Experimental Study On Flexural Behavior And Strengthening Of Glued Timber Beams With Small Span To Height Ratio

Wood structure building is green and environmentally friendly,which is in line with China’s sustainable development strategy.All countries around the world are advocating low-carbon life,and the advantages of wooden structures are gradually reflected.Wood structures are widely used in residential and public buildings in developed countries such as Europe and the United States.In recent years,more and more applications and studies have been made on wood structures in the field of architecture and civil engineering in China.Plywood beams,as one of the most important components in wooden structures,have been extensively studied by scholars at home and abroad.However,for a long time,the traditional bending test of plywood beams is based on the requirements of"Standard for Testing Methods of Wood Structures".The plywood beams with Span-to-height ratio(≥18)are used,and most of them are damaged by wood breakage at the bottom of the beams.This kind of glued wood beam has slender members,low bearing capacity and large deflection when bending,which can not satisfy the actual engineering requirements very well.In this paper,according to engineering practice,glued wood beams with Span-to-height ratio of 12 are selected.The flexural capacity of 9 wood beams in 4 groups is tested by using unreinforced,steel plate at the bottom,screw in the bottom bending-shear zone and steel plate at the middle of both sides.Through experiments and theoretical analysis,the failure modes,load-displacement curves,strain distribution in span and ultimate bearing capacity of the specimens are studied.The main contents of this paper are as follows:(1)Based on the three-point bending test of small span-height ratio plywood beams,the failure modes and mechanism are discussed,and the experimental phenomena in the test process are described and analyzed.The ultimate bearing capacity,load-displacement curve and strain distribution in span are obtained by summarizing the test data.(2)The flexural bearing capacity of small Span-to-height ratio plywood beams strengthened by bonding steel plates at the bottom,screwing in the bending-shear zone at the bottom and sticking steel plates at the middle of both sides are tested respectively.The failure modes and mechanism are studied.The wood strain variation and ultimate bearing capacity under bending are tested.The load-displacement curves and loads of reinforced small Span-to-height ratio plywood beams are obtained.-Strain curve.(3)The ultimate bearing capacity,mid-span deflection and strain variation of small Span-to-height ratio plywood beams after reinforcement are compared and analyzed.It is concluded that sticking steel plate on the bottom of beam can improve the bearing capacity and stiffness of wood beam;screwing screw on the bottom of beam can improve the shear capacity of wood beam;sticking steel plate on the side can not only improve the shear performance of wood beam,but also restrain the development of cracks to a certain extent.(4)After verifying that the cross-section strain distribution of beams basically conforms to the assumption of flat section,the critical Span-to-height ratio of small Span-to-height ratio plywood beams subjected to tension and shear failure is explored,and the formulas for calculating the ultimate bearing capacity of small Span-to-height ratio plywood beams and reinforced members subjected to shear failure along grain in three-point bending tests are proposed.The theoretical values are safer than the measured values,and the error is mostly less than 20%.It can provide reference for the design and engineering application of this kind of component.