Super Long-span Cable-stayed Bridges Research Articles

Study on The Mechanical and Economic Performance of Super Long-Span Cable-Stayed Bridges with UHPC-Girder

Study on The Mechanical and Economic Performance of Super Long-Span Cable-Stayed Bridges with UHPC-Girder

Pattern and mechanism of wind-induced static instability of super-long-span cable-stayed bridge under large deformation

Large deformation can occur in super-long span cable-stayed bridges at high wind speeds, resulting in the effective wind attack angle of the bridge deck exceeding the stall angle of attack. The unloading of wind loads due to the stall can lead to a change in the pattern and mechanism of wind-induced static instability, on which few studies have been conducted. Wind-induced static instability analyses are applied on a super-long-span cable-stayed bridge with a closed steel box deck. The instability pattern and mechanism after the effective wind attack angle exceeds the stall angle are investigated. The influence of initial attack angle and span length on the unloading is discussed. Results show that for positive attack angles when the negative aerodynamic stiffness approaches the structural stiffness, the bridge may not experience wind-induced static instability but can re-stabilize after a jump in the deformation. For negative attack angles, the structure can fail due to the fracture of cables, but the unloading may decrease the growth rate of cable stress and thus improve the critical wind speed. The unloading effect can remarkably increase the critical wind speed for larger attack angles, and the improvement effect increases with span length and the initial attack angle.

Approximate calculation of the static analysis of a lifted stay cable in super-long span cable-stayed bridges

The sag effect of long stay cables is one of the key factors restricting further increase in the span of cable-stayed bridges. Based on the formerly proposed concept of long stay cables lifted by an auxiliary suspension cable in cross-strait cable-stayed bridges, corresponding static approximate calculations and analytical theory based on catenary and parabolic cable configurations are established. Taking a main span 1400 m cable-stayed bridge as the research object, three typical lifting conditions and the whole process of auxiliary cable lifting are analyzed and discussed. The results show that the sag effect is effectively reduced. The support efficiency is only improved when the cables are lifted above the original cable chord. Reduction of the horizontal component force of the cable is limited. The equivalent elastic modulus and the vertical support stiffness of the lifted cables are significantly increased with increased horizontal projection length and not sensitive to the change of the lifting point position. The scheme of lifting the cable to the chord midpoint is more economical because of the less steel required for the auxiliary suspension cable, but its effect on improving the vertical support efficiency is limited. The support efficiency is better when the cable is lifted to the cable end tangential to the original cable chord, but the lifting force and the cross-sectional area of the auxiliary suspension cable are doubled. The approximate calculation results of the lifted cables are very close to the numerical analysis results, which verifies the applicability of the approximation method proposed in this study. The results of parabolic approximation calculations are approximately equal to that of catenary cable geometry. As the parabolic approximation analysis theory of lifted cables is more convenient in mathematical processing, it is feasible to use parabolic approximation analysis theory as the analytical method for the conceptual design of lifted cables of super-long span cable-stayed bridges.

Transverse seismic response and failure mode of towers of a cable-stayed bridge full-model: Tests and simulations

Severe damage to towers of cable-stayed bridges have been recorded in past actual earthquakes. Therefore, increasing attention has been devoted to the seismic failure of cable-stayed bridges under strong earthquakes. However, few experimental studies focus on the seismic failure of long-span cable-stayed bridges including both superstructures and substructures under strong earthquakes. In this paper, a 1/70-scaled bridge full-model was designed and assembled following a 1400 m-span cable-stayed bridge, which was composed of the towers, girder, cables, piers, pile groups, and artificial soil placed in four shear boxes. Shaking table tests were conducted to study the seismic response and potential failure mode of towers of the bridge full-model under transverse earthquake excitation. Test results show that the tower exhibits an unexpected failure mode with the double plastic hinges, which reveals a new feature for the seismic failure of the tower of super long-span cable-stayed bridges. The plastic hinges are firstly observed at near the junction region between the tower and lower beam, then at the proximal joint portion between the tower and upper beam. The tower firstly suffers from severe damage or even local failure for the bridge full-model under strong earthquakes, but it could carry the vertical load. The seismic damage evaluated by the curvature criteria or residual displacements are in good agreement with the observed damage under earthquake excitation with low shaking amplitudes. Moreover, numerical modeling of the bridge full-model could effectively predict the dynamic properties and seismic response of the bridge full-model, and capture the character of the failure mode of the towers compared to the test results.

