Journal of Bridge Engineering

This article provides a comprehensive state-of-the-art review of research on bridge deck fatigue under moving wheel loads and compares it to conventional fixed-point pulsating load fatigue. An overview and a brief history of the evolution of this test method from around the world are provided. The effect of key parameters on fatigue life and performance under moving loads are discussed, including loading magnitude and stress ratio, loading footprint, boundary conditions, loading eccentricity, loading frequency, dynamic effect and impact, reinforcement layout, slab thickness, crack control, concrete strength, and environmental exposure conditions. The fatigue accumulation rule and the incremental step (staircase) rolling load method are discussed. Cracking and failure mechanisms in slabs under rolling loads are presented and compared. It is clearly demonstrated that fixed-point pulsating fatigue loads inadequately simulate fatigue damage, stiffness degradation, and cracking patterns induced by rolling loads. For example, one rolling load cycle is shown to be equivalent to 80–1,800 pulsating load cycles. Varying the magnitude of the rolling load (dynamic effect) further reduces the fatigue life. Decreasing the spacing of the transverse rebar and compression reinforcement both can increase susceptibility to crack initiation, potentially reducing fatigue life. Environmental factors, particularly moisture intrusion, drastically reduced fatigue life. A conversion factor of stiffness degradation from pulsating to equivalent rolling load fatigue is proposed. Finally, recommendations for future work in this field are proposed.

During seismic ground shaking, the motion of a soil–pile system is different from that of the free field due to seismic soil–structure interaction (SSI). Kinematic soil–pile interaction is known to cause significant filtering of the ground motion, resulting in the foundation input motion (FIM) differing from the free-field ground motion. In certain situations, where embedment of the pile cap is ensured, such as in the case of a piled raft (PR), previous numerical studies have shown that embedment effects can cause additional alterations to the FIM. In this work, we investigated the influence of an embedded pile cap on the seismic response of a pile group (PG) employing physical and numerical modeling. A shaking-table test program was designed to investigate the embedment effects on the seismic response of a scaled 2 × 2 PG in clay, in the absence of superstructure inertia. Two identical PG models––one embedded and the other free standing––were subjected to a series of harmonic and white-noise signals, following which, the responses were assessed in terms of the transfer functions and spectral ratios. The ratio of translational response amplitudes of the PR to the PG indicated that embedment effects can lead to significant filtering of the ground motion at higher excitation frequencies. Unique experimental evidence is presented showing that pile-cap embedment can result in additional filtering of the ground motion, even for a highly nonlinear soil response. The results from the experimental program were complemented by numerical analyses of a real-world bridge support system where the influence of embedment on the bridge deck response was studied for a set of seismic ground motion records of varying intensity. We confirmed that the embedment effect is a SSI problem, independent of the earthquake-induced soil nonlinearity, and loss of the soil–pile-cap contact can lead to higher energy being transmitted to the superstructure.

When a ship–bridge collision occurs, prompt assessment of substructure damage is crucial. This study presents a novel approach for ship–bridge collision damage identification, addressing challenges inherent in traditional monitoring systems. The method overcomes issues such as complex installation, low efficiency, and high costs through a unique combination of the unscented Kalman filter (UKF) and computer vision technique. The approach exerts the structural equation of motion to derive a multirate UKF in the impact process, thereby identifying the stiffness of structures. Displacement and acceleration are fused to enhance the sampling rate of vision-measured displacement. Firstly, it monitors low sampling rate displacements on piers using computer vision, complemented by high-rate accelerometer data at the collision point. Secondly, displacement and acceleration data are integrated using a multirate UKF, addressing the challenge of image storage pressure associated with vision-based measurements. Finally, validation using finite-element and experimental models confirms the effectiveness of the approach in identifying substructure stiffness and recovering lost vibration characteristics. In experiment validation, the influence of computer vision algorithms and camera shooting distance on displacement monitoring and stiffness identification is also discussed separately. This approach provides a cost-effective and efficient solution for ship–bridge collision damage identification, contributing to advancements in the field of ship–bridge collision monitoring.

