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The steel jacket technique is used to strengthen or repair RC columns all over the world, as it has been shown to be effective, economical and easy to apply. Most studies carried out to date on this strengthening technique have focused on isolated sections of columns strengthened or repaired by angles or batten plates. In this study a new technique...
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Citations
... For those CFCST columns with horizontal corrugations, Tomii [19] employed the welded square corrugated steel tubes to confine the reinforced concrete columns and beam-to-column connections for the first time. Ghobarah et al. [20], Biddah et al. [21] and Assas et al. [22], then, investigated the seismic performance of RC columns rehabilitated using the horizontal corrugated steel jackets, exhibiting more effective confinement than that of the vertical corrugation. Experimental investigations on concrete-filled double-skinned steel tubular (CFDST) columns with inner helical CST or outer welded annular CST were also conducted by Han et al. [23,24] and Li et al. [25] respectively. ...
... Based on the projection of τ to the nominal cylinder, the T CST can be eventually calculated by Eq. (20). The indirect contribution of CST can be presented by comparing the T RC with the torsional moment of conventional RC specimens, as given by Eq. (22). ...
Concrete-filled galvanized helical corrugated steel tubes (CFCSTs) are newly proposed for strengthening the corrosion resistance, ductility, and constructability of traditional RC structures. Their composite effectiveness and basic compressive, bending, and shear properties have been investigated previously. However, the unique spiral shape and lock-seam connections of the helical CST may lead to complex torsional responses, which have not been studied. This paper, therefore, attempts to present static experiments for the CFCSTs subjected to pure torsion and combined compression-torsion loads. The main test variables are the member types, loading directions , boundary conditions, and axial compression ratios. The static loading test setup and instruments have been introduced in detail. The torsional working mechanisms are discussed carefully with the analysis of failure modes and torques versus torsional angle curves. The direct and indirect contributions in torsional resistances of the helical CST have been analysed and calculated through elastic-plastic stress/strain analysis. Finally, the applicability of the existing design methods for the torsional bearing capacity of CFCSTs is examined.
... One is directly for axial-load bearing (Chai 2019;Farahi 2016;Nassirnia 2015). Another way is to provide a more efficient confinement by reducing the helical angle of corrugation to 0° (Assas 2014;Ghobarah 1997;Tomii 1995), or using corrugated tube as the outer or inner tube of the composite member (Han 2010;Han 2015). They provide fresh concepts and options for composite members, especially for those serving in the oceanic regions, marine environments, or remote mountain areas. ...
... Among the sections in Fig. 1, the second circular CST-concrete composite section with small-angle corrugations was previously studied by Wang (2019), Yang (2020a) and Fang (2020 a&b), i.e., corrugated steel tube (CST) confined reinforced concrete (RC) or concrete-filled CSTs. To obtain satisfactory hoop confinement, the helical/spiral angle is suggested to be within 15° (Fig. 2), and the highly efficient confinement has been confirmed in previous tests with 0 -14° (Assas 2014;Ghobarah 1997;Tomii 1995 andWang 2019). The ultimate axial-load bearing capacity and ductility index of CST-confined RC specimens are, respectively, 28% and 63% higher than those of the RC specimen with the same steel consumption (steel ratio = 2.3%). ...
Corrugated steel tube (CST) confined reinforced concrete (RC) section, which consists of galvanized corrugated steel tube infilled with concrete and steel reinforcements, provides a solution for their practical application at the outdoor and offshore corrosive environment. To investigate its compression-bending cross-sectional behavior, a fiber model is established by treating it as a confined reinforced concrete section. The model considers the non-uniformity of concrete confinement pressure across cross-sectional depth and tensile axial-strain concentration at lock seam. The ultimate strength and lateral deflection of the CST confined RC sections are investigated. Further in-depth analyses are carried to study the influence of eccentricity ratio, geometric parameters (thickness, helical angle and corrugation profile of tube, and reinforcing bars ratio), as well as materials strength (concrete and tube). Finally, a design method is proposed to predict the compression-bending strength of CST confined RC sections, and its precision is verified by comparing with test and numerical results.
... The results showed that the ductility and equivalent damping ratio can be enhanced by replacing the flat tube with a corrugated steel tube. Majid Matouq Assas [16] utilised a corrugated steel tube and a flat steel tube to strengthen reinforced concrete columns. The axially loaded test results of these two types of columns demonstrated that the corrugated steel tube has a higher hoop confinement level than that of flat steel tubes. ...
