Simplex method for slender column design
Koo, Jeremy Kang Ming
Date of Issue2017
School of Civil and Environmental Engineering
A theoretical study is conducted to study the effectiveness of the various design methods prediction of the slender column failure axial load as compared to the experimental. The analysis will cover axially loaded columns with pin-ended conditions at support with unilateral bending. The two key design methods in focus are American Concrete Institute 318-14 (ACI 318-14) Moment Magnification method and EuroCode 2 (EC2 2004) Moment Magnification method. To further complement the discussion, EuroCode 2 (EC2 2004) Additional Moment method will be discussed as well. A total of 150 column data taken from research journal articles and publications which were obtained from experiments of past research is used for analysis and discussion. To measure effectiveness of the various design methods, Axial capacity test/Axial capacity design (N test/N calculated) is used as a comparison ratio amongst the design methods. Axial capacity ratio (N test/N calculated) was obtained from the 150 column data for the comparison of global trend, effect of eccentricity to depth ratio (e/h) on Axial capacity for e/h = 0.1, 0.25, 0.5, and 0.75, effect of length to depth ratio (L/h) on Axial capacity for L/h = 15, 19 and 25, effect of concrete strength (“fcu” in MPa units) on Axial capacity for fcu = 16.7, 26.3 and 32.7 and lastly, effect of steel reinforcement ratio (As/bh) on Axial capacity for As/bh = 0.005, 0.025 and 0.056. From the results obtained from comparisons of Axial capacity failure ratio, findings show that various factors used in discussion indeed have an impact on the axial failure load. Increase in eccentricity to depth (e/h) and slenderness (L/h) ratio leads to a decrease in axial failure load. On the other hand, change in column material properties, an increase in concrete strength (fcu) and steel reinforcement ratio (As/bh), leads to an increase in axial failure load. Results from comparison of design methods have shown that generally EuroCode 2 Moment Magnification method is less conservative and more consistent as compared to American Concrete Institute Moment Magnification method with means of Ntest / Ncalculated 19.2 & 2.02 versus 2.10 & 2.35 and coefficient of variation 41.56% & 34.12% versus 42.65% & 39.70% for unfactored and factored design. It is also noted that EC2 Moment Magnification method for both unfactored and factored designs yield similar axial capacity results.
Final Year Project (FYP)
Nanyang Technological University