Theory And Experimental Research On Bi-prestressed Concrete Beam

The Bi-prestressed concrete beam is a kind of pre-stressed concrete structure which is caused by the combination of concrete with pre-tensioned and pre-compressed stress.Applying this kind of structure system, the height of simple supported beam could be effectively reduced while the bearing capacity could be enhanced. International and domestic research concentrates more on the anchor system and the construction craft, and less on component performance, scarcely any research on the Bi-prestressed concrete fatigue properties. Based on a great deal of reference in such study field, this article has done the following work.1. After a systematic study on the construction craft of the pre-compressive method and the post-compressive method of the Bi-prestressed concrete component, according to the Bi-prestressed concrete model production, two important aspects of the construction process are summed up, also carried out are study on component of the anti-arch control during construction stage, loss of the pre-stress and effectiveness of the anchoring system.2. Finished is the static load test on the first four Bi-prestressed concrete beams with pre-compressive method, and also on comparison between a Bi-prestressed concrete beams with post-compressive method and a normal concrete beam. Parameters such as the deflection of the model beam, the turning angle of beam end, the strain of concrete section, the coordinate deformation between the pre- compressive steel pipe and the concrete are measured. Also bearing capacity of the bi-Brestressed concrete beams, rigidity, crack, coordination deformation between pre-stressed steel (steel pipe) and beam concrete, and the elastic restore performance are analyzed.3. Fatigue performance test on a Bi-prestressed concrete beam is made, and also analyzed is the influence of the fatigue load on rigidity, bearing capacity, strain of the Bi-prestressed Concrete beam.4. Finite Element Models on the Bi-prestressed components with the pre-compressive method and the post-compressive method are established, also Analyzed are mechanical properties between two construction crafts of the Bi-prestressed concrete beams in the construction and usage stage.The study indicates the followings: The reinforcement– pressure pipe system with pre-compressive method and the anchoring system with post-compressive method designed by the study group is reliable. The stress lose value of the pre-compressive pipe in the beams with pre-compressive method is 0.12σcon,and its anti-arch is no more than 0.031%L when the pre-compress are finished, the stress lose of the pre-compressive bar in the post-compressed one is ( 0 .3 ~ 0.4)σcon; compared with normal pre-stressed beam, the Bi-prestressed concretes beam can effectively reduce height of the beam, which will lead to that the beam stiffness come down. The test on the deflection and crack with load-off shown that the beam body has been restored , which indicated fine elastic recovery ability of Bi-prestressed concretes. The fatigue test has led to characteristic such as degradation of beam stiffness, reduction of cracking load, and dense development of the crack. Effects caused by finite element method's imitation and tests'achievement fit well, which has established a basis for finite element method analysis study of practical projects.