Self-anchored Suspension Bridge Research Articles

Effect change of extra-wide concrete self-anchored suspension bridge under blast loads and its prediction considering time-dependent effect

In order to study the dynamic response of self-anchored suspension bridge with extra-wide concrete girder under explosive load, a real bridge was taken as the background, which is the widest on in China at present. Firstly, the refined finite element model (FEM) of the whole bridge was established. The reliability of numerical simulation method was validated by the measured data of the bridge at completion state and explosive test results of scaled girder specimen. The vertical displacement, reinforcement strain, acceleration and failure characteristics of the girder specimen under the explosive load of 3 kg TNT were analyzed. Through parametric simulation, the effects of different scale distance, concrete strength and reinforcement ratio on the explosion response of girder specimen were studied. Secondly, the dynamic responses of girder were studied. Finally, the change law of dynamic response at different ages was analyzed. The results show that the elliptical crack is formed on girder top plate. The maximum girder vertical displacement reaches 135.9 mm under 1000 kg, and the maximum increasing ratio of hanger force is 27%. The influence brought by the extra width of girder is significant. The girder vertical displacement changes along transverse direction and the concrete breach sizes are different. In addition, with the increase of service age, the girder displacement increases from 60.50 mm to 106.16 mm under the same explosive load. The research results can provide an important basis for the anti-explosion protection and reinforcement of similar extra-wide concrete self-anchored suspension bridge.

Structural Response of an Extra-Wide Concrete Self-Anchored Suspension Bridge under Static Vehicle Loads: Testing and Numerical Simulations

The finite element (FE) analysis by ANSYS software based on field test was used to study the structural performance of an extra-wide concrete self-anchored suspension bridge under static vehicle loads. The longitudinal, transverse and vertical stresses of the extra-wide girder were analyzed, and the changing criteria of girder stresses induced by vehicle loads were presented. Additionally, the effects of the shear lag on extra-wide box girders were investigated. The results showed that the maximum shear lag coefficient was 1.89 at the junction of bottom plate and outer web at the middle of midspan. Moreover, the non-uniformity of cable force is perceptible under eccentric load. Furthermore, an optimization measure for comparable bridges and essential health monitoring locations were outlined.

An Analytical Model for Three-Tower Self-Anchored Suspension Bridges with Longitudinal Tower-Girder Connections

This study proposes an analytical model for three-tower self-anchored suspension bridges with different longitudinal tower-girder connections based on the deflection theory. The proposed model utilizes horizontal springs to model the stiffness of the tower-girder connections and includes the nonlinear effect caused by the stiffness of the towers and the tower-girder connections. The comparison analysis demonstrates that the structural responses predicted by the proposed analytical model agreed well with those gained by the nonlinear finite element method under various live load cases. A parametric analysis is carried out to examine the effects of different parameters, including the side-to-main span ratio, stiffness of the towers, sag-to-span ratio, axial and flexural stiffness of the girder, on the mechanical characteristics of three-tower self-anchored suspension bridges. The results show that decreasing the side-to-main span ratio and the sag-to-span ratio have the same effect as increasing the flexural stiffness of the girder on improving the static behavior of three-tower self-anchored suspension bridges. The tower-girder longitudinal connection has an apparent impact on the structural performances of the bridges, and the structural system with a tower-girder connection at the mid-tower always has the smallest structural responses under live loads.

