Mechanical Behaviors Study Of Prestressed Steel Reinforced Concrete Beams

With the application and development of prestressing technology in concrete structure and steel structure, it is used gradually in steel reinforced concrete (SRC) structure. Applying prestressing to SRC structure can enlarge elastic range of materials, increase bearing capacity and fatigue resistance, decrease deformation, delay it appearance and development of concrete crack and reduce engineering cost, so it can meet for request of building structure and function to a great extent. Nowadays, the study on prestressed steel reinforced concrete (PSRC) structure is in primary stage, and they are always validate experiment for practical engineering, so it is short of systemic and complete experiment study and calculation theory, especially for the unbonded prestressed lattice type steel reinforced concrete structure, and any reports about it appears yet. Thus, experiment, theory analysis and numerical simulation are combined in this paper to study the mechanical behaviors of PSRC beams. The main contents are:On the basis of experiment on unbonded prestressed lattice type steel reinforced concrete beams, the working mechanisms and failure pattern are studied firstly, and the bearing capacity, deformation, stress increment of tendon and strain distribution of concrete and steel of testing beams are analyzed further.The stress increment formulas of unbonded prestressed lattice type steel reinforced concrete beams with straight, polygonal and curve tendons are established in service load stage by use of the end strain compatibility method and energy method. The stress status of each elastic stage of PSRC beams consist of solid web and lattice type, bonded and unbonded tendons are analyzed, and then the calculation formulas of crack-bearing capacity, elastic bending strength and ultimate bending strength are established. The method of applying prestressing to the SRC beams with transversely tensioning is put forward firstly. And then the stress analysis models in each elastic stage are presented, the calculation formulas of ultimate bearing capacity in different failure mode are established too. The design method of transversely tensioned SRC beam is presented further.The creep effects analysis models of prestressed solid web and lattice type SRC beams are established by use of age-adjusted-effective-modulus method and time-dependent creep superposition method. Furthermore, the calculation procedures considering creep effects are developed; the section internal force, deformation of PSRC beams considering creep effects are studied, and the effects of main parameters to them are discussed too.Nonlinear full-range analytic programs of bonded prestressed solid web and unbonded prestressed lattice type SRC beams are developed by use of ribbon method, the effects of main parameters to moment-curvature relationship curves are discussed, and the ductile performance of PSRC beams are analyzed further.On the basis of experiment research, the whole load-bearing process of unbonded prestressed lattice type steel reinforced concrete beams is simulated by use of ANSYS procedure. The stress distribution after applying prestressing and ultimate status of concrete and steel are analyzed, and the development rules of tension and compression steel, as well as the development process of concrete crack are analyzed too.