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Girder Bracing
Posted by Ted Sheppard on April 4, 2011 at 2:22 PM.

ts.jpgYears ago when I was with Tri State Steel Construction, we had a big girder job in Cleveland. Some of the girders were deeper than the ones we had been dealing with on other projects. I was at the site when we erected the first girder, and, as usual, we braced it against rotation at the bearings.

 

The brace was a single angle from the top flange down to the pier top. We had used the same size angle we always used, but longer. Looking at it in person, it looked very flimsy. I went back to the office and calculated the L/r ratio. It was 244. When I was with Bethlehem Steel, we were told to give no compressive value to members whose L/r ratio was 250 or higher. In this case, we were almost using a wet noodle as a brace.

 

That’s when I also realized that I had never established a design standard for these braces, or for the braces between girders used to stabilize subsequent erected steel.

 

We made the correction in the field, then set the limit for the end bearing bracing so that L/r would never be higher than 180. The intermediate braces could not have an L/r greater than 200.

 

The lesson here is that if you have no standards, you can get into trouble. Others may not like the limits that we chose, and that is fine. Everything worked with these limits, and that is what matters.

 

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