Study On Mechanical Performance Of Tubular Roof Prefabricated Structures

The tubular roof prefabricate structures is a new type of integrated underground support structure.Due to its advantages of high stiffness and high integration degree,the structure has been applied in the areas where the surface subsidence is strictly required,and has achieved good results and attracted more and more attention.However,the research on the tubular roof prefabricate structures is not comprehensive and systematic,which brings great challenges to the design and construction of tubular roof prefabricate structures.In the practical projects at the present stage,the function of steel tubular roof on both sides and the change of section height are generally not considered,but the design of the equal section reinforced concrete structure is carried out according to the minimum section height of the tubular roof structure.In fact,the change of section height will inevitably affect the mechanical performance of the structure,at the same time,the steel tube on both sides must exist due to the construction needs,and consumption of steel plate is large.It is of great engineering significance to study the real contribution of the steel tubular roof in structural stress and take reasonable measures to maximize the use of steel tubular roof mechanical properties.In this thesis,the mechanical performance of the tubular roof prefabricate structure is studied from the perspectives of component and structure,which provides theoretical basis for the wide application of the tubular roof prefabricate structure.The main research contents and achievements are as follows:(1)Taking the connectors number as parameters,the new shear specimens of new tubular roof prefabricate structures(NTRP)were designed and manufactured,the shear failure process and oblique section failure mode of the specimens were compared,and the strains distribution and variation of transverse reinforcement,longitudinal reinforcement,steel tubular roof and concrete were analyzed at different loading stages.The results show that the failure process and mode of the shear members of the new tubular roof prefabricate structures equipped with sufficient transverse reinforcement in the shear span are similar to those of the traditional reinforced concrete(RC)members with web reinforcements,and the failure mode is the concrete crushing in the shear compression zone.The failure mode of the NTRP members is related to the steel ratio in shear span.Two NTRP members with the same shear span ratio will respectively suffer from the diagonal tension failure and shear compression failure and shear failure due to the different number of transverse reinforcement in shear span.The transverse reinforcement set in the shear span can give full play to its tensile properties and assist concrete shear resistance.(2)The finite element software was used to establish the shear models of the NTRP members,and the correctness of the finite element model was verified by comparing the load-deflection curves and failure mode.The Parameters of the new tubular roof prefabricate structure specimens are analyzed.The results show that the shear capacity of the specimens can be effectively improved by setting the transverse reinforcement in the shear span.The strength of concrete has a certain effect on the shear capacity of the specimens.The thickness of steel tubular roof has little effect on the shear capacity of the specimens.The current specification is too conservative for the prediction of the shear capacity of the new tubular roof prefabricate structure specimens,but the shear capacity proposed in this thesis can accurately predict the shear capacity of the specimens.(3)Two bending specimens of the tubular roof prefabricate structures were designed and made.Spot weld of the specimens was used to simulate the poor quality of the pillar support weld,and compare with the existing pillar support weld with good quality(full weld).The results of the study show that the quality of the pillar support welding has a significant impact on the failure of the specimens of the tubular roof prefabricate structure.And the specimens with poor pillar support welding quality reach the failure load immediately after the pillar support is pulled off.The quality of the pillar support welds has a significant effect on the yield load,ultimate load and bending stiffness of the specimens.(4)The model of the tubular roof prefabricate structure is established by using finite element software,and the feasibility of the finite element model was verified by comparison with the model test failure mode.Based on this model,the results show that the final failure pattern of the tubular roof prefabricate structure includes both bending and shear diagonal cracks.The location of the bending cracks appearing in the middle of the top and bottom(plates)and the diagonal cracks appearing in the top and bottom sides.As the thickness of the steel tubular roof increases,the yield and ultimate loads of the tubular roof prefabricated structure increase,but the increasing gradually decrease.The bending stiffness of roof and bottom plate increases linearly with the increase of steel tube thickness.The reinforcement ratio of the circumferential reinforcement has a great influence on the deformation,bearing capacity and stiffness of the structure.The bearing capacity and stiffness of the structure can be effectively improved by setting the steel tie connector at the steel tubes and the connecting steel plates of the tubular roof prefabricate structure.