I have a 10m column, 1m dia 10mm thick. I need stiffen it by filling it with grout. How do I model that combined property? One member with the equivalent stiffness (not sure how) or model an unreinforced conc column and put rigid links to the steel column?
SSRC[20] proposed a modified elastic modulus that is the sum of the moduli of elasticity for the steel and concrete, with a reduction factor of 0.4 imposed on the initial modulus of the concrete to account for creep and tensile cracking. This has been adopted as a design recommendation in, for example, AISC[21]. Other authors have proposed summing the individual rigidities of each component material[25*], which generally matches better with experiments and is thus appropriate for representing initial axial stiffness in a linear or nonlinear analysis[15*]. Stability behavior of CFTs is summarized in ref.[26].