Concrete-filled galvanized corrugated steel tubular (CFCST) columns have been proposed as new composite members to improve the corrosion resistances and reduce the anticorrosion maintenance costs of concrete-filled steel tubular (CFST) structures. In this study, the axial behaviour of CFCST columns embedded with structural steel (CFCST-S) was investigated using comparative experiments and non-linear finite element analysis accompanied by multiple monitoring and in-depth discussions. The study revealed that, even when they are not configured with transverse reinforcements, the local stability and post-peak behaviour of the CFCST-S are competitive owing to the effectiveness of the confinements provided by the thin-walled corrugated steel tube (CSP). The unique local bending effect in the CSP was verified and discussed to reveal the mechanical nature of CSP-concrete columns. Next, a theoretical model of the non-uniform stress distribution, after fully considering the bidirectional curvature of the CSP, was developed. It is found that the CSP mainly provides hoop confinements for the infilled components instead of bearing the axial load owing to its “circumferential tight effect” and “vertical offset effect”. Based on equivalent simplifications and parametric studies, the current formula to calculate the nominal hoop stress in the CSP was modified. Finally, a design method was proposed for the prediction of the axial bearing capacity of the CFCST-S.
Concrete-filled thin-walled galvanized corrugated steel tube (CFCST) is a novel composite member with competitive mechanical behaviour, durability and construction convenience. Several preliminary experimental and numerical works have been conducted on the compressive, flexural, shear, and monotonic torsional performances. However, the unique geometric characteristics of the helical corrugated steel tube (CST) may lead to significant torsional direction-dependent behaviour and complex cyclic torsional working mechanisms, which have not been investigated. This paper therefore presents an experimental investigation of the CFCST under cyclic torsional loads, encompassing the main test variables of member types, diameter-to-thickness ratios, axial compression ratios, and core concrete strengths. The failure modes, hysteretic curves, ductility, energy dissipation
capacity, and stiffness degradation are carefully addressed. The cyclic torsional working mechanism of CFCST is discussed through the cyclic test results and strain analysis. The cumulative damage caused by the cyclic torsional loading case is also analysed via the comparisons between the monotonic and cyclic experimental results. The applicability of the existing design methods for the torsional bearing capacity is examined, with specific design suggestions proposed.
Concrete-filled galvanized helical corrugated steel tube, abbreviated as CFCST, is a new type of composite member that has great potential to be used in seismically active regions or highly corrosive environments. However, the unique lock-seam connections of helical corrugated steel tube (CST) result in high difficulty in precise simulation analysis, and the effects of such connections on the mechanical properties are not clear, so further investigations are needed. This paper attempts to present a detailed finite element (FE) model of CFCST with the real dimension of lock-seam connections, and then investigate the effects of lock-seam connections on the basic compressive behaviour of CFCST stub columns. The FE models are developed with the consideration of the real shape of helical CST, the non-linearity of each constituent material, and the interfacial properties at lock-seam regions. The simulated results are verified carefully through comparisons against experimental results of 41 stub columns under axial compression in terms of failure modes, load–displacement histories, and local stress developments. The influence of lock-seams on the working mechanisms has been particularly investigated and discussed. Parametric studies have also been conducted to investigate the compressive behaviour of the CFCST. Finally, simplified design methods for axial compressive bearing capacity are proposed.
Concrete-filled galvanized corrugated steel tube (CFCST), is an innovative composite member, which is proposed for improving the ductility and durability of conventional reinforced concrete (RC) structures. In practice, combined shear-bending loads often exist in a CFCST pier/column. It is necessary to investigate the shear-bending working mechanism of CFCST and access the shear-bending bearing capacity interaction relationships for a more reasonable design. Twenty-seven columns including 21 CFCSTs and 6 TRC specimens are therefore tested comparably. The main test variables are the loading types, shear span-to-depth ratios, tube forms, and the end/support conditions. The test results show that a satisfactory deformative coordination among the core concrete, reinforcements, and CST can be obtained, resulting in a significant improvement in shear-bending performances compared with conventional RC structures. With the discussion of failure modes, deformation curves, load versus mid-span displacement responses, and strain/stress properties of CST, the shear-bending working mechanism of CFCST is particularly addressed. Based on the test results, reasonable design methods for predicting the individual shear/bending strength and the combined shear-bending bearing capacity interaction relationships of CFCST are proposed eventually.
