Masonry arches strengthened with composite unbonded tendons

In this paper an analytical model to evaluate the structural behavior of masonry arches and vaults strengthened with composite unbonded tendons placed at the extrados is presented. The tendons are fixed at the imposts. The model is formulated under the assumption of finite displacements. The displaced equilibrium configurations are identified by the stationariety of the potential of the acting forces. It is shown that when the tendon is not pretensioned an increase of the arch collapse load can be achieved only if the axial stiffness of the tendon is sufficiently large. Instead if the tendon is pretensioned an increase of the load that induces the first displacement of the arch is always achieved. If the stiffness of the tendon is sufficiently large the collapse load will be greater than the load that produces the first displacement of the arch

TRM versus FRP in flexural strengthening of RC beams: behaviour at high temperatures

The flexural behaviour of RC beams strengthened with TRM and FRP composites was experimentally investigated and compared both at ambient and high temperatures. The investigated parameters were: (a) the strengthening material, namely TRM versus FRP, (b) the number of strengthening layers, (c) the textile surface condition (dry and coated), (d) the textile material (carbon, basalt or glass fibres) and (e) the end-anchorage of the flexural reinforcement. A total of 23 half-scale beams were constructed, strengthened in flexure and tested to assess these parameters and the effectiveness of the TRM versus FRP at high temperatures. TRM exhibited excellent performance as strengthening material in increasing the flexural capacity at high temperature; in fact, TRM maintained an average effectiveness of 55%, compared to its effectiveness at ambient temperature, contrary to FRP which totally lost its effectiveness when subjected to high temperature. In specific, from the high temperature test it was found that by increasing the number of layers, the TRM effectiveness was considerably enhanced and the failure mode was altered; coating enhanced the TRM effectiveness; and the end-anchorage at high temperature improved significantly the FRP and marginally the TRM effectiveness. Finally, the formula proposed by the Fib Model Code 2010 was used to predict the mean debonding stress in the TRM reinforcement, and using the experimental results obtained in this study, a reduction factor to account for the effect of high temperature on the flexural strengthening with TRM was proposed

Textile-reinforced mortar (TRM) versus fibre-reinforced polymers (FRP) in flexural strengthening of RC beams

The aim of this paper is to compare the flexural performance of reinforced concrete (RC) beams strengthened with textile-reinforced mortar (TRM) and fibre-reinforced polymers (FRP). The investigated parameters included the strengthening material, namely TRM or FRP; the number of TRM/FRP layers; the textile surface condition (coated and uncoated); the textile fibre material (carbon, coated basalt or glass fibres); and the end-anchorage system of the external reinforcement. Thirteen RC beams were fabricated, strengthened and tested in four-point bending. One beam served as control specimen, seven beams strengthened with TRM, and five with FRP. It was mainly found that: (a) TRM was generally inferior to FRP in enhancing the flexural capacity of RC beams, with the effectiveness ratio between the two systems varying from 0.46 to 0.80, depending on the parameters examined, (b) by tripling the number of TRM layers (from one to three), the TRM versus FRP effectiveness ratio was almost doubled, (c) providing coating to the dry textile enhanced the TRM effectiveness and altered the failure mode; (d) different textile materials, having approximately same axial stiffness, resulted in different flexural capacity increases; and (e) providing end-anchorage had a limited effect on the performance of TRM-retrofitted beams. Finally, a simple formula proposed by fib Model Code 2010 for FRP reinforcement was used to predict the mean debonding stress developed in the TRM reinforcement. It was found that this formula is in a good agreement with the average stress calculated based on the experimental results when failure was similar to FRP-strengthened beams