Comparative Analysis of Buffer and Damper Positions for Increasing the Seismic Performance of Suspension Bridge

In this research, a finite element model is established to investigate effective seismic control schemes for a self-anchored suspension bridge (SASB) with three towers. Nonlinear dynamic analyses are conducted to evaluate the seismic performance of SASB with different layout schemes of viscous dampers and buffers, which were installed in longitudinal direction and transversal direction, respectively. The responses of the SASB designed with 10 seismic control schemes are compared to ascertain suitable seismic schemes for SASBs. The results show that the number and location of lateral buffers have an important impact on the dynamic characterization of the SASB, especially for the first lateral mode and lateral fundamental frequency. To effectively increase the seismic performance of SASBs with three towers, mounting buffers between the side towers and the main girder of SASBs is an appropriate scheme. The viscous dampers can effectively decrease the dynamic reaction of the towers and longitudinal deformation of the girder under earthquake excitations. The plan involves the installation of dampers between the main concrete stiffening girder and the side towers as the optimal longitudinal seismic scheme for the SASB. The study offers important insights into the seismic design of SASBs with three towers.

Study on the movements and bending stresses of hangers and control measures in self-anchored rail suspension bridges

As a critical component of suspension bridges, hangers face an increasingly prominent risk of deterioration and even breakage due to relative movement and fatigue stress, posing a serious threat to bridge safety. This study investigated longitudinal movements and bending stresses of short hangers in a typical self-anchored rail suspension bridge using transient dynamic analysis. We proposed an effective method to calculate the bending stresses of hangers based on a frame finite element model (FFEM). The effects of hanger breakage on the dynamic response of bridges were further analyzed. Results showed significant relative longitudinal movements between cables and girders, causing consequential periodic bending stresses on hangers. Furthermore, the bending stresses considerably increased as the lengths of these hangers decreased. The relative longitudinal movements and bending stresses of short hangers exhibited static characteristics in self-anchored suspension bridges. The breakage of hangers induced a significant dynamic response on adjacent hangers, which bore the most redistributed loads and became critical components. Based on the static deformation characteristics of self-anchored suspension bridges, two promising measures—adding central clamps or negative stay cables—were proposed to reduce the bending stresses and improve the fatigue performance of hangers. The improvements of the two measures were comprehensively analyzed and compared. The findings of this study are significant for improving the design of rail self-anchored suspension bridges in terms of hanger safety.

Design and performance assessment of a novel self-anchored pedestrian suspension bridge

Conventional suspension bridge systems generally adopt a symmetrical layout, which has limited applicability in asymmetric urban terrain. However, the span capacity of the asymmetric bridge system is not as good as that of the conventional suspension bridge. Therefore, under the constraints of limited space, it is very urgent to design a new asymmetric pedestrian bridge with a strong crossing ability on the complex asymmetric terrain of the city. However, the design faced two challenges. (1) Because of the asymmetry of the structure, the cable balance equation and calculation theory of the new bridge need to be redetermined; (2) Because of the restriction of terrain conditions, it is necessary that optimize the preliminary design of the new bridge to achieve better mechanical properties. To address above problems, a new self-anchored continuous steel box girder composite system is proposed for use in suspension footbridges. This system uses connectors to reliably connect the suspension, main girders, and pylons. The continuous beam structure is used in the side span of the pedestrian bridge and the cable-stayed beam composite system is used in the main span. Therefore, the mechanical behavior of the structure is complex. To investigate the mechanical characteristics of the new structural system based on the preliminary conceptual design, the static and dynamic stability of the proposed structural system is comprehensively analyzed. A new force mode is proposed to improve the mechanical properties of the proposed structural system, and the applicability of the tuned mass damper to the new structural system was verified. Finally, an improved multi-objective genetic algorithm (I-MOGA) algorithm is hired to optimize the layout and mechanical properties of the proposed-composite system. The effectiveness and feasibility of the proposed-composite system bridge is verified to design for urban pedestrian bridges in limited terrain. Moreover, I-MOGA is used to optimize the design of the proposed mixed systems and obtain an improved structural layout for a complex pedestrian bridge in terms of forces, stability, and reliability. This study will provide a reference for the design of urban bridges on asymmetric terrain.

