This paper presents a numerical model which is capable of predicting the behavior of
fibrous prestressed concrete beams and frames subjected to cyclic loads. The stiffness method with
the effective secant stiffness is used here in analyzing plane structures, while the analysis of member
cross sections that are subjected to cyclic loads is carried out in combination with the layered section
approach. Material nonlinearity has been taken in to consideration through the analysis of these
sections. This method deals only with axial forces and bending moments neglecting the effect of
shear forces. The study presents a program written with MATLAB language that analyzes structures
by the STIFFNESS method and divides the cross sections into small layers in order to utilize the
nonlinearity of the stress distribution along the section depth. The results at each section are
moments, curvatures, displacements, forces, stresses and strains under each load cycle. A cyclic
model for fibrous concrete subjected to uniaxial compression or tension has been proposed. Also the
cyclic model of Menegotto and Pinto for conventional and prestressing steel has been adopted. Full
bond between steel and concrete is assumed.
The study shows that the prestresssing force in concrete members has reduced the
ductility or capacity of energy dissipation, while a noticeable increase in the member failure load is
recorded. Moreover, the existence of steel fibers in concrete enhances its stiffness, delays the cracks
The scheme of and then narrows their openings in tension zone and decreases their negative effect.
the layered section presents more reliable stress distribution on the cross section of the concrete
Keywords: Concrete, Cyclic Load, Frames, Prestress , Steel fiber.