A south Korean military commando smashes a heap of stone plates in Seoul in 2010. 

Photo through Park Ji-hwan/AFP/Getty Images

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You are watching: How much force to break concrete

Answer through Isaac Gaetz, structural engineer, existing Brazilian jiu-jitsu practitioner, previous Wushu and childhood Shotokan karate student:

It is really a basic trick once you know the problem from a structural engineering perspective. The trick is composed of a moderate quantity of power and speed and a many careful an option of the target material and also geometry.

The block are generally unreinforced concrete “soaps” or pavers v a thickness of around an inch, a width of 8 inches and also a length of 16 inches. The blocks are set to expectancy the long means between two supports and are struck as close come dead facility as possible. The blow from the martial artist creates bending emphasize in the block. From product science we understand that when subjected to bending stress, one unreinforced concrete block the this thickness has really low strength. The observable habits will be a anxiety crack that develops on the opposite next of the surface ar being struck. The crack conveniently (instantaneously come the nude eye) propagates through the block and you are left with two pieces.

Crunching some fast numbers, i compute that it would, ~ above average, take around 125-175 lbs that static pressure to break among these blocks in this manner. Without any other reference, this may sound favor an superior feet, however consider that this is frequently less 보다 the athlete’s own weight; if he simply stepped onto the block that would perhaps snap. Heavyweight boxers have been understand to hit with as much as 1,000 lbs that force, in a an ext difficult, horizontal direction, when martial artists frequently go therefore far regarding employ a jump before striking the blocks. The biggest challenge for the typical martial arts athlete to rest a single concrete block is psychological, if he mentally commits and strikes through a full-force blow and also has great follow-through after ~ impact, he’ll quickly break the block.

You’ll an alert that in instances where a thicker concrete piece is broken, that is never one heavy concrete block—it is always a ridge of the very same thin blocks. Furthermore, if friend look closely, you frequently see the martial artist place small pebbles, seeds, or other spacers between the blocks. This enables the force to easily transfer together the blocks rest progressively. For this reason, breaking multiple blocks just takes marginally an ext force than breaking one. They space breaking choose a collection of dominoes, not prefer a solitary superthick block. Breaking an actual thick block would be much, much harder and also is rarely, if ever, done. Add even a small amount of stole rebar reinforcing come the block and it will certainly be utterly impossible to rest by hand.

Something similar is done v board breaking. The board are frequently pine 1 inch by X (actual thickness 3/4 inch) material, around 12 inches square, and also they are damaged along the grain lines. The strength along the serial is just a tiny portion of the strength across the grain. This is a result of the cellular structure of the wood. One analogy for wood grain is the it operation in lengthy strawlike tubes. Trying to break a board across the grain is favor trying come chop with these straws,while breaking follow me the serial is just sliding your hand in between the straws and separating the straws indigenous one another. This is relatively easy come do, as lumber fibers are only bound v a fairly weak natural glue. Comparable to bricks, breaking a solitary solid plank is lot more complicated than a series of boards through the same complete thickness.

Occasionally you’ll view someone break a thicker piece of wood, such together a 2-by-4 across the grain. This is a much much more impressive feet; in this situation you’ll see that he usually does this through a much much longer piece of wood, possibly 3 feet or 4 feet in length. The longer span helps compensate because that the special material and cross-grain breaking, however it is still generally evident from the artist’s own exertion that this is a much much more forceful and sometimes pains blow. Do the efforts to rest a knot-free board the is even a tiny thicker, such together a 4-by-4, in this manner, will certainly be basically impossible.

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So why nothing concrete pavers break every the time once we go on them? Simple: They room supported top top a constant bed the sand, so they only experience compression forces, i m sorry they space well-equipped to handle.