A New Simplified Method of Time-dependent Column Shortening Analysis in Concrete Moment Frames

Excessive column shortening in conventional one-step analyses is one of the most important aftereffects of ignoring the real behavior of concrete columns. This real behavior could only be achieved by staged application of gravity loads considering the long-term inelastic strains of concrete. Thereupon, consideration of adaptation between high-rise reinforced concrete structures’ design and practical stages of construction has always been staunchly held forth by researchers. Neglecting the fact above may lead to serious incorrect outcomes of analyses especially in high-rise structures. Some of these adverse structural effects are extra induced bending moments in beams, expansion of progressive cracks in second or non-structural elements, and wasting the intended capacity for structural elements in the design stage. This paper deals with comprehensive nonlinear staged analyses of structures with various geometrical specifications and represents simple empirical equations to evaluate column shortening caused by creep, shrinkage, and time changes of modulus of elasticity in such a way that the proposed relations could be independent of conventional variables of CEB-FIP code. Results of validation process show high conformity of all proposed equations for up to 30 floors and also demonstrate the accuracy of proposed shrinkage relation even for the structures higher than the aforementioned limit.