Abstract
Reinforced concrete structural elements can be strengthened by bonding external steel plates onto the concrete surface by means of an epoxy adhesive and are referred to as composite structural members.
The objectives of this Master’s research project on the Structural Behaviour of Composite Concrete-Steel Slabs were as follows:
To determine whether steel plates bonded externally to existing reinforced concrete structural elements can control the deflection
To determine whether steel plates bonded externally to existing reinforced concrete structural elements can increase the flexural resistance
To determine whether the various debonding mechanisms of the steel plate from the concrete surface of existing reinforced concrete structural elements can be theoretically predicted by existing theories.
Twenty-four reinforced concrete specimens were constructed using 25 MPa concrete and 5 Y12 internal bars in the longitudinal direction. The concrete and steel plate surfaces were prepared by scabbling and sandblasting respectively. The steel plates, which varied in thickness (from 6 mm to 8 mm), width (from 110 mm to 150 mm) and number (1 or 2), were bonded externally to the soffit of the concrete structural elements by means of epoxy glue. These composite concrete-steel specimens were simply supported and loaded until destruction by applying either a third-span line load (TSLL), mimicking a uniformly distributed load, or a mid-span line load (MSLL). The applied load, vertical deflection and strain on the bonded steel plates at mid-span were electronically logged.
The vertical deflection within the elastic range of the unplated and plated reinforced concrete structural elements was obtained using the double integration method. The cracked second moment of area (Icr) was calculated by transforming the cross-sectional area of the steel reinforcement to an equivalent area of concrete. It was found that the deflection of composite concrete structural elements decreased as the cross-sectional area of the bonded steel plates increased. A comparison between the theoretically analysed and experimentally measured deflections was done as part of this research study.
The findings of this study indicate that steel plates externally bonded to reinforced concrete structural elements increase the flexural and shear resistance of the members. The externally bonded plates are not, however, enclosed by the concrete as in the case of internal reinforcement and are therefore not as well anchored. This results in premature debonding of the steel plate from the concrete surface. Two design philosophies for the theoretical prediction of the flexural resistance were considered. The first was the anchorage design philosophy developed in Europe (fib-14, 2001) where the tension face plates are terminated in the uncracked region, which is beyond or at least to the point of contraflexure. The second is the hinge design philosophy developed in Hong Kong and Australia (Handbook 305-2008, Standards Australia) whereby the tension face plates are terminated short of the points of contraflexure; this latter philosophy was adopted as the bonded steel plates stopped 250 mm short of the support, which is also the point of contraflexure for simply supported structural elements. The following debonding mechanisms due to flexure and shear were investigated:..
M.Ing. (Civil Engineering)