ACI 318-19
ACI 318-19 Section 18.10 | Special Structural Walls (Seismic)
Special structural walls in high seismic zones must maintain their strength during severe earthquakes. This requires confinement elements at the wall boundaries when compression stresses become too high under overturning moments.
Governing Formula
Variables
Nominal shear strength of special structural wall
lb or N
Gross area of concrete section bounded by web thickness and length
in² or mm²
Coefficient defining the relative contribution of concrete strength
unitless
Ratio of area of distributed transverse reinforcement
unitless
Quick Example
1
Determine aspect ratio
Calculate hw/lw to find the coefficient αc. If the wall is short (hw/lw ≤ 1.5), αc is 3.0. For tall walls (≥ 2.0), it is 2.0.
2
Calculate steel contribution
Find the shear strength provided by horizontal steel.
3
Check limits
Ensure the total shear strength doesn't exceed the absolute maximum allowed.
When does this govern?
Boundary element confinement requirements usually govern the design detailing over raw shear strength in mid-rise and high-rise building cores.
Common Mistake
Neglecting to check if special boundary elements are required using the extreme fiber compressive stress rules.