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.

Steel prestressed cored slab superstructures are a common structural system for multi-span bridges in coastal North Carolina. However, due to the aggressive marine environment several such bridges are in need of major repairs or replacement after being in service for little more than 40 years. To address this issue two research projects were undertaken in parallel. The first project involved a critical assessment of non-destructive evaluation techniques in an attempt to predict the extent of corrosion deterioration and hence, the residual strength of cored slabs from existing bridges. Twelve cored slabs taken from two in-service bridges scheduled for superstructure replacement were tested to failure in the laboratory to validate residual strength predictions. The second project involved the design, manufacture and testing of a full-scale CFRP prestressed cored slab reinforced with GFRP stirrups, and a typical steel prestressed cored slab control specimen. The results of the destructive laboratory testing enabled validation of the prediction of the flexural performance and strength of CFRP prestressed cored slabs relative to existing design recommendations. Direct comparison to the new steel prestressed control cored slab and similar existing cored slabs with varying degrees of deterioration from the first the research project was also undertaken.

A commonly reported failure mode through experimentation of fibre-reinforced polymer (FRP)-concrete bonded interfaces is premature debonding of the FRP. Such undesirable failure can occur at strains significantly lower than the strain capacity of the FRP and it can be sudden. Anchorage of the FRP is an intuitive means to delay and even halt debonding, and the addition of anchors can also lead to more deformable FRP-strengthened elements. The so-called FRP anchor has been shown to be an effective anchorage device and while there have been several experimental studies reported to date on FRP-strengthened RC elements anchored with such anchors, there has been decidedly less research on numerical modelling. This paper presents the details of a partial interaction model and a constitutive model for the FRP-to-concrete bonded interface as well as FRP anchors. The models are then used to simulate FRP anchors in single-shear FRP-to-concrete joints. The results of parametric studies on key variables such as plate geometry and plate material properties as well as anchor location and number of anchors are then provided. The parametric studies enable insights to be gained towards the contribution of FRP anchors in FRP-to-concrete bonded interfaces.

Near surface mounted (NSM) is a promising strengthening technique provided that the full bond between the strengthening material and the existing structure develops. Wahab et al. (2011 and 2012) tested reinforced concrete beams to asses the bond strength between the prestressed NSM carbon fibre reinforced polymers (CFRP) rods and the concrete. The beams were tested in four points bending under different fatigue load levels. Failure was by slipping between the CFRP rod and the epoxy that started at the support and traveled to the loading point as the number of cycles was increased. Modeling of the failure of the beams is presented in this paper. When the CFRP rod is prestressed, the shear stress is largest at the free end and decreases along the transfer length. The prestressing shear stresses are taken equal to the cracking shear stress under monotonic load for non-prestressed beams. During loading, following flexural cracking, debonding occurs at the loading point and progresses towards the supports as the load is cycled. The debonding is modeled as a crack growing at the interface between the CFRP rod and the epoxy. A bond stress versus slip model is proposed. It consists of an ascending branch representing the strains and stresses ahead of the crack tip and a descending branch representing the region behind the crack tip. The driving force for the crack is the shear stresses at the interface between the CFRP rod and the epoxy. The overlapping of the two shear stress distributions increases the shear stress near the end of the beam, which becomes the critical shear stress that causes failure. The failure shear stress at the end is higher than the prestressing shear stress and is estimated to be 25.5 MPa (3.698 ksi) for the spirally wound rods and 30.4 MPa (4.409 ksi) for the sand coated rods. The model also predicts the number of cycles and the forces in the CFRP rod at all locations in the shear span at the onset of failure with reasonable accuracy.

This paper introduces a rectangular concrete-filled fiber reinforced polymer (FRP) tube (CFFT) hybrid beam with an inner voided tube. The beam contains an outer rectangular filament-wound glass fiber reinforced polymer (GFRP) tube, and an inner voided circular filament-wound GFRP tube shifted toward the tension zone. The space between the tubes is filled with concrete. Steel bars, at the tension side, were provided to enhance both stiffness and serviceability of the beam. The flexural behavior of this voided CFFT beam was compared with a fully CFFT beam and another conventional steel reinforced concrete (RC) beam having identical dimensions. The results showed that the new hybrid composite beam behaves positively in terms of strength, ductility, and failure propagation, in addition to its high durability. The results also showed that, while the weight of the voided CFFT beam is 30% lighter than the weight of the conventional RC beam or the fully CFFT beam, its flexural capacity is 141% and 6% higher than their flexural capacities, respectively.