Study On Application Of Waist Beam In Pile-anchor And Effect Of Waist Beam On Prestressing Loss Of Anchor Cable

The pile anchor supporting is a kind of support method, which reinforces the soil body actively by prestressing anchor cables. Due to its good supporting results,The pile-anchor supporting is widely used in deep foundation pit support. In pile-anchor supporting systerm, one end of the anchor cable embeded in stable sratum.,while the other is connected to the waist beam.With the contraction of the anchor cable,the tensile load transfers into the soil.The soil mass within the scope of compression state is reinforced.The stability of pile-anchor supporting system is the result of the joint action of anchor cable, waist beam, pile body and soils.The loss of the prestress due to the process of tension and locking, the unreasonable design or installation of the wai, the the indadequate detailed survery of the soil, that will cause the failure of the foundation pit supporting system, which leads to the occurrence of safety accidents. Therefore, it is very important to study the theory of the pile-anchor supporting system. In this paper, we investigate the application of the waist beam in foundation pit support,and the influence of the waist beams with different materials on the prestressing loss.The main research work and results we obtained are as follows:(1) Investigate about the influence of prestressing load in pile-anchor supporting system. Studies have shown that the loss of prestress can be reduced effectively with material durability, reasonable section, and construction as a whole.(2) Discuss the accident caused by the instability or failure of waist beam, the reason is that we don’t pay sufficient attention on tic shear settings, connection between waist beam segments, waist beam and the hanger connections between waist beams and the supporting piles, welding between the waist beam and the diagonal brace.(3) Analysis the design calculation theory and new construction technology for the design of the waist beam. The calculation model of the waist beam should be simplified according to the actual stress and deformation. Simply supported beam model can be used for the foundation pit and the free end of the beam, while the continuous beam model is appropriate for larger foundation pit.(4) Introduce the construction control of the waist beam in the foundation pit supporting project of Qingdao Haitian Hotel, and the monitoring of anchor cable prestress. Monitoring data show that the average loss rate of anchor cable prestressing in the stage of rapid descent, the steady stage, the basic stable stage were 7.6%, 5.6% and 3.2% respectively, the total loss rate after anchoring was about 16.4%.(5) Three dimensional modeling analysis is conducted on the influence of waist beam on the prestress loss of the cables, and the numerical analysis results are compared with the monitoring data, the result indicates that it’s feasible to use ABAQUS software to simulate the loss of the prestress of anchor cable; From the change of the disp-lacement of the waist beam, it will reduce the prestressing loss of the cable within the period of anchor stage and rapid descent.Through literature review, engineering practice and numerical simulation method, the paper analyzes the application of the waist beam in the pile-anchor supporting system and its impact of the loss on the cable prestress. The results show that the stability of waist beam is very important for the pile anchor support. In the future, we should pay more attention to the design, construction and stability of the waist beams.