Abstract
Recent advances in the production of super-fine cement and filler technology has made the production of high-strength concrete (HSC) of 120 MPa practicable in the industry. Nonetheless, the application of such HSC in real construction is still limited. One of the reasons that inhibits the use of HSC is the brittleness, which causes HSC structures to fail explosively if the concrete confinement is not adequate. The traditional method of installing transverse steel as confinement is not feasible in HSC structures, as the steel will be too congested to ensure proper concrete placing. To overcome the problem, double-skinned high-strength concrete-filled-steel-tubular (HSCFST) columns has been advocated, which could provide large, continuous and uniform confinement to HSC. However, a major shortcoming of the double-skinned HSCFST columns is the imperfect interface bonding that occurs at the elastic stage that reduces the elastic strength and stiffness of columns. To improve the situation, the authors have verified previously that using external steel rings on the outer steel tube can successfully restrict the dilation of HSCFST columns and thus restore an intact interface bonding condition. As a continued study, the authors will in this paper develop a theoretical model for predicting the uni-axial load-carrying capacity of doubled-skinned HSCFST columns.
Highlights
Because of the recent rapid development of superfine materials such as micro-silica and superfine cement, as well as the matured filler technology (Goldman, Bentur 1993; Haque, Kayali 1998), it is fairly easy to produce ordinary high-strength concrete (HSC) of compressive strength up to 120 MPa
Comparing with the average NEC/Nt ratio for all ring-confined double-skinned CFST columns, which is 0.815, it is evident that the proposed model can predict much more accurately the load-carrying capacity of ringconfined double-skinned CFST columns by taking into account the confinement effect provided by the external rings
A new method for providing external confinement to restrict the lateral dilation of double-skinned CFST columns has been proposed and verified previously by uni-axial compression test to have successfully restored the intact interface steel-concrete interface bonding during the elastic stage
Summary
Because of the recent rapid development of superfine materials such as micro-silica and superfine cement, as well as the matured filler technology (Goldman, Bentur 1993; Haque, Kayali 1998), it is fairly easy to produce ordinary high-strength concrete (HSC) of compressive strength up to 120 MPa. Compared with single-skinned HSCFST columns, double-skinned HSCFST columns further improve the strength-to-weight ratio by replacing the bulky central concrete with an inner steel tube with smaller cross-sectional area It provides a dry atmosphere within the inner steel tube, which is useful to house sub-sea oil production facilities for offshore structures (Shakir-Khalil 1991; Yang et al 2008; Zhao et al 2010). A preliminary test programme has been carried out and the results showed that the Poisson’s ratios of columns can be successfully reduced to close to 0.2, which is that of plain concrete It verified that the concrete would be in perfect bond with the steel skin under the extra confinement effect provided by the steel rings. The proposed model will be used to calculate the theoretical strength of double-skinned HSCFST columns tested by the authors as well as other researchers
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