Recently, the Third Company of China Construction Eighth Engineering Bureau successfully applied the “pre-stressed fishbelly beam prefabricated steel support” technology, solving the problems of high cost, long construction period, dense internal support, uncontrollable deformation, large amount of construction waste and noise pollution caused by dismantling of traditional concrete internal support. This is another favorable attempt of the new technology of foundation pit support after the application of the double splicing steel internal support developed by the Engineering Research Institute of China Construction Eighth Engineering Bureau..
Pre stressed fishbelly beam prefabricated steel support (IPS) is a technologically advanced and environmentally friendly large-span foundation pit internal support structure developed using the principle of prestressing. This technology uses H-shaped steel braces (or angle braces) to press down on both ends of the fish belly beam. By applying pre tension to the steel strands of the lower chord of the fish belly beam, the entire large-span fish belly beam generates a displacement trend towards the outside of the pit, stimulating passive soil pressure outside the pit and achieving the goal of controlling displacement. And apply preloading stress to the supports at both ends of the fish belly beam, forming a large-span, closed, and stable stress system..
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This system consists of upper chord beams (purlins), straight web members, diagonal web members, lower chord steel strands, diagonal braces, angle braces, and other steel components. It is a recyclable and reusable prefabricated foundation pit support system..
The Senlan International Phase VI (D3-10) project is located in Pudong New Area, Shanghai, with a building area of 44000 square meters and a land area of 9687 square meters. The excavation area of the foundation pit is about 8136 square meters, with a circumference of about 380 meters and a maximum excavation depth of 10.6 meters. It has two basement floors and four commercial buildings above ground. On the east side of the foundation pit of this project is Harrow International School, and on the north side are Shanghai Zhuyuan Middle School and Haoqiangqi Kindergarten. Among them, Harrow International School is less than 15m away from the edge of the foundation pit. On the east side, 9m and 11m away from the edge of the foundation pit are the rainwater and sewage pipelines inside the Harrow School campus; The gas pipeline is located 4.8m north of the foundation pit. The environmental protection level on the north and east sides of the foundation pit is Level 2, with high environmental requirements..
In response to the complex surrounding environment, considering multiple aspects such as construction period, economy, and safety, the second reinforced concrete support in the original plan has been replaced with prestressed fishbelly beam prefabricated steel support. The cost is controllable, the construction period is controllable, and the environmental protection is controllable. After expert argumentation, the plan is gradually implemented on site, with a focus on monitoring the axial force changes of the steel support and the deformation of the foundation pit. Ultimately, the deformation of the north pipeline and the east school is effectively controlled, ensuring the safety of the surrounding pipelines and buildings..
Prefabricated steel support with pre-stressed fishbelly beam is environmentally friendly, energy-saving and emission reducing, convenient for construction, and shortens construction period. It is a highly redundant and statically indeterminate structure, safe and reliable..
Economic benefits: After using pre-stressed fishbelly beam steel support for the second support, the maintenance time of cast-in-place concrete is saved, the construction period is shortened by 9 days, and the cost is reduced by 520000 yuan..
Social benefits: Standardized steel components and bolt connections for prefabricated prestressed fishbelly beams, easy installation and disassembly, no concrete maintenance, and shortened project duration; The fishbelly beam has a large span, providing a large space for earthwork excavation and underground structure construction, and has good construction convenience; After dismantling the support, it can be reused, saving costs; Dismantling supports will not produce noise, dust, and construction waste, which is energy-saving and environmentally friendly; The fish belly beam steel support effectively controls the deformation of the foundation pit by applying a large amount of prestress, and the prestress can be adjusted during the construction process, which is effective.
