Program AU3a – AS3600 ductile design tools: RC column
Confinement Design and Detailing of RC Column
Confinement Design and Detailing of RC Column
1. Input Parameters
Depth, Dc (mm) [Larger Cross-Section Dimension]:
Width, Bc (mm) [Smaller Cross-Section Dimension]:
Concrete Clear Cover (c):
Characteristic Compressive Strength (f'c):
Number of Vertical Reinforcement along Width (nb):
Diameter of Vertical Reinforcements (dv):
Diameter of Stirrups (ds):
Vertical Reinforcement Ratio (Pv ≥ 0.01):
Design Axial Force (N*) in kN:
Design Moment (M*) in kNm (at least 0.05N*xDc):
Moment Magnifier to include Slenderness (𝛿b):
Clear Length of the Column, Lu (mm):
Table 1: Summary of input parameters.
Figure 1. Diagram of design moment vs design axial load of the column.
2. Results
I. Confinement Design
The confinement demand (fr,demand), and capacity or effective confining pressure (fr.eff) are determined from Equation 1 and Equations 2-6, respectively, following Cl.10.7.3 of AS3600:2018.
The confinement parameters used in these equations are shown in Figure 2. The stirrups spacing in the special
confinement region is determined as follows:
a). For Lu > 5D, spacing = min [0.6b, 15dv, 300, spacing corresponding to fr,demand ≥ 0.01f'c];
b). For Lu ≤ 5D, spacing = min [0.5b, 8dv, 24ds, 300, spacing corresponding to fr,demand ≥ 0.01f'c].
Where, 'Lu' is the unsupported/clear length of the column; and 'D' is the overall depth of the cross-section in the plane of bending.
Figure 2. Confined concrete area for column.
$$ {fr_{demand} = 0.01f'_{c}}\tag{1}$$
$$ {b_{c} = B - 2c - d_{s}}\tag{2}$$
$$ {d_{c} = D - 2c - d_{s}}\tag{3}$$
Where,
'ke' is an effectiveness factors accounting for the arrangement of the fitments,
'fr' is an average confining pressure on the core cross-section taken at the level of the fitments,
'bc' and 'dc' are core dimension measured between the centre-lines of the outermost fitments,
'Ab.fit' is the cross-sectional area of one leg of the fitment,
'n' is the number of laterally restrained longitudinal bars,
'nb' and 'nd' are the number of fitment legs crossing each confinement plane,
'w' is average clear spacing between adjacent restrained longitudinal bars,
'fr.eff' is the effective confining pressure.
Figure 3. Cross-section of the column showing details of the vertical reinforcements and stirrups.
Table 2: Comparison of the confinement capacity (optimal solution) and demand (0.01f'c).
II. Length of confinement/critical region:
$$ {l_{cr} = max(1.2D, L_{cl}/6})\tag{7}$$
The largest cross-sectional dimension of the column 'hc', and the clear length of the column 'lcl' are defined in the input section.
Figure 4. Elevational view of the column.
3. References:
Standards Australia (2018). AS 3600:2018 Concrete structures.
Disclaimer: "The authors assume no responsibility for any injury, damage, liability, negligence and/or otherwise to any individual or property from the use or application of any of the methods, products, instructions, or ideas contained in the material herein."