deteriorated web analysis

huangyhg

deteriorated web analysis
we are performing the load rating of a bridge that exhibits significant corrosion of the steel webs near the abutments.  the webs have holes near the bottom flanges, the largest of which is 2" high, 16" long.  i am having trouble calculating the shear capacity.  i am uncomfortable using the reduced web depth for calculating a conventional shear capacity (reduced d x tw x fy), but i also believe i should not give a capacity of zero either.  is there any information out there for analyzing such a case?
thanks for any information.
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just a guess - what about following the shear capacity rationale of a castellated beam?
with the holes near the bottom flanges, is the girder bearing on the bottom flange or is it integral with the abutment?
if there is a hole near the bottom flange, then as the beam approaches the support abutment you transition into a "t" beam with the stem in tension.  assuming the web is adequately supported at the very end - you can determine a moment and shear capacity of the "t", ignoring the bottom flange altogether as it is not effective in resisting any stress at all.
thanks for the responses.
the girder does bear on the bottom flange, but it doesn't at the very end due to the hole.  i agree with your method for moment capacity, but what about shear?
perhaps you can utilize aisc's method for checking beams with "web openings".
now with the deteriorated opening very close to the bottom flange, you will probably violate some of the min. distance requirements between opening and flange.  but i do think it checks the shear across the sections with the opening either unreinforced or reinforced.
another option would be to simply reinforce the deteriorated opening by adding a web cover plate and perhaps some horizontal stiffner plates that run from the end of the beam out past the opening.  this would create a form of wide flange beam that could be checked in a traditional fashion.