Experimental Study On The Characteristics Of Bending And Torsion In Long-span Prestressed Floor Beams System

In this paper, by means of reversed cyclic loading tests on the specimens of long-span floor beams system, it analyzes the behavior of long-span floor beams system during the tests. It also investigates the effect of secondary torque, the characteristics of moment redistribution subjected to reversed cyclic loading, and the role of spandrel beams in the overall response. At last, it discusses the method of designing the spandrel beams properly, including the reduction of spandrel-beam-torque and the flexural strength ratio between columns and beams.Results from the tests show that the effect of secondary torque, especially the anti-symmetry, exists in the structure during the whole testing. Based on the theoretical analyses and the results from tests, the changing law of secondary torque is similar with that of the torque of spandrel beams subjected to the vertical loading. It points out the fact that secondary torque is a compatibility torque. At the same time, it provides an applicable method, which conforms to the changing law of secondary torque.Compounding stiffness is introduced for analyzing the characteristics of moment redistribution in the long-span floor beams structure subjected to lateral loading. It is shown from the testing result that the specimen can be analyzed by elastic theory before cracking. The development of cracking in the spandrel beams and the floor beams (including floor) causing the compounding stiffness and the bending stiffness of floor beams through the column to change distinctly, correspondingly moment-torque redistribution occurs. From the point of the behavior of spandrel beam in the course of test, there are four clearly stages based on the three characteristic points: bending cracking of floor beams through the column, diagonal cracking of spandrel beams and/or bending cracking of floor beams above the spandrel beams (including floor) and bending yield of floor beams through the column. In the last stage, the torque of spandrel beams seems more like an equilibrium torque than a compatibility torque. The law ofmoment redistribution in the structure subjected to lateral loading is different from that in the structure subjected to vertical loading. From the results of test, the torque when specimens fail mostly exceeds the torque, which is calculated by elastic theory.This paper discusses the torque-reduced factor of spandrel beams and the flexural strength ratio between columns and beams, and it gives some applicable suggestions...