The Fourth Nanjing Yangtze River Bridge is the first suspension bridge of three-span steel box girder using continuity and flexible bearing system with a main span of 1418 m, and makes use of the flexible bearing system and distributional force transmission system with main rope for the first time. It overcomes the deep foundation design and construction technical problems of oversized "∞" shape diaphragm wall and ultra-large well-sinking under complicated geological conditions, proposes the technologies of main rope mixed-knit and argon-rich gas shielded arc welding, and uses the pavement technique of compound gussasphalt at steel bridge deck. Additionally, it utilizes synthetical technique to control construction quality of bulk mass concrete. This text summarizes the construction management and key technical innovation.
Superior to conventional pre-stressed anchorage system, a new anchorage system design concept of cable-stayed bridge, the stress distributed transmitting anchorage system, is adopted to the Fourth Nanjing Yangtze River Bridge referencing to the design of conventional steel framed anchorage system. The conventional steel framed system relies on the back anchorage beam, which provides rigid bearing supports and results in large concentrated stress, and has certain risks on both structural and safety aspects. However, the stress distributed transmitting anchorage system is arranged with several rows of reinforced concrete tenon-joint shear connector (PBL) in anchoring area in order to transform the rigid bearing supports to flexible bearing supports which helps cable stress gradually delivering to concrete anchorage block, changes the pattern of stress distribution from concentrated to distributed, enlarges the stress region, decreases the degree of stress concentration, minimizes the structural risks, and provides plenty of emergency capacity by taking advantage of the ductility of PBL and allocating end bearing plates. The design concept of the new anchor system is briefly introduced in this paper.
With an extraodinary complex structure structure, the Fourth Nanjing Yangtze River Bridge, a three-span continuous suspension bridge, is scarce in the world. This paper is to elaborate the structure characteristic by comparing and analysising the following aspects： the span-rise ratio, support at cable tower, limitation of longitudinal displacement and vertical displacement, as well as to propose a propor structure system, three-span continuous elastic supporting suspension bridge structure system, according to the pactical issue of the Fourth Nanjing Yangtze River Bridge, which is of innovative significance.
This paper introduces the design of deep buried spread foundation with braced excavation system for the South Anchorage of the Fourth Nanjing Yangtze River Bridge. The braced excavation system applied can be described as shaft diaphragm wall foundation with the plane section of "∞" shape including two 1.5 m-thick 59 m-diameter semi-circle and one 1.5 thick separation wall, and total length of 82 m and width of 59 m. However the separation wall provides the support for two semi-circles, it will not separate the bottom plate of foundation as the bottom elevation of wall is constructed in a higher level; and the separation wall is to be removed slightly in order to construct the top plate as a whole. The form of "∞" shape is superior than that of circle and rectangular by smaller plane area, larger cross sectional moment of inertia, smaller radius, smaller circumferential stress of diaphragm wall and better safety and feasibility, which great reduces the total costs and improved the construction safety.
North anchorage of the Fourth Nanjing Yangtze River Bridge is a kind of gravity anchor. Distributed mortise-tenon anchor system of Reinforced Concrete is designed for its anchor system structure first time in China. Thermal stress and temperature control is the key technique in large mass concrete construction of this anchorage. This article will introduce large mass concrete temperature control method,anchor system fixing technology and high-accuracy survey technology of North anchorage of the Fourth Nanjing Yangtze River Bridge.
It is a difficult technical problem to make sure that the curve of girder segments without han-gers is transitioned smoothly and the system transformation is successful and that the internal force keeps consistent with the girder curve when connecting the segments near the tower rigidly and transferring structure system for the suspension bridge with three-span continuous stiffening girder. The system transformation methods at home and abroad of girder segments without hangers are discussed in this paper, and by taking a suspension bridge of over 1 000 m with three-span continuous stiffening girder as an example, the system transformation, curve adjustment and construction control of the girder segments without hangers are realized.
The Fourth Nanjing Yangtze River Bridge, the longest suspension bridge in China, as well as the third one in the world, is a two-tower three-span suspension bridge with the main span of 1 418 m. The key construction techniques for the superstructure, including lifting and installation of the cable saddles, erection of the traction system, walkways and main cables, rearrangement of the main cables, installation of the suspender cables and the cable clamps, erection of the steel box girders and wrapping of the main cables, are discussed in detail in this paper. It can provide some references for the construction of the superstructures for the similar suspension bridges in the future.
The Fourth Nanjing Yangtze River Bridge is a two-tower, three-span suspension bridge with the main span of 1 418 m, where in the catway with no wind cable and no vibration suppression mechanism for construction of the superstructure is a three-span continuous catway system. Structural design, erection, adjustment and demolition of the catway are systematically described in detail in this paper, which could provide great reference for catway structural design and construction of similar suspension bridges.
Unlike single-span suspension bridge,the three -span continuous suspension bridge is mainly characterized by slings set in both side spans, and the continuous transition of stiffening girders between the mid and side spans achieved by girders without slings in the main tower region, and usually restraint equipments set on the side span transition piers to achieve the coordinated deformation between the main cables and stiffening girders in the region, so the lifting method and key construction process for the stiffening girders of the type of suspension bridge is relatively complex. the Fourth Nanjing Yangtze River Bridge as the background, and according to the structural features of the large span three-span continuous suspension bridge, the reasonable lifting program is determined through the comparison and analysis on two different types of lifting sequence for steel box girders.
