CMAA rail bending equation

[jdkuhndog]

Can anybody give some guidance where CMAA came up with the equation for maximum stress allowed in the crane rail (Section 3.5.4.6 of CMAA 70-2000).

If you take the equation apart...they allow for 18ksi maximum stress, but the moment equates to PL/6 in lieu of a PL/4 (simply supported) or PL/8 (fixed both ends).

Any insight would be appreciated.

Thanks !

 

[SlideRuleEra]

The denominator of the point load moment equations is bounded by the ideal cases of simple supports (4) and completely fixed (8). Within this range (4 to 8) a combination of history, experience, and judgement may be used to assign a value. By using a value of 6, a decision has been made that the rail is "partially fixed".

The same situation occurs with the denominator of uniform distributed load equations, with a minimum value of 8 for simple supports and a maximum of 12 for completely fixed. An example of this "judgement call" is in the design of cofferdams. The denominator of the moment equation used for calculation of moment in steel sheet pile spans that are continuous across wales (supports) is routinely assign a value of "10". That is: M = (wl^2)/10