Debonding between external FRP strengthening and concrete substrate is an important limiting factor for the complete exploitation of the achievable strength upgrade, being itself the main cause of premature brittle failure of the strengthened member both in flexural and shear modes. Small unlevelled parts of the strengthened surface and substrate cracks characterized by slipping borders are typical discontinuities usually present in real applications and they may act as nucleation centres for debonding phenomena by creating a combination of shear and normal stress that strongly affects the bonding failure. Since different failure mechanisms become possible varying the ratio between shear and normal stress, around these discontinuities the failure may be driven out from the resin shear failure domain and into the concrete tension failure domain, causing a dramatic change in the typical strength that facilitates debonding initiation. Other parameters, such as the surface roughness of the concrete substrate, contribute to influence the phenomenon. This experimental research is aimed to investigate the bonding strength dependence on the ratio between normal stress and shear stress, and it was carried out trough a pull-off test set up modified in order to obtain loading at various inclinations between 15° and 90° with respect to the strengthening surface. The test programme includes various types of concrete surface and two different types of resin as well. A series of preliminary tests allowed the first author to obtain failure envelopes that well distinguish different failure mechanisms regarding both the concrete and the resin. In this research a greater number of tests have been performed and some additional parameters have been taken into account in order to allow a sensitivity analysis of the affecting factors.
Interaction between shear and normal stress at concrete-FRP interface
PASCALE GUIDOTTI MAGNANI, GIOVANNI;BONFIGLIOLI, BARBARA;
2004
Abstract
Debonding between external FRP strengthening and concrete substrate is an important limiting factor for the complete exploitation of the achievable strength upgrade, being itself the main cause of premature brittle failure of the strengthened member both in flexural and shear modes. Small unlevelled parts of the strengthened surface and substrate cracks characterized by slipping borders are typical discontinuities usually present in real applications and they may act as nucleation centres for debonding phenomena by creating a combination of shear and normal stress that strongly affects the bonding failure. Since different failure mechanisms become possible varying the ratio between shear and normal stress, around these discontinuities the failure may be driven out from the resin shear failure domain and into the concrete tension failure domain, causing a dramatic change in the typical strength that facilitates debonding initiation. Other parameters, such as the surface roughness of the concrete substrate, contribute to influence the phenomenon. This experimental research is aimed to investigate the bonding strength dependence on the ratio between normal stress and shear stress, and it was carried out trough a pull-off test set up modified in order to obtain loading at various inclinations between 15° and 90° with respect to the strengthening surface. The test programme includes various types of concrete surface and two different types of resin as well. A series of preliminary tests allowed the first author to obtain failure envelopes that well distinguish different failure mechanisms regarding both the concrete and the resin. In this research a greater number of tests have been performed and some additional parameters have been taken into account in order to allow a sensitivity analysis of the affecting factors.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
