Title:
Nonlinear EI Equation for Slender Reinforced Concrete Columns
Author(s):
Timo K. Tikka and S. Ali Mirza
Publication:
Structural Journal
Volume:
102
Issue:
6
Appears on pages(s):
839-848
Keywords:
columns; load; moment; reinforced concrete; stiffness
DOI:
10.14359/14792
Date:
11/1/2005
Abstract:
The ACI Building Code permits the use of a moment magnifier approach for the design of slender reinforced concrete columns. This approach was introduced into design practice to eliminate the need for extensive calculations, based on the solution to a differential equation, to compute second-order bending moments in columns. The moment magnifier approach is influenced by the critical buckling load Pc. The computation of Pc is strongly influenced by the effective flexural stiffness EI, which varies due to the nonlinearity of the concrete stress-strain curve, creep, and cracking along the length of the unsupported column. This study was conducted to examine the influence of different variables on EI used for the design of slender, tied, rectangular reinforced concrete columns in braced frames under short-term loads and also to examine the existing ACI EI equations. Over 11,000 isolated square reinforced concrete columns, each with a different combination of specified properties of variables, in symmetrical single curvature bending, were simulated to generate the stiffness data. A new nonlinear design equation to compute EI of reinforced concrete columns was then developed from the simulated stiffness data and is proposed as an alternative to the existing ACI design equations for EI.