Nonlinear Analysis Of Beams Prestressed With Unbonded Tendons

Due to the advantages of simple construction and economy, the unbonded prestressing technique has been widely used in many countries. However, the analysis of beams prestressed with unbonded tendon is much more complicated than that of bonded concrete beams, because the strain compatibility between tendon and its adjacent concrete is no longer valid. The previous literature mostly concentrated on the formula for the ultimate stress in tension f ps. Unfortunately, most of the formulas were based on the experience derived from date of large amounts of experimental beams, which are unprecise to other independent beams. Therefore, it is necessary to establish a reasonable analysis model of beams prestressed with unbonded tendon that should be based on structural compatibility condition. According to the analysis modle, further research can be carried out, such as simulation about flexural behavior of beams prestressed with unbonded tendons and giving impersonality evaluation to the important parameters. Main contributions of this thesis are as follows:(1)There is a review of research on beam prestressed with unbonded tendons. A summary of available prediction equations for f ps suggested by various researchers as well as relevant design codes is presented. And the main factors which influence on f ps are introduced.(2)Based on the summary of previous research which were focused on the analysis of concrete structure using commercial finite element program ANSYS, the method and technique are sum up by repetitious calculation. ANSYS was used to develop an analysis model for concrete beams prestressed with unbonded tendon under monotonic load and low cyclic load.(3)The influence of various parameters on the flexural behavior of beams prestressed with unbonded tendons under monotonic load is studied and significative conclusion is presented. These parameters include ratio of nonprestressed reinforcement, yield strength of nonprestressed reinforcement, ratio of unbonded prestressing tendon, compressive strength of concrete, effective prestress,composite reinforcement index,loading pattern and span-depth ratio. The analytical results give the reference in optimization design and modification of the equations.(4)Ductility and energy dissipation of beam prestressed with unbonded tendons under cyclic load has been studied with nonprestressed and prestressed reinforcement index,compressive strength of concrete and composite reinforcement index.