ABSTRACT
At the Department of Concrete Structures at Technische Universitaet Muenchen a lot of research work was done to proof the bond resistance of externally bonded reinforcement over the whole area of a flexural concrete member, which is subjected to shear. From this work a simplified verification of bond capacity for the most critical case of a beam, which is retrofitted with externally bonded reinforcement, at the area of the support moment was derived. The procedure of this simplified verification is as follows: First of all the decisive single section, which is located between two cracks, has to be determined. In the following article this single section is called decisive crack element. At the area of the support moment this decisive crack element is located at the point where the value of the flexural moment and the shear stress has its maximum. Thus the decisive crack element is located at a distance of a
from the intermediate support (see Figure 1). The decisive crack element can be determined with a maximum crack moment of the concrete M
. For this crack element the existing stress increase exist∆σ1
bonded reinforcement has to be determined. The
3 DETERMINATION OF EXISTING STRESS INCREASE EXIST∆σ1
determined at ultimate limit state. The existing stress increase exist∆σ1 Λ in the externally bonded reinforcement can then be calculated as follows:
= − (1)
4 DETERMINATION OF BOND RESISTANCE
The bond resistance is defined as maximum possible stress increase res∆σιΛ in the externally bonded reinforcement between two cracks. According to Niedermeier 2001 the maximum possible stress increase res∆σιΛ(σιΛ) is a function of the stress ∆σ1L at the lower stressed crack edge at the location x
see Figure 2. For the simplified verification of the bond resistance of externally bonded reinforcement at the area of the support moment the resisting stress increase at the decisive crack element (see Figure 1) can be determined using equation (2):
res G E
⋅ ⋅
+ − (2)
5 VERIFICATION OF BOND CAPACITY
The verification of bond capacity is provided, if the design value of resisting stress increase res∆σ1 Λ,δ at the decisive crack element is greater than the design value of existing stress increase exist∆σ1 Λ,δ:
6 SUMMARY
A simple and safe design concept to proof bond capacity of flexural concrete members strengthened with externally bonded reinforcement is presented. Based on this design model more factors that increase the bond capacity can be considered and integrated to this design model. That is subject of current experimental and theoretic research work that is done at the Department of Concrete Structures at Technische Universitaet Muenchen.
