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.

An experimental study was conducted to determine the transfer length of prestressed Glass Fiber Reinforced Polymer bars. This paper is a part of a broad program that studies the long-term behaviour of GFRP prestressed concrete beams. 16 GFRP prestressed concrete beams were cast in this study. The parameters included were; prestressing level; 300 MPa (44 ksi) and 500 MPa (73 ksi), concrete compressive strength; 30 MPa (4440 psi) and 70 MPa (10000 psi), and the GFRP bar diameter;12Φ (No. 4) and 16Φ (No.5). Accurate estimation of the transfer length is necessary for elastic stress calculations at the service limit state and for the shear design of prestressed members. Strain gauges were used to measure strains on the GFRP bars and DEMEC gauges were used to measure the concrete surface strains at the level of the prestressed GFRP bar to determine the transfer length. The transfer length of 16Φ (No.5) GFRP bars in concrete with compressive strength of 30 MPa (4440 psi) was found to be about 17 db, and 14 db for prestressing levels of 500 MPa (73 ksi) and 300 MPa (44 ksi), respectively. The measured transfer length values were used to improve the transfer length estimates provided by the ACI 440.4 R-04 equation by calibrating the material coefficient factor (αt) used in the ACI equation.

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.

Coarse recycled concrete aggregate (RCA) has been studied as a replacement for natural aggregate (NA) in concrete for decades. RCA is still predominantly used in non-structural applications such as filler, road sub-base, drainage material, and low quality concrete. However, there is increased interest in using RCA in new structural concrete due to restrictions on landfilling of construction and demolition (C&D) waste and on the scarcity of natural aggregates, especially in urban megacities. The compressive strength of concrete with coarse RCA is typically 15–30% less than that with NA. This feasibility study was conducted to evaluate the effect of FRP strengthening on RCA beams as compared with NA beams also strengthened with FRP. Four RCA and four NA beams were strengthened in flexure and in shear using hand laid-up carbon-epoxy FRP materials. A combination of longitudinal strips on the beam soffit and intermittent closed hoop wraps along the length were used. The FRP-strengthened beams were designed to yield and then fail in compression with the FRP still attached. The results of the testing are described. The ability of FRP strengthening to, (1) change the failure mode of RCA beams, and, (2) to improve the reliability of RCA concrete beams constructed or repaired with FRP materials is discussed. It was found, surprisingly, that the FRP-strengthening was effective in increasing the capacity of the RCA beams. This is attributed to a different failure mechanism of the RCA beams from that of the NA beams tested.