QUESTION
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?
In my particular case (bridge load rating with steel corrugated deck), the lever rule produces an acceptable result for exterior moment. But I was surprised to find that the relevant articles regarding moment distribution do not mention the lever rule (only for shear). Is the use of the lever rule for moment distribution factors of unique superstructure types permitted by LRFD/LRFR (even though it may be conservative)?
REPLIES
wiktor
Typically, the lever rule is not used in the distribution of moments - the only case when it may be applicable is multi-stringer or multi-girder bridge, with relatively flexible deck and without transverse beams - some temporary bridges are configured this way. The ratio of transverse to longitudinal stiffness of the structure could be used to determine applicability.
SOURCE
https://www.eng-tips.com/viewthread.cfm?qid=461411
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