Abstract
Externally Bonded Reinforcement (EBR) technique has been widely used for flexural strengthening of concrete structures by using carbon fiber-reinforced polymers (CFRP). EBR technique offers several structural advantages when the CFRP material is prestressed. This paper presents an experimental and numerical study on reinforced (RC) slabs strengthened in flexure with prestressed CFRP strips as a structural strengthening system. The strips are applied as an externally bonded reinforcement (EBR) and anchored with either a mechanical or a gradient anchorage. The former foresees metallic anchorage plates fixed to the concrete substrate, while the latter is based on an accelerated epoxy resin curing followed by a segment-wise prestress force decrease at the strip ends. Both anchorage systems, in combination with different CFRP strip geometries, were subjected to static loading tests. It could be demonstrated that the composite strip’s performance is better exploited when prestressing is used, with slightly higher overall load carrying capacities for mechanical anchorages than for the gradient anchorage. The performed investigations by means of a cross-section analysis supported the experimental observation that in case a mechanical anchorage is used, progressive strip debonding changes the fully bonded configuration to an unbonded end-anchored system. The inclusion of defined debonding criteria for both the anchorage zones and free length between the anchorage regions allowed to precisely capture the ultimate loading forces.
Highlights
In recent decades, several research initiatives has been devoted to the development of Fibre Reinforced Polymer (FRP) materials and related strengthening techniques used by the construction industry [1,2,3,4,5,6,7,8]
El-Hacha et al [16] pointed out the following main advantages: (1) superior durability since non-corrosive materials are used; (2) the existing deflections are reduced; (3) the crack widths reduction and the onset of cracking initiation is delayed; (4) internal steel reinforcement strains are relieved; (5) higher fatigue failure resistance; (6) more efficient use of the concrete and FRP; (7) opposes stresses due to both dead and live loads; (8) ultimate capacity can be further increased; (9) it can be worked as a substitute of internal pre-stress that has been lost; (10) shear capacity is increased by the longitudinal stresses induced by prestressed FRP laminates
The experimental program was composed of eight reinforced concrete (RC) slabs, as presented in Table 1: (1) two slabs were used as reference specimens (REF1 and REF2); (2) one slab (SL50_1.4_EBR) was strengthened with one laminate according to the externally bonded reinforcement (EBR) technique; (3) five slabs were strengthened with one EBR prestressed Carbon FRP materials (CFRP) laminate strip, three by using the mechanical anchorage (MA) system and two with the gradient anchorage (GA) system, with distinct geometry types of CFRP laminate strips, mainly 50 mm × 1.4 mm, 50 mm × 1.2 mm, and 80 mm × 1.2 mm
Summary
Several research initiatives has been devoted to the development of Fibre Reinforced Polymer (FRP) materials and related strengthening techniques used by the construction industry [1,2,3,4,5,6,7,8]. From all the proposed systems, two of them have been mostly used, mainly [17]: the mechanical anchorage (MA) system fixing the ends of the FRP reinforcement to the concrete substrate by means of metallic plates and bolts and the gradient anchorage (GA). By using a cross-sectional analytical model, numerical simulations were carried out to better understand the obtained results with regard to the overall structural behavior This calculation tool is able to predict the structural behavior of RC structures strengthened with an additional reinforcement. This external reinforcement can be implemented as either a fully bonded or an unbonded strengthening element
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