Review and Discussion of Proposed Changes to ACI 318-02 Slender Column Provisions

Abstract

ACI Committee 318 (Standard Building Code) established some time ago a Slender Column Task Group that was charged with formulating code provisions, to streamline, and if possible, to simplify the current requirements on slender column design in the ACI 318-02 code. Proposed revisions by the Task Group were presented in documents labeled CTG3.1 and CTG3.2. The Task Group has made a considerable revision effort, both with regard to layout and reduction in the volume of provisions, and also with regard to technical content. A major change is the proposed combination into one of the two currently separate sections on moment magnification for the nonsway and sway cases. This change simplifies the presentation and make the provisions easier to comprehend. The stiffness provisions would seem to have become more complex, on the other hand. It is further proposed to adopt a moment magnifier expression of an earlier code version. Other revision proposals concern effects of sustained loading, safety aspects through the stiffness reduction factors, and lower slenderness limits. In the present report, a review is made of, and comments are provided to, major items in the revision proposal. The rationality of some of the proposed changes are questioned.