As with most building disasters, there are any number of “usual suspects.”
- Long-term degradation of reinforced concrete structural support. In this instance, due to water penetration in the parking garage.
- Corrosion of the reinforcing steel
- Settling of the land
- Insufficient reinforcing steel
- Possible corruption during construction and inspection
Last week one article discussed how the pool deck collapse could have taken down the building. Somehow ignored are once-mentioned vibrations from the rooftop and nearby construction. The rooftop vibration, apparently nonstop, was reportedly so bad that at least one of the residents was about to move. I keep recalling the images of the “pancaked building,” and that got me thinking,…. what about those vibrations?
The power of vibrations:
Vibrations can cause strange and powerful things. The principle of directing sound vibrations to destroy a brittle object is harnessed in lithotripsy, the procedure which breaks up kidney stones. Perhaps you recall the physics lectures on the Tacoma bridge collapse, a consequence of wind vibrations that matched the frequency of the bridge. But that bridge moved wildly side-to-side before it fell –so presumably, the physics there don’t apply to a building that collapsed on itself as did Surfside Towers. [1] But what of the operatic voice shattering a glass goblet that it hasn’t touched? That may be more relevant. How does that happen?
It’s based on the principle of resonant frequency.
What is resonant frequency?
“Resonant frequency is the natural frequency where a medium vibrates at the highest amplitude.”
Objects or systems vibrate naturally, even if we cannot see it. That’s called their natural frequency or resonance - the number of times an object moves back and forth in one second. Every object has a unique natural frequency.
When an external vibration or energy source has the same frequency as the target object, and they interact, the vibrational pattern of the target object amplifies – that’s called resonant frequency. Sometimes, the amplification is so great that the object self-destructs. Various external stressors or mechanisms can bestow their vibrational patterns on a target object – and if they match in frequency – watch out.
Acoustic Resonance
One source of external vibrational energy comes from sound, called acoustic resonance. What we perceive as “sound” is actually (acoustic) waves that move through the air and displace air molecules, causing tiny hairs in our ears to vibrate. When the (acoustic) waves are directed at an object, and the acoustic frequency of the waves matches the object's natural frequency, the latter starts to vibrate at a larger amplitude. When the sound’s volume increases, so does its amplitude or “vibrational power,” potentially disintegrating the structure it strikes.
“Volume is a key player in the glass shattering game, because the loudness of a sound is directly related to the extent it displaces air molecules.”
Multiple synchronous sound sources amplify sound’s “vibrational power” even further. We find this in synchronous cheering. A “taste” of the sound of the North Korean army marching – synchronously - can be heard here.
But according to Jeffrey Kysar, a mechanical engineer at Columbia University, for a diva to demolish a wine glass, there also needs to be inherent microscopic defects “big enough to buckle under pressure.” So, while vocal vibrations can crack a glass– if loud enough (over 100 decibels), it needs help from additional flaws in the glass’s composition.
Ground Resonance
Vibrations do not die; they fade away. But the rate at which they fade depends on where they are transferred. Sometimes an object’s natural frequencies are amplified when its vibrations strike the ground where the object comes to rest, triggering “ground resonance.”.
"Ground resonance" results when the vibrations of the object and ground create a feedback loop, each round echoing and amplifying the initial vibratory force of the striking object, like a frenzied ping-pong match that starts slowly. Here, the striking object transfers external vibrations to the ground, which reverberate back to the generating object, then back to the ground – each round amplifying the vibrational impact from the prior round. Think of a swing. Each circuit becomes more powerful, each feeding off the power of the previous “push.” Helicopters that don’t have good shock absorbers and strike the ground can self-destruct as the object ultimately crashes down on itself or self-mutilates by flinging its parts wildly about due to “ground resonance.”
Mechanical resonance
Mechanical resonance occurs when two objects touching each other vibrate together. Once again, when the vibratory patterns occur at the same frequency, their amplitude can increase to the point of destruction
Multi-system Resonance,
When two or more of these phenomena combine or combine with a structure that is defective and prone to breakage, the system’s vibration amplitude can increase 10 to 30 fold. The Angers Bridge, a suspension bridge in France, came crashing down by a combination of ground resonance and weak structural support. Four hundred eighty-three soldiers marching in (synchronous) lock-step exacerbated the bridge’s structural defects (water-related corrosion!), killing over 200 soldiers. That debacle resulted in the order for soldiers to break lock-step whenever crossing bridges.
The structural issues seem strangely reminiscent of Surfside: The Anger’s cable anchorages were surrounded by cement. But the cable wire strands separated from their cement surroundings, allowing water to penetrate and corrode the wires. But that structural weakness was insufficient; it took almost 500 pairs of synchronous marching feet to initiate the disaster.
Vibrations and Building Collapses
"Vibration will do anything. It would only be necessary to step up the vibrations … to fit the natural vibration of the building and the building would come crashing down." Nicholas Tesla
Buildings, too, have natural resonances. If the ground vibrates, as in an earthquake, for example, at the same frequency, the combination of the two forces will gradually escalate, eventually causing the building to come crashing down.
That resonance could topple buildings was proven by Nikola Tesla when he experimented with mechanical oscillators, what was called his “earthquake machine” –Tesla could actually seriously damage modern buildings using a small pocket-sized “vibrating machine,” such that onlookers claimed it felt like an Earthquake. In one “experiment,” he almost brought down a ten-story building in New York City. [2]
Surfside
The exact constellation of vibrational factors that might cause a pancake collapse, as seen at Surfside, is probably rare. I am aware of only one eerily anecdotal case report that seems comparable.
In that case, the structure was described as a double-walled edifice housing residential structures. The structural integrity of the walls of the building in question was also problematic. The walls, which were six thousand to nine thousand years old, were composed of stone and dried brick. No mortar ‘glued’ them together. In addition to their age, there is evidence of multiple repairs and water damage.
It was subjected to ground resonance when somewhere between 40,000 and 600,000 soldiers [3] marched around the structure daily for six days. On the seventh day, the circumlocution occurred an additional seven times. Augmenting the ground resonance of the soldiers were acoustic vibrations in the form of repeated trumpets blaring. (You can get a sense for the sound level, reproduced here), and finally the shouts of some 2 million people. While that might not sound particularly threatening, the loudest football crowd recorded a decibel level over 137 decibels, high enough to cause damage.
The report notes that the amalgamation of three vibratory forces (marching, trumpeting, and shouting) resulted in“the wall fell beneath itself.” [4] - language eerily similar to the situation at Surfside.
By now, dear reader, you must have figured out that I am referring to the Battle of Jericho – often discounted by contemporary theorists- because walls just don’t fall down like that.
Or do they?
Maybe, if subjected to multiple vibrational stressors coupled with a weak foundation, they just might. My longer description of the Battle of Jericho collapse can be found here.
[1] A good description of the physics involved in the Tacoma bridge case can be found here.
[2] “Nikola Tesla revealed that an earthquake which drew police and ambulances to the region of his laboratory at 48 E. Houston St., New York, in 1898, was the result of a little machine he was experimenting with …." the New York World-Telegram, July 11, 1935. Further information can be found here.
[3] Joshua ch. 4 v. 12-13; Numbers, ch 2.the total of fighting me of the entire nation (excluding the tribe of Levi) was 603,550.
[4] Joshua ch 6. v. 20, “Vatipol Hachoma Tachteha
