Preliminary Design and Cross-Sectional Form Study of Closed-Type Concrete-Filled Steel Tube Support for Traffic Tunnel

In view of the structural form and common construction methods of traffic tunnels, the bearing performance of the closed-type CFST support designed for traffic tunnels is studied. The closed-type CFST support, which consist of a CFST girder with external shotcrete, is improved from the CFST support used in mine roadways. The reasonable cross-sectional form of closed-type CFST support is analyzed by the FEM. The closed-type CFST support is mainly composed of CFST arches, a shotcrete layer, sleeves, and blind flanges. The post-buckling analysis of the closed-type CFST circular arch members using circular-shaped, rectangular-shaped, triangular-shaped, and trapezoidal-shaped steel tubes is implemented. The result shows that the closed-type CFST support has better performance than the traditional tunnel support. The study also found that for closed-type CFST support, the triangular-shaped steel tube section has the highest bearing capacity, stiffness, and steel utilization rate, which is the preferred cross-sectional form. The bearing capacity of the circular-shaped steel tube section is acceptable. Moreover, the circular-shaped steel tubes are more convenient to obtain and process, so it is also an optional cross-sectional form. The square-shaped and trapezoidal-shaped steel tube sections have neither performance advantages nor economic efficiency, so these two forms are not recommended.

Investigation on the characteristics of single-phase gas explosion and gas-coal dust coupling explosion in bifurcated tubes

In order to deeply understand the overpressure propagation characteristics of explosion shock wave of single-phase gas explosion and gas-coal dust coupling explosion in bifurcated tube, this paper makes a comprehensive and in-depth study on the change and distribution law of explosion shock wave overpressure of single-phase gas explosion and gas-coal dust coupling explosion in bifurcated tube by means of experimental research, the results show that: The explosion shock wave overpressure of single-phase gas explosion and gas-coal dust coupling explosion is all affected by the bifurcation angle of the tube, the larger the bifurcation angle of the tube is, the greater the explosion shock wave overpressure is. In terms of explosion shock wave overpressure distribution, single-phase gas explosion and gas-coal dust coupling explosion show a similar overall development trend, and the maximum explosion shock wave overpressure is obtained in front of the bifurcation point. The mutation coefficients of explosion shock wave overpressure of single-phase gas explosion and gas-coal dust coupling explosion before and after the bifurcation point of the tube are all affected by the bifurcation angle of the tube. In the straight tube section, the mutation coefficient of explosion shock wave overpressure increases gradually with the increase of the bifurcation angle of the tube, while the situation in the inclined tube section is just the opposite. Under the condition of the same bifurcation angle, the shock wave overpressure mutation coefficient of gas-coal dust coupling explosion is smaller than that of single-phase gas explosion.

Flexural Behavior of Concrete Composite Beams with New Steel Tube Section and Different Shear Connectors

Steel hollow sections used widely in many engineering applications as structural members. This paper aims to present a study about the flexural behavior of composite beams with steel tubes sections through a series of bending tests in order to study and examine the influence of using different shapes of steel tube section (square, rectangular and hexagonal) with the same shear connector type (headed stud or angle or perfobond) on the flexural behavior and the bending properties of these sections. As well as study the effect of using different shear connectors types (headed stud, angle and perfobond) in the same steel tube section (hexagonal or square or rectangular) on the flexural behavior of composite beams. The experimental program divided into two groups, the first consists of testing nine specimens which focusing on testing three types of steel section when using shear stud at first, angle at second, perfobond at third as shear connector type. Second group consists of testing nine specimens of composite beams too, this group focusing on testing every steel section (hexagonal or square or rectangular) alone when using three types of shear connectors with it. All specimens are with length, width and height equal to 2000, 400 and 130 mm respectively. The tested steel tubes have thickness of 2 mm, yield stress of 322 MPa and the ultimate strength of 390 MPa. The results showed that these shapes of hollow steel sections (hexagonal, square and rectangular) sustain the quality of services for the buildings, and these tested specimens are applicable by giving a distinctive strength and stiffness starting from 114 kN as ultimate load reaching to 170 kN. The experimental results proved that the perfobond and angle connector types are clearly effective shear connectors, shear connector of perfobond type increased the ultimate load of composite beams by (6.25-9.74) % compared with stud shear connector.

Dynamic axial crushing of bitubular tubes with curvy polygonal inner-tube sections

Bitubular structural configurations, where the outer tube is circular, square and curvy square in shape while the inner-tube section is curvy triangular, square and hexagonal in different proposed configurations, are numerically crushed under dynamic axial loading. The crashworthiness effectiveness for changing inner-tube polygonal cross-section for each of the outer tube sections is studied and compared with changing outer tube shape. The deformation plots and energy absorption (EA) parameters such as peak crushing force (PCF) mean crushing force (MCF), energy absorption and crush force efficiency for each case are evaluated. Most of the configurations showed ovalization with low PCF and MCF and moderate crush force efficiency. Afterwards, effects of [Formula: see text] and [Formula: see text] on deformation modes and EA are demonstrated by selecting one of the configurations from each group using published experimental results.

Predicting Tube Ovalization in Cold Bending: An Analytical Approach

Ovalization (or flattening) of tubes in cold bending operations causes dimensional inaccuracy that may lead to loss of fit-up and function of the formed product. The particular distortion mechanism is governed by radial bending stress components forcing the extremities of the tube section towards the neutral layer of the cross-section. Thus, the magnitude of distortions is limited by the instantaneous stiffness of the tube section upon plastic bending. In order to proactively consider tube ovalization in the product design process, it is necessary to develop a practical methodology that takes into account the impact of governing parameters such as material, tool and section geometries. In the present work, an analytical model of the ovalization problem has been developed using the deformation theory of plasticity. The results show that the diameter of the tube is the most important parameter with respect to tube ovalization, while the thickness of the tube section and the bending radius are of the same relative importance. The developed model indicates that strain hardening is the most important material parameter, whereas tube ovalization is nearly unaffected by the initial yield stress. The present model shows good correlation with a number of experiments.