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BAR7 Rating Analysis Program

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Candi Anderson wrote:

"I'm looking for information on the "assumptions" used in the BAR7
rating
analysis program (PennDOT) for Floorbeam Type P members.  Specifically,
since these frame into main fascia girders of significant depth, I'm =
looking
for the end conditions that the program would be using in determining =
the
moments in the floorbeam.=20

I have an output with results, but no user guide that explains this.  =
I've
checked online and can't find a website to download a user guide, but am
=
not
sure if it would tell me anyway.
Any help is greatly appreciated.

Candi Anderson, P.E."


Candi,
First, to your question: calculate the dead load moment on the floor
beam using wL^2/8.  Compare it to the output moment.  Hopefully they're
the same; I personally feel that considering floorbeam end fixity is
bogus, since the girder or truss usually has very low torsional
stiffness, the floorbeam end connection is almost invariably a simple
shear connection, and a long truck is making the adjacent floorbeams
bend and twist the supporting girders that you're counting on to be
vertical.

I also strongly recommend doing this with the live load moments, so you
know the program is putting the wheel lines where it needs to to
maximize the moment (remember the rule?  Midspan centered between the
load CG and one of the wheel lines...).  These aren't difficult
calculations to do by hand.

On a more general note, I wouldn't use a bridge rating program without
doing the hand calc first, which is to say, there's really not much use
for them except on trusses, at least until you've used them enough to
trust them; and as a check on your hand calcs.  It doesn't sound like
that's the case here, especially since you don't even have a User's
Guide.  Many years ago, our state DOT had a bridge rating program (it
might have been BARS--I don't remember) that they made available to
consultants to rate truss bridges on the county road system.  When I
looked at the output for one such bridge, run 8 years before and trusted
ever since (and the bridge posted to its recommendations), I found that
the governing member was a brace from the bottom chord panel point to
the top chord, a member with no force in it.  Nobody had ever
looked--neither the previous engineer in that consultant's office, the
DOT guy who ran it, or the county engineer.

At the risk of sounding like a broken record, calculate the entire
bridge by hand, then check it with the program.  If you don't have the
budget for it, do it anyhow.  If you don't know how, you have no
business using the program, because those programs all have problems.
If you don't understand and agree with the output, it's probably crap.

HTH

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota
Who used to rate a whole lot of bridges




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