Super Long-span Suspension Bridge Research Articles

Effects of non-stationary wind velocity models on buffeting performance of closed-box girder suspension bridges

Non-stationary characteristic in nature wind has a great effect on buffeting performance of long-span bridges. The influence of key parameters in non-stationary wind velocity models on nonlinear buffeting responses of a super long-span suspension bridge was investigated in this paper. Firstly, four non-stationary wind velocity models are established by combing the time-varying average wind velocity with an exponential function and the fluctuating wind velocity with four modulation functions, respectively. These non-stationary wind velocity models have obvious non-stationary characteristics and then are validated by the classical power spectrum densities. Finally, three displacement responses of the bridge deck under four different independent variables of β in the exponential function and four modulation functions were compared, respectively. Results show that the turbulence intensities using two non-uniform modulation functions (NMF) are larger than those using uniform modulation functions (uMF). Moreover, the root mean square (RMS) values of three displacement responses increase with the decrease of β. Besides, the RMS values of three displacement under two NMFs are larger than those under two uMFs, and their RMS values under the second uMF are the smallest.

Experimental studied on suppressing vortex-induced vibration of closed-box girder bridges with various moveable guide vanes

A new moveable guide vane with the combination of the spring and guide vane was proposed to suppress the vortex-induced vibration (VIV) of closed-box girder bridges. This paper studies the influence of two important parameters (i.e., horizonal length and spring stiffness) of a moveable guide vane on controlling the VIV of a super long-span suspension bridge with closed-box girder by using VIV control tests. The VIV test of 1:50 scaled ratio of sectional model of the original closed-box girder under three wind attack angles were firstly conducted. The suppression ratios of vertical and torsional VIV displacements of the closed-box girder as well as the movement characteristics of moveable guide vane were then analyzed, respectively. The results show that the movable guide vane could significantly reduced the Root Mean Square (RMS) values of VIV displacement of the closed-box girder are after installing, especial for the torsional VIV displacement. A moveable guide vane with a relative smaller horizontal lengths or a relative larger spring stiffness could produce a better outcome of VIV control. The double VIV amplitude of the moveable guide vanes results in the energy dissipation of the closed-box girder in the lock-in VIV wind speed region, while the vertical displcement of the moveable guide vane are close to those of the closed-box girder in non-VIV wind speed region. Besides, the nonlinear exponential fitting function could effectively reflect the relationship among the wind speed, the VIV displacement of the MGV and the closed-box girder.

Seismic Reduction Analysis of Super-Long Span Suspension Bridge with Lattice Composite Tower and Damping System: A Case of Study for Qiongzhou Strait Bridge

In this paper, we proposed a lattice composite tower damping system to reduce the seismic response of super-long-span suspension bridges. Taking the QiongZhou strait bridge as a case study, we evaluated seismic performances through a finite element analysis (FEA) and shaking-table tests. First, the seismic responses of a super-long-span suspension bridge with or without a lattice composite tower to far-fault and near-fault earthquakes were analyzed and compared. The influence of the lattice composite tower on the dynamic characteristics and seismic performance was then investigated using shaking-table tests. Finally, the influences of different damping systems on the seismic response were evaluated, considering factors such as the damper type, damper arrangement scheme and design parameters. The results indicated that lattice composite tower could significantly increase the seismic performance of super-long span suspension bridge, while the optimal damping system could markedly improve the energy dissipation ability of whole system. Subsequently, this could provide references to enhance the seismic safety of the super-long span suspension bridge under strong earthquakes.

Effects of vertical central stabilizers on nonlinear wind-induced stabilization of a closed-box girder suspension bridge with various aspect ratios

The aerodynamic shape of a closed-box girder plays an important role in the wind-induced stabilization of long-span suspension bridges. The purpose of this study is to investigate the effects of the combination of five aspect ratios and a downward vertical central stabilizer (DVCS) on nonlinear flutter and aerostatic behaviors of a super long-span suspension bridge with closed-box girders. Through conducting a series of wind-tunnel tests and nonlinear finite element analysis, the results show that the nonlinear self-excited forces and the critical wind speed (Ucr) gradually increase as the increase of the aspect ratio (i.e. the width to depth ratios). Furthermore, the application of 20% deck depth DVCS could significantly increase the nonlinear self-excited forces and Ucr for small aspect ratios of 7.9 and 7.1. Particularly, the installation of the DVCS could change the flutter divergence patterns of the bridge from soft flutter to hard flutter, especially for a relatively small aspect ratio. In addition, the aerostatic force coefficients and torsional divergence critical wind speeds of the larger aspect ratio with DVCS are significantly larger than that without DVCS. A relatively small aspect ratio of the bridge has better aerostatic performance than that with a larger aspect ratio.

