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..
In traditional foundation pit engineering, the common support method for retaining structures is as follows: crisscrossing concrete or steel structures for internal support, resulting in small excavation construction space, laborious and time-consuming installation and dismantling.
We witnessed a new type of foundation pit enclosure structure support method in the Jiangyin City Construction South Gate Commercial Block Project: prestressed fishbelly steel support system. Its construction site is like this:.
In intuitive comparison, the first impression this new type of support gives us is that the support rods are very sparse, and the excavation construction space is very large; The supporting materials are few and standard parts, which are easy to install and disassemble, and can be recycled and reused.
So, what is the principle and composition of this new type of support system?.
Let’s take a look at the overall schematic diagram. The support system structure consists of four major components: ① waist beam, ② fishbelly beam, ③ diagonal/angle brace, ④ column, as well as connections between and inside the components..
The reason why it is called a “pre-stressed” support system is because the entire structure resists the deformation of the foundation pit enclosure by applying pre-stress. Let’s take a look at the force diagram: the diagonal braces/angle braces are subjected to pre-stress through jacks and retaining boxes, and the fishbelly beams are subjected to pre-stress through steel strands to resist the lateral pressure of the foundation pit enclosure..
Next, we will delve into the site and analyze the specific composition of these four components based on the drawings..
H-shaped steel waist beam: continuously set along the crown beam around the foundation pit through bolts, bearing pressure on both sides.
Bracket: set below the waist beam, connecting the retaining pile and waist beam, providing support.
Ties: set between adjacent cover plates to provide lateral restraint and improve overall stability.
Square steel tube concrete column: used to bear the weight of the supporting system itself.
On site, we also saw that in addition to the advantages of large excavation space, low material consumption, and recyclability mentioned at the beginning, the support system itself adopts a fully automatic continuous monitoring system, which can effectively control the deformation of the foundation pit by dynamically applying prestress..
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