| At present,the research on fire resistance of shield tunnel segments at home and abroad mostly focuses on high-strength concrete and steel fiber concrete segments,while the research on fire resistance and post-disaster performance of self-compacting concrete segments of hybrid fiber(steel fiber and polypropylene fiber)is relatively few.Therefore,the mechanical properties of hybrid fiber concrete self-compacting segments under(and after)high temperature are studied in this thesis,including the following contents:(1)A high temperature test was carried out on five self-compacting concrete segments,focusing on the influence of preloading and hybrid fibers on the mechanical properties of the segments at high temperature,and the changing laws of temperature distribution,crack development,deformation and horizontal binding force at the support of hybrid fiber self-compacting concrete segments at high temperature were obtained.The results show that with the increase of preloading,the number of concrete cracks at the arch foot decreases.The reason is that the initial pressure at the arch foot is larger under the larger preloading,which reduces the tension value during the heating process.Fiber is helpful to reduce the average crack spacing and high temperature damage of concrete at segment arch foot.(2)Based on ABAQUS software,the temperature field and mechanical analysis model of hybrid fiber self-compacting concrete segments were established.The rationality of the model was verified by the test results.The influences of transient thermal strain and preload on the axial force,bending moment and equivalent plastic tensile strain of the segments were analyzed.The results show that,with the increase of preloading,the negative bending moment(absolute value)of the cross section at the neutral and loading point of the segment decreases in the heating stage,and the equivalent plastic tensile strain of the curved surface of the segment increases in the cooling stage.The transient thermal strain has an important effect on the distribution of the equivalent plastic tensile maximum strain on the curved surface of the segment in the cooling stage.When the transient thermal strain is considered,the equivalent plastic tensile strain of the segment develops from the inner curved surface to the side.At the end of the cooling stage,the larger strain area is located on the inner curved surface,which is more consistent with the crack distribution area in the test.However,ignoring the influence of transient thermal strain or implicitly considering the transient thermal strain,the region with large equivalent plastic tensile strain is located at the bottom of the loading point on the side of the segment,and the strain value of the inner curved surface is relatively small,which has a certain difference from the crack distribution in the test.(3)Residual bearing capacity tests were carried out on 5 segments after high temperature,and mechanical properties tests were carried out on 2 segments at normal temperature.The influence laws of preloading and hybrid fibers on crack development,deformation,strain,failure load and failure mode of 7 segments after high temperature were obtained.Numerical analysis and theoretical calculation of residual bearing capacity of 7 segments were also carried out.The results show that with the increase of pre-loading,the crushing area of the outer curved surface of the segment changes from mid-span to the loading point area after high temperature,and the fiber helps to reduce the crushing degree of the outer curved surface and arch foot of the segment after high temperature.In addition,based on the existing calculation theory of the bearing capacity of concrete segments,considering the influence of fibers on the stress distribution in the tensile zone of the segments,the calculation results and test results of the residual bearing capacity of the segments after high temperature are reasonable. |
