Experimental and Theoretical Study of Concrete-Filled Steel Tube Columns Strengthened by FRP/Steel Strips Under Axial Compression

Abstract

Concrete-filled steel tube (CFST) columns are widely used in civil engineering because of their excellent bearing capacity; however, the reinforcement of CFST columns lacks effective measures. To strengthen CFST columns quickly and effectively, two methods, namely, winding FRP (fiber reinforced polymer) or steel strips, were explored in this work. Two unconfined CFST columns, eight FRP-strengthened CFST columns and four welded steel strip-strengthened CFST columns were manufactured and tested. The failure modes and axial load–strain curves of all specimens under compression load were concluded and compared. The effects of the primary parameters, such as FRP layers (1, 2, 3 and 4 layers) and steel strip thickness (3.0 and 6.0 mm), on the bearing capacity and deformation capacity were also investigated. The ultimate load of CFST columns increased from 28.72 to 64.16% after being confined by FRP with one to four layers. The ultimate load of the welded steel strip-strengthened CFST column with 3.0 mm steel strips and 6.0 mm steel strips increased by 28.46% and 49.82%, respectively, compared with the unconfined CFST column. Thus, the increase in FRP layers and steel strip thickness can markedly improve the compressive behavior of the FRP/welded steel strip-strengthened CFST columns. The cost performance of the two different reinforcement methods also showed that the cost of the welded steel strip-strengthened CFST column is nearly 40% of that of the FRP-strengthened CFST column when the same strengthening effect was obtained, which indicated that the welded steel strip-strengthened CFST column is more cost-efficient than CFST columns confined by FRP. Finally, six existing models for the ultimate load of FRP-strengthened CFST columns were presented and evaluated. From the evaluation results, the Zhang et al.’s model, Lu et al.’s model and Hu et al.’s model for FRP-strengthened CFST columns were shown to provide the best applicability and accuracy. Based on the Mander et al.’s model, a model for the ultimate load of welded steel strip-strengthened CFST columns was proposed and evaluated. The proposed model can accurately predict the ultimate load of welded steel strip-strengthened CFST columns.

Modeling and Calculation of Improved Centrifuged Reinforced Concrete Columns with Variotropic Structure

“…It can be seen (Figure 13a,b) that in a variotropic column, cracking begins in the upper part of the column, and in a homogeneous column, in the middle (Figure 17c,d). A similar character of deformation is observed in [73,74] during experimental studies.…”

A Critical Review of Cold-Formed Steel Built-Up Composite Columns with Geopolymer Concrete Infill

“…They are employed in various applications, such as multi-storied buildings, extended bridges, bridge piers, floodwall structures, and submarine pipeline systems [26][27][28]. Achieving strain continuity at the steel-concrete interface ensures optimal performance, especially in regions where the materials are not loaded simultaneously [32]. Recent developments in composite columns reported by Shanmugham et al [33] have highlighted the efficiency of utilising the interactive behaviour of steel and concrete, providing both strength and fire resistance.…”