Traditional sacrificial concrete retaining blocks (CRBs) play a significant role in reducing the excessive transverse displacements of bridge superstructures and protecting the substructures from severe damage during seismic events. However, rehabilitating these CRBs after earthquakes is very difficult. Thus, many previous studies proposed the prefabricated retaining blocks (PRBs) with the unbonded post-tensioned prestressing tendons (PTs), which has been proven to be effective in maintaining the same functionality as that of traditional sacrificial CRBs while also simplifying their postearthquake rehabilitation. However, the response mechanisms and influential parameters of the abutment PRB under the horizontal seismic loads are unclear, affecting its further application in practical bridge engineering. This study established the three-dimensional (3D) finite-element (FE) model of the abutment PRB designed by the previous researcher and validated the feasibility and effectiveness of studying its seismic behavior through the available experimental results. Additionally, comprehensive parametric studies were performed to examine the effects of the friction coefficients, initial tension forces, and tensile strength of PTs on the seismic behavior of the abutment PRB. Subsequently, to fully utilize the mechanical merits of ultrahigh-performance concrete (UHPC), this paper proposed the modified abutment UHPC-PRB structures and their hysteretic behavior and damage modes were compared with those of the original ones through numerical simulations and available test results in the literature. Finally, the results indicated that (1) the developed FE models could accurately simulate the seismic behavior of the abutment PRBs; (2) the friction effect between the PRB body and side surface of the abutment stem wall had significant impacts on the hysteretic behavior and energy-dissipation performance of the abutment PRBs; (3) the critical rotational load, horizontal loading strength, deformation ability, energy-dissipation ability, and self-resetting capacity of the abutment PRBs could be improved with the increase of the initial tension force and tensile strength of PTs; and (4) the proposed replaceable abutment UHPC-PRB structures exhibited superior seismic performance and outperformed mechanical merits compared to traditional sacrificial CRBs.

Despite the historical tendency toward proportioning and spacing braces based on rules of thumb, modern specification guidance stipulates that cross-frame design be supported with a rational analysis, which is commonly aided by computer software. While cross-frame research has advanced over the last 30 years, the relatively vague nature of specification language related to rational analysis is still utilized and often misunderstood by engineers leading to uneconomical chase-your-tail design solutions—particularly related to the fatigue limit state. To improve the design specifications and economy, an extensive analytical parametric study was conducted to quantitatively investigate the sensitivity of load-induced cross-frame response in varying bridge geometries. The study included multiple three-dimensional analyses on 4,104 unique steel I-girder bridges. Among other observations, the results demonstrated that load-induced cross-frame forces are generally higher in heavily skewed systems. From these studies, two primary recommendations are proposed to improve specification guidance on fatigue design of cross-frames. First, designers can avoid overly conservative and iterative designs by utilizing staggered and/or discontinuous cross-frame configurations, thereby alleviating force demands in heavily skewed systems. Second, the study concluded that refined analyses are not warranted in straight bridges with little to no support skew since cross-frame force magnitudes are generally not significant. Geometric limits based on skew and connectivity indexes are proposed to serve as the delineation between when a refined analysis is recommended.

Abstract

The bundled parallel strand stay cables are important structural components of modern cable-stayed bridges. Strands commonly used in modern stay cables are seven-wire greased-and-sheathed strands. Stay cables primarily resist tension loads imposed by various loads, but they also resist bending stresses due to wind loads, vibration, and any traverse load applied on the cable. The movements of the deck and towers (at termination points of stay cables) also impose rotations at the cable ends, which will induce bending stresses in the strand bundles. Calculating and analyzing a stay cable’s bending-induced stresses is an important consideration, especially regarding fatigue resistance. Traditionally, designers have assumed a noncomposite moment of inertia for the bundle of parallel strands because of the presumed lack of sufficient interstrand bond along the length of cables. Therefore, the composite effect is generally not considered, and the moment of inertia is typically assumed to be equal to the number of strands times the moment of inertia of an individual strand. This assumption neglects the fact that unrestrained relative slippage between strands cannot occur because the anchorage plates enforce displacement compatibility at cable ends. Also, deviation clamps and periodic cable bands (tying of the strand bundle together) along the free length of the cable may provide some degree of composite action. This study examines the global bending-induced stresses developed near the termination points of stay cables due to the application of transverse loads on the cable. Experiments and computational analyses are conducted to assess these stresses. The computational models are verified using laboratory experiments performed on a five-strand cable. Detailed and simplified finite-element models are developed. Bending-induced stress calculation procedures are developed using a simplified stay cable model.

