tesi A. Caggiano.pdf - EleA@UniSA - Università degli Studi di Salerno

Chapter 1. Introductionsumed due to the very reduced extension of the compressed region. The same assumptioncan be taken for slabs.In case of serviceability limit states analysis, the constitutive relationship adopted forplain concrete in uniaxial tension, can be also used up to the peak strength f ct . Then,in post-cracking regime, the multilinear laws proposed in Figure 1.9d are considered.The post-cracking residual strength is defined by means of two points correspondingto (ɛ SLS , f F t sd ) and (ɛ U LS , f F tud ), where ɛ SLS and ɛ U LS are defined according to theconsidered limit states as outlined by the fib Model-Code [2010a].Partial safety factorsBased on the stress-crack opening displacement relationship reported in Figure 1.12and used for the ULS-design, the following strength values must be considered indesignf F t sd = f F t skγ F(1.7)andf F tud = f F tukγ F(1.8)being f F t sk and f F tuk the characteristic values for the strength values given in Eqs.(1.3) and (1.4). The values for the material partial safety factors γ F are recommendedaccording to the fib Model-Code [2010a]:• FRC in compression: γ F as for plain concrete;• FRC in tension (limit of linearity): γ F as for plain concrete;• FRC in tension (post-cracking residual strength): γ F = 1.5.Finally, for serviceability limit states, the partial factors should be taken as 1.0.Design of FRC membersThe above constitutive laws and post-cracking strengths are then used for design rulesas outlined in the “PART III: DESIGN” of the fib Model-Code [2010b]. For the sake of22