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The near surface mounted (NSM) method of inserting fiber reinforced polymer (FRP) elements (rods or lamina) into notches has been shown to be a good way for restoring reinforced concrete (RC) elements. The knowledge about the use of Glass-FRP rod following the NSM to reinforce RC beams is limited. This paper deals with the analysis of static and dynamic behaviour of RC beams with and without strengthening. The response of RC beams was assessed at different concrete's damage level by non-destructive vibration tests. First, a couple of beams have been analysed: one RC beam subjected to bending and under vibration tests; another one beam, damaged by bending and strengthened with NSM Carbon-FRP rods tested again under vibration. Further, one RC beam damage was analysed under bending and vibration tests without strengthening; successively, the beam model with NSM GFRP rod has been tested following the same loading path. Below experimental results are shown and commented; in particular, changes in frequency values are related to the evolution of damage level affected RC beams with NSM CFRP and GFRP rods. [ABSTRACT FROM AUTHOR]

Abstract Undamaged and damaged simply supported homogeneous in scale beams were investigated by free vibration. The damage of beams was obtained by notches; two different types of damage have been considered in the paper: concentrated damage on the midspan section of beams and diffused damage in a middle zone. The analysis of free vibration of specimens was carried out also by verifying response using numerical modelling by the finite element method (FEM). Two beam models, one with double concentrated notches and one with diffused damage, strengthened by epoxy resin in the notches and with one unidirectional CFRP lamina at the intrados were subjected to cycles of bending loading. After each cycle of static loading the free vibration response was experimentally evaluated considering the beam hinge at the ends. The envelope of frequency response functions (FRFs) obtained by the dynamic experimental tests was elaborated and the changes of natural frequency values are then correlated to the damage degree both to non-strengthened beam and to the strengthened beam models also damaged by static loading. Comparison of experimental and theoretical frequency values is shown and discussed to validate nondestructive monitoring based on vibration tests and the behavior of homogeneous beam strengthened by CFRP lamina. [ABSTRACT FROM AUTHOR]

The aim of the paper is to investigate the dynamic behaviour of undamaged and damaged reinforced concrete (RC) beams with different constraints: hinged and free-free ends. Two RC beams were analysed experimentally, strengthened with near surface mounted (NSM) glass fibre reinforced polymers (GFRP). One of RC beams was also reinforced with GFRP strips in the compressive zone. Damage of the RC beams was obtained by cracking of concrete for one of the beams, under bending tests, and for the other beam by artificial notches. In this paper, the envelope of Frequency Response Functions (FRFs) obtained by the dynamic experimental tests are shown and the changes of natural frequency values are correlated to the damage degree of beam elements. Finally, modelling of RC beams by finite element method (FEM) is developed for the undamaged beam and for the beam damaged with notches. Experimental results are discussed and a comparison between the experimental results and the theoretical and numerical data obtained is shown. [ABSTRACT FROM AUTHOR]

Four reinforced concrete (RC) beam models undamaged, damaged by notches and strengthened by external bonded (EB) glass fiber reinforced polymer (GFRP) strips have been experimentally studied. The paper aims to assess the availability of strengthening with EB GFRP strips in RC beams having a deep localized damage. The behavior of RC beams has been analysed under bending loading until failure. Furthermore, the assessment of RC beam models foresaw nondestructive control of damaged and strengthened models by free vibration tests to obtain frequency values at different damage degree. Damage, artificially obtained by notches with different width, on the midspan section and on the lateral location of beams, has been analysed. The envelope of frequency response functions (FRFs) obtained by dynamic tests was elaborated and changes of natural frequency values are then correlated to damage both to non-strengthened beam with notches and to strengthened beam models. Results of static tests on RC beams strengthened with filled mortar in the notched sections and EB GFRP strips have allowed to validate the strengthening of RC elements with composite material characterized by relatively low elastic modulus; further, it has been assessed maintenance of bond between concrete surface and GFRP strips until failure under bending loading. [ABSTRACT FROM AUTHOR]

Inserting FRP rods into grooves using the NSM technique has been demonstrated to be a suitable method for repairing reinforced concrete (RC) beams. There is limited experience with the use of GFRP in the strengthening of RC elements due to low Young's modulus of glass fibers. The aim of the paper is to analyse the static and dynamic behaviour of RC beams damaged and strengthened by glass fiber reinforced polymer (GFRP) rods utilizing the near surface method (NSM). Undamaged and damaged three RC beams have been experimentally tested under bending loading with and without strengthening by GFRP rods. For a beam, damage has been represented firstly by notches on concrete cover. The beam has been successively strengthened by epoxy resin and NSM GFRP rod and then subjected to bending tests. Vibration tests have been adopted as nondestructive method of control during the experiments to assess the response of RC beams at different damage steps of concrete or due to decrease of bond of GFRP rod. Vibration tests foresaw two boundary conditions, respectively, free-free and hinged ends. Experimental static and vibration results are below shown; discussion and comments on the strengthening bond of NSM GFRP rod have been developed. [ABSTRACT FROM AUTHOR]