Doubled beams and experiments on the force of blows
How to build a reinforced beam with corbels, and studies of hammer-blows and percussion.
Leonardo specifies how to make a doubled (reinforced) beam: two beams joined, one braccio high and no longer than sixteen braccia, with notches one-sixth deep every two braccia, resting on oak corbels; seen end-on the section reads as two squares over a third. The rest of the sheet studies blows: a blow struck by another blow (a second hammer driving the first) is far stronger than a single motion, a supported horse's bone breaks when struck at its middle, and a falling weight produces a motion equal to one made by force. He also notes that the struck side of a body suffers more than the far side (a stone struck in the hand), and that the smaller a nail's tip is relative to the hammer, the deeper it drives for the same blow.
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How to build a doubled beam on corbels
Two beams are joined into a doubled beam one braccio high and no more than sixteen braccia long, half a braccio the other way, with notches one-sixth of a braccio deep every two braccia and a one-sixth rise at a n. The corbels are half the width of the reinforced timber and must be of oak, or the notches will not last.
A blow doubled in a single motion
The motion of a blow has greater effect than any other movement, so a blow driven by the motion of a second blow is much greater than a blow made by a single movement. The sketch shows a sledgehammer propped on a nail while a second hammer strikes its handle.
A supported bone breaks under a blow from above
Prop a horse's bone a quarter-braccio above an ax head on a wisp of straw and strike its middle with your fist or a tight sheaf of straw, and the bone breaks under the blow given from above.
A falling weight equals a blow made by force
Leonardo states that the motion made by a falling weight is equal to the motion made by force. The accompanying sketch shows a hammer driving a knife partway through a round object.
The struck side suffers more than the far side
A body receiving a blow is less damaged on its opposite side than on the side struck: a stone struck in a man's hand hurts his hand less than if the hand itself received the blow. The sketch shows a hammer striking a brick held in a man's hand.
A fine nail-tip drives deeper than the hammer
For a blow of equal movement and force, the smaller the nail's tip is compared to the hammer head striking it, the more deeply it is driven into the board than the hammer would be.