Study on Dimensionless Mid-tower Stiffness of Three-Tower Self-Anchored Suspension Bridges Based on an Analytical Approach

Different from the earth-anchored suspension bridges, both the main cable and the stiffening girder significantly contribute to the stiffness of self-anchored suspension bridges. Meanwhile, the mid-tower effect is also non-negligible when extending the traditional self-anchored suspension bridges to the multi-tower system. This study derives a load distribution coefficient to include the coupling effect between the main cable and girder based on displacement compatibility conditions. The load distribution coefficient determines the live-load deflection of the girder and the cable forces on both sides of the mid-tower, corresponding to the lower and upper bound of the mid-tower stiffness. This study also proposed an analytical approach to determine the feasible dimensionless range of the mid-tower stiffness for three-tower self-anchored suspension bridges. The nonlinear finite element method is utilized to validate the accuracy of the analytical model, and a parametric analysis is carried out to examine the effects of different parameters, including the live-load ratio suffered by the main cable, the geometric and loading parameters, the cable-girder connections, and the tower-girder connections, on the range of dimensionless mid-tower stiffness. The results demonstrate that the feasible stiffness range of mid-tower depends on more parameters, including the live-load ratio supported by the main cable, the dead-to-live load ratio, the sag-to-span ratio, and the cable-girder connections, compared with three-tower earth-anchored suspension bridges.

Investigation on fatigue cracks of diaphragm cutout in bridge orthotropic steel deck

Fatigue cracks were found at the diaphragm cutouts in the orthotropic steel deck (OSD) of a self-anchored suspension bridge while the in-service time of the bridge was less than 10 years. The causes of fatigue cracks of the diaphragm cutout are investigated in this study. The fatigue cracks initiated from the intersections of the arc curves and the straight lines, which form the geometrical discontinuity to the cutout edge. The in situ monitoring and finite element analysis under fatigue load model indicate that the cracking region in the cutout is in bidirectional compression. However, the thermal-structural analysis and tests show that the rib-to-diaphragm welding process produces high tension residual stress at the cracking points of the cutouts. The cutouts are under tension-compression cyclic loading because of the coupled stress, which is derived from the vehicle-induced stress and the welding residual stress. The results show that the strain energy method can present a reasonable fatigue life estimation for the diaphragm cutouts with full consideration of the residual stress.

Study on Static Analytical Method of Multi-Tower Self-Anchored Suspension Bridge

Based on the deflection theory and the characteristics of multi-tower self-anchored suspension bridges, considering the influence of longitudinal stiffness of main tower and bending effect of stiffening beam, the equilibrium differential equation and deformation coordination equation of multi-tower self-anchored suspension bridges are established. By “replacing beam” method, the practical calculation formula of internal force and deformation of multi-tower self-anchored suspension bridge was deduced, and the corresponding calculation program was implemented. The correctness of the analytical method and calculation program was verified by an example. The analytical method of static analysis of multi-tower self-anchored suspension bridges established in this paper can theoretically explain the mechanical characteristics of the structure, and the calculation method has a clear calculation flow. The internal force and deformation of the structure under live load can be approximately calculated only by inputting the main design parameters of the structure, which is suitable for structural design and parameter analysis of multi-tower self-anchored suspension bridge.

The San Francisco–Oakland Bay Bridge, CA, USA – eastern span

With daily traffic of 260 000 vehicles, the San Francisco–Oakland Bay Bridge is a major connection in the San Francisco Bay area (CA, USA). The new bridge is a designated lifeline structure (to remain open for emergency traffic after a major seismic event) with a design life of 150 years. The new bridge is 3.6 km long and consists of four distinct structures: a low-rise post-tensioned concrete box girder near the Oakland shore; a 2.4 km long segmental concrete box girder (skyway); a first-of-its-kind self-anchored suspension (SAS) bridge with a 385 m main span over the navigational channel; and a post-tensioned concrete box girder that connects to the east portal of the Yerba Buena Island tunnel. Opened in 2013, the signature span of the bridge is the SAS bridge with a length of 624 m and a total deck width of 79 m accommodating ten lanes of traffic in addition to a bike/pedestrian path. The US$6.4 billion megaproject was procured under multiple contracts and was delivered using the traditional design–bid–build method. This paper describes the key design innovations and construction methods which address the unique challenges on this project.

