurate baseline correlation models were established. The performance alarming was implemented combining with kernel density estimate, which deals with the modeling error nonnormal distribution, and X-bar control chart. Finally, an engineering application to a cable-stayed bridge was carried out, which demonstrates the validity of eliminating the temperature-induced change in modal frequency based on long-term monitoring data.

Evaluating the fire performance of bridges is necessary for damage mitigation as more fire-related accidents occurred on bridge structures. Current solutions adopting temperature curves can result in significant inaccuracy by neglecting the inhomogeneous characteristic of the fire-induced thermal environment. This paper proposed a numerical methodology for analyzing the coupled thermomechanical response of various bridges exposed to fires. The computational fluid dynamics (CFD) approach was implemented to reproduce the fire condition more realistically by modeling the combustion process and fire-driven flow. Then, an interface was adopted to extract the thermal boundary from the fire model. At last, the thermomechanical finite-element method (FEM) was coupled with the CFD model for determining the fire-induced response of the global bridge, thermally and structurally. By incorporating the multiscale FEM, this methodology can be extended to various large-scale bridges subjected to localized fires. The proposed approach was validated through a real fire experimental study on a steel column. To demonstrate the application of this strategy, a complex case study was carried out. A long-span cable-stayed bridge was investigated considering its girder segment was exposed to an under-deck tanker fire. Numerical results showed that the proposed method was able to capture the surrounding temperature field with strong thermal gradients and can predict not only the localized thermomechanical response of exposed segments but also the global structural performance evolution for large-scale complex bridges. The under-deck fire can introduce a significant impact on the entire cable-stayed bridge. Thereby, the multiscale FEM modeling strategy is required for the long-span bridges exposed to localized fires.

This study focuses on the development of an analysis methodology for predicting the ultimate seismic capacity of a concrete-filled steel tube (CFST) to reinforced concrete pile cap connections. This methodology is similar in form to a moment–curvature analysis. The first step involves discretizing the connection elements in the cap into individual fibers and then imposing a rigid body rotation of the embedded CFST. The strains in the individual fibers in the cap are then obtained from this rotation based on strain–displacement compatibility, and the resulting stresses are determined using nonlinear material responses. Equilibrium is then enforced between the associated force resultants and the external shear and moment delivered by the CFST. Specifically, a double-iterative procedure is used in which both the rotation angle and the axis of the rotation location are varied until equilibrium is achieved. Once developed, a set of experimental tests was used to preliminarily calibrate the methodology and demonstrate its feasibility for predicting the ultimate capacity of the CFST to concrete pile cap connections. The average ratio of the measured-to-predicted capacities was 0.99 with a coefficient of variation of 5.4% for the nine test specimens in the test series.

A simplified added-mass model is proposed in this paper for evaluating the seismic response of rectangular hollow piers in deep water, which are widely used in railway bridges. For this purpose, the accurate and concise formulas for the outer and inner hydrodynamic pressures were first derived after smoothing the pier outer surface corners by using small circular arcs. Then, the kinematic equation of the pier–water system was solved in the frequency domain and converted to the time domain with an inverse Fourier transform. In addition, the expressions for the outer and inner water added masses that were induced by elastic vibration and rigid motion were obtained. To verify the accuracy of these analytical solutions in terms of hydrodynamic pressures and added masses, a finite-element modeling approach, based on potential-based fluid elements (PBFEs), was employed to define numerical models of bridge piers in water. A comparison of the added mass coefficients induced by elastic vibration and rigid motion indicates that the former can be substituted by the latter. Meanwhile, water compressibility effects on the hydrodynamic forces have been fully discussed and proven to be negligible for general piers under most earthquakes. Finally, for convenience of application, simplified formulas for added mass and a simplified added model were presented to simulate the seismic response of rectangular hollow piers in water. The good agreement between the dynamic results from the simplified expressions and numerical method confirmed the former’s accuracy and convenience for engineering applications.