Practical Applications

This study proposes calculation procedures to address the important issue of bending-induced stresses in the design of the most crucial components of cable-stayed bridges—stay cables. At present, there are no reliable equations to estimate the maximum strand stresses due to bending action of stay cables under transverse loading. Therefore, qualification tests of relatively short stay cable specimens are sometimes utilized to evaluate fatigue resistance under bending action. For bridge design engineers, the proposed analysis approach and equations can be useful in assessing the long-term fatigue resistance of strands. This study establishes that bundles of greased-and-sheathed seven-wire strands do not act independently within the transition zone of stay cables near anchorages, and the angle change imposed due to transverse loading is not the only factor affecting bending-induced stresses. The size (number of strands) and the length of the cable are the other influential factors that must be considered.

Several recent studies have investigated the opportunities of differential interferometry synthetic aperture radar (DInSAR) using satellite data for structural health monitoring (SHM) of civil structures. However, its use in structural engineering is still debated because of the lack of a general understanding of the potential and limitations of the technology for bridge SHM. To overcome this issue, specific methods of data processing and displacement assessment with error quantification need to be developed. The present paper aims at giving an insight into the use of small baseline subset-differential synthetic aperture radar interferometry (SBAS-DInSAR) as a remote-sensing technology for civil infrastructure monitoring combining information at a large scale with those associated with a single bridge. In particular, an operational framework for the selection and processing of a measurement time series representative of the structural behavior of the bridge of interest is designed in a way that fully remote characterization and assessment can be carried out by exploiting web-mapping platforms according to the crowd-sensing paradigm. The workflow, designed consistently with a structural engineering perspective, has been tested with reference to a number of bridges crossing the Tiber river in Rome (Italy), showing that the proposed fully remote monitoring procedure can effectively support satellite data processing and interpretation. Moreover, some issues in view of the general use of satellite data for bridge monitoring emerged from the study. Gaps in the measurement point distribution over the bridge decks are frequently observed over all the monitored area, therefore simplified methodologies aimed at estimating expected displacement ranges of different bridge typologies under serviceability loads have been defined enabling a rational interpretation of the data in the light of the selected radar sensor band of operation. Simplified formulations and charts for service and environmental loads are then presented with a twofold objective: (1) supporting the satellite data elaboration and interpretation by means of easy to manage open-source tools; and (2) providing estimates of the expected operational displacements of healthy structures to guide data interpretation and even algorithms for radar signals processing able to incorporate the response of structures to temperature variations.

The superstrong typhoon Lekima landed twice along the Yellow Sea of China in 2019; its wind characteristics and impact on bridges’ buffeting performance are still unclear. Based on the measured wind and temperature data of a long-span composite girder cable-stayed bridge along the Yellow Sea, this paper studies the wind characteristics and wind–temperature correlation of typhoon Lekima at the bridge site. First, the non-Gaussian and nonstationary tests of the typhoon are carried out at three stages, namely, before, during, and after the landing of the typhoon. Second, the turbulence intensity and gust factor at the three stages are statistically analyzed, and then the power spectra and the turbulence integral scale are compared by using four evaluation methods. Finally, the joint distribution model of the wind speed and structural temperature at the bottom of the composite girder is constructed, and their parameter estimation and the density functions of five copula functions are calculated, respectively. The results indicate that the wind speed has obvious Gaussian and nonstationary characteristics during the typhoon, while it has non-Gaussian and nonstationary characteristics before and after the typhoon. The gust factor is consistent in characterizing the turbulent characteristics of the fluctuating wind and linearly changes with the turbulence intensity. Besides, the power spectrum is consistent with four classical spectra in the low-frequency region before and during the typhoon, and the autocorrelation index method and power spectrum method are not suitable for calculating its turbulence integral scale. By comparing the square Euclidean distances, root mean square error, and the Kendall and Spearman rank correlation coefficients, the Frank-copula function has the best fitting accuracy for the correction between the wind speed and temperature among the five copula functions with a symmetric U-shaped distribution in thick-tails’ location.

