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Re: Crane Design; SE v. ME

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>He asserts that dynamic forces created by the crane starting and
>stopping under load are generally greater than any which might occur in an
>earthquake,
That might be true (although doubtful since the deceleration is limited 
the product of weight and the friction coefficient which is no greater 
than maybe 0.2) in the case of the bridge rolling direction, because all 
the crane mass is involved, but it sure isn't true for loads in the 
spanwise direction of the bridge girders, since only the trolley moves in 
that direction. Lateral (spanwise) seismic excitation will put 
considerable loading about the weak axis of the bridge runway supports 
because it involves the whole mass of the machine. Likewise the vertical 
loading is certainly higher than the loaded weight of the crane times 
whatever impact factor is required by CMAA-70.

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw