Steel Beam Bearing Pockets and Thermal Expansion

[mcc202]

Hi There,

I was wondering if anyone had any insight into how to allow for thermal expansion/contraction of structural steel beams bearing on CMU or Concrete walls. I've had some issues with cracking at the bearing pocket where the beam has engaged the bearing plate as it expands/contracts and cracked the wall. Our current detail uses a bearing plate with oversized holes, plate washer, and hand tightened anchor rods. The steel beam gets welded to the bearing plate. Even though the holes are oversized, I believe the grout below the bearing plate is still engaging the wall below. Has anyone had any experience in with a bearing pocket detail that provides stability of the beam while still allowing thermal movement of the steel?

Thanks

 

[KootK]

That's a tough one. Some possible strategies:

1) Keep spans short and thermal variation minimal where possible. Obviously, you'd have thought of this already on your own.

2) Provide a joint that provides a teflon bearing pad. This will be costly, often prohibitively so.

3) Reinforce the wall locally around the connection to, hopefully, minimize crack widths.

4) Design a stiff beam to reduce the magnitude of incidental moment transfer at the joint and, thereby, reduce accidental binding.

For better or worse, my impression is that it is typical to ignore this in many conventional situations. Heck, in many regions, the "connection" will be pretty much just sticking the beam into the pocket and grouting it all up solid.

 

[dhengr]

Mcc202:
Give some thought to moving the bearing pl. back from the very edge of the pocket (or face of the conc. or masonry wall). When the beam deflects under load it tends to overload (in bearing) the very edge of the pocket/wall and cause cracking and spalling of the wall. Maybe slot holes in both the pl. and the beam, or just in the beam, finger tight nuts, and then don’t weld. This will allow some beam movement in the pocket. As KootK suggests, thermal movement is often pretty small, and is ignored. A 10' stl. bm., with a 100̊F temp. swing, changes length by about .078", that’s about 2.5/32"; a 50̊F temp. swing causes the same length movement on a 20' bm.

 

[Roukkia]

My firm uses a bearing plate detail more similar to the one dhengr proposed. We provide nelson studs welded to bottom of the plate, A325 bolts through normal size hole in plate and long slotted holes parallel to beam. These bolts are tack welded to the bottom of the plate for installation purposes. Automatically welded threaded studs to the top of the plate would also work I think. This is the only detail I have seen used but I have also not been around for long…

 

[MotorCity]

If the building is tempered thermal expansion of the steel should not be an issue.