The application of FRP reinforcement in concrete structures is quite popular nowadays. In this article the cracking moment of flexural concrete structures reinforced by steel and FRP reinforcement bars is investigated. There is estimated that the behaviour of tensile concrete is nonlinear when crack opens. The nonlinearity was estimated by two different cases. In the first one the coefficient of elastic and plastic strain of tensile concrete were applied and in the second the stress-strain relationship were expressed by polynomial function. That function prepared according to compressed concrete stress-strain diagram described in design standard EN 1992-1-1. Those two different stress-strain relationships were used for cracking moment calculation. Also the cracking moment calculations were performed using mentioned standard EN and Technical building code STR 2.05.05:2005. In all cases the calculations were performed in assumption that the behaviour of compressed concrete is elastic when crack opens. The obtained results were analysed and presented base conclusions.

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