Compression reinforcement

In general, the elasticity modulus and the stiengthof FRP bars in compression seem to be significantly lower than their counterparts in tension, particularly for GFRP and AFRP bars. For that reason, and also because only a limited number of studies have been performed on the compressive behaviour of FRP bars, their use in columns or as compression reinforcement of members in flexure is not recommended (ACI Committee 440, 2006). 

For a rectangular section of width b with compression reinforcement, the ultimate unit resisting moment is... 

Rectangular Sections with Tension and Compression Reinforcement with Moment Redistribution Applied (Based on the UK Annex to EC2)... 

The enhancement of strength usually leads to a reduction in ductility, unless special measures are taken (e.g., in reinforced concrete elements, the increase of the tensile reinforcement should be in principle accompanied by a sufficient increase of the compression reinforcement and of confinement). 

---