Lever Rule for Moment Distribution Factors
Lever Rule for Moment Distribution Factors
(OP)
For interior girder shear distribution factors, the lever rule is recommended for structure types not found in table 4.6.2.2.3a-1 (see LRFD section 4.6.2.2.3a). Similarly, for exterior girder shear distribution factors, the lever rule is recommended for cases not addressed in Tables 4.6.2.2.3a-1 and 4.6.2.2.3b-1. However, sections 4.6.2.2.2b and 4.6.2.2.2d, which pertain to flexural moment distribution factors for interior/exterior girders, do not recommend the use of the lever rule for cases not found in the applicable tables. Is there any reason that these LRFD sections do not explicitly permit the use of the lever rule to obtain flexural moment distribution factors?
RE: Lever Rule for Moment Distribution Factors
RE: Lever Rule for Moment Distribution Factors
RE: Lever Rule for Moment Distribution Factors
RE: Lever Rule for Moment Distribution Factors
RE: Lever Rule for Moment Distribution Factors
Though the moment distribution for exterior girders with a corrugated steel deck doesn't appear to be addressed (an oversight?), the first 2 items in Table 4.6.2.2.2d-1 would seem to envelope the stiffness of a corrugated steel deck; i.e. a wood deck is more flexible and a concrete deck is more rigid. Both specify the use of lever rule to calculate the distribution factors, so I believe it would be proper to use it for a corrugated steel deck.
Using the lever rule would be accurate for a deck with no moment continuity over the interior girders, and conservative to some degree for any continuous deck. The lever rule is essentially the worst-case scenario for the exterior girder. The stiffer the deck, the more conservative the lever rule will be.
Rod Smith, P.E., The artist formerly known as HotRod10
RE: Lever Rule for Moment Distribution Factors