Lateral bracing of bridge girders 4

[2134]

Can anybody give me guidence (or suggest any book) for design of lateral (wind) bracing of bridge girders.How we can incorporate/add wind load in to the load calculations during construction i.e before placement of concrete deck?

 

[civilperson]

This looks like the same horizontal deflection question for bridges that was asked and answered. ASCE 7 has the wind forces and judgement can lower these forces if shielding or sheltering of interior girders apply. I use no deduction from full wind on each girder when spaced 3 times the height apart.

 

[bridgebuster]

You can design the bracing system as though it were a truss. I assume you checked AASHTO to see if bracing is needed.

If this is LRFD you have to perform the calculation for bracing the compression flange during construction. If you're using the Standard Specs no check for construction conditions is required. However, there are methods you could use. For instance, check the girder about the weak axis assuming the diaphragms act as a support.

The old old US Steel bridge design manuals had an example.

 

[Dinosaur]

I was asked to check flange bending stresses during construction on a job for Florida DOT due to a "reduced wind load" of ~50% x 50 psf if memory serves.

I multiplied the 50 psf x half the girder height to get a plf load on each flange. Then I analyzed the flange as a simply supported beam and checked the stress. I believe I divided the load by the number of gitrders in the transverse section since all girders would participate, although that may not be the case since there may only be 2 girders up when the big wind storm comes along.

Anyway, this is a method for determining a good minimum width for a flange to avoid problems during construction. Good Luck. Oh, I'd ask your boss. He has a better understanding of what your client wants.

 

[Qshake]

You can find a wind bracing example in the AISC Highway Bridges Design Guidelines. Check out AISC's website

Regards,
Qshake

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