Research On Demolition Technology Of Long-span Prestressed Concrete Truss Composite Arch Bridge

The structural system and structural design of truss composite arch bridge are not reasonable,and there are many problems.Many old bridges are facing the situation of demolition and reconstruction.The old bridge demolition is difficult,high risk,and lack of demolition construction for reference,so the study of reverse demolition method is necessary.Based on a prestressed concrete truss composite arch bridge with a main span of 150 m,this paper studies the demolition method of such bridges by numerical simulation.The main research results are as follows :(1)According to the idea of " first construction and then demolition," the construction scheme of demolishing truss-type composite arch bridge with concrete-filled steel tube arch support is designed,the demolition process is formulated,and the key technologies of demolition construction are discussed.Combined with the finite element software,the static and stability analysis of the whole demolition process of the old bridge is carried out.The results show that the axial force of vault before arch opening is 136.5 k N(compression),the stress is 0.9MPa(tension),the deflection before and after arch opening is about 7 mm,and the minimum elastic stability coefficient is 15.23.In the process of demolition,the old and new bridges have uniform stress,gentle deformation and small cable force,which ensures the construction safety of the whole demolition process and provides intensive new ideas and methods for similar bridge demolition.(2)According to the idea of " post-construction first demolition," the construction scheme of lifting and dismantling the truss composite arch bridge with inclined cable is conceived,and the finite element software is used to simulate the same demolition process.The results show that the axial force of vault before arch opening is 125.3 k N(compression),the stress is 1.4 MPa(tension),the deflection before and after arch opening is about 22 mm,and the minimum elastic stability coefficient is 10.83.The maximum tensile stress,maximum compressive stress and maximum step displacement of the old bridge are 5.3 MPa,20.2 MPa and 33 mm,respectively.The maximum cable force in the demolition process is 858 k N.This method is a conventional and safe construction method with universality and applicability.(3)Through the comparative study of the two demolition schemes before optimization,it can be concluded that the demolition scheme of concrete filled steel tubular arch support is more advantageous in the relying project,but it has certain limitations in the construction conditions and the demolition of the old bridge span.(4)Through the optimization design and comparative study of the demolition sequence of the old bridge,it can be concluded that the demolition scheme of concrete filled steel tubular arch support is still more dominant in the relying project,and the advantages of the oblique pull buckle hanging cable hoisting demolition scheme are further highlighted.