Bayesian inference for the dynamic properties of long-span bridges under vortex-induced vibration with Scanlan’s model and dense optical flow scheme

The dynamic properties of long-span bridges with flexible and light-weight features are of critical importance in safety assessment and response prediction. The primary concern of this study was to infer the dynamic characteristics of long-span bridges subjected to vortex-induced vibration (VIV) by reasonably accommodating the fluid–structure interactions during VIV and the various uncertainties arising in the dynamic characterization of the structures due to measurement noise and modeling errors. By taking the advantage of advanced image processing techniques, the Farnebäck dense optical flow method was used to process the vibration video to extract the displacement time history. In contrast to conventional operational modal analysis (OMA) approaches, which are usually based on the white noise assumption, a new frequency-domain Bayesian method is proposed to make a statistical inference for the dynamic characteristics of the bridge based on the power spectral density of the VIV measurements and the Scanlan’s empirical VIV model for bridge decks. A fast computation scheme is also proposed to achieve the posterior uncertainties of the modal frequency of the bridge, the structural damping of the bridge, and the total damping of the VIV system. The efficiency and the accuracy of the proposed algorithms have been verified with the VIV motion of a super long-span suspension bridge. Comparison with those identified using different OMA approaches in the time domain and the frequency domain is also be presented.

Analysis of suspension bridge response due to earthquake under different soil conditions

A suspension bridge is a long span bridge that has the advantage of the possibility of not having a pillar in the middle and using cables as the primary load bearer. Due to its long spans, the analysis of the bridge should be treated very carefully, especially under an earthquake. The earthquake that occurs will cause ground movement to affect the performance of the bridge structure. Furthermore, various soil conditions will also cause the existence of the bridge structure to experience differences. In this study, a super long-span suspension bridge is analyzed under different soil conditions. It is assumed that each support of the bridge is on the same ground condition and has a uniform ground movement. The bridge is then analyzed relating to the response of the bridge structure due to a uniform earthquake in the form of internal forces and displacement both in terms of static and dynamic analysis. Results show that soft soil induces a more massive internal forces response structure compared to hard soil.

Flutter mitigation of a superlong-span suspension bridge with a double-deck truss girder through wind tunnel tests

As flutter is a very dangerous wind-induced vibration phenomenon, the mitigation and control of flutter are crucial for the design of long-span bridges. In the present study, via a large number of section model wind tunnel tests, the flutter performance of a superlong-span suspension bridge with a double-deck truss girder was studied, and a series of aerodynamic and structural measures were used to mitigate and control its flutter instability. The results show that soft flutter characterized by a lack of an evident divergent point occurred for the double-deck truss girder. Upper central stabilizers on the upper deck, lower stabilizers below the lower deck, and horizontal flaps installed beside the bottoms of the sidewalks are all effective in suppressing flutter for this kind of truss girder. By combining the structural design with aerodynamic optimizations, a redesigned truss girder with widened upper carriers and sidewalks, and double lower stabilizers combined with the inspection vehicle rails is identified as the optimal flutter mitigation scheme. It was also found that the critical flutter wind speed increases with the torsional damping ratio, indicating that the dampers may be efficient in controlling soft flutter characterized by single-degree-of-freedom torsional vibration. This study aims to provide a useful reference and guidance for the flutter design optimization of long-span bridges with double-deck truss girders.

Aerodynamic Countermeasure Schemes of Super Long-Span Suspension Bridges with Various Aspect Ratios

The purpose of this study is to investigate the flutter control scheme of super long-span bridges with various aspect ratios (e.g. width to height (B/H)) using passive aerodynamic countermeasures. Through a series of wind tunnel testing and theoretical analysis, three types of passive aerodynamic countermeasures, i.e. vertical central stabilizer (VCS), wind barrier and inspection rail, were investigated for five typical aspect ratios of a closed-box girder bridge. The results show that both the aspect ratio and flutter critical wind speed generally increase with the decrease of the ratio of torsional and vertical frequencies of the bridge. In the case of an aspect ratio of 8.9, a downward VCS (DVCS) has a much better flutter performance than that of an upward VCS (UVCS) because aerodynamic damping of Part A and Part D could produce a higher heaving degree of freedom (DOF) participation level. Furthermore, the position variation of wind barriers is superior to their shape variation for the bridge with an aspect ratio of 8.3, and the flutter performance of the girder with a combination of the wind barrier (WB3P3) and UDVCS with 0.3[Formula: see text]h/H DVCS appears to be better than that without countermeasures. In addition, the installation of an inspection rail near the bottom point of an inclined-web (IR3) has the best flutter control effect among four positions of inspection rails.

Multifunctional Robotic Crawler for Inspection of Suspension Bridge Hanger Cables: Mechanism Design and Performance Validation

This paper presents a robotic system, called multifunctional robotic crawler for cable INspection II, which is developed for inspection of hanger cables of suspension bridges. The robot can move over hanger cables and perform inspections with instruments such as cameras, nondestructive testing tools, etc. The novel mechanisms for the robotic system are proposed under the consideration of the environmental conditions of suspension bridges. Its driving mechanism adopts a crawler type one driven by brushless direct current motors, and the detachable adhesion tool ensures simple and quick installation procedures. The safe-landing mechanism for emergency situations guarantees the retrieval of the robot while preserving the safety of operators. This paper presents the robot system and its field test results under a super long-span suspension bridge, called Yeong-Jong Grand Bridge in South Korea. For practical applications, the real environmental conditions of a suspension bridge and the other fields where the robot can be applied are discussed.

