reinforcing cantilevered girder

[jdbpe]

We have an existing W24x55 that cantilevers out 7 feet and we are increasing load on it because of a hanging partition. We are overstressing the beam by 10 percent with partition. How do we reinforce beam for negative moment with a metal roof deck directly above top flange?

 

[DaveAtkins]

Try to not reinforce the cantilever. 10% overstress is not that much. Look at live load reduction, fine tuning the dead loads, etc., to prove that it works.

DaveAtkins

 

[UcfSE]

You can add steel to the underside of the top flange or to the bottom of the bottom flange. Adding to the top flange isn't as efficient as you would want but if you can't put it on top then you have to do what you can do. If you add steel to the bottom flange you will increase Sx and Ix much better than adding steel to the underside of the top flange. It should also be easier to reach in the field.

 

[miecz]

If you add to the top flange, be careful to check for compactness of the web, as your neutral axis will have shifted, thereby increasing your d/t ratio.

 

[jike]

A simple way to reinforce any beam is to add a WT to the bottom. Other ways are to add flange plates, channels to the web,

I agree with Dave. 10% is not much. One flange plate on the bottom only may just give you what you need with an unsymmetrical section although I probably would go ahead with the top reinforcement to keep it more symmetrical but that will be way more than you need.

I would try to refine the loads and utilize live load reduction factors to justify not having to reinforce the beam.