FE analysis
A smeared crack analysis of reinforced concrete T-beams strengthened with GFRP composites,
Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G.
, Engineering Structures, 11//, Volume 56, p.1346-1361, (2013)
AbstractThe strengthening of reinforced concrete structures with laminates of fibre reinforced polymeric (FRP) matrix has received considerable attention, although there still is lack of information on the more adequate modelling of the interface between FRP composites and concrete. An experimental programme is described and was designed to: (i) characterise glass FRP-to-concrete interface by shear tests; (ii) analyse reinforced concrete T-beams with external GFRP plates. Double shear tests were carried out based on 15 cm cubes with GFRP bonded to two opposite faces. The concrete T-beams were 3.0 m long and 0.28 m high and were loaded till rupture in 4-point bending tests. The external reinforcement system showed great strength increment in relation to the non retrofitted T-beam, confirming to be an effective approach to the flexural strengthening of RC beams. The computational analysis was based on a three dimensional smeared crack model. In total, 22 computational analyses were made. Models with and without interface FE associated with Mohr–Coulomb failure criterion for the FRP-to-concrete interface were defined and different strength types of concrete were considered. The rigid interface does not predict the rupture of the T-beam with precision; however, the results obtained for low concrete strengths revealed that rigid interfaces can be assumed when conjugated with the fixed crack approach. Consequently, a slightly stiffer response of the beam is obtained. The maximum bond stresses obtained from Finite Element Analysis (FEA) revealed that the models with rigid interfaces developed lower bond stresses due to the lack of relative displacements between both materials. The effects of assuming either fixed or rotated crack approaches were also compared. The rotated crack conjugated to a fine mesh in the vicinity of the GFRP-to-concrete stress led to a very good estimation of the bond stresses along the interface. The prediction of the T-beam rupture was also estimated with better results when the rotated crack was used in the model. In general, the FEA predicted with very good results the de-bonding of the GFRP-to-concrete interface of T-beams externally bonded with GFRP composites.
Modelling GFRP-to-concrete joints with interface finite elements with rupture based on the Mohr-Coulomb criterion,
Biscaia, Hugo C., Chastre Carlos, and Silva Manuel A. G.
, Construction and Building Materials, 10//, Volume 47, p.261-273, (2013)
AbstractThe strengthening of reinforced concrete structures by means of externally bonded fibre reinforced polymers (FRPs) is now routinely considered and applied in the retrofit or strengthening of structures. FRP composites have received a considerable attention from civil engineers in recent years due to the high strength-weight and stiffness/weight ratios when compared to other materials. However, when FRP composites are bonded to a concrete surface, there is a persistent potential problem that the FRP plates may debond prematurely from the concrete. This is a very important issue for the engineers who have to focus on the computational modelling of this phenomenon. Some studies can be found in literature on computational modelling. However, there is very little information about the best modelling of the interface between FRP composites and concrete and this work is intended to help bridge this gap. The computational analysis presented here is based on three-dimensional software which assumes the smeared crack model, and the interface finite elements (FEs) used have a rupture criteria based on the Mohr-Coulomb criterion with tension cut-off. The definition of these FEs was based on double shear tests that were performed specifically for this purpose and they have shown that the debonding phenomenon can be predicted with some accuracy. In total, 10 double shear models were studied and the results were compared with the 21 experimental tests performed. The double shear tests consisted of applying loads to 2 layered GFRP laminates bonded to a 150 mm concrete cube with a bonded area of 150 × 80 mm (length × width). Double shear models with and without a gap interface were considered in order to emphasize the importance of modelling the GFRP-to-concrete interface with interface finite elements. The effect of the concrete strength on the interface performance was also considered. An externally bonded reinforcement (EBR) concrete T-beam strengthened with 2 GFRP layers is presented to illustrate the application of the method. The wet lay-up technique was used for the external reinforcement of a reinforced concrete T-beam and then tested under a four point bending test until rupture. The results are reported and differences between the numerical and the experimental results are discussed.
