Slip And Uplift Effects Of Timber-Concrete Composite Beams Study On Mechanical Properties

With the rise of the concept of ecological architecture,the wood as a kind of green material has been paid more and more attention by building engineers.In order to make full use of the characteristics of good tensile properties of the timber,timber-concrete composite(TCC)beams are gradually favored and studied by architectural engineers.The TCC beam combines the upper concrete flange plate and the lower glulam beam into a force community through different types of shear connectors,so that the mechanical characteristics of the two materials can be effectively utilized.Compared with the commonly used reinforced concrete beams,TCC beams are more in line with the concept of ecological and environmental protection.Affected by different material characteristics,as well as the reason that the stiffness of shear connectors cannot reach infinity in practical engineering applications,it is inevitable that slip and uplift will occur at the interface position of timber beam and concrete slab.Scholars at home and abroad have carried out a large number of theoretical and experimental studies to explore the mechanical properties of various shear connectors,and have achieved relatively rich results.However,the research results of TCC beams are relatively few.In this thesis,after summarizing the existing achievements of TCC beams,and found that there are still the following problems need to be addressed:(1)Both the slip and lift will lead to the decrease of the bending bearing capacity of timber-concrete composite beams,but the research on the flexural behavior of TCC beams is carried out without considering the vertical uplift.Therefore,from the point of view of structural safety,it is necessary to study the influence of uplift effect on the flexural performance of TCC beams.(2)The shear stress of TCC beams is very complex.At present,few scholars have deeply studied the shear properties of TCC beams,so there is a lack of understanding of their shear failure modes and mechanisms.In order to study the effect of slip and uplift on the flexural behavior of TCC beams,five glulam-concrete test beams were made in this thesis.The test beam takes different bolt shear connection ratios and arrangement as the research parameters,and explores the variation rules of horizontal relative slip,vertical uplift,deflection,strain and bending capacity of TCC beams under different shear connection ratios and arrangement mode.At the same time,considering the vertical lift effect,the bending resistance of TCC beam is analyzed theoretically.In order to explore the shear failure mode and mechanical properties of TCC beams,five glulam-concrete test beams were made in this thesis.The influence of different connection ratios,shear span ratio and web width of timber beam on the shear behavior of composite beam is studied.The shear failure mode and failure mechanism of TCC beam and the distribution law of stress and strain of concrete slab are discussed.Moreover,the calculation method of shear bearing capacity is put forward.The main achievements and innovations of this study are summarized as follows:(1)Through the experimental study,the variation of lift force and slip and the influence of bending performance are proved.And in view of the elastic state,the analytic solution of the lifting force under the symmetrical concentrated load of two points is derived by using the balanced differential equation.Furthermore,the analytical solutions of deflection and flexural capacity of TCC beams under sliding and uplift effects are derived.(2)This thesis analyzes the limitation of the reduced stiffness method commonly used in steel-concrete composite beams when applied to TCC beams,and corrects them to solve the problem of simplified calculation of TCC beams.(3)The failure mode of the shear bearing capacity shear capacity of TCC beams is studied in depth.And the theoretical values of shear stress of TCC beams in elastic state under complete shear connection and no shear connection are derived,and a simplified calculation method for maximum shear stress of concrete neutral axis with partially connected TCC beams is proposed.By analyzing the shear distribution law of concrete slab and timber beam,a simplified calculation method of shear bearing capacity of TCC beam is put forward.In conclusion,the flexural and shear mechanical properties of TCC beams under two symmetrical loads are studied systematically in this thesis.The research results can be used in the design and calculation of TCC beams,which has important theoretical significance for the development of TCC beams as green building structures.