The idea of reinforcing glued laminated timber (glulam) beams came in response to the need to improve the mechanical properties, as well as to ensure higher reliability of this type of structural elements. This paper describes an experimental program which examines the reinforcement in flexure of glulam beams with carbon fibre reinforced plastic (CFRP) plates. Fifteen beams reinforced with CFRP at the tension side and five unreinforced control beams were instrumented and tested to failure in a four-point bending configuration. The mechanical properties of reinforced beams are compared to those of unreinforced beams with regard to the load-deflection behaviour, failure mode, ultimate load capacity, stiffness and strain distribution. The experimental results demonstrated the beneficial effect of the proposed reinforcing solution in terms of strength, stiffness and ductility.

This paper presents an analysis of bending behaviour of glued laminated timber (glulam) beams reinforced with carbon fibre reinforced polymer (CFRP) plates, based on finite element numerical modelling. Nonlinear 3-dimen­sional model was developed and validated by experimental tests carried out on unreinforced beams and beams reinforced with two different reinforcement arrangements. Suitable constitutive relationships for each material were utilised in the model, as well as anisotropic plasticity theory for timber in compression. Adhesive bond between CFRP plate and timber was modelled as a perfect connection. Beam failure in the model was defined by maximum stress criterion. The predicted behaviour of beams has shown good agreement with the experimental results in relation to load-deflection relationship, ultimate load, elastic stiffness and strain profile distribution. The non-linear behaviour of reinforced beams before failure was also achieved in the numerical analysis, confirming the finite element model to be accurate past the linear-elastic range. Experimentally tested reinforced beams usually failed in tensile zone after compressive plasticiza­tion of top lamination, which was also simulated in the numerical model. The results proved that the load carrying ca­pacity, stiffness and ductility of glulam beams were successfully increased by addition of CFRP plate at tension side of the section.

No abstract

UVODDrvo kao jedan od najstarijih građevinskih materijala nalazi primenu i u savremenoj građevinskoj praksi zahvaljući tome što predstavlja prirodan, obnovljiv, biorazgradiv i estetski atraktivan materijal. Potreba da se ojačaju drvene konstrukcije može nastati iz različitih razloga, kao što su mehanička oštećenja, destruktivni uticaji okruženja ili povećanje korisnog opterećenja. U ovom kontekstu, razvoj efikasnih metoda ojačanja od velike je važnosti.Poslednjih godina, primena polimera ojačanih vlaknima (Fiber Reinforced Polymer -FRP) u oblasti sanacija i ojačanja građevinskih konstrukcija omogućena je zahvaljujući povećanoj dostupnosti i sve nižoj ceni. FRP materijali su grupa naprednih kompozita u okviru kojih se nalaze vlakna izraženih mehaničkih karakteristika (najčešće staklena ili karbonska) povezana izuzetno čvrstom, hemijski otpornom i trajnom sintetičkom smolom (kao matricom). Ovi kompozitni materijali dostupni su kao gotovi fabrički proizvodi najčešće u formi traka, tkanina ili šipki. Povezivanje FRP ojačanja za konstrukcijske elemente izvodi se uglavnom lepljenjem uz primenu odgovarajućih polimernih lepkova. Ovi materijali se već dugo uspešno koriste pri ojačanju betonskih i zidanih konstrukcija [1,2], dok je njihova primena za ojačanje i sanaciju drvenih konstrukcija još uvek u fazi ispitivanja kako bi se obezbedila pravilna i optimalna Marija Todorović, Asistent -student doktorskih studija, mast. inž.

This paper presents an experimental procedure for obtaining the fracture resistance (R curve) of solid wood specimens made of spruce. Double Cantilever Beam (DCB) tests were performed in order to determine energy release rate vs crack length in Mode I wood fracture (crack opening). Ten wood specimens were loaded using the Universal Testing Machine and force-displacement curves were recorded. The most important parameter -crack length was monitored as the crack propagates using Digital Image Correlation (DIC) method. In order to obtain accurate R curve results, procedure which includes calculating cumulative released energy was employed. The cohesive energy Gf was determined based on the R curves. These results can further be analysed in order to obtain cohesive law for Mode I fracture of wood.