Pinch Beam Lintel

[Vertexx]

I'm working on a renovation to an existing building. The walls are 8" block w/ 4" brick. We're making a rather large opening in the existing wall for the new entrance (roughly 20' long) and the customer wants to go with a pinch beam lintel (2 channels with thru-bolts). The lintel will have about 8' to 10' of wall on top of it and the thru-bolts will be through the block with the brick sitting on one channel.

What's the best way to design the block for the local shear and bearing from the thru-bolts? Is there a rule-of-thumb that generally rules this?

 

[JAE]

We use a bottom cover plate -installed sequentially as the masonry below is removed - this is welded to the channel flange tips.

Another detail we've seen:

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[Vertexx]

Yeah, a plate across the bottom would be best. Thanks!

 

[dhengr]

Vertexx:
A good sketch (cross section) of what you have and what you intend to do would certainly be helpful. I assume the toes of the channels point in to pick up the brick and the conc. blk. I wouldn’t expect the through bolt bearing to pick up much of the load or shear, they just can’t do it, they just hold the channels together width wise. The outer channel height should match brick coursing, the inner channel may or may not match the blk. coursing. You will have removed the brk. to the outer upper flg. elev. and you will have removed the conc. blk. outer shell to the mortar joint above the inner channel top flg. I’d weld a bottom pl. on the channels and put a light rebar cage in btwn. the channels. Slide this lintel into place from the inside and fill it with conc. or grout. You could accomplish about the same thing with a cleaner look, with the bottom lintel pl. plus a WF/I beam atop the pl. Leave the brk. in place down to the bot. pl., remove a couple courses of the conc. blk. so you can get the new stl. lintel in place. Infill with half blks. or 4" blks, but leave a couple upper blks. out so you can grout the void space, and finally replace the outer shell of those couple blks.

 

[Vertexx]

dhengr:

My sketch will be similar to the one JAE provided, but probably with a continuous plate spanning from flange to flange rather than the tabs. I figure the brick will sit on the channel flange (will also be using C15x33.9) and use some post-installed veneer anchors at the bottom, letting the existing veneer attachment hold the rest. This will have a canopy covering it, so the customer would like to go with this over the WF.

 

[sticksandtriangles]

Just curious, when you guys design these sort of pinch beams, what do you assume to be the bearing length of the bolt on CMU? After some discussion in our office, we have decided to use only 2" on ea side of the channel to count towards shear resistance (believed that bolt would deflect beyond this region and take no shear load). I feel that we often get laughed at by contractors based on our spacing of bolts compared to other companies.

Thoughts?

 

[jayrod12]

We only use 2" at each end as well, because you can't guarantee the block you are bolting through is even grouted, so you only get bearing at the face shells.