Due to the influence of the three-dimensional (3D) effect, the identification accuracy of 3D aerodynamic admittance functions (AAFs) would inevitably be influenced by the ratio of turbulent integral scale to model dimension (dimensionless integral scale). For this, the two-dimensional (2D) AAFs of a streamlined bridge deck in different turbulent flow fields are experimentally investigated, wherein the 2D AAF is determined by separating out the 3D effect from the 3D AAF. Consistent with the previous studies, the 3D AAFs exhibit significant flow field dependence, and are less than the Sears function in low-frequency range. Different from the 3D AAF, the 2D AAFs obtained in two turbulent flow fields are higher than the Sears function and have a good consistency in various turbulent flows. It can be therefore considered that the identification accuracy of 2D AAF of a streamlined bridge deck is not related to the dimensionless integral scale, which might avoid the possible deviation caused by the mismatch of integral scale in the wind tunnel test. An empirical formula for the 2D AAF of a streamlined bridge deck is then proposed by fitting the experimental data. In addition, to further examine the validity of above conclusion, a comparison between the 3D AAFs of a streamlined bridge deck measured in other wind tunnel tests and the predictions calculated with the present 2D AAF is also made.

This study introduces a new main cable protection system designed to mitigate the issue of cable corrosion by circulating dry air from within the main cable. The proposed protection system effectively addresses the limitations of traditional anticorrosion techniques. In this study, the primary focus was on the initial design of the key structure for the new main cable protection system. Moreover, a comprehensive dehumidification test was conducted on a full-scale model of the main cable to validate the radial strength of a new ventilation pipe and assess the impact of the proposed corrosion protection system. The dehumidification efficiency of the new main cable protection system was verified in comparison to the traditional main cable protection system. The results indicate that the newly designed ventilation pipe exhibited minimal radial deformation when subjected to cable clamp pressure. Therefore, the ventilation pipe meets the strength criteria for the internal utilization of the main cable. The ventilation pipe's opening hole scheme was configured at 6 × Ø4 to guarantee that the entire main cable is enveloped by the dry air supplied into it. Relative humidity at each measurement point along the main cable was observed to decrease to below 60%. Consequently, the proposed main cable dry air protection system can attain the anticipated anticorrosion outcome. Under the test conditions, the dry air utilization rate of the proposed system exceeded that of the traditional main cable anticorrosion system by approximately 15.4%. This suggests that the new system exhibits a higher dry air utilization rate and dehumidification efficiency than the traditional system. The study results validate the dehumidification effect of the new system and endorse its utilization in primary cable anticorrosion projects.

In response to the issue of reduced transverse connection strength (TCS) in box-girder bridges, this paper presented a technique using a concrete-filled steel tube truss (CFSTT) to improve the transfer of loads between girders. The Euclidean norm-deflection method was proposed to address the challenge of quantitatively evaluating TCS, which existing methods struggle with. The effectiveness of these approaches was evaluated based on experiments and simulations. Static loading experiments revealed reductions of 14.29% and 18.99% in the deflection and strain, respectively. Under the moving loads, the deflection was reduced by approximately 21.80% and remained unaffected by the velocity. In addition, there was a slight increase (about 5.90%) in the ultimate load of the strengthening model, whereas the failure mode and damage evolution were almost unaffected. However, the strengthening effect was influenced by factors such as the initial damage ratio (IDR), overloading ratio (OR), and CFSTT quantity. When the IDR exceeds 10%, the initial damage affects the strengthening effect. The TCS increased when the OR was below 50% but decreased when it surpassed this threshold. However, CFSTT could sustain its strengthening effect for ORs below 100%. As CFSTT quantity increased, the maximum deflection of the bridge initially decreased and then increased, suggesting that increasing CFSTT quantity did not necessarily enhance strengthening effectiveness. Therefore, there might be an optimal quantity for specific bridges. Finally, the long-term monitoring results demonstrated that over a 60-month monitoring period, the maximum strain reduction rate of the strengthening bridge changed by 3%, indicating the durability of the CFSTT strengthening method.