ATTEN: Manager Liu
ADD: Longhua Development Zone, Jing County, Hengshui City, Hebei Province
4. Foundation design and boundary conditions of steel structure support; artificial excavated cast-in-place pile is used in foundation design of Rainbow Bridge. The main bearing stratum at the end of the cast-in-place pile with manual excavation is the second third gravel stratum, the length of the pile is 10m and the length of the pile is 1000mm. The eigenvalue of vertical bearing capacity of single pile is 1800 kN, the eigenvalue of uplift bearing capacity of single pile is 1000 kN, and the eigenvalue of horizontal bearing capacity of single pile is 9. The layout of pile foundation of Rainbow Bridge (the boundary condition of bearing of steel structure design 42 of Rainbow Bridge). During the construction of cast-in-place piles with manual excavation of Caihong Bridge, the groundwater permeability in the gravel layer is strong and the amount of water in the hole is large. The construction unit fails to take drainage measures according to the design requirements, which results in a large number of drifting sand collapse holes when manual excavation reaches about 7.5 M. If the construction drainage scheme is reorganized to meet the design of 10 m pile length, or the supplementary pile scheme is adopted, the construction period is not only long, but also long. Therefore, according to the vertical and horizontal bearing capacity of the existing effective pile length, pile foundation design and upper steel structure support boundary strip 1) vertical bearing capacity of single pile are carried out.
The original design pile length is 10m, and the characteristic value of vertical bearing capacity of single pile is 1800kN. After actual construction, the effective length of existing piles is 5 meters. The number of pile foundations in this project is controlled by the horizontal bearing capacity. Through calculation, the vertical bearing capacity of 7.5m effective pile length can meet the requirements. Because the floating sand layer at the bottom of manual excavated L-cast-in-place pile can not be cleaned up in the construction process, all pile foundations are treated by post-grouting method after pile bottom pressure to ensure the bearing capacity of pile body and reduce settlement of manual excavated L-cast-in-place pile. 2) Horizontal bearing capacity of single pile. The original design pile length is 10m, and the characteristic value of horizontal bearing capacity of single pile is 380kN. After actual construction, the effective length of piles is 7.5 meters, and the horizontal bearing capacity of single pile can no longer meet the design requirements. In order to reduce the horizontal thrust of rigid bearing caused by spatial arch structure, the treatment scheme of adjusting the boundary conditions of bearing in the construction process of upper steel structure is adopted. Fixed connection joints are adopted to support, and the bottom plate of right steel column foot is circular. After the installation of the upper steel structure, the right support is allowed to move 30 meters horizontally under the weight of the arch structure, and the main structure is re-calculated with SAP2000. The results show that the horizontal push of the support is greatly reduced.
The existing pile number and effective pile length of 7.5m can fully meet the stress requirements of the main steel structure of Hongqiao Bridge. Comparisons are made between the space cable-pipe truss and the space steel pipe truss. Stress analysis under different load conditions is carried out by using SAP20ANSYS finite element software. The results show that the space cable-pipe truss and the space steel pipe truss can meet the stress requirements. Compared with the space cable-pipe truss structure system, the space steel tube truss structure system has the characteristics of low total steel consumption, high site utilization ratio and convenient construction. At the same time, in order to enhance the overall stability of the structure and reduce the peso-pipe truss structure of space steel pipe truss, a larger section size should be adopted. Fig. 10 Rainbow Bridge Pile Construction Site (Rainbow Bridge Steel Structure Design) is adopted to reduce the horizontal thrust of rigid bearing caused by space arch structure. In order to reduce the horizontal thrust of rigid bearing caused by the construction process of the upper steel structure, the side of the bearing is adopted. The treatment plan of boundary condition adjustment and the finite element calculation of the main structure with the bearing deformation as the calculation condition are re-carried out. The results show that the horizontal thrust of the bearing has been greatly reduced according to the vertical and horizontal bearing capacity of the existing effective pile length. The pile foundation design and the adjustment of the upper steel boundary condition shorten the construction period and save a lot. The amount of investment ensures the smooth progress of the project.