Issue 18

S. Marfia et alii, Frattura ed Integrità Strutturale, 18 (2011) 23-33; DOI: 10.3221/IGF-ESIS.18.03 23 A coupled interface-body nonlocal damage model for the analysis of FRP strengthening detachment from cohesive material S. Marfia, E. Sacco, J. Toti Department of Mechanics, Structures and Environment, University of Cassino, Cassino (Italy) marfia@uncas.it , sacco@unicas.it , jessica.toti@unicas.it A BSTRACT . In the present work, a new model of the FRP-concrete or masonry interface, which accounts for the coupling occurring between the degradation of the cohesive material and the FRP detachment, is presented; in particular, a coupled interface-body nonlocal damage model is proposed. A nonlocal damage and plasticity model is developed for the quasi-brittle material. For the interface, a model which accounts for the mode I, mode II and mixed mode of damage and for the unilateral contact and friction effects is developed. Two different ways of performing the coupling between the body damage and the interface damage are proposed and compared. Some numerical applications are carried out in order to assess the performances of the proposed model in reproducing the mechanical behavior of the masonry elements strengthened with external FRP reinforcements. S OMMARIO . Nel presente lavoro si propone un modello di interfaccia FRP-calcestruzzo o FRP-muratura, che tiene conto dell’accoppiamento tra il degrado del materiale coesivo ed il distacco del FRP; in particolare, si sviluppa un modello di danno non locale accoppiato interfaccia-corpo. Si presenta un modello di danno non locale e plasticità per il materiale coesivo ed un modello di interfaccia che tiene conto del modo I, II e misto di danno, del contatto unilatero e degli effetti dell'attrito. Si propongono e confrontano due diversi modi di accoppiamento del danno del corpo e del danno d’interfaccia. Si sviluppano applicazioni numeriche per verificare l’efficienza del modello proposto nel riprodurre il comportamento meccanico di elementi in muratura rinforzati con FRP. K EYWORDS . Interface-body damage; Detachment phenomenon; Nonlocal model. I NTRODUCTION he use of Fiber Reinforced Plastic (FRP) materials for the strengthening of existing concrete and masonry elements is growing; in the last twenty years, many structures have been reinforced adopting FRP and several experimental and modeling scientific works have been developed [1-9]. The use of FRP materials applied on the external surface of concrete or masonry structures aroused new modeling problems. One of the main problem in the use of FRP is the detachment phenomenon, which consists in the sudden decohesion of the FRP reinforcement from the concrete or masonry surface. Indeed, the concrete and the masonry are quasi-brittle materials, whose mechanical response is characterized by damage with softening, which is due to the development of micro-cracks. Thus, two damage effects could be presented in the quasi-brittle reinforced structural elements: the body damage, which develops inside the domain of the strengthened element, and the interface damage, which occurs at the FRP -concrete or -masonry interface. Experimental evidences demonstrate that the detachment of the FRP from the support material occurs often with peeling of a thin layer from the T