Research On Shear Behavior Of RC Beams Strengthened With External Prestressing Steel Wire Rope

With the rapid development of our economy and society, the maintenance of many old bridges presents increasingly serious problems. In many bridge reinforcement methods, the external prestressing strengthening technology is widely used in old bridge reinforcement construction because of the short transportation time, the simple construction, economical and efficient, the good strengthening effect,etc. In the existing bridges, the beam-end shear failure is a common form. It includes too much crack of main tensile stress, width limit exceeded and diagonal crack development to the mid-span, it affect seriously the safety of the structure. The main reasons of shear failure are the poor shear force, the material deterioration, the vehicle overloading, etc. Currently, the main methods of shear reinforcement are to paste steel plates or high-strength composite materials, section enlargement and external prestressing, etc. They all belong to the passive reinforcement but the external prestressing reinforcement method. It looks good when coordinates with the flexural strengthening, but it need setting the deviators, so the structure is complex and the construction is complicated. The external prestressing method of the steel wire rope adopts the distributed ones to strengthen, it has so many advantages such as the small tonnage, the simple anchorage, without steering device and the convenient construction because of the dispersion of wire rope. It is a new attempt of shear reinforcement. It provides a new way for diagonal cracks reinforcement of the old concrete bridges and part of the long-span prestressed concrete bridges. This method can improve the stress condition, ensure the safety of the bridge operation and extend the service life of the bridge. It brings obvious economic benefit. The main contents of this paper include:(1) Study on the reinforcement effect of externally prestressed tendonsThe damage state of an old bridge in use was simulated. There were3reference beams and23strengthened beams in the test of external prestressed steel wire rope reinforcement. The shear effect of reinforcement beam was studied systematically. The test content included the effect of steel wire rope reinforcement on ultimate bearing capacity, crack changes and stirrup strain. The test results showed that strengthened method with externally prestressed steel wire rope can improve the shear capacity of reinforced concrete beams, delayed cracking of beams and improved the stirrup yield load.(2) Influence on the effect of reinforcement of design parameters of the test beamThe nonlinear finite element calculation model was established according to the design parameters of test beams and the shear capacity of the model was calculated. The design parameters were set to make up for the lack of test beams.The effect of shear reinforcement was analyzed based on the factors such as concrete strength grade, shear span ratio, stirrup ratio, steel spacing, prestress, sustained load level and damage degree, etc. by means of the nonlinear finite element method. Mechanism shear reinforcement of in vitro of wire rope, and summing up influencing of the original beam parameters and external parameters. Summing up strengthening effect influencing of the original beam parameters and external parameters. The calculation results show that the results of finite element calculation agree well with the experimental ones; the design parameters of test beams have an certain influence on consolidation effect; The shear capacity of reinforcement beam was improved gradually along with the increase of concrete strength grade, shear span ratio, stirrup ratio and prestressing. The shear capacity of reinforcement beam was decreased with the increase of shear span ratio, steel spacing, sustained load level and damage degree.(3) To establish the calculation formula of shear capacity for external prestressing reinforcementThe calculation method of shear resistance at home and abroad was analyzed synthetically. With the optimized analysis of the test data and the finite element calculation data, based on the genetic regression method and Matlab, the calculation model of shear bearing capacity was established based on the formula of Arch-Truss method. Put forward vitro of wire rope, load level and the concrete damage three coefficient η1、η2、η3, and according to the shear strengthening test data test the reliability of this subject.The results of this study provides a theoretical calculating basis for strengthened design, construction scheme, calculating bearing capacity reinforced concrete beams strengthened with external prestressed wire rope.lt can be used for reference.