| Buried excavation methods are often used to construct underground structures.The pipe roofing method,a kind of construction method of pre-supporting large section excavation,has been widely used in the construction of underground structures.However,the traditional piperoofing structure is only connected by interlock to result in the poor stiffness.So the temporaray supports need to be used when soil below the pipe-roofing structure is excavated.At present,the Pipe roofing structure can greatly enhance the lateral stiffness of the supporting structure by adding connections between the adjacent steel tubes,but the complex connection system between the adjacnet tubes increases difficulties and period of the construction.Based on this,the Secant Pipe Roofing Structure(SPRS)is proposed,steel tubes are first to be cutted,and then the adjacent steel tubes are weldded to form acomplete and stable structure system.It is easy to excavate the soil within the tubes and possesses a good waterproof performance.In this investigation,the influences of different parameters on the flexural behavior of the proposed structure are studied using laboratory testing and numerical simulation.A total of six specimens were conducted to investigate failure model of SPRS using the single-point concentrated loading.The load versus mid-span deflection curves can be divided into three stages:elastic working stage,elastic-plastic working stage and strengthening working stage.The results show that the overlapping length of the adjacent tubes has a great influence on the bearing capacity and lateral stiffness of the specimens.The tensile reinforcement has a slight effect on the bearing capacity and lateral stiffness of the specimens,while it has more effect on the bearing capacity and lateral stiffness of the specimens.The welding the upper side of the steel tube has a significant effect on the bearing capacity and lateral stiffness of the specimens.Meanwhile,the DIC technique was used to observe the deformation development trend of the specimens during loading,and the results showed that the strain concentration area of the specimens was consistent with the experiental observationin the tests.Combined with the results of laboratory test,the finite element models were established to investigate the diameter of tube,the overlapping length of the adjacent steel tubes,the tube thickness,the diameter of the and the welding the upper tube on the flexural behaviour of specimens.Then different parameters were carried out to study the variation rule of the flexural properties of specimens under the proportion of different parameters using orthogonal simulation.The results show that with the increase of the ratio of the overlapping length of the adjacent steel tubes to the diameter of the tube,the failure pattern of the specimens can be divided into three categories.When the most unfavorable section of the specimens is located at the connected section of the steel tube,bearing capacity of the specimens is generally lower,and the lateral stiffness is mainly dominated by the overlapping length of the adjacent tubes.When the most unfavorable section transforms from the aforementioned section to the midspan section,the bearing capacity of the pattern of specimens increases notably with the increase of the ratio,and the increase take on faster and faster.Meanwhile,the lateral stiffness is dominated by length of the specimen and the overlapping length of the adjacent steel tubes.When the most unfavorable section is located at the mid-span section of the specimens,and the amplification of bearing capacity gradual change slow,moreover the lateral stifness is mainly dominated by the length of the specimens.A linear relationship is presented between the tube thickness and the diameter of the reinforcement,and the bearing capacity.When the tube thickness and the diameter of the reinforcement increase 1 mm,the bearing capacity enhances 50 kN and 12 kN.The least square method was used to fit the bearing capacity and lateral stiffness of the specimens,and the calculation formulas of bearing capacity and lateral stiffness under different parameters were obtained,which provided theoretical guidance for engineering application. |