A design spectrum of characteristic acceleration response to pedestrian-induced dynamic loading has been developed for footbridge structures. The novelty of the proposed spectrum over the existing spectra is that: (1) it is underpinned by a recently developed comprehensive statistical model of pedestrian dynamic loading; (2) it is applicable to a broader natural frequency range of structures up to 10 Hz; and (3) it accounts for uncertainties in both dynamic loading and structure dynamics that are typically encountered in structural design. In addition, the importance of correct modeling of pedestrian’s walking speed and narrow-band nature of the force signal has been demonstrated. Comparison with the design spectra recommended in contemporary design codes reveals that the existing approaches are not being applicable for structures with natural frequency in the range of third, fourth, and fifth harmonic of the dynamic force. In addition, they could both underestimate and overestimate the structural response for lower-frequency structures. The proposed design spectrum is a design tool applicable to structures whose mode shape can be approximated by half-sine, span length between 12.5 and 100 m, and damping ratio between 0.25% and 2%.

Recent high-profile collapses coupled with an aging bridge stock, increased loading, and the pressures of climate change have led to a greater focus on bridge management by policymakers. To prevent any negative socioeconomic impacts, timely inspection of bridges becomes of prime importance. Visual inspection is standard practice around the world but is subjective in nature and is influenced by many factors that can affect the accuracy of results and future decisions. The research presented here critically compares the conventional visual inspection approach with a virtual reality (VR) inspection technique that combines Lidar and VR, applied for the first time to bridges made of reinforced concrete. Inspection of the Mancunian Way, an elevated motorway in Manchester, UK, is performed by the conventional visual approach and the VR approach. Digital virtual twins of the bridge are developed. Lidar is used to capture a 3D image of the geometric surface of the bridge incorporating all its defects. The image is postprocessed and a VR application is created using Unity, a software development kit, for inspection of bridges in an immersive 3D virtual environment. The resulting VR app is evaluated subjectively by conducting a critical comparison between both methods. The results demonstrate promising improvements over the conventional inspection technique. It is intended that this research will benefit civil engineers in inspecting bridges as well as policymakers who may revise bridge inspection codes and procedures.

Inclined single-tower self-anchored suspension bridges feature a high adaptability to geological conditions but involve complicated structural behaviors during construction due to system transformation. The erection of the tower and main cable is accompanied by changes in internal loading and represents a challenge in bridge construction. This paper reports a new construction scheme for the tower and main cable, introduces the characteristics of temporary structures, and presents the monitoring and control method for construction, through a case study of the Yingbin Bridge. The responses of the temporary structures, girders, cables, and suspenders were monitored using a structural health monitoring system and analyzed using a finite-element model. The results show that the proposed construction scheme can satisfy the safety and quality requirements of bridge construction, and the finite-element model can reasonably predict the bridge behaviors in construction. This study is expected to promote the construction of self-anchored suspension bridges with inclined towers.

Large-amplitude wind-induced vibrations of hangers have been observed on the Xihoumen Bridge, and the excitation mechanism is still unknown at present. In the present study, the mechanism of the wind-induced vibration of the hangers of the Xihoumen Bridge was investigated based on field measurements, wind tunnel tests, and theoretical analyses. First, a series of field measurements on the No. 2 hanger of the Xihoumen Bridge were carried out. It is shown that the oscillation amplitudes of the downstream cables were significantly larger than those of the upstream cables under two different wind yaw angles. Second, a three-dimensional aeroelastic test model of the hanger was designed and manufactured with the No. 2 hanger of the Xihoumen Bridge as a prototype, and a series of wind tunnel tests were carried out to obtain the responses of the cables. The results show that large-amplitude oscillations of the downstream cables can be reproduced by using wind tunnel tests under the same wind directions as the field measurements, whereas the upstream cables keep calm in the meantime. This indicates that wake-induced vibration (WIV) should be the reason for the hanger vibration in the Xihoumen Bridge. In the wind tunnel tests, the effects of the structural damping and spacers on the WIV of the hanger were examined. It is shown that the spacers are significantly effective to reduce the WIV of the hanger. However, it seems that the oscillation amplitude of the hanger cannot be effectively mitigated by increasing structural damping. Finally, the WIV of the No. 2 hanger of the Xihoumen Bridge under the wind yaw angle α = 40° was theoretically analyzed. The results show that the main characteristics of the hanger vibration observed in the field measurements and wind tunnel tests were successfully reproduced by theoretical analyses. This indicates once again that WIV is the mechanism for the hanger vibration of the Xihoumen Bridge.