| The urban traffic problem and utilization of underground space were increasing with the development of social and national economy. Due to the certain limitation of the conventional underground construction technologies, some new construction technologies were springing up. This paper presents a new underground construction technology -- New Tubular Roof Method (NTR method). The NTR method originated in South Korea. There were some successful structures constructed by NTR method in South Korea and Italy. Today metro and other underground space constructions were rapidly developing. Because of the incomparable advantages compared with the conventional technologies, the NTR method had wide application and good prospects in the future. In general, the structure constructed by NTR method was named the NTR structure. The development for the design of the NTR structure in theory lagged behind that in application and there were not a systematic theory model for calculation because the NTR structure system was a new type of underground structure. In South Korea, the qualitative analysis and the experience method came from similar engineering were used during the design because of the difficulty in setting up the mathematical model. A basic unit of the NTR structure was used in the dissertation for the experimental study, aimed at establishing the primary calculation theory and design method for the NTR structure. The main contents and methods of this paper were as follows:(1) Experimental study on the flexural behavior of the NTR structureThe paper presents an experimental research on flexural behavior of two groups of the NTR structures with different deviation ratio of section to improve the analysis theory. The experiment was conducted by a monotonic static loading to investigate the failure modes, deformation and strength properties of the specimen during the flexural failure. The cracking load and bearing capacity of the structure with the two kind of deviation ratio of section were experimentally determined and the failure modes of the two structures were also discussed, and the experimental results were compared with the theoretical one.(2) Experimental investigation on shear behavior of the NTR StructureMeanwhile, the paper also presents an experimental research on shear behavior of two groups of the NTR structures with different deviation ratio of section to set up the analysis theory. The similar experimental method was used. The cracking load and bearing capacity of the structure with the two kind of deviation ratio of section were also experimentally determined and the failure modes of the two structures were also discussed.(3) Theoretical method for calculation of the bearing capacity and deformation of the NTR structureThe bearing capacity equations for the normal and diagonal sections were set up by the elastic-plastic analysis of the section for the NTR ribbed beam structure under the hypothesis of the strain plain. Two kinds of deflection calculation methods which were the limited difference method and elastic arch method were respectively used to calculate the deformation at the middle span of the structure. The calculating results were compared with that of the experiments and they matched well.The experimental results indicated that the features and shear failure for both the flexural and shear specimen were apparent during the ultimate states. The flexural destruction happened with great deformation during the failure, belonging to the ductile failure with obvious sign of damage. The shear failure suddenly occurred with brittle failure characteristics. Compared with ordinary reinforced concrete beam, the NTR structure can resist much higher vertical load and cracking load. Meanwhile, the cracking load and the ultimate bearing capacity were both improved and the stiffness was also increased with the increasing of the deviation ratio of section.
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