Study On The Effect Of Rigid Polyurethane Foam Filling On The Properties Of Original Bamboo Joints For Building

In recent years,with the continuous improvement of economic level,people continue to put forward higher requirements for living standards and environment.The natural original bamboo building has a variety of shapes,beautiful structural forms,friendly to the human body,low carbon and environmental protection characteristics,and is an extremely excellent building.However,the original bamboo is naturally hollow and multi-knotted,the upper and lower dimensions are different,and the growth error is large,which makes it difficult to connect the nodes when it is used in the building structure,so it is often only used for some residential buildings and temporary buildings with relatively simple structures.In this paper,natural bamboo is taken as the research object.Aiming at the difficulties in the construction of existing original bamboo structures,a structural component that fills the bamboo cavities with a mixture of rigid polyurethane foam(RPUF)and bamboo-strips/pine-sticks is proposed.This structure can conveniently and efficiently form a variety of bamboo structure building nodes,improve the bearing capacity of bamboo structure building nodes,and expand the node structure.The specific research contents and conclusions are as follows:(1)The experiments were designed to explore the factors affecting the mechanical properties of RPUF and the results showed that: the apparent density and surface hardness of RPUF can be decreased by 37.93% and 71.05% by improve the pphp(parts per hundred of polyol by weight)of water in the raw material proportionratio of RPUF.At the same time,the improvement of pphp value of the water also reduced the mechanical properties of the RPUF,such as tensile strength,bending strength and compression strength.Adjusting the isocyanate index in the raw material proportionratio of RPUF can make the mechanical properties of RPUF more excellent.The increase of the isocyanate index increased the density of the RPUF;the flexural strength continued to decrease;the surface hardness and tensile and compressive strength increased first and then decreased,and the overall trend increased.Considering comprehensively,when the water content in the ratio is 0.1pphp and the isocyanate index is 1.1,relatively excellent mechanical properties can be obtained.At this time,the tensile strength is 9.48MPa;the bending strength is 20.60MPa;and the compressive strength is 16.72 MPa.(2)The axial compression properties,damaged mode and influencing factors of the specimen were explored,and the results showed that: compared with the round bamboo tube,the use of rigid polyurethane foam filling can effectively improve the axial compression performance of the component.When the volume ratio of the internal reinforcing materials is the same,the ultimate bearing capacity of the components combined with bamboo-strips is 15.30～32.34% higher than that of the components combined with pine-sticks;The axial bearing capacity gradually increased,and reached the highest when the volume fraction of bamboo-strips was 75%.At this time,the ultimate bearing capacity was increased by 96.09% compared with the round bamboo tube.For this type of specimen,the correlation coefficient between the calculated bearing capacity and the actual bearing capacity is 0.8757 according to the calculation formula of the axial compression ultimate bearing capacity,which shows a strong correlation.The proposed method is suitable for predicting the ultimate bearing capacity of polyurethane composite filled members.(3)To explore the influencing factors of the nail-holding force of the specimen,as the volume ratio of bamboo-strips in the filling material increases,the nail holding force increases gradually.As the diameter of the pilot hole increases,the nail holding force decreases gradually.When the aperture ratio is 48.07%,the best nail holding force can be achieved.When the diameter of the guide hole is less than 4mm,the nail holding force is maintained at more than 77.21% of the maximum nail holding force;when the diameter of the guide hole is less than 2mm,the round bamboo is prone to splitting during screwing and pulling.(4)The uniaxial double shear damage mode and bearing capacity influencing factors of the specimen were analyzed,and the experimental results showed that there are four typical damage modes in the uniaxial double shear failure of polyurethane filled specimen,including two ductile damage modes and two brittle damage modes.Increasing the bolt diameter and bolt end distance within a certain range can effectively improve the ultimate bearing capacity of the uniaxial double shear.Based on the analysis of the classical mechanical model of the bolted joints of wood structures based on the solution method of plasticity theory,the calculation formula for the bearing capacity of this type of member is proposed.The correlation coefficient between the calculated bearing capacity and the actual bearing capacity is 0.9920,which indicating a strong correlation.This theoretical model can be used as a reference formula for the calculation of bearing capacity of polyurethane composite filled members.