Evaluation of pile-soil-structure interaction effects on the seismic responses of a super long-span cable-stayed bridge in the transverse direction: A shaking table investigation

This paper presents shaking table studies to evaluate the pile-soil-structure interaction (PSSI) effects on the seismic responses and dynamic properties of a large-scale full model of a super long-span cable-stayed bridge with pile groups and site soil in the transverse direction. The dynamic interaction of the bridge full model, including superstructure and substructure, was investigated under earthquake excitations with increasing shaking amplitudes and various frequency contents in the transverse direction. The influences of the artificial soil on the dynamic properties were clarified statistically. The experimental results show that the maximum transverse relative displacements between the pile groups top and shear boxes top significantly increase as the shaking amplitude increase, indicating that a larger shaking amplitude implies a more apparent pile-soil interaction effect. The PSSI effects significantly change with the variation of the frequency contents of earthquake waves. Moreover, the substructure has an obvious influence on the seismic responses of the bridge full model in the transverse direction, accompanied by an acceleration increment in structural components. The seismic demands of the cable-stayed bridge may be underestimated and even misinterpreted to a certain degree when the substructure effects are neglected, which suggests that the substructure effects should be considered in the seismic analyses of cable-stayed bridges.

Experimental assessment of soil–structure interaction effects on a super long-span cable-stayed-bridge with pile group foundations

Soil–structure interaction (SSI) plays an important role in overall structural seismic behavior. However, there is a scarcity of experimental studies evaluating the SSI effects on a full bridge including superstructure, pile foundations and site soil. This paper focused on shaking table investigations on the effects of SSI on a super long-span cable-stayed bridge model with pile groups and mixture soil modelled by using uniaxial laminar shear boxes. The cable-stayed bridge model was subjected to a series of earthquake excitations in the longitudinal direction, including white noise and various earthquake waves. The dynamic interactive behavior of the cable-stayed bridge model was explored for various shaking amplitudes and frequency components. Furthermore, the influences of the soil on the system dynamic characteristics were clarified statistically. The test results show that the SSI obviously affects the seismic response of the cable-stayed bridge model in the longitudinal direction, and corresponding accelerations of structural members are amplified. The bridge seismic response may be underestimated and misinterpreted to some extent while the SSI effects are ignored. It is, therefore, suggested that more attentions should be poured into the SSI effects when performing the seismic design of super long-span cable-stayed bridges. Moreover, the SSI effects on the bridge seismic responses decrease with the increase of shaking amplitude, and significantly change as the frequency components of the input motions vary. When evaluating the system damping ratio with the SSI, the system seismic responses may be varied to a certain degree if the soil viscous damping contribution is neglected.

Experimental and numerical verification on effects of inelastic tower links on transverse seismic response of tower of bridge full model

This paper aims to verify the effects of inelastic tower links on mitigating the transverse seismic response of towers for super long-span cable-stayed bridges under unidirectional uniform earthquake excitations. A 1/70-scale bridge full model of a preliminary design super long-span cable-stayed with a central span of 1400 m was designed and tested on a shaking table array. The bridge full model included superstructure, pile groups and artificial soil placed in laminar shear boxes. Inelastic tower links used as sacrificial links scheme were installed in the top region between both tower shafts in the transverse direction. The dynamic characteristics and seismic responses of the bridge full model with and without the inelastic tower links were analyzed and compared under various uniform earthquake excitations in the transverse direction. The experimental results show that the addition of inelastic links to the tower improves the seismic performance of the cable-stayed bridge, and the tower seismic demands are reduced, including the displacement and strain responses. Especially, the inelastic tower links significantly decrease the strain responses in the tower top region. It is indicated that the inelastic tower links can tune the seismic response and mitigate the seismic damage of towers in high seismic regions. Moreover, an updated finite element (FE) model was conceived to replicate the experimental results using OpenSees, and the numerical simulations of the bridge full model were performed. Consequently, the numerical results are in good agreement with the experimental counterparts, thus validating the effectiveness and accuracy of the updated FE model.

Design and behavior of super-long span cable-stayed bridge with CFRP cables and UHPC members

This paper proposes a cable-stayed bridge with carbon fiber-reinforced polymer (CFRP) cables and ultra-high performance concrete (UHPC) members and presents its design and structural behavior to analyze its feasibility with a super-long span. Based on the geometrical dimensions of a real cable-stayed bridge with a steel girder and cables in addition to a normal concrete (NC) pylon and main-span of 1088 m, a new counterpart cable-stayed bridge using CFRP cables and a UHPC girder and pylon was designed. The dimensions of the UHPC girder were quantified by the section stiffness, punching resistance, local stability, and shearing resistance. The cross-section sizes of the CFRP cables were determined by the principle of equivalent strength. The geometric and physical conditions of the UHPC pylon satisfied the principle of similarity theory. Using the finite element method, a comparative analysis of the mechanical behavior of two cable-stayed bridge schemes was conducted, specifically regarding the static behavior, global stability, aerostatic stability, dynamic mode, and seismic performance. The results indicated that the detailed design and superior performance of the CFRP and UHPC made it practical to form a highly efficient and durable concrete cable-stayed bridge system with CFRP cables and UHPC members. Moreover, these properties could enlarge the main-span of a concrete cable-stayed bridge to approximately 1000 m.

