Load rating live load factor calculation error

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Visitor (not verified)
Load rating live load factor calculation error

I am running a Load Rating in PGSuper, but an error is occurring somewhere in the calculations. For my Routine/Annual Permit Vehicles, the Live Load factor gamma(L) is being calculated as -9.999e+003. This is obviously an error, but I can't seem to manually override the live load factor value or determine how it is calculated by the program. According to AASHTO MBE Table 6A., for ADTT >=5000, the load factor should be between 1.3 and 1.8, depending on the weight of the truck. All other types of loads (Design, Legal and Special/Limited Crossing Permit) work just fine. I'm attaching my file. Can anyone offer any insight on what's going on here?



Rick Brice
Please provide addition

Please provide addition details. When I run you file I get live load factors of 1.591 for the CT-P204 truck and 1.66 for the CT-P76.5 truck for the Routine/Annual Permit rating. This is true for all girder lines. I've attached the load rating summary from my run of your file.

mappleby (not verified)
Almost the same results

Thanks for taking a look at this for me. I was ogiginally running a different beam than you (Beam C, where you were running Beam A), but now that I run beam, I get all the same results as you, except that my live load factors for the one particular case still explode. I'm attaching my output.

Rick Brice
The PGSuper project file was

The PGSuper project file was not the same file (or at least the same version of the file) used to create the Load Rating.pdf file you posted. The report you posted lists dfg as the name of the load rating criteria (Refer to the Library Usage information). However, no such criteria is defined in your PGSuper project file.

I get good live load factors for all girder lines when I run your file. This leads me to beleive that the problem is in the "dfg" load rating criteria.

Please re-post the exact same project file that you used to create the Load Rating.pdf output.

Also, I'm out of time for the day. I'll have to return to this on Monday. If you need immediate resolution to this issue, I suggest contacting BridgeSight for their per-incident support service.

mappleby (not verified)
Still trying

I really appreciate your efforts here. I thought you had nailed it with the Load Rating Criteria thing, so I switched back to the Master Library MBE criteria, but unfortunately that didn't help. I was wondering if there was some sort of problem with my live load definitions for the two Annual permit vehicles in particular, so I tried both including them in the Limited Crossing category, and I also added other vehicles to the Annual Permit category. It's always the vehicles in the Annual Permit category that blow up, so it seems like the problem is in the calculation of those live load factors specifically. I don't know what other settings or inputs I could be defining that is making this happen, but I'm attaching my latest output and file if you care to review it any more.

Rick Brice
I've uncovered the root cause

I've uncovered the root cause of the problem. The live load factor is computed by Table 6A. in the MBE. The load factor is computed based on ADTT and Permit Weight. In this case, you had the ADTT set to 5000. We covered the case of ADTT < 5000 and ADTT > 5000. We missed ADTT = 5000 (oops). I'll get this fixed in the next version of the software.

As a work around, set your ADTT to 4999 or 5001 and the load factors come out fine.


mappleby (not verified)
Thank you

That certainly fixed it! Who would have thought? I really appreciate the help.

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