Inelastic Effective Length Factor of Nonsway Reinforced Concrete Columns

This paper proposes a new equation for the effective length factor (k-factor) for reinforced concrete columns in braced frames. The new formula is valid both for normal and high-strength concrete. The equation was obtained from a sensitivity analysis performed on a two-dimensional nonlinear finite-element numerical model that takes into account the inelastic behavior of the concrete columns (cracking, yielding, and second order effects). The numerical model was calibrated with 44 experimental tests performed by the writers' research group. A comparative study was carried out between the numerical model and different national design codes, displaying important differences with respect to all of them: the ACI code (from 37 to -3%), the Spanish code EHE (from 26 to -9.26%), and the Eurocode 2 (from 14 to -14%). It was decided to propose two additional simplified equations: one for checking and the second for design.