Abstract
The purpose of this investigation is to clarify the basic behavior of the simply supported prestressed lightweight concrete beams under quasi-static loading with once removal of load preceding the final failure. The prediction method of moment-curvature relationships of beams is also discussed.
Ten post-tensioned grouted prestressed concrete beams with the uniform eccentricity of tendons and the accompanying concrete test cylinders (φ10×20cm) were employed in this study. The test beams were loaded at the third points of the span.
The test program includes two beams with monotonously increasing load and six beams under the loading with once removal of load near failure. The start of unloading was controlled by the compressive extreme fiber strains in the bending span of the test beam, ranged from 1.9‰∼2.8‰.
The residual and ultimate strains in the compressive extreme fiber of the beams have no relation with the amount of their compressive strains at the beginning of unloading. The ultimate rotation strains, the failure strength and the initial bending stiffness at the beginning of reloading do not deteriorate due to the load history including once unloading.
It is found that the relations of the bending stiffness to the bending moment in the repeated cycles are simply represented as bi-linear relation from the experimental curves according to the index of the compressive extreme fiber strains of concrete prior to unloading.
Using this relation, the bending moment-curvature curves under the loading with such removal of load are predicted with accuracy.
