Design of column strengthening with CF sheets - Strengthening of Concrete Structures with Adhesively Bonded Reinforcement - page 111

Fig. 7.10 In uence of creep-relevant quasi-permanent loading component M 0Eqp / M 0Ed on

loadbearing capacity in M-N interaction diagram

The evaluation of the modi ed expressions of Jiang (7.19) and (7.20) enables M-N
interaction diagrams to be drawn with relatively little effort. Figure 7.9 shows the
decrease in a member's load-carrying capacity compared with the load-carrying
capacity of its cross-section depending on slenderness, and Figure 7.10 the decrease
compared with the creep-relevant quasi-permanent loading component M 0Eqp / M 0Ed
according to first-order theory. The empirical definition of the factor

ξ 1 leads to a
disproportionate increase in the curvature for axial loads N Rk < N bal and, subsequently,
to a distinct decrease in the theoretical flexural strength depending on the slenderness.
This effect, which lies on the safe side, occurs with larger eccentricities and hence
essentially lies outside the current scope of applicability. The confined column cross-
section considered in the figures corresponds to the cross-section of the member in the
design example considered in the next section.

7.7 Analysis at Serviceability Limit State
When it comes to serviceability, appropriate requirements regarding the design and
detailing of strengthened reinforced concrete columns with a wrapping of fibre-reinforced
materials are not known. The Technical Report No. 55 of the Concrete Society [120] limits
the permissible compressive strain in the concrete to 3.5 ‰ , mainly in order to avoid a
brittle failure as a result of damage to already signi cantly stressed con ning measures in
the case of large longitudinal strains. As can be seen from Figure 7.5, the level of loading
on the strengthened column for such a strain, which corresponds to the theoretical ultimate
strain

ε cu2 ,

is already signi cantly higher than the load-carrying capacity of the