Strengthening of r.c. columns

The main advantages of FRP strengthening of concrete and masonry floors can be synthesized as follows  

An important application of FRP sttengthening on r.c. members is the strengthening of r.c. columns. In the case of stressed columns with central and normal stress or with a slight eccentricity, it can lead to an increase in strength and ultimate strain of 

5 Strengthening of Reinforced and Prestressed Reinforced Concrete Structures 

With values of axial strain equal to 0.2 %, the strain of confined concrete is only slightly greater than that of non-confined concrete, which is greater than its strength. 

The failure of an r.c. column confined with composite materials occurs following failure of the composite fibers. Moreover, due to the disaggregation of confined concrete, the column loses its mechanical features and, thus, its strength against transversal forces. In order to prevent this state of degradation of concrete regulations, there is a call for a limit value of fiber strain of 0.004. 

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Therefore, it is recommended that the local strengthening of r.c. frames should mainly focus on perimeter joints and columns, with a priority focus on comer ones. 

Thermou GE, Papanikolaou VK, Kappos AJ (2014) Monolithicity factors for the design of R/C columns strengthened with R/C jackets. In The 2nd European conference on earthquake engineering and seismology, Istanbul... 

Eurocode 8, Part 3 ( A.4.2, 2005), and the Greek Code for Interventions (KANEPE 2013) suggest the monolithicity factors presented in Table 2 to be used in the design of R/C members (slabs, columns, beams, and foundation system) when strengthened with additional reinforced concrete layers. In the case of Eurocode 8, Part3 ( A.4.2, 2005), the values of the monolithicity factors for columns of Table 2 should be used under the assumptions of (i) full composite... 

Vandoros KG, Dritsos SE (2008) Concrete jacket construction detail effectiveness when strengthening R/C columns. Constr Build Mater 22 264-276 Vassilopoulou I, Tassios P (2003) Shear transfer capacity along a R/C crack under cyclic sliding. In Proceedings fib symposium. Technical Chamber of Greece, Athens, paper no 271... 

An interesting example of the fiber-reinforced polymer (FRP) strengthening of reinforced concrete (r.c.) buildings is the stmctural adjustment of Hotel Boscolo Exedra in Nice, France. In order to achieve an increase of the live loads and a seismic adjustment of the structure, alongside traditional r.c. interventions, several carbon fiber-reinforced polymer (CFRP) strengthenings have been carried out on both the beams and the columns, as shown in Figs. 10.1,10.2, and 10.3. 

The analytical model presented in section Analytical Model for R/C Jacketed Columns explicitly accounts for the slip at the interface between the existing member (core) and the jacket. The transfer of normal and shear stresses in the interface between the external layers of the jacket and the existing member determines the composite action developed by the strengthened members (Thermou et al. 2007). An alternative to this approach is presented in section Simplified Analytical Expressions for R/C Jacketed Columns where simplified analytical expressions in combination with the monolithicity factors may be used for designing the retrofit scheme. 

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