MDX Software - FAQ #5<BR><BR>

Why did I get a significant overstress when designing with self weight as the noncomposite dead load?<BR>
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<UL>
A preliminary analysis is necessary to provide load effects for the
    design effort.  Since self weight is not known prior to the design
    effort, an estimate of self weight must be provided at this stage.
    (See WDL for line girder projects and W-i for system projects.)
    After the design is generated, the actual self weight then is used
    for a reanalysis to provide loading effects for rating.

    If noncomposite dead load is underestimated prior to the design effort
    (as apparently was the case leading to the question), an underdesign will
    be generated which will overstress when the actual self weight of the
    generated design is imposed for reanalysis and rating.  If noncomposite
    dead load is overestimated, an overdesign is generated.

    The girder design can be modified in subsequent rating runs to correct
    overstress or understress, however the most efficient design is
    achieved when a thoughtful effort is made to arrive at a noncomposite
    dead load estimate which anticipates the self weight of the generated
    design.
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