Luca Righetti

Bond Strength of Composite CFRP Reinforcing Bars in Timber

The use of near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars is an interesting method for increasing the shear and flexural strength of existing timber members. This article examines the behaviour of carbon FRP (CFRP) bars in timber under direct pull-out conditions. The objective of this experimental program is to investigate the bond strength between composite bars and timber: bars were epoxied into small notches made into chestnut and fir wood members using a commercially-available epoxy system. Bonded lengths varied from 150 to 300 mm. Failure modes, stress and strain distributions and the bond strength of CFRP bars have been evaluated and discussed. The pull-out capacity in NSM CFRP bars at the onset of debonding increased with bonded length up to a length of 250 mm. While CFRP bar’s pull-out was achieved only for specimens with bonded lengths of 150 and 200 mm, bar tensile failure was mainly recorded for bonded lengths of 250 and 300 mm.

Durability of GFRP grids for masonry structures

The application of Textile Reinforced Mortars (TRMs) may cause a significant increase of the lateral capacity of unreinforced masonry elements. This paper presents relationships between the durability and the governing material properties of GFRP (Glass Fibre Reinforced Polymers) grids used to produce TRMs. Measurements of the tensile strength were made using specimens cut off from GFRP grids before and after ageing in aqueous solution and high cycle fatigue testing with a number of cycles of 60,000, 150,000 and 300,000. The tensile strength of two GFRP grids was tested after up to 210 days of storage in deionised water and NaCl solution. A degradation in tensile strength up to 30.2% and 10.8% was recorded for the specimens subjected to treatment in aqueous solution and to high cycle fatigue testing, respectively. This degradation indicated that extended storage in a wet environment may cause significant decreases of mechanical properties.

Fiberglass Grids as Sustainable Reinforcement of Historic Masonry

Fiber-reinforced composite (FRP) materials have gained an increasing success, mostly for strengthening, retrofitting and repair of existing historic masonry structures and may cause a significant enhancement of the mechanical properties of the reinforced members. This article summarizes the results of previous experimental activities aimed at investigating the effectiveness of GFRP (Glass Fiber Reinforced Polymers) grids embedded into an inorganic mortar to reinforce historic masonry. The paper also presents innovative results on the relationship between the durability and the governing material properties of GFRP grids. Measurements of the tensile strength were made using specimens cut off from GFRP grids before and after ageing in aqueous solution. The tensile strength of a commercially available GFRP grid has been tested after up 450 days of storage in deionized water and NaCl solution. A degradation in tensile strength and Young’s modulus up to 30.2% and 13.2% was recorded, respectively. This degradation indicated that extended storage in a wet environment may cause a decrease in the mechanical properties.