Experimental Research On Flexural And Shear Bearing Capacity Of Wood-like Beams

China's wooden structure is an important part of China's history and culture.The Forbidden City in Beijing,the ancient city of Lijiang in Yunnan,the Confucius in Qufu in Shandong,and the ancient city in Pingyao in Shanxi are famous for their scale.The wooden structure has the characteristics of low carbon,warm in winter and cool in summer,energy-saving and heat preservation,suitable for residence and good seismic performance,and can also realize prefabrication and assembly construction of the factory.In addition,it can be dismantled after use,and the solid waste is easy to recycle and the waste disposal price is low.It is a veritable green building.The greenhouse effect,rural housing transformation,sustainable development and world livability demand provide an opportunity to choose wood as a structural material.As urbanization accelerates,it is necessary to develop and implement low-carbon building solutions of all sizes.Multi-story timber-framed buildings not only reduce greenhouse gas emissions,but also meet the demand for housing by urban dense populations,and are one of the important strategies for urban development.Vigorously developing wooden structures conforms to the green development concept proposed by the Chinese government.Modern wood structure buildings and traditional wood structure buildings learn from each other and develop synergistically.Modern wood-framed buildings not only retain the advantages of traditional wood-framed buildings,but also combine contemporary advanced pre-stressing techniques and metal joining techniques to break through the size and length limitations of native wood to achieve long-span construction.In the"Code for Design of Wood Structures",the wood structure includes ordinary wood structure,glued wood structure and light wood structure.Among them,ordinary wood structures are common in landscape design and public buildings,not only solemn and beautiful,but also beautiful in appearance;the glulam structure uses its excellent mechanical properties and processing properties to build schools,clubs,villas,industrial buildings,large-span commercial buildings,With its excellent anti-corrosion properties,the construction of gymnasiums and chemical processing workshops,in addition to large public buildings,glulam-wood houses have also been promoted;light wood structures are mostly used in low-rise residential buildings,and a few are used in commercial and public buildings.This paper briefly introduces the development history of wood structure design methods and the four international main design methods,namely the limit state design method based on probability theory,MFLSD,load and resistance coefficient design method LRFD,allowable stress design method ASD and full probability.Design methods and a brief description of the pros and cons of each method.Wood-based buildings use plantations as the main raw material.Excessive felling of trees will result in sharp decline in forest resources,quality degradation and uneven distribution,which will lead to secondary damage such as land desertification,soil erosion,water shortage,species reduction,sandstorms and other natural Frequent disasters reduce the quality of human life and even threaten human health.Protecting forest resources means protecting humans,abandoning wood consumption,and finding substitute wood materials is imminent.In order to alleviate the pressure on the supply of wood resources,non-wood wood-based panels made from non-wood materials have been vigorously promoted.In the past,agricultural surplus straw could only be burned on the spot and raised livestock.After it was applied to the production of wood-based panels,the formaldehyde of wood-based panels could be avoided,and the raw materials were not restricted by region or type.Compared with wood,bamboo has better impact resistance,extrusion resistance and wear resistance and can be used as a structural material.Professor Zhang Huagang proposed a new type of wood-like material.The raw material is composed of plant fiber and magnesia mixture,magnesium chloride solution,additive solution prepared by soluble sulfate and phosphate,and analytical pure tartaric acid explosion-proof additive.After mixing,in the mold The inner part is solidified and solidified by high pressure.It has good fire performance and waterproof performance.It has certain mechanical properties based on plant fiber artificial materials,and artificial materials are mainly made from grass fibers and used in building structures.The wood-like frame structure,the wood-like hollow wall structure,the wood-like two-way hollow floor structure,the wood-like staircase and the wood-like double-beam beam staircase structure are all made of plant fiber or wood chips,and the raw materials have good compactness and Plasticity ensures the fireproof performance and anti-corrosion performance of the components.The source of raw materials is wide,which can promote the resource utilization of crop waste,and does not consume forest resources,which is conducive to ecological environment protection.The connection form of the new wood-like structure is mainly made up of special connecting pieces,which ensures the rigid connection of the nodes in the wood-like frame structure,the length of the columns at the frame joints,and the assembly of hollow walls and hollow floor covers.It has the characteristics of various forms,clear transmission,safe and reliable,strong toughness and tight performance,and convenient construction.In this paper,the mechanical properties test of wood-like materials,the bending resistance test and the shear test of wood-like beams are carried out.The following important conclusions are obtained through the test:1 In the material property test,when the water content is 18.0%,In terms of tensile strength,the material's compressive strength,flexural strength,and dispersion of the elastic modulus are large.Among them,the tensile strength is4.7N/mm~2,the compressive strength is 24.1N/mm~2,the flexural strength is 6.9N/mm~2,and the flexural modulus is 4119N/mm~2.Through the material test design,it is found that the wood-like materials of the current mix ratio are used for building load-bearing members,and the look-ahead size is slightly larger than that of the wood structural members,but is roughly equivalent to the concrete members,which is acceptable for engineering applications.2 In the bending test of wood-like beams,when the water content is 17.1%,the pure bending modulus of the wood beam is 447.0027N/mm~2,the apparent flexural modulus is 36302.32N/mm~2,and the shear modulus is 55.698N/mm~2,bending strength is 4.889N/mm~2,bending partial coefficient is 1.7,elastic modulus design value is 4119N/mm~2,and the standard value of material bending strength is 0.709 times of bending strength of small sample of clear material;The ultimate bearing capacity of the wood-like beam test is 3.873kN,which is slightly larger than the theoretical value,but the two are basically consistent.There are two main reasons for this phenomenon:1)During the bending test of wood-like beams,the water content is 17.1%,which is slightly lower than the moisture content of 18.0%in the material test.2)The wood beam is larger in size and easier to process,while the size of the clear material is smaller,the quality of the sample is lower than the mass of the component;the main cause of the failure of the wood beam is that the fiber on the tension side is broken and destroyed,and the damage belongs to Damaged by fragility.Throughout the destruction process,the wood beam only experienced an elastic phase.The degree of mechanization of the test piece is not high,the raw material is unevenly mixed,the delamination phenomenon is serious,the defects and the water content are high,and the performance of the test piece is lowered.In the shear test of the three types of wooden beams,the shear failure occurred in the test beam under the condition of water cut rate of 17.1%and shear span ratio of 2.3.The shear strength value of the wood beam was calculated to be 0.563N/mm~2,the standard deviation was 0.077N/mm~2,and the coefficient of variation was 0.137.In addition,the moisture content is too high and the mechanical properties of wood-like wood are significantly reduced.Finally,this test provides a reference for future research on wood-like materials.