Beam Reinforcement Calculation

[Nick6781]

Let's say I need to use a web plate instead of a flange cover plate (I know...) to reinforce a beam. How do I calculate the required weld to ensure the section acts compositely? The shear flow equation gives the shear along a horizontal plane, but in this case, the faying surface is vertical. I can't quite wrap my head around it.

 

[jerseyshore]

Is this for repairing a corroded beam or reinforcing it for an increased shear load? If it's purely for bending, the increase in capacity here is going to be small so I can't imagine it's even worth it. When the centers line up shear flow is greatly simplified. You just have to design the connection to take the shear at any particular point. Then when the reinforcing ends, you have to get the shear back into the original member to transfer it out to the supporting column, bearing wall, etc.

 

[skeletron]

Size the weld to develop the capacity of the plate in shear.

 

[aalmasri]

Using web plate helps in resisting shear stresses mainly, while using flange cover plate helps in resisting mainly bending stress, so basically you cant use one instead of the other. Everyone has its own use. Be careful.
You can calculate how much shear the additional web plates can carry, and design your weld based on that.

 

[jhnblgr]

Likely cheaper to replace the beam. Need more background on what the actual issue is

 

[DaveAtkins]

I would use the shear flow formula, VQ/I, to determine the load per lineal foot in the weld. Then design the weld accordingly.

 

[HTURKAK]

I suppose the question is how to calculate the required fillet weld thick. and stress so the section acts compositely rather than effectiveness of web stiffening .

The shear flow equation gives the shear along a horizontal plane, but in this case, the faying surface is vertical.

Using the shear stress formula ( at Mr Atkins' respond ) you can calculate the horizontal and vertical shear stresses. Moreover , you need to design the fillet welds still for horizontal . The following figure from the book Mechanics of Solids, by POPOV.

 

[XR250]

Is there really any actual "shear flow"? If the plates are symmetric and centered top to bottom it is just addiitve stiffness so the welds only need to be sized to transfer the load based on relative stiffness - which should be quite minimal. Channels would be more effective.

 

[TRAK.Structural]

All the centroids and neutral axis locations would be in line with each other so I agree with @XR250, really just need enough weld to get load into the new plates.

 

[Nick6781]

Is there really any actual "shear flow"? If the plates are symmetric and centered top to bottom it is just addiitve stiffness so the welds only need to be sized to transfer the load based on relative stiffness - which should be quite minimal. Channels would be more effective.

I agree. This is what I was thinking. It's similar to the flitch beam situation, except that the plates do not have their own end supports.

 

[RWW0002]

Is there really any actual "shear flow"? If the plates are symmetric and centered top to bottom it is just addiitve stiffness so the welds only need to be sized to transfer the load based on relative stiffness - which should be quite minimal. Channels would be more effective.

I also agree but might add that lateral bracing of the plate members by the existing section should be considered as well.

 

[jerseyshore]

I agree. This is what I was thinking. It's similar to the flitch beam situation, except that the plates do not have their own end supports.

Which is why I mentioned above that you just have to get the shear out of the ends back into the main member for support. So because it's a partial reinforcement you have to get the shear into these plates then back out.