Minimum Eccentricity in the Ultimate Strength Analysis

Abstract

The nominal allowance for eccentricity due to construction tolerances as specified in three different codes of practice (ACI 318-77, CP 110, and CEB-FIP Model Code) was studied and compared with actual values of construction errors measured on building sites. It was found that the three specifications do not compare favourably with one another, neither do they agree very well with site results. Some inherent flaws in the way these codes specify the nominal eccentricity was also discussed. An alternative specification was then proposed which not only corrects these flaws but also compares favourably with site results. Unlike in the three codes referred to above the proposed specification may be built-in into the design formulae and it was shown that this simplifies the ultimate strength design formulae. Finally, this alternative proposal was utilized to develop a set of formulae which allow for a uniform approach to the design of concrete sections under different combinations of bending moments and axial loads.