AS 3600:2018 - Confinement Design of the Boundary Elements of RC Walls
1. Input Parameters
| Ductility Class of the Wall: |
| Number of storeys above the base of the building: |
As per Cl.14.6.2.2 of AS3600:2018, for structure of not more than 4 storeys above the structural base, boundary elements shall consist of "two N16 bars tied with an N12 U-bar or four N12 bars enclosed with R10 closed stirrups as shown in Figure 14.6.2.2". "Figure 14.6.2.2" which is shown below.
| Length of the Wall, Lw (mm): | |
| Thickness of the Wall, bw (mm): | |
| Characteristic Compressive Strength (f'c): | |
| Concrete Clear Cover (c): | |
| Number of Vertical Reinforcement along Thickness of the Boundary Element (nb): | |
| Diameter of Vertical Reinforcements (dv): | |
| Diameter of Stirrups (ds): | |
| Vertical Reinforcement Ratio or Spacing in mm: | |
| Design Axial Force (N*) in kN: | |
| Design Moment (M*) in kNm : | |
| Height of wall, Hw (mm): | |
| Clear Storey Height, hs (mm): |
1. Summary of Input Parameters
2. Results: Reinforcement Details
Confinement Design of the Wall Boundary Element
The confinement demand (fr,demand), and confinement capacity or effective confining pressure (fr.eff) in the boundary element are determined from Equation 1 and Equations 2-6, respectively, following Cl.10.7.3 of AS3600:2018. In the equations, the wall thickness 'ds', wall clear cover 'c' and diameter of stirrups 'ds' are used from the user defined input, and the length of boundary element 'Lbe)'is calculated as max(1.5bw, 0.15Lw), and the stirrups spacing (S) in the boundary element is determined from lesser of [0.5tw, 8dv, 24ds, 200, spacing corresponding to fr,demand ≥ 0.01f'c]. The effective area of confinement is shown in Figure 3.
$$ {fr_{demand} = 0.01f'_{c}}\tag{1}$$
$$ {b_{c} = L_{be} - 2c - d_{s}}\tag{2}$$
$$ {d_{c} = b_{w} - 2c - d_{s}}\tag{3}$$
$$ {k_{e} =(1-\frac{nw^2}{6b_{c}d_{c}})(1-\frac{s}{2b_{c}})(1-\frac{s}{2d_{c}})}\tag{4}$$
$$ {f_{r} =\frac{min(n_{b},n_{d}) \times A_{b,fit} \times f_{sy,f}}{d_{s} \times s}}\tag{5}$$
$$ {f_{r.eff} =k_{e} \times f_{r}}\tag{6}$$
Figure 3. Confined concrete area in the wall boundary region.
'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 fitments,
'Ab.fit' is the cross-sectional area of one leg of the fitment,
'n' is the number of laterally restrained longitudinal bars in the boundary region,
'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.
Table 1: Comparison of the confinement capacity and demand (0.01f'c).