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This paper introduces new contributions for construction procedures designed to enhance the robustness and precision of stress control in active anchorage and short presetressing units for long-span bridges, particularly addressing potential technical risks. The primary focus is on optimizing stress management for bridge stays, suspension cables, and short prestressing units by emphasizing a unified parameter: stress. The contributions of this research encompass (1) the introduction of advanced load cells for stress control in active anchorages and (2) the implementation of a novel synchronized multi-strain gage load cell network for short prestressing units, crucial in situations where prestressing losses can attain significant magnitudes. To validate these advancements, the authors present (3) a practical experience and results obtained from applying these methodologies in monitoring the structural response during the construction of the Tajo Bridge using the cable-stayed cantilever technique. [ABSTRACT FROM AUTHOR]

Bridge aerodynamic studies are essential in ensuring the safety and acceptable performance of long-span bridges vulnerable to the effects of cross-winds. Aerodynamic studies were traditionally carried out in wind tunnel facilities, but there are now greater opportunities for using computational fluid dynamics (CFD) modelling. Few three-dimensional (3D) aerodynamic simulations of lightweight vehicles on bridges exist, but limited validation and verification work has been carried out. In the study reported in this paper, 3D CFD models were developed for Queensferry Crossing – a cable-stayed bridge in Scotland – containing wind shields and sample vehicles. The models considered the wind effects from a range of yaw wind angles and subsequently determined the aerodynamic coefficients of vehicles. The models were verified by means of a mesh sensitivity study, a domain sensitivity study and comparisons with wind tunnel tests. The models were then validated using the same modelling process but with a different type of wind shield and again comparing the results with wind tunnel test data for the same configuration. The results showed that CFD modelling can determine aerodynamic coefficients to a level of accuracy similar to that of wind tunnel tests. [ABSTRACT FROM AUTHOR]

The profile of the rail expansion joint (REJ) would affect the stable operation of high-speed trains, so it needs to be optimized. An optimization method was presented for the switch rail declining values (SRDV) of REJ at the beam end in a long-span cable-stayed bridge (CSB) through the co-simulation based on SIMPACK and MATLAB. First, based on the theory of rigid-flexible coupling, a high-speed vehicle-REJ-CSB multibody dynamics model was established. The model conducted a detailed simulation of the beam end track system and performed a parameterized design of the REJ profile. Then, 8 dynamic indicators of high-speed vehicles were selected as optimization objectives. The Simulated Annealing Particle Swarm Algorithm (SA-PSA) was employed to solve the objective function and obtain the optimal SRDV of REJ. Finally, the effect of the optimization was verified by the model test. The results indicated that the optimal SRDV had the most significant reduction in the wheel-rail forces, followed by the motion of the bogie frame. The wheel-rail vertical force was reduced by 9.59%, and the wheel-rail lateral force was reduced by 20.56%. The lateral acceleration of the bogie frame was reduced by 8.69%. Under the damping effect of the primary and secondary suspension system, the influence of the REJ profile on the acceleration of the vehicle was relatively small. Therefore, the optimization for SRDV had little effect on the acceleration of the vehicle. Through the model test, the superiority of the optimization results in this paper was verified. [ABSTRACT FROM AUTHOR]

The interface force condition on the cross section of parallel steel wire strands is an important basis for studying the longitudinal friction and slip behavior of wires. In this study, force-chain superposition was proposed to solve the transmission and distribution of transverse forces between parallel wires. The calculation rules for the basic parameters in the solution were determined, and a wire-drawing experiment was designed to verify their applicability. A two-dimensional discrete model corresponding to the cable cross section was established. According to the source and characteristics of the transverse load, the force system is decomposed into two directions to form two force chain analysis paths so that the model assumptions can be applied properly. A recursive algorithm was proposed to solve the two force chains, and symmetry conditions were applied at the coupling position to make the system self-consistent. The normal forces acting on the interface points were obtained by superimposing the results onto the two force chains and were verified against finite element analysis (FEA) results. A long-span cable-stayed bridge was considered as an example to investigate the interface force condition of its cables, based on which the approximate development length of the broken wires and the interface extrusion force of the multilayered beam model were established. The results indicate that the slight twisting of the parallel wire strands under the action of a large cable force provides 85% of the total interface forces, and the normal force is significantly concentrated in the central area of the cross section. The approximate development length of the central wire is only 25.9% of that of the outermost wire, and the minimum slip friction force between the layers accounts for only 21.2% of the maximum value for the multilayered beam model, confirming that the interface force condition has a significant impact on the longitudinal friction and slip behavior of cable wires. [ABSTRACT FROM AUTHOR]

