Experimental Study On Mechanical Characteristics Of Horizontal Anchor Bolt For New Tubular Roof Member

With the rapid development of China’s underground construction projects,new construction methods are gradually applied in engineering.To solve the problems of urban subway construction blocking traffic due to underground large excavation,a New Tubular Roof(NTR)method is proposed and applied.The method uses the underground actuator to force large-diameter steel pipes into the soil in the horizontal direction,and the pipes are connected by connecting members into a whole structure.Then,the inner tube soil is removed,and concrete is poured into it to form a permanent composite structure.As we all know,in a new tubular roof structure,the anchorage performance of connection is very important.Currently,the tubular roof connection is used in a relatively simple way,commonly used through locking connection.After the tubular roof structure formation,waterproofing agent or mortar was injected at the locking spot to form a seal roof.However,this connection significantly reduces the lateral rigidity of tubular roof structure.This paper improves an inter-pipes connection approach by using lateral bolt connections,to enhance the overall stiffness of the tubular roof structure and reduce the difficulty of construction.The study will use a comprehensive method which is based on experiments and partly based on theoretical analysis to research the anchorage performance of anchoring member laterally connected with bolts.By changing test parameters of the length of the anchor,the anchor mode,bolt diameter,bolt material,and longitudinal direction multiple bolt space,we can obtain different load-displacement curves and failure modes to clearly understand the main factors affecting the performance of the anchor and its impacting law,to provide a foundation for future design and construction.The main work in the dissertation includes:(1)Summarizes the theory and construction experience for existing tubular roof construction method on the basis of relevant abroad information of tubular roof construction technology,and improves the new tubular roof method,and generalizes the mechanical performances of bolt connection,to propose the ’goal,contents,and methodology in the dissertation.(2)In order to verify the effect of bolt connection,an experiment for bolt connection of new tube structure is conducted to determine the ultimate bearing capacity,deformation characteristics,and failure mode of bolt anchoring.In the experiment,the various parameters influencing the connection performance are changed to clearly understand the mechanism which will provide a reference for the calculation model selection and design for the new tubular roof structure.The experimental results show that two kinds of typical failure modes of tensile break and adhesive failure for anchorage members are observed,and different load-displacement relationship curves are obtained as changing the pullout order of the bolts.As pulling out three bolts at the same time and keeping no additional stress in local nearby compression area,the bolts also break under pulling force.We can conclude that the installation of nuts along the bolts and the steel pipe with a certain thickness can greatly help for the increase of the anchorage performance,and the group anchorage effect exists for relatively small distance of the bolts.The proposed anchorage method can meet the requirement of engineering.(3)Through the theoretical calculation and finite element analysis,we got the anchor axial force,shear force curves with the anchorage length distribution,and the failure mechanism of anchorage.The numerical simulation results show that,for the concrete anchorage body,as anchor bolt for the length of 300mm and diameter of 27mm,and bond slip usually occurred,and failure load range of the structure in 300kN-350kN is observed.