Reinforcing a Steel Beam 1

[Megamoule]

When reinforcing a beam by a adding a steel section (like putting an upside down channel on the bottom flange of an H beam), is there any standard on the spacing of welds or bolts to ensure that both beams will work as one?

 

[Lomarandil]

This webinar (potentially including part 2?) had great information on the topic.

https://www.aisc.org/education/cont...-of-reinforcement-for-steel-members---part-1/

----
just call me Lo.

 

[centondollar]

Shear flow should pass through the weld. From the elementary beam theory, we have:

q = V*S / I , where V = shear force, S = first moment of area, I = 2nd moment of area.

This gives you the force per unit length along the weld (e.g., along a web-to-flange connection).

If you wish to connect something to a flange from "above" or "below" (so that it does not connect to the web), you use the normal force (from normal stress due to pure bending) per unit length instead:

sigma_xx = (M/W) * b , where M=bending moment, W = section modulus, b = width of flange.

If you have an axial load, that must also be resisted by the weld.

 

[KootK]

In Canadian parlance:

1) Design for shear flow along the length of the beam using VQ/I.

2) If your reinforcing does not run the full length of the member, provide concentrated welds/bolts at the ends according to:

a) MQ/I where M = moment where the reinforcing is terminated.

b) Just develop the tensile capacity of the reinforcing piece in one go to keep it simple.

3) If the reinforcing cross section possesses significant transverse stiffness in its own right and does not make it to the beam support, it will tend to pull away vertically from the member being reinforced. I wouldn't bother to consider this for a channel on the flat however.

4) At some point you're bound to ask yourself "wait, how is it that I'm designing my beam for plastic bending capacity (phi x Fy x Zx) but designing the reinforcement connections using elastic theory?". Not to worry , the demand calculated using elastic theory will be conservative for plastic beam capacity. Most folks find this counterintuitive initially. I know that I did.

5) CSA imposes some geometrical limitation on stitch weld lengths and spacings which you can read about in this thread: Link.

6) This is a decent AISC Steelwise article on steel reinforcing written by the same guy that presented in Lomarandil's video: Link

 

[Settingsun]

normal force (from normal stress due to pure bending) per unit length instead:

sigma_xx = (M/W) * b , where M=bending moment, W = section modulus, b = width of flange.

This would give force/thickness, assuming the stress is constant and equal to the extreme fibre stress. Does it also translate to a force/unit length independent of thickness?

 

[dik]

Just a caution for intermittent welds; don't use them for fatigue environments.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JLNJ]

No, there is no one-size-fits-all standard.

Like so many things, the answer is, "It depends".