This study proposes a simplified analysis method that couples the bridge and train-track subsystem in a weak form to facilitate the dynamic analysis of the train-track-bridge coupled system (TTBS) under earthquakes. The method includes three main steps: (i) performing dynamic analysis of the bridge under seismic conditions to obtain the response of the bridge deck; (ii) interpolating the bridge displacement beneath each wheelset based on the train's velocity, departure time, and the initial positions of the wheelsets; and (iii) assessing the running safety of the train by incorporating the interpolated bridge response as track irregularity into the train-track coupled system. Steps (i) and (iii) can be analyzed separately using finite element and multibody dynamics software, eliminating the need to create a complex TTBS model that is challenging to achieve within a single software platform. Additionally, based on the method's assumptions, the earthquake excitation on the train can be separated into the seismic inertial effect and seismic-induced bridge deformation, enabling a quantitative analysis of the impact of these two types of excitations on train safety. Taking a 10-span simply supported bridge and a long-span cable-stayed bridge as examples, the proposed method's assumptions are verified by comparing its results with those obtained from a complex TTBS model. Furthermore, the impact characteristics of inertial effects and seismic-induced bridge deformation on train safety for these two types of bridges are analyzed. The proposed method offers robust support for seismic design of bridges and facilitates a comprehensive analysis of the mechanisms through which seismic excitations affect train safety. • Proposal and validation of a simplified method for running safety evaluation of train on bridges under earthquake excitation. • Separation of seismic excitation on the train into seismic inertial effect and seismic-induced bridge deformation. • Analysis of impact characteristics of inertial effects and seismic-induced bridge deformation on train running safety. [ABSTRACT FROM AUTHOR]

Since the excessive seismic support uplift force may cause the support failure of long-span cable-stayed bridges, this study focused on the support uplift force at the auxiliary pier for a double-tower cable-stayed bridge with a main span of 1088 m. A shake table test was designed and performed based on the 1/35-scale test model scaled from the prototype bridge. Details of the test model, including the scale factor, structural member configurations, boundary conditions, and the numerical validation were briefly presented. The test results show that although only the longitudinal ground motion was applied, significant seismic support uplift and compression forces would be generated in the bearings at the auxiliary pier, resulting in the bearing uplift. The vertical vibration of the deck contributed by the first vibration mode of the test model was one of the main causes of the bearing uplift, but no rigid-like pounding effect occurred due to the vertical nonlinear mechanical behaviour of the bearing. Furthermore, the effect of the bearing uplift on the main seismic responses of the test model was negligible. • The support uplift force of a long-span cable-stayed bridge under longitudinal ground motions is experimentally studied. • The seismic responses of the tests model related to the support uplfit force are obtained and analyzed. • Significant seismic support uplift force and compression force will be generated, resulting in the bearing uplift. • The vertical vibration of the deck contributed by the first vibration mode is one of the main causes of the bearing uplift. [ABSTRACT FROM AUTHOR]

New issues of wind-induced cable vibration, i.e., multi-mode vibrations, increasingly occur in long-span bridges, which are closely associated with underlying damping features. In this study, an analytical method is proposed to identify nonlinear aerodynamic damping in multi-mode wind-induced cable vibrations in fields, involving the assessment of total and mechanical damping. The method is available to extract a series of mono-component resonances/decays from the measured signals based on the analytical mode decomposition (AMD) and random decrement technique (RDT), and then to determine the damping parameters using the Hilbert transform (HT) combined with the smoothing spline or linear least-square fitting. Furthermore, this method is applied to address the vortex-induced vibrations (VIV) of an ultra-long stay cable on the Sutong Bridge. Firstly, the vibrations are reported in terms of a typical event and one-year statistics. Subsequently, the damping parameters are identified to illustrate the in-situ aeroelasticity. The results show that the cable exhibits high-frequency vibrations primarily in the 41st to 43rd modes, and the aerodynamic damping exhibits significant amplitude-dependent nonlinearity. Finally, the damping identifications are employed to reveal the onset mechanism for the vibrations, and a Scruton number (Sc) criterion, i.e., Sc > 5.4, is suggested for mitigating the vibrations. • An analytical method is proposed to identify nonlinear aerodynamic damping during multi-mode wind-induced cable vibrations in the fields. • High-order multi-mode vortex-induced vibrations of an ultra-long stay cable are reported in terms of a typical event and one-year statistics. • The underlying aeroelastic mechanism for the vibrations is revealed through aerodynamic and mechanical damping identification. • A Scruton number criterion, i.e., Sc > 5.4, for mitigating the vibrations is suggested based on the damping identification. [ABSTRACT FROM AUTHOR]

