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With the steel couplers at 12" horizontal x 16" vertical centers while using the cellular concrete as the interlocking infill, you have effectively created a hybrid structural system.

In this configuration, your wall is no longer just a "modular" assembly held together by infill; it is a reinforced panelized system.

The Hybrid Structural Mechanism

When the cellular concrete fills those cavities, it acts as a secondary structural matrix that bridges the distance between your mechanical steel couplers.

• Load Distribution: The steel couplers provide the necessary high-tensile connection to resist "peeling" or suction forces (the most common cause of envelope breach in extreme wind events).

• The Infill "Web": The cellular concrete, once cured, effectively acts as the structural web between the two faces of the wall. Because your couplers are on a 12x16 grid, the cellular concrete is confined into "cells" or "pockets."

• Arching Action: Because the panels are roughened and the cellular concrete is a cohesive mass, the wall will exhibit arching action under uniform wind pressure. The load is transferred from the panel to the cellular concrete, which then transfers the load to the steel couplers.

Why This is Robust for Tornado Resilience

1. Redundancy: Even if the cellular concrete were to experience minor cracking under extreme vibration (typical of high-wind events),the steel couplers are still independently holding the two structural faces of the wall together. You have a fail-safe.

2. Increased Mass and Damping: While cellular concrete is lightweight, it adds sufficient mass to the wall assembly to reduce the amplitude of vibrations caused by buffeting wind forces—potentially reducing the fatigue stress on your couplers over time.

3. Containment of Debris: The continuous nature of the cellular concrete core provides a solid backing that helps prevent localized penetration. If debris strikes one side, the cellular concrete spreads the force over a larger area of the rear panel, preventing a clean-through breach.

Engineering Validation Note

Since your steel couplers are already proven at 700 lbs, you are in a very strong position for your ICC Evaluation Report. When you present this to your engineering partners for the FEA, you should frame it as a "Mechanically-Tied, Cellular-Filled Composite Wall."

You should specifically ask them to verify:

• The Composite Stiffness: Does the addition of the cellular concrete increase the overall flexural rigidity ($EI$) of the wall compared to the panels alone? (It almost certainly will).

• The Effective "Tributary Area": Does the current 12" x 16" coupler layout allow the cellular concrete to remain effectively confined without "bursting" the joint under maximum expected pressure?

Given that you are using 14.7 pounds-per-square-foot modular panels and these established coupler spacings, does your engineering firm see any risk of the cellular concrete weight causing bulging in the lower courses during the pour, or are your jigs holding the geometry strictly enough?