I35W over the Mississippi

[VoyageofDiscovery]

After reading the Executive Summary of the Bridge 9340 Study by URS, I noticed that the main truss had members with interaction ratios greater than 1.0 when checked by LRFD. In retrospect, the report appears to down play this aspect as the bridge had performed well up to date. When checked against "actual" loads, the members were less than ultimate. This may also not be the cause of failure, however:

1) As a US bridge engineer what would one do in such a case when ASD shows no overstress?

2) With LRFD not applicable in many cases to date, what is the typical standard in the US when rehabing existing bridges?

 

[VoyageofDiscovery]

Correction, "actual" should say unfactored.

 

[NS4U]

I'm not a practicing bridge engineer, but from what I've heard from people that are is that if the design is OK by ASD standards, but not LRFD, a weight restriction has to be imposed on the bridge which will satisfy an equivalent LRFD design.

Essentially you have to back calculate an acceptable load based on LRFD.