Saddle position is an essential parameter in the form-finding of main cables and for the construction control of suspension bridges. In actual suspension bridges, the center of the arc-shaped tower saddle in the completed bridge state may sometimes deviate toward the river and the river bank. However, the influencing factors and the judgment method for the deviation have yet to be thoroughly studied. This study proposes an analytical approach for estimating saddles positions in the completed bridge state of suspension bridges under two definitions of the intersection point (IP) of the main cable in the tower top: (i) IP between the two extended catenary segments of the main cable and (ii) IP between the two extended straight lines of the main cable. For catenary-based IP, the calculation of the saddle position is separable from the form-finding of the main cable. Once the shape of the main cable is derived, equations can be established based on the geometric compatibility conditions for the saddle and main cable, their solving required for deriving saddles positions. For straight line-based IP, the calculation of the saddle position is inseparable from the form-finding of the main cable, and the two processes are conducted simultaneously. Equations can be established based on mechanical equilibrium and the geometric compatibility conditions for the saddle and the main cable and then solved. The relationship between the position of the center of the arc-shaped tower saddle and the centerline of the tower is analyzed, proving that the saddle deviates toward the side with a smaller catenary parameter. The eccentric compression of the tower is analyzed, implying that the eccentric moment acting on the tower in the completed bridge state is primarily produced by the self-weight of the saddle and the main cable segment in the saddle. Finally, the feasibility of the proposed method and the correctness of the above findings are verified through a suspension bridge with a main span of 730 m. • An analytical approach for estimating saddles positions in the completed bridge state of suspension bridges is proposed. • The relationship between the position of the center of the tower saddle and the centerline of the tower is analyzed. • This paper analyzes the eccentric compression of the tower, and clarifies the reason for eccentric compression of the tower. • The impact of two definitions of the intersection point on the form-finding of suspension bridge is analyzed. [ABSTRACT FROM AUTHOR]

The steel-UHPC composite deck is an effective solution to fatigue cracks of orthotropic steel decks (OSD) in steel bridges. However, limited research has been reported on the hot spot stress distribution of the steel-UHPC composite deck. This study investigates the hot spot stress distribution and residual fatigue life evaluation of the steel-UHPC deck in a long-span cable-stayed bridge. The two extrapolation points' strain at fatigue-prone details were continuously measured under in-service traffic flow. The hot spot stress time history at each detail of the conventional OSD deck and steel-UHPC deck were analyzed and compared. The residual fatigue life of each detail was calculated. A three-dimensional finite element (FE) model was established and validated through experimental results. The bridge deck's deflection, the asphalt pavement's tensile stress, and the stress distribution at the floor beam cutout were numerically studied using the validated FE model. The results showed that the UHPC layer significantly reduced the hot spot stress and extended the fatigue life at each fatigue detail. The UHPC layer reduced the bridge deck's deflection and the asphalt pavement's tensile stress. Compared with nominal stress method, the hot spot stress method can better describe the large stress gradient distribution induced by the stress concentration at fatigue detail. • Field strain monitoring was conducted on a long-span cable-stayed bridge under in-service traffic. • The hot spot stress were obtained through two points extrapolation method. • Hot spot stress distribution of the conventional deck and steel-UHPC deck was compared. • Fatigue performance of steel-UHPC deck were evaluated based on monitored data. • Numerical simulation of steel-UHPC deck was conducted by a validated FE model. [ABSTRACT FROM AUTHOR]