Trilinear FRP model - frp_tl

This is a simplified uniaxial trilinear FRP model that assumes no resistance in compression.

Four model calibrating parameters must be defined in order to fully describe the mechanical characteristics of the material:

Tensile strength - ft
This is the tensile strength of the frp material. Its value usually oscillates between 2100 and 4800 MPa for carbon-based fibres, between 1900 and 4800 MPa for glass fibres, and between 3500 and 4100 MPa for aramid fibres [fib, 2001; 2006]. The default value is 3000 MPa.

Initial stiffness - E1
This is the initial elastic stiffness of the frp confining material. Its value usually oscillates between 215 and 700 GPa for carbon-based fibres, between 70 and 90 GPa for glass fibres, and between 70 and 130 GPa for aramid fibres [fib, 2001; 2006]. The default value is 300 GPa.

Post-peak stiffness - E2
Upon rupture, frp material looses its strength in abrupt fashion; i.e. it features an infinitely high value of post-peak negative stiffness. In order to warrant numerical stability, however, the possibility of assigning a finite post-peak stiffness is herein given, which is thus employed to "take" the material from peak to zero tensile strength. The default value is -500 GPa.

Specific weight -
This is the specific weight of the material. The default value is 18 kN/m3.