If you add load to a bridge, wouldn't you check everything, INCLUDING the gusset plates? But connections typically have a larger factor of safety than the truss members themselves, so perhaps that is why they weren't checked.
"Transportation Secretary Mary Peters was expected to issue an advisory urging states to check the gusset plates when modifications are made to a bridge — such as changes to the weight of the bridge or adding a guardrail, said a federal official with knowledge of the plans. The official spoke on condition of anonymity because Peters had not yet made the announcement."
"Currently, such calculations are done for the entire bridge, but not down to the gusset plates, the official said."
So, it seems to be implied that modifications to the original design were made, but the gusset plates not rechecked. For them to be undersized by 50% seems to be a pretty substantial "modification". And the statement that it is still the practice not to recheck the plates really concerns me.
"And the statement that it is still the practice not to recheck the plates really concerns me."
Me too. It is NOT standard engineering practice to ignore connections. Then again, it's a statement coming from some "official" speaking anonymously from stolen tidbits.
In the bridge industry, especially at DOTs where knowledge and money are limited for bridges of these types, it is not common practice to check connections.
This is not the standard that the rest of the industry is held to. Bridge Building engineers typically are expected to check everything from load path to members to connections.
It is true that much of the software in use, BARS, Virtis etc do not provide detailed results to the connections but that shouldn't prevent someone from checking them.
Speaking of checking....the undersized plates should have been caught in the original design.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
This really does not make sense. The bridge worked for 40 years. The construction loads to support the decking operation sould not have exceeded the deck capacity. There must have been a trigger. Corrosion or a frozen bearing must have started this. Once it fell, the plates would look like spagehti no matter what caused it. It sounds like the Feds were hell bent on proving their boss's theory. I'm not buying it yet.
DRC1 - As I read the report, they're not saying the plates alone are the reason for the collapse, just that the undersize plates represent a design flaw that contributed to the collapse. In the news conference the spokesman noted that they continue to look for the 'straw that broke the camel's back'.
Regards,
Qshake
Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
The "Adequacy of the U10 & L11 Gusset Plate Designs for the Minnesota Bridge No. 9340 (I-35W over the Mississippi River" report available from the link below provides detailed analysis of the main truss gusset plates:
I'm not a bridge guy so forgive my ignorance, but were there 1/2" gussets on both sides of the flanges? I can see the outer gusset plates but I wonder if they use another 2 on the inside of the flange that straddle the web.
When I design a butt splice in a tower leg member, I put an angle on the inside and 2 gusset plates on the outside legs so the bolts are in double shear. The total thickness of the inside splice angle and the outside gusset plates add up to more than the leg thickness so bearing is not a problem.
_____________________________________
I have been called "A storehouse of worthless information" many times.
When you look at the elevation of the truss in the report, it looks like there was a drafting error. The gusset plates in the main span may have been transposed with those in the backspan at the two nodes in question.
![[pipe]](/data/assets/smilies/pipe.gif "[pipe] [pipe]")