Study and Prototype Design of a Suspension Bridge with Ultra-Long Span and CFRP Main Cables

Using nonlinear numerical methods, the structural systems of cables system, stiffening beams, pylons, and bearing systems are comparatively analyzed. This study demonstrates the technical feasibility of suspension bridges with a 3,500 m main span and Carbon Fiber Reinforced Plastic (CFRP) main cables. Using fine finite element structural simulation, the parameter sensibility of a suspension bridge structural system with a 3,500 m main span and CFRP main cables is analyzed, and the influence of structural parameters on the static and dynamic performance of super-long span suspension bridges is discussed. In combination with numerical analysis of a structural system model, the optimum structural system of a suspension bridge with a 3,500 m main span and CFRP main cables is determined. The physical model is set up to allow theoretical measurements of the anchorage, sliding, and bending moment of the CFRP main cable strands as well as static load and fatigue testing. A bond-type anchorage that can be applied to real bridges is developed, which has an anchorage efficiency coefficient of 100%. The sliding resistance and bending performances are verified: the frictional coefficient between CFRP main cable strand and saddle is about 0.5, the frictional coefficient between the CFRP main cable strand and clamp is up to 0.331, the bending strength of the CFRP wire at the saddle point is over 90% of its tensile strength, and there is almost no bending problem at the clamp. A bridge prototype design is produced based on the test results.

Elasto-plastic behaviors and ultimate strength of 4 super long-span suspension bridges

Elasto-plastic behaviors and ultimate strength of 4 super long-span suspension bridges

Advanced aerostatic analysis of long-span suspension bridges

As the span length of suspension bridges increases, the diameter of cables and thus the wind load acting on them, the nonlinear wind-structure interaction and the wind speed spatial non-uniformity all increase consequently, which may have unnegligible influence on the aerostatic behavior of long-span suspension bridges. In this work, a method of advanced aerostatic analysis is presented firstly by considering the geometric nonlinearity, the nonlinear wind-structures and wind speed spatial non-uniformity. By taking the Runyang Bridge over the Yangtze River as example, effects of the nonlinear wind-structure interaction, wind speed spatial non-uniformity, and the cable’s wind load on the aerostatic behavior of the bridge are investigated analytically. The results showed that these factors all have important influence on the aerostatic behavior, and should be considered in the aerostatic analysis of long and particularly super long-span suspension bridges.

Aerodynamic characteristics of a 2-box girder section adaptable for a super-long span suspension bridge

According to the previous investigation on the suspension bridge with a 2-box and 1-box combined girder, which is newly developed to apply to the super-long span bridge having a main span of 2500 m or more, it is indicated that unbearable large torsional displacement induced in the high wind velocity and decreased flutter stability are the problems to be solved. This paper deals with the investigation of an improvement of steady pitching moment characteristics on the girder cross section to decrease the torsional displacement under wind loads, and also an improvement of flutter stability. As a result of investigation on the 6-lane-type girder, it is found that the steady pitching moment characteristics and flutter stability can be improved by attaching rails for an inspection cab to the bottom of fairing and by attaching vertical plates to the lower flange of the girder. Furthermore, a study is conducted on the subject of a 4-lane-type girder having similar cross section to the 6-lane-type girder section.

Monitoring the Akashi Kaikyo Bridge: First Experiences

From monitoring and maintenance work on the Akashi Kaikyo Bridge, a super long-span suspension bridge, new information has been obtained. This paper describes some of the new technologies used. To protect the main cables from corrosion, a dry-air injection system was newly developed and found capable of keeping the relative humidity low enough in the cable bundles. To suppress unexpected wind-induced oscillation observed in hanger ropes, an aerodynamic countermeasure was employed and its performance was confirmed in typhoon-strength winds. Girder displacement records were stored by monitoring with Global Positioning System (GPS) measuring instruments. The relationships between girder displacement and both wind speed and temperature were analysed to compare actual bridge behaviour with design values. Results indicate the possibility of more accurately diagnosing the soundness of bridges. These technologies are expected to contribute towards maintaining the soundness of the Akashi Kaikyo Bridge.

Suppression of Coupled Flutter of a Suspension Bridge by Tuned Pendulum Damper. 3rd Report. Suitable Arrangement of Dynamic Dampers by a 3D Bridge Model Analysis.

In this paper, the effect of a tuned pendulum damper (TPD) for suppression of the coupled flutter of a super-long span suspension bridge was examined by using a three dimensional FEM model. In the previous paper, using a flutter analysis for a 2 D bridge deck model without horizontal motion, a major effect of TPD on the bridge deck flutter is confirmed. However, it is also clarified that the horizontal force induced by TPD motion brings about the horizontal vibration mode of the deck and the TPD actually loses its ability to control flutter. We theoretically derived a suitable arrangement and mass distribution of TPDs which reduces the horizontal forces. As a result of this method, it was confirmed by a 3 D FEM model that the flutter speed for a 2 500 m span suspension bridge was greatly improved by TPDs.