Choosing Shear Wall Thickness: h/25 vs h/16 — What Should We Follow?

In seismic design, setting the right shear wall thickness is far more important than just passing code checks.

It’s about ensuring stiffness, strength, and ductility — the true foundations of seismic resilience.

Yet many engineers face a simple but serious question:

Should I follow ACI 318’s h/25 minimum, or SEAOC’s h/16 practice?

Let’s go deeper.

ACI 318 h/25 Limit

ACI 318-19 mandates that concrete walls must have:

• Minimum thickness = h/25

• But not less than 150 mm (6 inches).

where h is the unsupported story height.

This is the absolute minimum thickness — just enough to meet strength and basic stiffness requirements under code-based demands.

However, it does not guarantee excellent seismic behavior, especially for mid- to high-rise or irregular buildings.

SEAOC h/16 Practice

On the other hand, SEAOC Seismic Design Manuals and high-seismicity experts recommend:

• Minimum wall thickness = h/16.

This guideline is not code, but comes from real-world seismic performance experience.

It aims to enhance:

• Lateral stiffness,

• Crack control,

• Ductile energy dissipation,

• Story drift control.

Walls thinner than h/16 often show excessive cracking, inelasticity, and may compromise seismic behavior even if they satisfy code strength.

Quick Comparison

Source	Rule	Binding?	Purpose
ACI 318	h/25 (≥150 mm)	Mandatory (minimum)	Code compliance
SEAOC	h/16	Recommended (good practice)	Seismic resilience

Professional Judgment

In high seismic zones (SDC C, D, E, F):

• Following only h/25 risks underperforming walls under major earthquakes.

• Following h/16 (or even thicker for critical walls) provides better safety margins.

• For high-rise or core walls, thicknesses of h/12 to h/14 are common to ensure stiffness.

In short:

Design to h/25 to pass the code.

Design to h/16 to pass the real earthquake.

Conclusion

As modern structures become more complex, the depth of engineering matters more than ever.

Going beyond the minimum code requirement — by applying true seismic wisdom like the h/16 rule — protects lives, properties, and the long-term resilience of society.

Great engineers don’t just follow the rules —

They design for the realities behind the rules.

If you want, I can also create a small infographic summarizing this blog visually too (good for presentations, website, or posts).

Would you like me to add it?

(Should take just a minute.)