| Shield tunnel has been widely used in the construction of urban municipal,transportation and other infrastructure due to its high mechanization and little construction disturbance.With the continuous improvement of underground space development requirements,shield tunnels are also developing in the direction of large cross-section,ultra-deep burial,and multi-form,which brings more challenges to the design of shield tunnel linings.The load on the segment structure of large-section shield tunnels increases significantly,and the segment joints,as the weak link of the lining structure,are in a complex three-dimensional stress state,which is prone to cracking,damage,local failure and other diseases,affecting the structural safety of the lining ring and whole tunnel.Fiber reinforced concrete(FRC)provides a new solution for local damage of segment structure.Therefore,it is of great practical significance to carry out the opening failure test and model study of rebar-steel fiber-reinforced concrete segmental joint structure of large section shield tunnel under three-dimensional loading.In this thesis,considering the large section shield tunnel under complex stress as focus,the mechanical behavior and failure characteristics of rebar and steel fiber reinforced concrete segment joints were studied by means of full-scale tests.Focusing on the effect of steel fiber,a mesoscopic numerical model considering the random distribution and bond-slip properties of steel fibers was constructed.Then,a macro damage plastic model was modified based on meso-scale numerical tests,which was used to construct the refined finite element model of rebar-steel fiber-reinforced concrete joint considering the detailed structure and steel fiber reinforcement.Moreover,the model verification and analysis under multi-condition are carried out.The research results can provide a theoretical basis for the design of rebar-steel fiber-reinforced concrete composite segmental joint in large section shield tunnels.1.Considering reinforced concrete segments as focus,a series of deformation and failure tests of full-scale segment joints of shield tunnel under the combined loading of compression(N),bending(M)and shear(Q),including N-M,N-Q and N-M-Q,were carried out,and the loading response curves of joints are obtained under all conditions;especially focused on the generation and expansion of joint cracks.Moreover,quantitative comparison of the overall mechanical behavior and failure modes of segment joints in N-M-Q and N-M conditions.It is found that the joint exhibits obvious nonlinear characteristics under the various combinations of compression,bending and shearing.The deformation process can be divided into several stages.The shear force accelerates the failure process and leads to the decrease of joint ductility.In addition,the shear force significantly reduces the flexural bearing capacity of the joint under the positive moment but the effect is not obvious under the negative moment.Digital image correlation(DIC)technology is applied to record the failure process of concrete in the joint area.It is shown that the occurrence of inclined shear cracks is sudden and the expansion process is fast,which is the main factor leading to the mentioned shear effect.2.Two steel fiber to rebar replacement ratio are designed.Considering those two replacement ratios,and N-M,N-M-Q loading conditions,a serial of full-scale tests of rebar-steel fiber-reinforced concrete composite segment joint was carried out.The test results are presented in the form of vertical load-joint deflection,moment-joint rotation angle,bolt strain,failure mode,concrete strain distribution and crack width.The results show that the change of the steel fiber to rebar replacement ratio has little effect on the nonlinear mechanical behavior and failure mode of the joint,indicating that the existing joint design method is still applicable in the design of the rebar-steel fiber-reinforced concrete segment.However,steel fiber can improve the bearing capacity,crack resistance and ductility of the joint.In addition,increasing the content of steel fiber can alleviate the adverse effects of shear on joint structure,cracking and brittleness,to a certain extent.3.A meso numerical model considering the random distribution and bond-slip properties of steel fibers is proposed to improve analysis efficiency and convergence.Then,the model is verified by test results under different conditions.It is shown that the meso modeling method is not only close to the data of real tests,but also more realistic to reproduce the cracking and failure behavior of members.Based on the secondary development(Python programming)in the ABAQUS environment,a complete set of modeling programs for the model was formed.This program is flexible and convenient in modelling and parameter modification,which can provide support for pre-test design,result prediction,and parameter analysis.4.Based on meso numerical modeling tests,the existing damage plastic model is modified to reflect the reinforcement effect of steel fiber,such as peak stress,fracture energy and residual strength.Using the modified macro equivalent damage plastic model,a refined finite element model of rebar-steel fiber-reinforced concrete joint considering detailed structure and steel fiber reinforcement was constructed,and the model was then verified by tests.The results show that the model can accurately simulate the local failure mode of the concrete at the corner of the segment and the detailed behavior of the bolt in the joint structure.At the same time,the model study shows that using steel fiber to partially replace rebars can effectively alleviate the local damage and failure of segments while maintaining the bearing performance of joints,which provides a reliable analysis method and a new idea for the design of rebar-steel fiber-reinforced concrete segment joints. |
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