Investigation of seismic performance of super long-span cable-stayed bridges

Investigation of seismic performance of super long-span cable-stayed bridges

Transverse failure modes and control strategies of super long-span cable-stayed bridge under extreme earthquake

This work is focused on the failure modes and control strategies of a trial designed super long-span cable-stayed bridge (Abbr. CSB) with a main span of 1400 m under various seismic intensities, exploring the key characteristic of the failure modes of super high tower. Then several control strategies, such as the use of conventional viscous fluid dampers (Abbr. VFDs) and a new combination strategy comprising sacrificial inelastic links and conventional VFDs, are presented for the failure modes improvement and the seismic damage mitigation of the CSB under extreme earthquake (PGA = 1.0 g). It is found that the super high tower experiences an unexpected failure mode with double plastic hinges that shows a new characteristic on the tower failure in the transverse direction, which is different from that of the short- and medium-span cable-stayed bridge during earthquake excitation. Whereas the piers show a typical and expected flexural failure mode with only one plastic hinge in the transverse direction. Although conventional control strategies using the optimal VFDs can help to significantly reduce the seismic damage of the CSB, they cannot entirely make the tower satisfy seismic control targets. It is also observed that the new combination strategy can successfully improve the failure mode and seismic damage of the CSB that satisfies seismic control targets, the effects of proposed combination strategy on the CSB are superior to those of the convention control strategy with the optimal VFDs.

Reliability Assessment for the Balanced Cantilever Construction Phases of Super Long-Span Cable-Stayed Bridges with Steel Box Girder

Balanced cantilever construction phases are of great importance for the total life cycle processes of super long-span cable-stayed bridges. For assessment purpose, a systematic study on the reliability evaluation of these phases is carried out. Taking Sutong bridge as the sample structure studied, a series of load and resistance models are then established on the basis of field measurement. Using all these achievements, a typical phase of girder segment 6# lifting is chosen for reliability evaluation. Results of the analysis show that the established models are quite representative and reflect actual random nature perfectly. Furthermore, compared with pylon and stay cables the stiffening girder seems more likely to fail in accordance with reliability index. The major failure mode of it in terms of present analysis is the stability failure due to the action of bending and axial load. Nonetheless, the components on the whole are still in a high level of reliability, which can guarantee the proceeding of construction with efficiency.

Evaluation of FRP and hybrid FRP cables for super long-span cable-stayed bridges

Abstract This paper evaluates the safety factors, the applicable lengths, and relative cost of FRP (fiber reinforced polymer) and hybrid FRP cables that are potentially suitable for cable-stayed bridges with a super long-span of between 1000 m and 10,000 m. Following previous studies on 1000-m scale cable-stayed bridges with FRP cables, two kinds of hybrid FRP cables – the previously discussed hybrid basalt and carbon FRP (B/CFRP) cable and the newly-developed basalt and steel-wire FRP (B/SFRP) cable – as well as conventional steel cable, CFRP cable, and BFRP cable are further investigated focusing on their promise in meeting potential requirements for super long-span bridges. Some major results are as follows: (1) a three-stage model for determining safety factors of cables with different kinds and lengths is proposed; (2) a threshold of λ2 is suggested to achieve both high material and stiffness utilization efficiency, based on which the applicable lengths for different kinds of cables were evaluated; and (3) hybrid B/SFRP cables and BFRP cables are comparable in cost to steel cables within a 3000 m span, while hybrid B/CFRP cables and CFRP cables demonstrate a superior performance/cost ratio over a longer span.

Mechanics feasibility of using CFRP cables in super long-span cable-stayed bridges

To gain understanding of the applicability of CFRP cables in super long-span cable-stayed bridges, by taking a 1400 m cable-stayed bridge as example, mechanics performance including the static behavior under service load, dynamic behavior, wind stability and seismic behavior of the bridge using either steel or CFRP cables are investigated numerically and compared. The results show that viewed from the aspect of mechanics performance, the use of CFRP cables in super long-span cable-stayed bridges is feasible, and the cross-sectional areas of CFRP cables should be determined by the principle of equivalent axial stiffness.

Study on wind-induced instability of Super Long-Span Cable-Stayed Bridge

Study on wind-induced instability of Super Long-Span Cable-Stayed Bridge

On the Applicability of the Effective Tangent Modulus Method for Evaluating the Ultimate Strength of Super Long-Span Cable-Stayed Bridges

On the Applicability of the Effective Tangent Modulus Method for Evaluating the Ultimate Strength of Super Long-Span Cable-Stayed Bridges