FRP Cables to Prestress RC Beams: State of the Art vs. a Split Wedge Anchorage System

Abstract

Versatility and high performance in terms of specific stiffness and strength, as well as non-corrosive sensitivity, make FRP (Fiber-Reinforced Polymer) cables a viable alternative to steel ones in the development of prestressing systems. On the other hand, the orthotropic and brittle nature of FRPs could trigger a premature failure of the cable in the anchorage system, for which several solutions have been proposed so far in civil structural applications. In this context, after a preliminary state of the art, the work introduces a split wedge anchorage for FRP (ϕ = 12 mm) cables proposing two different solutions for steel wedges having the external surface: either (1) a constant (3 degrees) slope or (2) a double slope obtained by shaping it with an angle of 3.0 degrees before and then of 3.1 degrees along the most tapered part. The goal was to exploit the nominal cable capacity (257 kN), avoiding stress peaks that cause its premature failure. The proposed solutions have been experimentally tested and, as far as the double angle solution is concerned, the failure loads were equal to 222 and 257 kN, denoting that the proposed solution can reach the cable capacity. Clearly, further investigations are needed to check the variability of the results and eventually improve the system.

A Split-Wedge Anchorage for CFRP Cables: Numerical Model vs. Experimental Results

“…According to the literature, anchorages for FRP cables can be divided into bonded and mechanical, which contain the split-wedge systems. A review of bonded anchorages is provided in [11], while principles are illustrated in [30], where a hybrid bonded/splitwedge anchorage is also presented. Split-wedge anchorages are composed of (Figure 1): (1) an external tapered-steel barrel; (2) two or more wedges and (3) the FRP cable, often protected by metallic sleeves (made of aluminum or copper), which envelope the cable portions arranged inside the wedges.…”

“…Focusing on split-wedge systems for FRP cables, modifications to the traditional anchorages for steel tendons are requested due to their high tilting angles, usually in the order of 5-7 • [22] and small anchoring lengths. The experimental tensile test [11] on a CFRP tendon blocked through a traditional anchorage highlighted the premature slippage of the cable. Improvements proposed in the literature so far mainly concerned the shape of barrel/wedge interface, that governs the magnitude and distribution of the stress components on the cable.…”

“…Research efforts aimed (Damiani et al [11]) to investigate the validity of an optimized steel anchorage, for CFRP cables, having a double-tilted surface for the wedges: experimental tensile tests highlighted the efficiency of the device.…”

Improvement of Anchorage Performance of Carbon Fiber-Reinforced Polymer Cables

“…Zhuge (2010) also evaluated the stress of a conical barrel based on the mechanical behavior of the wedge-type anchor for CFRP tendons. Campbell et al (2000) observed the performance and changes in the wedge for individual and cyclic loads based on the wedge-type stainless steel anchorage system using FRP tendons [ 22 , 23 , 24 , 25 , 26 ]. Thus, most existing studies have focused on the wedge-type anchorage system using steel strands [ 27 , 28 , 29 , 30 ].…”

Advanced Methods for Structural Rehabilitation

“…Damiani et al [9] proposed an original split wedge anchorage for fiber-reinforced polymer (FRP) cables to prestress existing RC members for structural rehabilitation purposes. A remarkable literature review of FRP cables is reported, including the short-and long-term effects of mechanical properties for aramid-, glass-, and carbon-fiber-based cables.…”