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.