Welded joints in steel bridge decks are vulnerable to the fatigue damage caused by heavy-loaded trucks. A realistic probabilistic model of truck loads provides a basis for simulating the fatigue stress spectrum of these welded joints, where the fatigue reliability assessment can subsequently be carried out. In this paper, a stochastic fatigue truck load model was developed for probabilistic modeling of fatigue stress ranges to investigate the fatigue reliability of welded steel girder bridges. To deal with the uncertainty-induced computational complexity, a framework including deterministic finite-element-based hot-spot analysis and probabilistic modeling approaches is presented. In addition, a learning machine integrating uniform design and support vector regression is used to substitute the time-consuming finite-element model. The development of both the framework and the learning machine provides a reasonable, efficient, and accurate probabilistic fatigue damage model. Finally, a limit-state function of fatigue damage is established with the consideration of traffic parameters, including the growth factors of traffic volume and the vehicle weight. A prototype steel box-girder bridge is presented as a demonstration to illustrate the feasibility of the proposed stochastic fatigue truck load model and the corresponding framework. Parametric studies indicate the impact of traffic parameters on fatigue reliability indices of the welded joint in the lifecycle. The stochastic fatigue truck load model provides a new approach for probabilistic modeling of fatigue damage and reliability assessment of welded steel bridges.

Dynamic responses of highway bridges induced by wind and stochastic traffic loads usually exceed anticipated values, and tuned mass dampers (TMDs) have been extensively applied to suppress dynamic responses of bridge structures. In this study, a new type of TMD system named pounding tuned mass damper (PTMD) was designed with a combination of a tuned mass and a viscoelastic layer covered delimiter for impact energy dissipation. Comprehensive numerical simulations of the wind/traffic/bridge coupled system with multiple PTMDs (MPTMDs) were performed. The coupled equations were established by combining the equations of motion of both the bridge and vehicles in traffic. For the purpose of comparing the suppressing effectiveness, the parameter study of the different numbers and locations, mass ratio, and pounding stiffness of MPTMDs were studied. The simulations showed that the number of MPTMDs and mass ratio are both significant in suppressing the wind/traffic/bridge coupled vibration; however, the pounding stiffness is not sensitive in suppressing the bridge vibration.

Residual stresses are an inevitable result of the welded fabrication process of corrugated steel webs (CSWs), resulting in structures with high and unpredictable stress fields, causing unexpected failures. The residual stress field is affected by structural parameters and the welding path of CSWs. This study proposes the welding process simulation method for CSWs with element birth and death technology. The optimization design method of heat source parameters is proposed. The feasibility of the simulation method is verified by comparing the numerical results with the experimental results of relevant literature. As a part of the study, a comparison of residual stress fields upon cooling welded CSWs with bending angles of 30, 45, and 60 degrees is presented. Thereafter, the effect of two types of single-sided welding paths and double-sided welding construction processes on residual stress distribution is discussed. Generally, the study results have shown that the equivalent residual stress near the weld reaches the maximum 344 MPa, which is very close to the Q345 steel yield strength. The size of the bending angle has no major effect on the residual stress distribution pattern, but it influences the residual stress value at the bending position. The residual stress at the bending position increases with the bending angle of CSWs. Different welding paths significantly impact the residual stress of the weld toe, and selecting a reasonable welding path can effectively reduce the residual stress value by 20 to 40 MPa.

The application of reinforced concrete (RC) beam with near-surface mounted (NSM) pre-stressed carbon fiber reinforced polymer (CFRP) plates has been increasingly widespread in civil engineering. However, debonding failure occurs easily in the early loading stage because of the prestress change at the end of CFRP plate. Therefore, it is important to find reliable, convenient and economical technical means to closely monitor the secure bonding between CFRP and concrete. In this paper, an active sensing approach for generating and sensing stress wave by embedded smart aggregates (SAs) is proposed, which provides a guarantee for the secure connection between CFRP and concrete. Two specimens with different non-pre-stressed bond lengths were fabricated in the laboratory. Six SAs were installed at different positions of the structure to monitor the degree of debonding damage during the loading process. The experiments showed that the optimal length of non-pre-stressed CFRP bond section (300 mm) can significantly improve the load characteristics and enhance the service performance of the structure. The theoretical analysis of wavelet packet shows that increasing the length of non-pre-stressed CFRP bond section can slow down the occurrence and propagation of debonding cracks. The debonding crack in the tension end region is earlier than that in the bond end region. The research results reflect that the developed approach can monitor the damage process caused by debonding cracks and provide early warning for the initial damage and the debonding failure.

Steady traffic growth may pose a safety hazard to in-service bridges, especially long-span bridges subjected to the simultaneous presence of multiple heavy-duty trucks. This study presents a methodology for evaluating the statistical extrapolation of traffic-load effects on long-span bridges. As part of the contributions advancing the state of the art, this study addresses several challenging issues, including traffic growth, and the resulting dynamic impact, and actual traffic patterns. The nonstationarity of the traffic-load effects due to traffic growth is considered in a series system compounded by several interval traffic models. The dynamic impacts of traffic loads were simulated by a traffic-bridge-coupled vibration system, and the statistical characteristics were captured using a level-crossing model. The actual traffic pattern was simulated by stochastic traffic flows on the basis of the statistics of the weigh-in-motion measurements of a highway bridge. Two numerical examples show the ability of the interval-traffic-growth model to capture the nonstationarity of the growing traffic loads. In addition, a case study of a long-span suspension bridge shows the effectiveness of implementing the proposed methodology for the statistical extrapolation of the maximum deflection. The numerical results of the case study also reveal that the degradation of road-roughness conditions leads to more level crossings but also results in a slight increase in the extrapolation of the deflection. However, traffic growth results in rapid increases in both the extrapolated deflection and the probability of exceedance of the deflection limit.

This paper develops an improved analytical algorithm on the main cable system of suspension bridge. A catenary cable element is presented for the nonlinear analysis on main cable system that is subjected to static loadings. The tangent stiffness matrix and internal force vector of the element are derived explicitly based on the exact analytical expressions of elastic catenary. Self-weight of the cables can be directly considered without any approximations. The effect of pre-tension of cable is also included in the element formulation. A search algorithm with the penalty factor is introduced to identify the initial components for convergence with high precision and fast speed. Numerical examples are presented and discussed to illustrate the accuracy and efficiency of the proposed analytical algorithm.