Analysis of Stress and Deformation Characteristics of Deep-Buried Phyllite Tunnel Structure under Different Cross-Section Forms and Initial Support Parameters

Deep-buried soft rock tunnels exhibit low strength and easy deformation under the influence of high ground stress. The surrounding rock of the soft rock tunnel may undergo large deformation during the construction process, thereby causing engineering problems such as the collapse of the vault, bottom heave, and damage to the supporting structure. The Chengwu Expressway Tunnel II, considered in this study, is a phyllite tunnel, with weak surrounding rock and poor water stability. Under the original design conditions, the supporting structure exhibits stress concentration and large deformation. To address these issues, three schemes involving the use of the double-layer steel arch to support, weakening of the steel arch close to the excavation surface, and weakening of the steel arch away from the excavation surface to support were proposed. Using these schemes, the inverted radius was varied to explore its influence on different support schemes. For simulation, the values of the inverted radius selected were as follows: 1300 cm, 1000 cm, and 700 cm. The proposed support plan was simulated using FLAC3D, and the changes in the pressure between the initial support and surrounding rock, the settling of the vault, and the surrounding convergence were investigated. The numerical simulation results of monitoring the surrounding rock deformation show that the double-layer steel arch can effectively reduce the large deformation of the soft rock well. When the stiffness of one of the steel arches was weakened, the support’s ability to control the deformation was weakened; however, it still showed reliable performance in controlling deformation. However, changing the radius of the invert had an insignificant effect on the deformation and force of the supporting structure.

Influence of pattern anisotropy on the structural behaviour of free-edge single-layer gridshells

Free-edge gridshells represent the majority of built gridshells. Indeed, the gridshell reference geometry usually needs to be trimmed in order to provide building access or to insert the gridshell within an existing building, giving rise to one or more elastic boundaries. Despite the current design practice, so far a very limited number of scientific studies has been devoted to investigate the influence of elastic boundaries on the overall structural behaviour of gridshells. This paper focuses on the effects of the orientation of the boundary structure with respect to the grid direction. This is done by studying the buckling behaviour of an ideal single-layer steel gridshell, for different grid layout (quadrangular, hybrid, triangular) and orientation. The results of the parametric study demonstrate that the sensitivity of free-edge single-layer gridshells to the free-edge orientation strongly depends on the grid pattern. In particular, isotropic gridshells have shown an almost negligible influence of the free-edge orientation in terms of buckling load, in opposition to orthotropic gridshells. Moreover, the change in free-edge orientation induces significant variations of the global structural stiffness for all the layouts, resulting in possibly unacceptable displacements in service conditions.

Axial Compression Behaviour of Concrete-Filled Double-Layer Steel Tubular Column

<p>Nowadays, height of supertall buildings with height over 300 meters have been successively renewed in the world. To improve the global stability of the supertall building, mega-columns with excellent seismic, wind-resistance and axial compressive performance are recommended to be set in its perimeter. Concrete-filled double-layer steel tubular column (CFDLT column) transforming from the concrete-filled double-skin steel tubular column (CFDST column) by filling the hollow part of cross-section with concrete was proposed by the author. In this study, axial compression tests of CFDLT column, CFDST column and conventional concrete-filled steel tubular column (CFT column) specimens were carried out to investigate the axial compression behaviour of them. The experimental results showed that the CFDLT column specimen exhibits higher axial compressive strength and larger energy dissipation capacity than the CFDST column and the conventional CFT column specimens. It was found that the axial stiffness of CFDLT column degrades slower than that of the conventional CFT column right after the peak load. And, it is expected that the CFDLT column can be used as a mega-column in the tomorrow’s supertall buildings.</p>

Research on the design of multi-layer steel structure module and steel frame composite building structure

The composite of multi-layer steel structure module and steel frame, as an important design form in Chinese house construction, is widely used in the architectural design of houses. The multi-layer steel structure module and steel frame composite building structure are different from the traditional. This kind of building mechanism adopts the prefabricated type, which has the advantages of fast construction speed and few limiting factors, and plays a very important guiding role in modern building construction. Based on this, this article will analyze and compare the similarities and differences between steel structure modular buildings and traditional steel frame structures, and explore the design of multi-layer steel structure modules and steel frame composite building structures, hoping to be helpful to relevant people.