Research on the Control Method for the Reasonable State of Self-Anchored Symmetry Suspension Bridge Stiffening Girders

Most existing methods for the determination of the reasonable finished state of self-anchored symmetry suspension bridges were based on the stress state of the stiffening girders used in the construction. A simple and practical control method for the reasonable completion state of stiffened beam based on double control indexes of deformation and stress was proposed. In this paper, the long-term effects of shrinkage and creep were taken into consideration, and a finite element model was built to study the change in the stiffening girder stress during operation. The mid-span deflection of the middle span sustained increasing and the compression stress in the bottom slab of the stiffening girder consistently decreased under the effects of shrinkage and creep. The speed changes from fast to slow and tends to become stable in 50 years. Furthermore, stiffening girders under the action of hanger force, dead weight, cable force, and pre-stress were investigated to study the mechanism of the stress change during operation. Based on the safety stress state of stiffening girders after 50 years, a new control method for the reasonable finished state was proposed. Moreover, the total cross-section of stiffening girders maintained the compression stress state during the developing processes of shrinkage and creep in 50 years. Finally, the utilization in the Hunan Road self-anchored symmetry suspension bridge verified the simplicity and practicality of this new control method and confirms that the method can be implemented to guide the design and construction of the similar bridges.

A Simplified Calculation Method for Multi-Tower Self-Anchored Suspension Bridges Based on Frame Structure Theory Model

A Simplified Calculation Method for Multi-Tower Self-Anchored Suspension Bridges Based on Frame Structure Theory Model

Construction Monitoring of Self-Anchored Suspension Bridge with Inclined Tower

Abstract Inclined single-tower self-anchored suspension bridges feature a high adaptability to geological conditions but involve complicated structural behaviors during construction due to system t...

Force Analysis of Self-Anchored Suspension Bridges after Cable Clamp Slippage

The slippage of cable clamps during the long-term operation of suspension bridges is a common and detrimental phenomenon. From an experimental point of view, the cable clamp slippage of a suspension bridge was investigated to reveal the effect of this sliding on the force acting on the full bridge. The forces acting on the bridge before and after the slippage were analyzed using a finite element model. The calculation results showed that the cable clamp slippage directly affects the cable forces of the hangers. The hanger cable force decreased by 19.2% when the slippage reached 10.2 cm, while the maximum increase in the cable force of adjacent hangers was 147.7 kN, an increase of 7.25%. The variation of forces in the hanger cable disrupted the force balance of the main girder, thereby producing a torque effect at the corresponding position in the girder, i.e., increased torque. Meanwhile, the slippage affected the axial tension in the main cable and the main girder. The impact of the tower internal force was less than 1%. Hence, the study concluded that the effect of cable clamp slippage is better understood, ensuring the safety of the suspension bridge.

Sensitivity analysis in seismic reliability of an urban self-anchored suspension bridge

Seismic resistance and disaster prevention for self-anchored suspension bridge (SASB) are important, but the seismic reliability of this complex structure is time-consuming or low-accuracy based on existing methods, let alone the relative sensitivity analysis. A sampling-based hybrid methodology of sensitivity analysis in seismic reliability, combining subset simulation (SuS), explicit time domain method (ETDM), BP neural network (BPNN) and Pearson’s Linear Correlation Coefficient (PLCC), is proposed herein. The separated treatment of low and high variabilities of structural and earthquake parameters based on ETDM with BPNN accelerates the computing efficiency. With the application to the SASB, sensitivities of structural parameters to seismic reliability are obtained, where three largest ones are ambient temperature, Young’s modulus and density of girder. The failure probability of this bridge is mostly smaller than 1.0 × 10-3, but it takes only about 10 ~ 15 min to obtain single failure probability with a deterministic parameter vector based on the proposed method, which is in lieu of hundreds of days based on Monte Carlo simulation. Hence, it is verified a sound approach with great accuracy and efficiency used in engineering structures.

