Earthquake Performance

Although I’m not an expert at all on earthquakes, there are consensual numbers that describe their behavior.  Ground turns into a wave with a frequency (cycles per second) and an amplitude (the vertical up and down) that the ground is heaving.  An accepted frequency for substantial earthquakes is 20 Hz, which means 20 cycles per second.  That means a wall will be going up and down and side to side 20 times per second.  An accepted amplitude is 4 inches, meaning the whole building will be forced up and back down 4 inches, 20 times per second.  That sounds and is pretty violent and it’s no wonder so many buildings collapse with tragic results for occupants.

As far as this system would behave, there is some simple arithmetic.  There may be other aggravating factors that I don’t know.  Ductility is the key to building survival.  Being ductile means a material that is stretched and then compressed a particular amount and then goes back to its original shape without damage. That amount is called strain and of course depends on the magnitude of force acting on it and its stiffness.  Just for the heck of it, the fancy name they give it is “Modulus of Elasticity”.  Ductility also means adjacent building components being able to move against each other, sliding, so that motion is a force dissipation. 

In a two story building, for example, there may be 12 to 16 rows of system panels high.  The panels are not bonded together  (they are keyed by splines fit into slots) but encased by any concrete columns and beams that compose the structural load carrying system.  These beams and columns are what need to stay intact as long as possible to allow escape from the building and hopefully its survival. Each joint between the panels are vertical and horizontal slip joints which can dampen the earthquake force.  Dampen in this context means dissipate.  A four inch amplitude of vibration would be distributed over 16 rows vertically.  The action on each row would be 4” divided by 16 rows or a quarter inch per row.  That may significantly reduce the vulnerability to collapse.  And then horizontally, the same phenomena would occur again distributing destructive forces.

A post tensioned concrete roof, of minimal thickness, would act as a diaphragm to further distribute forces over all the structural members.  I may be completely wrong in this understanding but to me the basic principle is sound.  Another huge factor is the expanded steel attachment between the wall faces.  Under ordinary circumstances it is rigid and very strong.  Under catastrophic conditions it is very ductile meaning it can bend and twist to a very large degree without failing.  There is truly three dimensional ductility inherent in this system.  That could be a huge life saver.

Another unexpected contributor is that the connecting pvc splines, as the wall deteriorates out of alignment, will lock into their slots with a cam pinching action to activate the splines tensile strength.  It's tensile strength is around 5,000 psi so with a cross sectional area of 0.2 sq inches another thousand psi of resistance is called into action. 

So that can be a bonus with the cozy system to dissipate forces where the cast in place mates into the panel voids on the interior wall

Yes, exactly. That interface can act as an engineered energy dissipation mechanism when properly detailed.

In traditional structural engineering, cold joints or shear planes are often viewed strictly as potential failure points. However, in an insulated cavity or precast panel system, the controlled interaction between precast concrete and cast-in-place (CIP) core/void infill offers unique structural advantages during a seismic event:

Key Structural & Energy Dissipation Advantages

1. Controlled Micro-Yielding & Energy Absorption

• Unreinforced or rigidly monolithic concrete is brittle—it tends to crack suddenly when ultimate strength is exceeded.

• In a system where CIP concrete keys into panel voids, the interface acts as a controlled boundary. Under severe ground motion, microscopic slip or localized micro-cracking along this interface can actually absorb and dissipate kinetic energy (similar to friction dampers), reducing the seismic force transmitted to the rest of the superstructure.

2. High Shear Transfer Through "Concrete Keys"

• When CIP concrete flows into formed voids, cores, or pockets within precast panels, it creates mechanical shear keys.

• Even if the immediate surface adhesive bond breaks during cyclic shaking, the structural load is instantly transferred to physical interlocking (shear friction). The concrete keys physically block the sections from sliding past one another, providing substantial residual shear resistance.

3. Redundant Load Paths & Confined Core Action

• Cast-in-place concrete placed inside interior panel voids operates under three-dimensional spatial confinement provided by the surrounding panel walls.

• Confined concrete exhibits significantly higher compressive strength and ductility compared to unconfined concrete. During seismic shaking, even if localized interior bond detachment occurs, the core remains structurally sound and continues to transfer axial and shear forces safely.

Design Considerations to Maximize Performance

To ensure this boundary acts as an advantageous energy absorber rather than a structural flaw, standard concrete design principles emphasize:

• Intentional Surface Roughness: Leaving the interior surface of the panel voids rough or textured (typically a aggregate-revealed finish) maximizes mechanical friction once the initial chemical bond breaks.

• Continuous Reinforcement (Dowel Action): Steel rebar extending from the CIP cores into the surrounding panel elements bridges the interface. This ensures that after initial interfacial movement, the steel engages in tension and shear, preventing catastrophic separation and providing post-yield ductility.

yet that is what the embedded steels will do spanning across the wall cavity

That is precisely where dowel action and shear-friction theory come into play.

When high-strength steel rebar bridges the cold joint between the cast-in-place (CIP) core and the panel walls, it alters how seismic forces are handled once the initial concrete-to-concrete adhesive bond breaks.

How Embedded Steel Converts Shear into Ductile Energy Dissipation

1. Shearing and Dowel Action

• As lateral seismic motion attempts to slide the CIP core relative to the panel face, the embedded rebar is subjected to direct cross-sectional shear (dowel action).

• Steel undergoes plastic deformation (yielding) before it fails, which absorbs a substantial amount of kinetic energy from seismic waves without a sudden, brittle fracture.

2. Clamping Force & Shear Friction

• When lateral displacement causes micro-cracking at the interface, the concrete surfaces try to ride up over each other's roughness, forcing the joint slightly open (dilatancy).

• This expansion stretches the rebar crossing the gap, putting the steel in high tension.

• In response, the tensioned steel pulls the concrete faces back together with massive clamping force. This dramatically increases the physical friction between the rough concrete surfaces, preventing bulk sliding.

3. Progressive Force Transfer Strategy

Instead of a rigid, brittle structural element that snaps under extreme load, a steel-bridged cavity interface acts as a multi-stage system:

Stage

Interface Behavior

Primary Load Mechanism

Stage 1 (Normal Operations)

Full structural rigidity.

Chemical adhesion & micro-interlock.

Stage 2 (Minor-to-Moderate Seismic)

Initial micro-bond yield; friction engages.

Shear keys & surface friction.

Stage 3 (Severe Seismic Event)

Interfacial sliding & micro-cracking.

Steel dowel bending + high clamping tension.

Design Optimization for Embedded Ties

To ensure the steel performs reliably across the cavity interface:

• Sufficient Embedment Depth: Steel ties must be anchored deep enough into both the panel shells and the core void to prevent pull-out (development length failure) before the steel reaches its yield strength.

• Ductile Steel Grade: Utilizing high-ductility rebar ensures the steel bends and stretches under cyclic load without breaking prematurely.

• Corrosion Protection: Ensuring the steel bridging the gap is properly encrusted in the cementitious matrix prevents moisture penetration at the cold joint boundary over time.