Study On The Flexural Behavior Of Locally Prestressed And Horizontally Axillary Prestressed Concrete Beams

Prestressing technology is widely used in concrete structure engineering.In addition to the conventional prestressed structure,there are also various prestressed derived structures.For example,prestressed tendons are tensioned at important parts of the beam,The prestressed reinforcement is anchored on the intersecting beam by adding the horizontal axils at the beam end.Local reinforcement of damaged parts with external prestressing technology,etc.The mechanical properties of these special prestressed structures are much more complex than those of conventional prestressed structures.And there is no specification for structural designers to refer to,In order to understand the mechanical properties of these structures,detailed analysis is needed.Based on the finite element theory,a unified analysis model of prestressed beams considering material and geometric nonlinearity is established in this paper.The rationality of the model is verified by co MParing with three existing experiments.Unified modeling method is used to construct a variety of special prestressed structures.A systematic study the effects of different parameters on local prestressed beams,external prestressed beams and horizontal axillary prestressed concrete beams on flexural performance.Main research contents:1 The equivalent load calculation formula is derived from the differential equation,which verifies the reliability of the load balance method under the condition of large curvature of prestressed tendons.Based on the classical load balance method and the force method,the theoretical analysis of the locally prestressed beams is carried out,and the formulas for calculating the secondary internal forces of several common locally prestressed structures are calculated.The applicability of the classical load balance method to the locally prestressed beams is verified by the finite element program.(2)By selecting the appropriate material constitutive model,the connection between the unbonded prestressed tendon and concrete is reasonably constructed(mainly the arrangement of the rigid spring),and the contact relationship between the components is reasonably defined to ensure the accuracy of the model.The rationality of the finite element model is verified by co MParing the existing test data of prestressed structure with the analysis results.(3)For local prestressed beams with a variety of reinforcing methods,five series of finite element model beams were designed and built,and the nonlinear analysis of these model beams was completed by using the finite element program.The influences of the main parameters such as the area and length of the non-prestressed tendons on the mechanical performance of the locally prestressed structures are studied in detail.(4)For prestressed beams with horizontal axils,two series of finite element model beams were designed and established to simulate the anchorage of two prestressed reinforcement respectively:1)The prestressed reinforcement is anchored on the intersecting beam at the beam end,and the horizontal axillary structure is arranged;2)The prestressed tendon is anchored on the side of the prestressed beam body,and the horizontal axillary structure is arranged.The influences of prestressed bars’ linear shape in the horizontal axillary zone and non-prestressed bars’ area in the negative bending moment zone on the flexural performance of prestressed concrete statically indeterminate beams are studied and analyzed.The research results of this paper can provide reference for the designers of prestressed structures,and help the rational and correct use of special prestressed structures.