164
Molesworth’s pocket-book
Theorem of Thbee Moments.
If A, B, C, be three consecutive supports of a continuous
girder of any number of spans, whether equal or unequal,
and ?! the consecutive spans; then let p, p. = the loads
per unit of span on l3 respectively; and m, M? M3 — the
bending moments on A, B, and C respectively. The relation
between M, M, and M, is always expressed by the equation
Mj'll + 2 + Z3) + M.• J3 = i ‘ Ji3 + P2'?»’)•
Load on the Supports of a Continuous Gibdek of Equal
Spans unifokmiy loaded.
When the number of spans exceeds five, the loads on the
supports are nearly the same as when the number is infinite.
Deflection of Wkought-ikon Girders,
Deflection of -fa to of the length may be allowed under
special circumstances ; out under ordinary loads the deflection
should not exceed t of these, say to .
The practice In America is to allow after the girder
has taken its permanent set.
In small bridges there is a slight increase in deflection from
high speeds, about ith or |th of the normal deflection, with
the same load moving at slow speed.
In large girders there is no perceptible difference between
tbe deflection at high and low speeds.