Thread: Cut End on Steel I Beam

I saw this modified steel I beam in a house today. The top and bottom of the "I" were cut off leaving just the flange in the middle which was welded to the adjacent steel I beam. The house is 23 years old and I saw no evidence of weaking, cracking, or failure on the cut beam but it just doesn't seem kosher.

Thoughts?

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Nick,

That's a very common bearing connection used in structural steel construction. The end of one member is coped where it frames into the other member of similar (or identical) depth. The flanges of the first member are cut (coped) leaving the web to transfer the shear loads to the other member. (The flanges are the parallel top and bottom parts of this member and the vertical part is called the web.)

For connections of this type the connection angles are typically welded to the web of the first member in the fab shop and holes are drilled in the connection angles and in the web of the other member at the appropriate locations. This way the erectors can simply bolt the connection rather than having to weld the connection in the field - an operation that requires special tools and a qualified welder AND would also likely require an additional inspection. (The welds made in the fab shop are much easier to have inspected than those made in the field.) AND the bolted connection does not have to be painted after completion like a welded connection. Another plus of not welding the connection in the field is that the web of the second member can be damaged or weakened if it is overheated (less likely to happen in the shop).

The coped flanges at a connection of this type are not a concern - if they were coped in the fab shop. (If Bubba took a torch and coped the beams himself that is a different matter entirely and may need a look-see by an engineer.) The reason it is OK to cope the flanges at the ends of a beam like this is the beam is a simple span and is supported at the ends (or so I am assuming). The greatest bending stresses on the beam are at its mid-point (assuming uniform loading) so the flanges are required at this point to resist the bending stresses. The ends of the beam do not see any bending (or very, very little anyway). The end beam connections simply transfer vertical loads (no bending or moment loads) to the other member and the cross-section of the web is adequate for these loads (something that would be addressed in the calcs when the members and connections were designed).

Did you report the missing bolt (bolts?) at the connection? If too few bolts are used in the connection the loads may exceed the shear capacity of the remaining bolts.

Thanks for the info Bruce (very detailed). I haven't sent the final report yet so the missing bolt will be included.

Originally Posted by Nick Ostrowski

Thanks for the info Bruce (very detailed).

It's a curse really. It's the engineer in me. Years ago in my other life as a structural engineer I designed structural steel and connections like this for nuclear and fossil fuel power plants.

That connection is pretty common but if you haven't been around structural steel much it may look odd. In the attached image the beam in Connection D has both flanges coped like the one in your pic.

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