Study On Short-time Flexural Behavior Of Internal Prestressed Glulam Beams

Glulam beams and columns are widely used in timber architecture.The bending failure mode of glulam beams is brittle failure,so the strength of timber especially the compressive strength cannot be fully utilized.To improve and enhance the mechanical properties of glulam beams,the domestic and alien scholars constantly attempt and explore to use metal materials and fiber reinforced composite material to reinforce the glulam beams,and achieved good results.However there are still following problems after reinforcement of glulam beams:(1)The high strength of the strengthen materials generally cannot be fully utilized;(2)The limit state of glulam beams is mainly controlled by deformation and the strength of timber cannot be fully used.By applying prestress on the tensile region of the glulam beams,the span deformation can be reduced,the ultimate load,bending stiffness and ductility can be improved,and material properties are more fully utilized.Considering the situation stated above,enhancing the research of prestressed glulam beams is full of great significance.In this paper,the internal pretressed glulam beams was studied.At first,the bending test was conducted.Then a simulation was carried out based on ABAQUS,and the theoretical analysis was carried out using section method.The contents of this paper can be divided into several parts above.(1)The achievements refer to prestressed glulam beams obtained by domestic and alien scholars was concluded.(2)Based on ABAQUS,The method to analyzing flexural behavior of internal prestressed glulam beams was used and tested to be accurate by an example of glulam beams reinforced with prestressed CFRP bars.(3)Experiments on internal prestressed glulam beams were carried out,including 3 unreinforced glulam beams,3 straight-bonded prestressed glulam beams,6 curved-bonded prestressed glulam beams,and 3 curved-unbonded prestressed glulam beams.The results indicate that the failure mode of prestressed glulam is ductile failure,and the ultimate strain of timber is improved greatly.Compared to the unreinforced glulam beams,the ultimate load of bonded prestressed glulam beams increased by 29.9?50.1%,the bending stiffness increased by 27.2?30.8%,the ductility increased by 32.8?48.0%.The ultimate load of unbonded prestressed glulam beams increased by 23.7^32.3%,the bending stiffness increased by 17.3?20.4%,the ductility increased by 24.8?25.6%.(4)Based on ABAQUS,a simulation of internal prestressed glulam beams was conducted out and the differences including failure mode,load-deflection curves,stress distribution between experiment and simulation were compared.It was found that the simulation can accurately reflect the experiment.(5)The flexural behavior of the internal prestressed glulam beams were analyzed in theory.The calculation formula of ultimate load,bending stiffness were deduced,and result of theory match well with the experiment.The paper defned the upper and lower limit of the effective tension,and deduced the calculation formula.The relationship between the effective tension and flexural capacity was analyzed.It is found that the descending branch of compression behavior for timber greatly effects the relationship between effective tension and flexural capacity.