Mortar-based systems for externally bonded strengthening of masonry

Mortar-based composite materials appear particularly promising for use as externally bonded reinforcement (EBR) systems for masonry structures. Nevertheless, their mechanical performance, which may significantly differ from that of Fibre Reinforced Polymers, is still far from being fully investigated. Furthermore, standardized and reliable testing procedures have not been defined yet. The present paper provides an insight on experimental-related issues arising from campaigns on mortar-based EBRs carried out by laboratories in Italy, Portugal and Spain. The performance of three reinforcement systems made out of steel, carbon and basalt textiles embedded in inorganic matrices has been investigated by means of uniaxial tensile coupon testing and bond tests on brick and stone substrates. The experimental results contribute to the existing knowledge regarding the structural behaviour of mortar-based EBRs against tension and shear bond stress, and to the development of reliable test procedures aiming at their homogenization/standardization

Experimental analysis on bond between PBO-FRCM strengthening materials and concrete

The effectiveness of externally bonded strengthening for reinforced concrete (RC) elements strongly depends on the bond between the strengthening material and the concrete and on the mechanical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based matrix and the concrete is experimentally analyzed. Experimental results of double shear tests involving different bond lengths and fibers cross sections are presented. The results allow to estimate the effective anchorage length and evidence that the debonding occurs at the fibers/matrix interface after a considerable fibers/matrix slip. They also confirms the effectiveness of the FRCM materials as external reinforcements for concrete. The obtained experimental results can be used to calibrate a local bond-slip relation to be used in the design of the external reinforcement

Bond-slip relations for PBO-FRCM materials externally bonded to concrete

Existing reinforced concrete (RC) structures often need to be repaired, strengthened and upgraded to sat- 22 isfy current code requirements. In recent years many interventions have been done bonding composite 23 materials to the surface of existing RC elements. The structural effectiveness of these interventions 24 strongly depends on the bond between the strengthening material and the concrete and on the mechan- 25 ical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix 26 (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based 27 matrix and the concrete is analytically analyzed with reference to the approach generally adopted for the 28 fiber reinforced polymers (FRP) materials, which is based on the local bond-slip relation between the 29 strengthening fibers and the supporting concrete. A local bond-slip relation is calibrated on the base of 30 the results of an experimental investigation previously performed by the authors. The bond-slip relation 31 is essential in the modeling of the structural behavior of RC elements strengthened with PBO-FRCM, in 32 that it allows to calculate the force that can be transferred to the concrete, the effective anchorage length, 33 the concrete cracks distance and opening

Bond-slip relations for PBO-FRCM materials externally bonded to concrete

Existing reinforced concrete (RC) structures often need to be repaired, strengthened and upgraded to sat- 22 isfy current code requirements. In recent years many interventions have been done bonding composite 23 materials to the surface of existing RC elements. The structural effectiveness of these interventions 24 strongly depends on the bond between the strengthening material and the concrete and on the mechan- 25 ical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix 26 (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based 27 matrix and the concrete is analytically analyzed with reference to the approach generally adopted for the 28 fiber reinforced polymers (FRP) materials, which is based on the local bond-slip relation between the 29 strengthening fibers and the supporting concrete. A local bond-slip relation is calibrated on the base of 30 the results of an experimental investigation previously performed by the authors. The bond-slip relation 31 is essential in the modeling of the structural behavior of RC elements strengthened with PBO-FRCM, in 32 that it allows to calculate the force that can be transferred to the concrete, the effective anchorage length, 33 the concrete cracks distance and opening

Performance of different types of FRCM composites applied to a concrete substrate

This research aimed to investigate the performance of fiber reinforced cementitious matrix (FRCM) composites employed as externally applied strengthening system for reinforced concrete members. The results of an experimental campaign conducted on FRCM composites applied to a concrete substrate are shown and discussed. The composites were comprised of different types of fibers, namely carbon, glass, steel, and basalt fibers, and different types of cementitious matrix. Single-lap direct-shear tests were performed to study the behavior of the different composites. Specimens with different bonded lengths were tested to investigate the stress-transfer mechanism and to investigate the existence of an effective bond length. Comparisons between the peak loads obtained with the direct-shear tests and the tensile strength of the fibers, which provide an indication of the exploitation of the fibers, were carried out