Experimental Study On Long-term Bending Behavior Of Prestressed Glulam Wood Continuous Beam

As an important part of modern wood structure,glulam has the advantages of free section shape design,strong compression resistance and reduced natural defects.Glulam effectively shortened construction period and green degradability,which greatly promoted the development of modern wood structure,and added a lot of color to the development of green building structure.But at the same time,due to the limited bearing capacity of simply supported glulam beams,brittle failure is easy to occur,and the influence of creep of wood makes the deformation of glulam beams increase.By combining prestressing technology with glulam continuous beam reasonably,the strength of reinforcement and glulam can be fully utilized,the brittle failure is transformed into ductile failure,and the span limit of glulam continuous beam is improved.The deformation of prestressed glulam continuous beam is smaller and the span is larger than that of simply supported glulam beams.At present,there are few researches on the deformation of prestressed glulam continuous beams at home and abroad,so it has important scientific research value and use value to study the long-term bending test of prestressed glulam continuous beams.Based on the above background,the research contents of prestressed glulam continuous beams in this paper are as follows:(1)First of all,the selected glued timber is tested for compressive strength and tensile strength along the grain,and the selected prestressed steel wire is tested for tensile strength,so as to obtain the corresponding elastic modulus and strength values,which can be used as a reference for subsequent test data analysis.(2)Ten prestressed glulam continuous beams were subjected to long-term loading for 180 days under normal indoor use in Harbin under five working conditions.To test according to two parameters:different pre-tension value and different number of prestressed steel wires,those beams were divided into two groups A and B.Group A has the same pre-tension value and changes the number of steel wires;The number of steel wires in Group B is the same,which changes the pre-tension value.The test results show that compared with beams with two steel wires,beams with four steel wires are 1.71 times and beams with six steel wires are 2.87 times.Compared with beams with 0 kN pre-tension value,beams with 7kN pre-tension value are 1.58 times and beams with 14kN pre-tension value are 2.98 times.From the mid-long-term deflection change of the left span,it can be seen that compared with the beam with two steel wires,the beam with four steel wires is reduced by 29.71%,and the beam with six steel wires is reduced by 54.57%;Compared with the long-term deflection variation of beams with pre-tension value of 0 kN,it is 1.3 times that of beams with pre-tension value of 7 kN and 1.87 times that of beams with pre-tension value of 14kN,and the variation laws of left and right spans of beams are the same.The creep model is used to predict the 50-year long-term deflection of glued wood beams and calculate their creep coefficient.(3)After long-term loading,the test beams are directly destroyed in short term and then destroyed after regulation.The failure modes of beams are studied,and the ultimate load-deflection curves of beams under various working conditions are drawn and compared.The results show that compared with beams without creep,the ultimate load of test beams with direct failure is reduced,with the number of steel wires changed by 13.51%-37.65%,and the pre-tension value changed by 19%After adjustment and control,the limit load of a set of steel wires increased by 10.67%-44.79%,and the limit load of a set of prestressing force increased by 26.87%-46.41%.The reasons are as follows:due to the influence of creep,the stiffness of the beam decreases in different degrees,and the internal force arm in the middle of the test beam is increased after adjustment and control,thus improving the bearing capacity of the beam.