FLEXURAL STRENGHTENING CONCRETE BEAMS WITHOUT INTERNAL STEEL REINFORCMENT: EXPERIMENTAL ANALYSIS OF ULTIMATE LIMIT STATE

The use of non-metallic composite materials such as Carbon Fiber Reinforced Polymer (CFRP) is today the fastest and most convenient way of improving the bending characteristics of concrete structures. A brief look at the literature on the subject reveals a number of accounts of experimental tests on the behavior under bending of beams bound with FRP (Arduini 1994, Neubauer 1997, Rostasy 1984. 1993). Research regarding the theoretical aspects and finite element modeling is listed in Bencardino et al. All the papers mentioned involve steel reinforcement but do not consider cases in which corrosion problems make it impossible to quantify the ultimate bending moment because of the corrosion itself. To tackle this problem, which applies to a number of buildings in the ex industrial zone of Marghera, Venice, listed and protected as examples of historic industrial architecture, a research program was set up at the laboratories of the Venice University Institute of Architecture so as to be able to study the behavior under bending of this type of structure. It is well known that in the hypothesis of full composite action, the failure mode of a beam with steel reinforcement can be one of the following: steel yielding followed by concrete crushing or steel yielding followed by FRP fracture and concrete crushing. In the case of loss of composite action, debonding can be localized in the concrete, between the concrete and the adhesive, or between the adhesive and the FRP with failure by peeling-off. This research project aims to study the failure modes and identify a type of strengthening which avoids fragile type failure. At this point in the progression of the work, not all the experimental tests have been completely carried out. The results shown here regard the mechanical characteristics of the FRP, of the concrete and the bending tests with four different types of strengthening solutions tension wrapped at the stress zone. For comparison, the tests were carried out on a series of beams without the strengthening. The specimens tested were named as follows: UCS - Unstrengthened concrete test specimen; TWL - Test specimen tension wrapped with longitudinal strengthening; TWH - Test specimen tension wrapped with hoop strengthening; TWLH - Test specimen tension wrapped with longitudinal + hoop strengthening; TWHL - Test specimen tension wrapped with hoop + longitudinal.