On Stiffness Of Prefabricated Prestressed Fish-Belly Steel Support System

With the increase of building height and the development of underground space and facilities,deep foundation pit project is getting more and its requirements are getting higher,and the focus of foundation pit support is also changed from "strength control" to "stiffness control".Therefore,it is particularly important to select appropriate foundation pit support forms according to the project conditions.In recent years,an innovative prefabricated prestressed fish-belly steel support system(IPS system)developed for the lack of traditional concrete supports and steel supports is gradually emerging.Compared with traditional support system,IPS system has advantages in safety,excavation space,assembly and disassembly convenience,construction period,economy and environmental protection,and has broad development and application prospects.However,since this support system is a new type of foundation pit support technology,there is no formula in current industry standard to directly calculate its stiffness,and the support stiffness is an important basis for calculating the support force in practical projescts to analyze the force of the support system and determine the prestressing value.Based on this background,this paper conducts an in-depth study on the stiffness of the IPS system,and also optimizes the design,as follows:First of all,this paper describes the working mechanism of IPS system,including the stress mechanism of the structural system and the displacement control mechanism of the foundation pit,so as to reveal the change rule of support structure stress and foundation pit displacement.Subsequently,this paper studies the stiffness of the IPS system comprehensively,and introduces the concept of the equivalent average stiffness of fish-belly beam.The force method was used to derive the equivalent stiffness of fish-belly beam.The expression of the average stiffness of fish-belly beam,combined with the angle brace stiffness,gives the stiffness expression of IPS system that before and after the prestressing.After,this paper uses the finite element software MIDAS/GTS NX to verify the equivalent average stiffness of fish-belly beam.And then,uses MIDAS/GTS NX to build the 3D model of Xiamen Diamond Building,comparing its result with the theoretical derivation result and monitor data,verifying the derived IPS system stiffness expression and explain that this software is feasible for simplified simulation of foundation pit.Finally,this paper analyzes the influence of purlin cross-section dimensions,rise span ratio,the number of web menmebers and the number of steel support system on IPS system based on the Diamond Building project,and put forward some optimization proposal.