Mechanical Performance Analysis and Parametric Study of a Self-Anchored Suspension Bridge with Ultra-Wide Double-Sided Steel Box Girder

A sufficient understanding of mechanical performance of self-anchored suspension bridge with double-sided steel box girder is essential for design and normal use as such bridges are widely built in urban bridge. Using the Yunlongwan Bridge which is a suspension bridge with ultra-wide double-sided steel box girder as an example, this paper investigates its deformation and mechanical performance under vehicle load. Firstly, based on the field test results, the deformation performance of the bridge and the stress distribution of the main girder are analysed, with emphasis on the shear lag effect of double-sided steel box girder. Then, a multiscale model of the bridge was built, and the accuracy of the model was verified by comparison with the test data. Finally, the influence of design parameters on the mechanical behaviour of double-sided steel box girder is studied by numerical simulation. The results show that the deformation of the bridge has good symmetry, there is obvious shear lag effect on the main girder, and the U-rib thickness, diaphragm spacing, and vehicle load could significantly affect the stress of the main girder top plate. The obtained analytical results lead to a better understanding of the mechanical performance and provide reference for the design of self-anchored suspension bridge with double-sided steel box girder.

A Novel Shape Finding Method for the Main Cable of Suspension Bridge Using Nonlinear Finite Element Approach

The determination of the final cable shape under the self-weight of the suspension bridge enables its safe construction and operation. Most existing studies solve the cable shape segment-by-segment in the Lagrangian coordinate system. This paper develops a novel shape finding method for the main cable of suspension bridge using nonlinear finite element approach with Eulerian description. The governing differential equations for a three-dimensional spatial main cable is developed before a one-dimensional linear shape function is introduced to solve the cable shape utilizing the Newton iteration method. The proposed method can be readily reduced to solve the two-dimensional parallel cable shape. Two iteration layers are required for the proposed method. The shape finding process has no need for the information of the cable material or cross section using the present technique. The commonly used segmental catenary method is compared with the present method using three cases study, i.e., a 1666-m-main-span earth-anchored suspension bridge with 2D parallel and 3D spatial main cables as well as a 300-m-main-span self-anchored suspension bridge with 3D spatial main cables. Numerical studies and iteration results show that the proposed shape finding technique is sufficiently accurate and operationally convenient to achieve the target configuration of the main cable.

Numerical and theoretical research on spatial shear lag effect of self-anchored suspension bridge steel box girder

Numerical and theoretical research on spatial shear lag effect of self-anchored suspension bridge steel box girder

Concept and Preliminary Static Analysis of Hybrid Anchored Suspension Bridge

Abstract Inspired by the structural system and the construction technique of self-anchored suspension bridges and earth-anchored suspension bridges, a new type of suspension bridge, named hybrid an...

Analytical formulas of thermal deformation of suspension bridges

Deformation of a long-span suspension bridge is mainly caused by ambient temperature changes. The temperature-induced deformation of a bridge is usually calculated using complex three-dimensional finite element analysis, the mechanism of which is often unclear. In this study, we derive general, succinct analytical formulas of the thermal deformation of three-span suspension bridges. The deformation of different components is unified into a one-dimensional thermal expansion formula (δL=LEθ·δT) by introducing an equivalent length LE. The sag effect of side-span cables is characterized by the modification coefficients, which demonstrate that the neglect of the sag effect overestimates the thermal deformation. Furthermore, the thermal deformation of the main- and side-span cables and towers is found to interact with each other as a result of the cable tension changes with varying temperature. The analytical formulas are validated using eight long-span suspension bridges including the Akashi Kaikyo bridge, the longest main-span suspension bridge in the world. The closed-form solutions herein also apply to the self-anchored suspension bridges.