| Glulam which is the main material of the modern timber structure has the decentralized imperfection, high strength, free section size and member shape and reasonable load. However, there are some defects in the glulam when glulam timber beams are bent, such as compressive strength incompletely used, insufficient tensile strength of beam bottom glulam and brittle failure, and the like. Based on above situation, a new steel and wood composite member named steel plate strenghthened glue-lumber beam is proposed in this paper, by which the compression is borne by glulam, the tensile is borne by steel plate and the prestress can be applied during production process. This kind of glulam will make full use of the compressive strength of glulam and the tensile strength of steel plate, and then improve the bearing capacity of beams and decrease the beams section size. This thesis, therefore, is of great significance in academic value and social practice. The following research is made in this paper.For steel plate strenghthened glue-lumber beams, a set of assist device was developed, which had two founctions:the first was it can pressure transversely on the steel plate strenghthened glue-lumber beams as well as precisely control the value of applying pressure to ensure a more uniform layer of paste so that steel and glulam beams can work together to improve their carrying capacity; the second was it can apply prestress to ordinary steel plate strenghthened glue-lumber beams and the external prestressing tendons did not destroy the beam section as well as the small space required for the construction so that the prestress would be more conveniently and easily applied to glulam and the deflection would be effectively controlled, making full use of high-strength steel plate.Through the bending tests of thirteen batches(in all:39) beams, the influence of plate thickness, paste position of steel plate and additional screw or not on bending performance of ordinary steel plate strenghthened glue-lumber beams was researched. Compared with ordinary glulam beams, when the 2mm,3mm and 4mm thick steel plates were affixed, the bearing capacity was increased 30.28%,56.91% and 32.05% respectively, and with the increase of steel plate thickness, the bearing capacity was increased first and then dicreased. Compared with ordinary glulam beams, when the same thick steel plates were affixed and screws were set, the bearing capacity was increased 41.60%,57.53% and 59.04% respectively. With the increase of steel plate thickness, the bearing capacity was increased;compared with the same thickness steel plate strenghthened glue-lumber beams, the bearing capacity was increased 11.32%, 0.62% and 26.99% respectively, and reinforcement effect of screws was more obvious with thicker steel plates. Compared with ordinary glulam beams, when the 2mm,3mm and 4mm thick steel plates were affixed at the second layer bottom beams, the bearing capacity was increased 3.83%,21.20% and 44.34% respectively, and with the increase of steel plate thickness, the bearing capacity was increased. Compared with ordinary glulam beams, when the same thick steel plates at the second layer bottom beams were affixed and screws were set, the bearing capacity was increased 5.54%,33.54% and 26.63% respectively, and with the increase of steel plate thickness, the bearing capacity was increased first and then dicreased. Compared with the same thickness steel plate strenghthened glue-lumber beams in bottom two layers, the bearing capacity was increased 1.71%,12.34% and 11.18% respectively, and when the thickness of steel plate was thicker the reinforcement effect of screws was not very obvious because the integrality of the beams was destroyed by screws. Based on expeimental data, the plane section assumption was verified, and the bearing capacity calculation formula of such kind of member was proposed according to the test results, as well as the maximum thickness value of allowable yield steel plate for steel plate of glue adhered and screwed fixed strenghthened glue-lumber beam was given.Through the bending tests of six batches(in all:18) beams, the influence of plate thickness and the ways of pasting steel plate on bending performance of prestressed steel plate strenghthened glue-lumber beams was researched, and compared it with the ordinary steel plate strenghthened glue-lumber beams. Compared with ordinary glue-lumber beams, when the 2mm,3mm and 4mm thick steel plates were affixed and beams were applied prestress, the bearing capacity was increased 21.3%,51.5% and 57.8% respectively; when the same thickness steel plates were affixed, screws were set and beams were applied prestress, the bearing capacity was increased 40.46%、50.57% and 67.26% respectively. For these two beams, with the increase of steel plate thickness, the bearing capacity was increased; after the screws were set, the enhance of effect was more obvious. Compared with ordinary steel plate strenghthened beams, when the 2mm and 3mm thick steel plates were affixed, the bearing capacity had little difference; when the 4mm thick steel plates were affixed, the bearing capacity was increased 19.5%; with the applying prestress, the steel plate yielded to ordinary steel plate strenghthened beams and the failure mode changed from a plastic plate destruction to the top beam compression failure, and the bearing capacity of the beam was significantly improved; when the same thick steel plates were affixed, after the screws were set and beams were applied prestress, the bearing capacity had not changed significantly because the steel plates had already yielded when steel plate strenghthened beams reached the ultimate bearing capacity, and prestressing just made steel plates reach the yielded strength in advance and plastic deformation of the beams increased but not improved the bearing capacity. When the thickness of the steel plates allowable yielded more than the maximum thickness, the application of prestressing force would increase the ultimate bearing capacity of prestressed beams. In the elastic stage, the more the prestress applied, the larger the beams inverted arches were, which led to the bigger deflection offset generated by the external load and smaller beam total deformation.Through the ABAQUS finite element software, this thesis analyzed the bending performance of ordinary and prestressed steel plate strenghthened glue-lumber beams, established the anisotropic elastoplastic constitutive relation of glue-lumber and a simplified model of screws, considered the adhesive thickness value and the contact relationship between the adhesive layer and the steel plate, glue-lumber, and made research on the influence of plate thickness, the ways of pasting steel plates and the position of steel plates on bending performance of ordinary and prestressed steel plate strenghthened glue-lumber beams. Compared them with experiment results, the bending performance of steel plate strenghthened glue-lumber beams on the many working cases except experiment was analyzed, and the experiment results were supplied and perfected. Finally, the maximum thickness value of allowable yielded steel plates for ordinary steel plate strenghthened glue-lumber beams was given and the influence of prestress value on bending performance of steel plate strenghthened glue-lumber beams was researched. |
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