The Study On Flexural Performance Of Regulable Reinforcement Glulam Beams Based On The Creep Behavior

Recently,timber structure as a sustainable structure form with its green,safety,low carbon as well as environmental protection is strongly advocated in our country.As the main material of modern timber structure,glue-lumber has its advantages,such asscattered defects,high strength,free section and shape of the component.However,the beam made by glulam easily lead to brittle tensile failure whenit’s bended,and glulam beams often have larger deformation for the lumber lower elastic modulus.Meanwhile,with the creep properties of wood,glulam beams is often controlled by deformationin the design process.The strength of the timber,especially compressive strength,which always can’t be got into full play.Under this background,this paper puts forward a regulablereinforcement glulam beams with the bottom slot and reinforced steel bar,which to form a combined component that its steel bar is tensile and glulam is compressive.This formal beam can make full use of the compressive strength of glulam and make it plastic compression failure.It can also reduce or eliminate the influence of creep on long-term deformation by adjust the size of the prestress when used.Due to reinforcement glulam beams is a new typecomponent and the domestic and foreign related research is relatively less,morely the creep is one of the basic characteristics of wood as well as largely effect of it on long-term mechanical properties of glulam beams,which has a certain academic value and engineering significance to study long-term flexural properties of the regulablereinforcement glulam beams.The specific research contents and results are as follows:According to the type,load levels,rebar diameter and prestress value,to divide regulablereinforcement glulam beams into A,B,C,D four groups,then to do respectively load test for a long time indoor in Harbin under normal using environment.Among the four groups,A,B are respectively pure glulam beams and general reinforcement glulam beam both under different load levels,C is normal reinforcement glulam beams with same load levels and different bar diameter,D is prestressed reinforcement glulam beams with same load levels and bar diameter,but different prestress value.Within 90 days loading test for each group,firstly test data for the long-term creep deformation of regulablereinforcement glulam beams.The analysis shows thatthe creep deformation of L_A2,L_A3 increased 32.37%and 126.97%respectively,PL_B2,PL_B3 increased 37.85%and 131.49%compared with the beam with load level 20%,which indicates creep rate increases with load level improved and beam creep deformation development was more obvious when load level more than normal using load.Compared with PL_C1,PL_C2,PL_C3 respectively increased 33.80%and 73.60%,whichillustrate that increased bar diameter was helpful to reduce beam creep deformation.The creep deformation of YL_D2 increased 74.12%more than YL_D1,thus to be seen the creep rate of beam growth along with prestress value increase.According to the above change rule,the power law model of regulablereinforcement glulam beams for predicting long-term deflection were set up,and provided formula to calculate beams long-term deflection and creep deformation coefficient values of different type beams.Short-term load destructive test was conducted after completing long-term load test of the A,B,C,D group to get the ultimate load of the beam after creep andafter creep deformationrecovery,and compared with experimental beams which were not creep.The bearing capacity of beams without deformation recovery both have decreased,among which group A beams have fallen by 4.22%⁹.83%,B have decreased by 2.64%¹3.23%,C is8.16%¹1.25%and D is 2.90%⁹.16%.However,the bearing capacity of beams wich its deformation returned to the initial value have improvedby 4.62%⁴.62%.The results show that adjusting prestress can effectively improve the bearing capacity of reinforcement glulam beams.