Structural analysis of cracked R.C. members subjected to sustained loads and imposed deformations

A structural analysis of cracked R.C. members under instantaneous or sustained loads and imposed displacements is presented. In the first part of the paper the problem of deriving feasible moment-curvature diagrams for a long term analysis of R.C. sections is approached in an exact way by using the Reduced Relaxation Function Method in state I uncracked and the method suggested by CEB in state II cracked. In both states the analysis of the main parameters governing the problem has shown that it is possible to describe the concrete creep behaviour in an approximate way by using the algebraic formulation connected to the Effective Modulus Method. In this way the calculations become quite simple and can be applied in design practice without introducing significant errors. Referring to continuous beams, the structural analysis is then approached in a general way, applying the Force Method and the Principle of Virtual Works. Finally, considering single members, the structural analysis is performed by means of a graphical procedure based on the application of feasible moment-rotation diagrams which allow to easily solve various structural problems and to point out the most interesting aspects of the long term behaviour of cracked R.C. members with rigid or elastically deformable redundant restraints.