The drawing below is from Gustave Eiffel's book describing the tower that bears his name. There are 53 of them in total.
XXXII. Determination of the resistance of the lower part
This technical board is a calculation board, expressed in various forms. There is the diagram of the sharp forces and the resistance of the rafters to the forces of the wind. Here we are in the heart of the calculation of the resistance of the Eiffel Tower.
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