Beam Reinforcement Calculation 2

[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.

 

[human909]

This "diatribe" is relevant as it goes to the core of the original question.

The longitudinal shear flow between the plates and the I beam would be zero. All you need to do to have them act as a compositive section is to sister them together. So bolts or spot welds at the centroid would be sufficient.

 

[BAretired]

This "diatribe" is relevant as it goes to the core of the original question.

The longitudinal shear flow between the plates and the I beam would be zero. All you need to do to have them act as a composite section is to sister them together. So bolts or spot welds at the centroid would be sufficient.

Shear flow between the I-beam and plates is not zero. Depending on the thickness of side plates, it may actually reduce the shear stress in the beam web for the height of side plates, but that is a questionable advantage since the shear stress in the remainder of the web remains the same as it was without side plates. So I see your point...side plates as shown in the original post are not useful. To sister the side plates is equally useless, so why not simply do nothing? Leave the I-beam alone.

 

[RWW0002]

Shear flow between the I-beam and plates is not zero.

I still disagree and have tried to make my point numerically, but have not had time for sketches or examples. Shear flow at that point may be non-zero, but shear flow between elements (in this case) is 0.

This has been shown numerically (see my previous post and sketch below)


Case I

This has been shown thru FEM - See detailed FEM approach above
This has been shown empirically via discussions about the two sections not being truly composite with examples such as comparison of Moment of Inertia and others.

There seems to be a basic disconnect on mechanics here and confusion between shear flow within the overall member at the top of the plate and shear flow being transferred to the plate. This topic is worth continued discussion as there seems to be some confusion on the topic and it gets brought up in here alot (although generally via a more"common member arrangement). Shear flow in the I shaped member at the top of the plate is not zero. But shear flow transferred across the joints to plates can be taken as zero as calculated above. BA - it seems like you are calculating shear flow as though the section is as below (full member joint at top of plat), but this is not the reality of the situation. Shear flow at the bottom of the WT "stays within" the W beam and is not transferred to the plates. (empirically, a section with a horizontal joint as shown below would behave differently than the web-plated beam above - and have more horizontal shear demand across the joint. It is my opinion that Case I would have no shear flow between elements and Case II would have shear flow across elements.

Case II

 

[Stress_Eng]

Just thinking allowed. Immediately below the top flange, there will be a shear flow in the web. Progressing down the web, the shear flow will increase. As you get to the top of the two side plates, the shear flow will suddenly be confronted with three load paths, into the side plates through the two welds and down the web. If you take the shear flow in the web at the bottom of the welds (two vertical sides), will the thickness be the two welds and the web (V.Q/[I.(2.t+w)]? One or two have posted something similar.

Edit: the weld thicknesses could be at the 45 degree plane (min weld section).