Human Cantilever
A
Demonstration Devised by Benjamin Baker
Royal Institution Lecture (1887)
The
Forth Railway Bridge designed by John Fowler and Benjamin
Baker was a bold application
of the cantilever principle at a time when it had been used for only
two
decades by modern engineers for major bridges.
The background shows a diagram
the Forth
Bridge drawn to the same scale as the human cantilever. Two men sat
with their chairs positioned in front of the main piers on the diagram
they
represented. They were flanked by piles of bricks that simulated the
anchor piers. The outspread arms of the seated men were supported by
wooden struts from each hand butted against their seat. The tops
of the two outermost ends of the sticks were steadied by ropes down to
the anchorages. A central span was suspended between the top ends
of the sticks held by the two men's inner hands.
This arrangement easily
supported the weight of a third person, seated
on the central span. A consideration of the perfect balance
of forces involved recognises that the arms and ropes carry
tension forces, whereas the torso of each man and the wooden
struts carried compression forces.
In recognition of the ancient
origins of the cantilever design attributed
to the Far East, Fowler chose a young
Japanese to be supported on the central span for the focal point of
the demonstration. Kaichi
Watanabe studied at Glasgow University, served as chief foreman for the
bridge construction, and later became president
of several Japanese companies.
See also:
- Short biography of Sir Benjamin Baker, born 31 Mar 1840.
- Short biography of Sir John Fowler, born 15 Jul 1817.
