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Experimental investigation of two novel FRP retrofit schemes for strengthening steel columns
Abstract
Fiber reinforced polymers (FRP) are increasingly being used to retrofit structural members due to their low weight-to-strength ratio and corrosion resistance. Results from an experimental program conducted to evaluate two recently proposed techniques for retrofitting I-shape steel columns are presented. The first retrofit technique involves the construction of a steel-concrete column, which is subsequently wrapped with resin impregnated FRP sheets with the fibers oriented in transverse direction to confine the concrete. The second retrofit technique utilizes a glass FRP (GFRP) composite tube that is placed around the column and filled with concrete. The GFRP tube acts as a stay-in-place form and provides uniform confinement. Slenderness ratios of the retrofitted specimens are selected such that they cover a range of stub to intermediate long columns. Experimental results show significant increase in load carrying capacity and ultimate displacement of the retrofitted columns due to composite action behaviour. The second proposed retrofit technique, using a GFRP tube, provides increased confinement uniformly which results in greater enhancement in the axial behavior of the retrofitted specimens. Confinement efficiency decreased by increasing the specimen length as failure occurred due to overall buckling of the columns.
... Up to date, FCSRC systems have been adopted to strengthen/repair steel structures [32][33][34][35][36]52,55] and as new hybrid structural members (e.g., hybrid columns, beams [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51]53,54,56,57], or buckling restrained braces (BRBs) [58][59][60][61][62][63][64][65][66][67][68]). Extensive studies have been carried out to understand the performance of such forms of hybrid structural members, and they have been shown to have excellent performance. ...
... The capabilities of hybrid systems constructed with continuous and split FRP tubes are assumed to be similar provided that the bond strength between the epoxy and the FRP tube is efficient. Subsequently, the so-called onion-skin retrofitting technique was suggested to be applied to strengthen existing steel columns [33,36,37]. It should be mentioned that Karimi et al. [37] still utilized the continuous FRP tubes, and only Linde et al. [36] applied the typical retrofitting system to an existing I-shaped steel column. ...
... Based on the experimental results, Linde et al. [36] concluded that the ultimate capacity of the composite columns could be significantly enhanced by using the proposed split-tube retrofitting technique, although the columns finally failed by FRP rupture at the gap in the GFRP tube that was externally wrapped with two plies of CFRP sheets (i.e., the weak point in the cross section) (see Figure 5b). isting steel columns [33,36,37]. It should be mentioned that Karimi et al. [37] still utilized the continuous FRP tubes, and only Linde et al. [36] applied the typical retrofitting system to an existing I-shaped steel column. ...
Fiber-reinforced polymer (FRP) composites have been widely used for strengthening or constructing structures due to their excellent corrosion resistance and high tensile strength. An emerging hybrid structural member form with FRP composites—which consist of a steel section as internal reinforcement, an external FRP wrap/tube, and concrete filled between them (referred to as FRP-confined steel-reinforced concrete systems (FCSRC) systems)—has attracted increasing research interest. To date, the concept has been adopted to strengthen/repair steel structures or used as new hybrid structural members (e.g., hybrid columns or beams, including buckling restrained braces (BRBs)). The FRP confinement and composite action between the three components in FCSRCs result in the excellent performance of the hybrid member. This paper presents a state-of-the-art review of FCSRCs for structural applications. The gaps in knowledge and future research opportunities on FCSRC structural members are also identified.
Fiber-reinforced polymer (FRP)-confined concrete-steel composite columns have been recently introduced as a retrofit technique for structural steel columns. This technique involves placing a two-part FRP tube around an existing steel column and subsequently filling the void between the steel section and the FRP tube with concrete to create a composite column. The composite action occurs due to the concrete encasing the steel section and the FRP confining the concrete. Within this focus, an experimental investigation has been undertaken with the objectives of evaluating the effect of adding confined concrete to encase a steel W section, the effect of using a split-tube system as a practical encasement technique, and the effect of adding shrinkage-reducing admixtures (SRA) to the confined concrete. A total of 18 stub columns comprising six different column types were tested to achieve these objectives. The test results showed that the load-displacement response of the composite columns was similar to that of confined concrete combined with the elastic-perfectly plastic steel contribution. The experimental findings also demonstrated the enhanced composite column performance, including a significant increase in the ultimate capacity using the proposed split-tube retrofit technique. The results also indicated that the use of a SRA in confined concrete has an indistinguishable effect on the confined concrete strength.
This paper presents the experimental and analytical evaluation of the feasibility of a proposed fiber reinforced polymer (FRP) retrofit method to strengthen corroded steel columns. This method consists of two steps: (1) wrapping the corroded steel column with an FRP jacket, and (2) filling the jacket with expansive light-weight concrete. Seven steel columns were tested in the laboratory including five strengthened columns with the proposed technique. The first two were used as control units where one was a virgin shape and the second was notched in the center zone to simulate the loss of section due to corrosion. The remaining five were all notched, and confined with FRP composite pipes within the simulated corroded zone and subsequently filled with light-weight concrete. All specimens were axially loaded to failure while strain and displacement readings were measured to demonstrate the feasibility of this repair concept. Test results show that the proposed FRP retrofit method for steel columns can be successfully applied. Furthermore, an analytical model was developed that can predict the load capacity of the FRP retrofitted steel column.
The current study is a part of an extensive research program conducted to assess the use of Glass Fibre Reinforced Plastic (GFRP) sheets in enhancing the flexural capacity of steel beams. The properties of a heavy-duty adhesive system that can be used to bond GFRP sheets to the flanges of steel beams were experimentally determined in a previous study. The excellent performance of a W-shaped steel beam strengthened using GFRP sheets has encouraged the authors to assess the applicability of this technique to composite steel bridges.
The dimensions and cross section properties of a real composite steel plate girder bridge are considered in a case study analysis. A detailed nonlinear numerical model is developed for the bridge before and after attaching GFRP sheets to the bottom flange of its steel girders. Nonlinear moving load analyses are first conducted to determine the critical truck locations that will lead to maximum GFRP axial stresses, and maximum adhesive shear and peel stresses. Using these configurations, nonlinear analyses are then conducted to assess the increase in the bridge capacity that can be achieved by bonding 38 mm GFRP sheet to the bottom flange of its steel girders.