Influence Of Welding Quality Of Reinforced Cage Of Surrounding Protection Pile On Engineering Performance Of Foundation Pit

At present,many cities in China have built a large number of high-rise buildings.The construction of these high-rise buildings will inevitably be accompanied by the excavation of deep foundation pits,which also puts higher and higher requirements on the enclosure structure of foundation pit projects.However,after excavation of many deep foundation pits,a large amount of lateral displacement and vertical displacement occurred around the foundation pit,and even local collapse accidents occurred,most of which were the failure of the retaining pile and the cracking of the crown beam(enclosure).We found that in these accidents,foundation pits often have many quality problems,such as the lack of stirrups in the reinforced joints of the enclosing structure,the leaking welding of the main reinforcement connection joints,and the lack of full welds,resulting in serious insufficient bending capacity of the enclosing structure.This paper analyzes the mechanical effect of weld length on the envelope structure by designing and carrying out flexural tests of reinforced concrete simply supported beams with different weld lengths,and proposes that the lack of weld quality is an important reason for the premature cracking or even destruction of the envelope,The specific degree of influence is given.This article completes the research by carrying out the following work:(1)Firstly,the surrounding protection piles were simplified into reinforced concrete simply supported beams that are also flexural members to conduct component tests.Seven groups of 21 reinforced concrete simply supported beams with different weld lengths were designed to simulate the bending piles with different weld quality.The effects of different weld lengths on the bearing capacity,failure shape,deflection,crack width,reinforcement and concrete strain of the reinforced concrete beams,and the bending moment of the weld cross section of the beam are studied in detail.The influence of the cross-section properties of the retaining pile;(2)The same model as the test beam was established through the ANSYS finite element model software,the accuracy of the flexural test results of the simply supported reinforced concrete beam and the feasibility of the ANSYS finite element simulation were verified,and the inverse algorithm was used to simulate the elastic modulus of the reinforcement The specific reduction factor of the quantity,and then further obtain the reduction coefficient of the section stiffness of the members with different weld lengths through the section stiffness formula;(3)Using MIDAS / GTS software and cross-section stiffness reduction coefficients of different weld lengths,the parameter sensitivity analysis of the influence of welding length on the engineering performance of the foundation pit was carried out,and the general law of the influence of welding quality on the foundation pit performance was obtained;(4)Investigate a collapsed foundation pit in Hangzhou,systematically collect and arrange the drawings,exploration data,monitoring data and the specific conditions of the accident pit,and apply the previous research content to this accident analysis.Research indicates:(1)The welding quality problem of the reinforcement cage will lead to the reduction of the rigidity of the enclosing pile section,which will cause the flexural bearing capacity of the enclosing pile to be seriously insufficient,resulting in a large horizontal displacement at the weld seam,so that it will advance when the external load does not reach the design value Cracking caused damage to the envelope;(2)Due to the change of the weld length,the failure mode of the reinforced concrete beam is also changed.The weld length from short to long appears on the beam body.?1 pure tension side failure,?2 compression area after the tension area is damaged There are also three cases of crushing,?3 crushing in the compressed zone occurs before the damage in the tensile zone,or both occur in the same loading stage;(3)The horizontal displacement of the welding seam of the envelope structure basically shows a gradual decrease trend with the increase of the weld seam length,but it is not that the longer the welding length,the better the bending resistance of the envelope structure.The research in this paper finds that it will have a specific guiding role in the design and construction of the envelope structure,and also have reference value for the investigation of the cause of the collapse of the foundation pit of the latecomers.