At present, the diseases of steel bridge deck pavement in long-span bridge are still very common, and steel bridge deck pavement has become a difficult problem of long-span bridge development. The stress analysis of compound casting type asphalt pavement was made using the finite element method. Taking the orthotropic steel deck and the pavement as a whole, a finite element model was established which can be used to study the stress and strain features of the surfacing layer.
Based on the steel bridge deck pavement test results of The Fourth Nanjing Yangtze River Bridge, the paper analyzes performance of composite guss asphalt concrete. Through systematic analysis of the relationship between dynamic stability and temperature, wheel load, speed and driveway, combined with the study of the phenomenon of overloading in Nanjing area, rutting evaluation model of steel deck pavement of composite guss asphalt concrete were put forward and validated by field test.
Gussasphalt concrete has been widely used in steel bridge deck pavement because of its high deformation. In this paper, Factors impacted on Gussasphalt mixture performance are systematic studied by four type gradation, three asphalt content. The best asphalt content was determined by fluidity tests and penetration tests. The road performance was verified by high temperature rutting test and low temperature bending test. The study shows that gradation and asphalt content have a great influence on the performance of mixture. Therefore, the gradation and asphalt content should be strictly controlled in the actual construction.
Based on the steel deck pavement of the Fourth Nanjing Yangtze River Bridge, this paper carried out fatigue performance tests of the pavement at 20 ℃. In order to make the results reflecting the actual situation of pavement more realistically, we used main bridge pavement's mixes for molding specimens; molding and rolling composite beam with steel was at the construction site. The splitting fatigue tests and five stress levels of 0.2, 0.3, 0.4, 0.5, 0.6 were used to study the fatigue property of each layer; in dition, the fatigue tests of composite beams with steel plates and three load levels of 6 kN, 7 kN, 8 kN were chosen to study the fatigue property of the composite structure. Finally, the fatigue equation by regression analysis was got.
The geometric structure of steel deck plates is complex. So it is difficult to get precise results in the mechanics calculation of deck pavement with traditional methods. This paper adopts the finite element method for the mechanics analysis of the composite guss asphalt surfacing layer of curved steel box girder bridges. By taking the orthotropic steel deck and the pavement as a whole, a reasonable finite element model which established can be used to study the stress and deformation features of the surfacing layer. According to the common diseases in steel deck pavements and the effect of the overload and the horizontal load in braking to the pavement, this paper puts forward the comprehensive control indicators for pavement failures.
Shot blasting process is a process which use of shot blasting material to effect high-speed impact on the surface of material to achieve the purpose of surface treatment. In order to make the working efficiency and process of shot blasting machine more optimization, this research through mathematical analysis and validation adjustment by experimental machine design new type of shot blasting machine. This research conduct optimize design and discussion for the size and position of key parts of shot blasting machine, adjust position and angle of throwing head and orientation sleeve by experiment to make the shot blasting width reach 1 000 mm, and at the same time ensure best shot blasting effect.
To investigate the structural behavior of segmental precast prestressed concrete box girder the regular service stage and the construction state, a span of 48 m full scale box girder model of this type was tested for the Fourth Nanjing Yangtze River Bridge approach. The assembling and loading plans were determined according to the geometric parameters as well as the actual constraints of the girder. This paper focuses on the static performance, such as stress and displacement changes of the girder during segment loading and transporting. Comparative finite element method analysis was also performed for checking. The model test results show that at the regular service stage, the residual deformation of the girder after unloading is small, which demonstrates that the girder keeps in elastic during loading. The tooth joints of segments work well with each other and have no relative slip; the global performance of the girder is good as monotonous. The vertical distribution of longitudinal strain at joint and between joints basically accords with hypothesis of plane section. Also, the stress increment of prestress tendons is linear to the mid-span moment change. Finally, during the segment transport stage, it shows that there is sufficient compressive stress of the lower flange of the girder to meet the security requirements of transporting girder.
Reinforced blocks are common anchorage forms for external tendons. However, there was no mature design method. Through finite element analysis, the paper revealed that the tensile stress concentration was caused by three typical local actions. On this basis, three equations for calculating resultant forces of these local actions were formulated. Thus a quantitative reinforcement design method of anchor blocks was proposed. Finally, an anchor block of the Fourth Nanjing Yangtze River Bridge was presented as a design example to demonstrate the effectiveness and convenience of the proposed method.
For the pier segment of the segmental precast bridge, the diaphragm is often casted in place to reduce the lifting weight. Considering the volume of the diaphragm, it belongs to massive concrete,in which concrete hydration heat may cause excessive tensile stress in some parts. Without right control measures often lead to cracking of the precast segments during the construction phase. Based on three-dimensional transient temperature field theory, numerical simulation with ANSYS was performed, to investigate the distribution law of hydration heat temperature and stress. The analysis shows that, the tensile stress at the outside of the webs is sufficient to lead to concrete cracking, longitudinal micro-cracks along the webs is also observed during the hydration heat test. With the distribution of temperature and stress obtained from numerical simulation, a series of control measures were proposed and adopted to the Fourth Nanjing Yangtze River Bridge approach project, which were proved to be feasible and effective.
Two corrugated steel pipe culverts were chosen in north connection highway project of the Fourth Nanjing Yangtze River Bridge. From testing the strain conditions of corrugated steel pipe culvert under different soil fill heights, the fiber Bragg grating sensors were set in the inner or outer of corrugated steel pipe culverts. Corrugated steel pipe culvert has the capacity of larger formation. So in the soft soil area, using its good ductility can solve the problem of uneven settlement.