Effects of Mix Property On Time Dependent Behavior of Reinforced Concrete Slabs


A nonlinear, layered, finite element model for predicting the time dependentbehavior of reinforced concrete slabs under sustained transverse loading ispresented. The effects of biaxial creep and shrinkage are considered by usingthe provisions of ACI Committee 209. Both elastic- perfectly plastic and strainhardening plasticity approach have been employed to model the compressivebehavior of the concrete. The yield condition is formulated in terms of twostressinvariants. The movement of the subsequent loading surfaces iscontrolled by the hardening rule, which is extrapolated from the uniaxialstress-strain relationship defined by a parabolic function. Concrete crushing isa strain controlled phenomenon, which is monitored by a fracture surfacesimilar to the yield surface. A smeared fixed crack approach is used to modelthe behavior of the cracked concrete, coupled with a tensile strength criterionto predict crack initiation. An attention is given also to the post-cracking shearstrength. The steel is considered either as an elastic perfectly plastic materialor as an elastic-plastic material with linear strain hardening. Steelreinforcement is assumed to have similar tensile and compressive stress-strainrelationship. A computer program coded in FORTRAN77 language is writtento implement the present study. This program is arranged to give a completelisting of stresses and deformations in every concrete or steel layer. Severalexamples for which experimental results are available are analyzed, using theproposed model .The comparison showed very good agreement especially forthe maximum deflection, the different about 1%.