International Concrete Abstracts Portal

The use of Fiber-reinforced polymer (FRP) composite materials in new construction and repair of concrete structures has been growing rapidly in recent years. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published several guides providing recommendations for the use of FRP materials based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

Lap splices are an easy to implement low cost method of transferring force between reinforcing bars in concrete structures. However, the bond between lap spliced bars is usually the weakest region in a reinforced concrete structure. Fiber reinforced polymer materials (FRP) are widely used to strengthen and repair lap splices because of their high strength, durability and ease of handling. Researchers have found that increased concrete cover provides an increase in bond strength similar to that supplied by wrapping with FRP sheets. Currently the FRP industry produces a new generation of high stiffness FRP sheets that provide a high degree of confinement and large increases in bond strength to lap splices.

This paper compares the effectiveness of wrapping with very high stiffness carbon FRP sheets (CFRP 900), wrapping with low stiffness glass FRP sheets (GFRP 430) and no wrapping on the bond strength of lap splice connections for various concrete covers. The test variables were the amount of concrete cover and the wrapping condition. The results showed that the GFRP wrapped beams had an increased in bond strength of approximately 25% compared to the unwrapped beams for each of the concrete covers. However, the CFRP wrapped beams had a percentage increase in bond strength that decreased as the concrete cover increased. The CFRP wrapped beams had increases in bond strength of 71%, 60% and 44% compared to the unwrapped beams for concrete covers of 20mm, 30mm and 50 mm, respectively.

This study investigates the effect of aggressive regime of 300 freeze-thaw (FT) cycles, at a core temperature range of +5 oC (+41 oF) to -18 oC (-0.4 oF) on the structural behaviour and bond integrity of concrete beams cast onto glass fiber reinforced polymer (GFRP) stay-in-place (SIP) structural forms. The study aims at comparing two configurations of the SIP forms, namely a flat plate with T-shape ribs and a corrugated plate, under the potential ‘frostjacking’ effect arising from FT cycles. The study explored specimens with no surface treatment, wet adhesive bonding to freshly cast concrete, and bonded coarse aggregates to enhance roughness of SIP form. It was clearly shown that flat-ribbed form specimens are superior to the corrugated form ones, as no loss in strength occurred after the FT exposure, whereas the corrugated form specimens lost 18-21%. This is attributed to the anchorage advantage provided by the T-shape rib embedment into concrete. Specimens with untreated corrugated forms showed strengths that are only 21-26% of treated ones. For flat-ribbed form specimens, the one with untreated form had 44% the strength of that with bonded aggregates.

This paper presents the results of tests done on concrete beams reinforced with glass fibre reinforced polymer (GFRP) longitudinal bars and GFRP stirrups. The main test variables were the size, the amount, and the arrangement of longitudinal reinforcement as well as the size and spacing of closed loop stirrups. Six beams are divided into two series defined by stirrup spacing, or three pairs defined by longitudinal bar arrangement. The results indicate that the specimens with no stirrups failed in shear-tension while the beams with stirrups failed in shear-compression showing deep beam behaviour. The results were compared to predictions from several methods, namely a novel Indeterminate Strut-and-Tie (IST) method formulated specifically for use with brittle reinforcements, as well as the shear models of the ACI 440.1R-06 guidelines, the CSA S806-12 standard, and the Nehdi et al. (2007) method. The IST method produced the best predictions followed by the method of Nehdi et al. as both are formulated for use with deep beams.

This paper describes the behavior of precast hollow-core fiber-reinforced polymer (FRP)-concrete-steel columns (HC-FCS) under combined axial and lateral loading. The HC-FCS column consists of a concrete wall sandwiched between an inner steel tube and an outer FRP tube. This study investigated two large-scale columns: the traditional reinforced concrete (RC) and the HC-FCS column. The steel tube of the HC-FCS column was embedded into the footing while the FRP tube was stopped at the top of the footing level (i.e., the FRP tube provided confinement only). The hollow steel tube provided the only reinforcement for shear and flexure inside the HC-FCS column. The FRP in HC-FCS ruptured at a lateral drift of 15.2%, while the RC column displayed a 10.9% lateral drift at failure. The RC column failed due to rebar rupture when the moment capacity dropped more than 20%. The HC-FCS failed gradually with concrete compression failure and steel local buckling followed by FRP rupture. Finite element (FE) analysis was conducted using LS-DYNA to develop a static cyclic analysis of a three-dimensional HCFCS model. The FE results mirrored the experimental results. The bending strength of HC-FCS columns could easily be calculated with a high degree of accuracy using a sectional analysis based on Navier-Bernoulli’s assumptions and strain compatibility concepts.