The Study On Flexural Performance Of Prestressed Glulam Beams String Structure Based On The Creep Behavior

The glued laminated timber was formed by timber, whose thickness was less than 45mm and was mainly glued together along the grain, which was shorted for glue-lumber. The glue-lumber beam, column, and the arch, truss and framework formed by glue-lumber, were known as glue-lumber members. For series of typical advantages, such as scattered deficiency、small variability、free length and cross section size、high compressive strength and reasonable force, etc, the glue-lumber became the preferred material in modern timberwork buildings. However, because of the essential characteristic of timber, it was of lower tensile strength and significant creep deformation, as a result, in actual engineering, the brittle tensile failure was more usually happened in ordinary glue-lumber beam, which lead the compressive strength was not fully exerted. Besides, the deformation was obviously, which lead the deformation became the main control factor of beam section size. Introduced the prestress technology into glue-lumber beam could make full use of compressive strength, which reached the purpose of ductile failure; it also could control the beam deformation, and reduce member section size. At present, in domestic and foreign, the research on prestressed glue-lumber beam was most remained on theoretical research stage, and the research on its long-term deformation was blank. Therefore, it was of high theoretical significance and practical value to carry out the long-term bending properties of prestressed glue-lumber beam string structure. Based on above reasons, the following works were carried forward in this paper:First, in order to satisfy the date analysis requirement of prestressed glue-lumber beam string structure after long-term loading test, the compressive test on glue-lumber along the grain and the tensile test on prestressed steel wire were arranged, and then the corresponding strength and elastic modulus were obtained. In addition, considering the large size and multi number of prestressed glue-lumber beam string structure in long-term loading test, the existing device cannot meet the test requirement, therefore, according to the specific research purpose of long-term loading test, a set of self-developed loading device was designed, and the support spacing could be adjusted by beam length.Second, under the indoor environment of normal use in Harbin, the prestressed glue-lumber beam string structure was divided into A, B groups. For group A, remained total pre-tension value invariable, and change the prestressed steel wires number; for group B, remained prestressed steel wires number invariable, and change the total pre-tension value. According to the relation between bearing capacity and load effect, the loading value of group A & B was finally confirmed—30% of the standard value of ultimate bearing capacity under short-term loading test. The test was divided into two batches, and 5 beams were loaded in each batch. Through continual monitoring of 45 days on beams of each batch, the first-hand data of prestressed glue-lumber beam string structure under normal use environment was obtained, and the two batch beams mid-span deflection change law with time were analyzed, and then, the influence of prestressed steel wire stress variation and timber creep on total pre-tension value and prestressed steel wires number were obtained.Finally, on the basis of long-term loading test, the short-term damage test was conducted on group A & B. Compared the beam ultimate load without long-term loading, under long-term loading without deformation recovery, under long-term loading with deformation recovery to initial loading state, the influence of prestressed glue-lumber beam string structure limit load and stiffness on creep and prestressed control were analyzed.