Experimental Study On Flexural Behavior Of Flax Fiber Reinforced Polymer Reinforced Glulam Beams

Today’s building structures pay more and more attention to the utilization rate of materials,the load of buildings on the environment,the cost of time,and modern aesthetics.As a kind of renewable natural resources,wood has been widely used in buildings all over the world because of its environmental protection and energy saving,easy to realize prefabrication and assembly,good seismic performance,and the ability to provide comfortable and healthy living space.China’s forest resources,especially high-quality wood resources,are relatively scarce,so planting fast-growing forests and improving the utilization rate of materials through the use of engineering wood is an effective way to alleviate the contradiction between supply and demand and improve the status quo.Laminated glulam(referred to as glulam)is a kind of engineering wood product which is widely used in modern wood structure building.The failure of glulam beam is a kind of brittle failure of the bottom laminate,especially the natural defects such as knots.In order to reduce or avoid this kind of failure mode,improve the bearing capacity and bending rigidity of the beam,reduce the deformation,increase the ductility of the beam,and give full play to the compression performance of the wood at the top of the beam and the tensile performance of the wood fiber at the bottom of the beam,this paper proposes a new method of strengthening the glulam beam with fiber composite.In this paper,flax fiber reinforced polymer(FFRP)was prepared by grafting nano-TiO2 onto flax fiber to improve its mechanical properties.24 pieces of glulam beams with the size of 2850mm × 50mm × 150 mm were made with SPF plates,and the modified linen fabric was pasted with glulam beams in different ways.Glulam beams with U-shaped hoop not pasted along the whole span are glulam beams without hoop,and glulam beams with U-shaped hoop pasted along the whole span are glulam beams with hoop.Eight groups of beams were tested by changing the length,number and reinforcement of FFRP.Based on the analysis of the ultimate bearing capacity,failure mode,deflection,stiffness,strain and other indexes of glulam beams,this paper explores the strengthening effect of FFRP on the bending performance of glulam beams.The test results show that the length of FFRP has little effect on the glued beam without peeling failure,and the calculation method of the minimum anchorage length of FFRP at the bottom from the point of full utilization is put forward.It can be seen that the number of FFRP pasted on the bottom of glulam beam should not be too large.The flexural capacity of the glued beams with three and six layers of FFRP pasted on the bottom is 44.59%and 56.76%higher than that of the ordinary glued beams,and the flexural rigidity is 23.94%and 119.88%higher,respectively.When the bottom is pasted with three layers of FFRP,the difference between the flexural capacity and flexural rigidity of the glued beam with hoop and the glued beam without hoop is not significant,but the ductility of the beam is significantly improved.When the FFRP at the bottom of the beam is 6 layers,the flexural capacity of the glued beam with hoop is not improved,but the flexural rigidity is improved obviously.The failure mode of the glued beam without hoop is brittle as that of the ordinary beam,while the failure mode of the beam with hoop is ductile.The u-hoop can improve the failure mode of glulam beam,avoid the cracking and transverse tearing between wood layers,and enhance the coordination performance of FFRP and wood at the bottom of beam,so as to improve the bending resistance of beam.Using ABAQUS software to simulate the test,the finite element models of FFRP reinforced glulam beams and FFRP reinforced glulam beams are established,and the accuracy of the model is verified by comparing the test results.By changing the length and the number of FFRP at the bottom of the beam,the influence of the length and the number of FFRP on the bending performance of the beam is studied,and finally the suggestions for strengthening methods are given.