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Re: Grade Beam Design - HELP![Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Grade Beam Design - HELP!
- From: Mlcse(--nospam--at)aol.com
- Date: Fri, 4 Jun 2004 20:45:01 EDT
I am not sure I completely understand the picture. But a couple of comments:
Grade Beam Width:
The flange of the W14x38 column is bf = 6.75" wide (assuming strong column axis for the moment frame. The width of the grade beam should probably not be less than 20" wide(3" cover each side, 1/2" for tie diameter (add 1/8" to rebar actual diameter (3/8+1/8 = 1/2")for detailing to account for deformations on the rebar) + 7/8" for #6 rebar each side of the col. plus at least one inch clear to column flange so you have some room to work, recommend more though, closer to 2"). Therefore total width = 3"+1/2"+7/8"+1"+6.75"+1"+7/8"+1/2"+3" = 17.5" use 18" min, but recommend not less than 20" min.
Grade Beam Depth:
I would make the grade beam at least the same depth as grade beam width, probably deeper by 6" than the grade beam width.
Top of footing:
The top of the erection pad for the column, I call it a footing, should be 4" to 6" below the bottom of the grade beam, this allows room for the base plate and anchor bolt projection to remain below the bottom of the grade beam reinforcing.
Grade Beam Reinforcing:
You call out for the grade beam rebar to be 8" o.c., I don't think that works, since you want the rebar to extend past the sides of the steel column, so you are probably limited to 1 or 2 top and bottom bars each side of the column flange, confined by the ties and terminated with 90 degree hooks at the end of the grade beam. I assume you are extending the grade beam to the far end of the footing beyond the steel column.
Are you welding any rebar to the flange of the column in the grade beam to help transfer the bending moment from the column to the grade beam (this may not be an issue if you can show that you can transfer all the bending by column flange bearing on the concrete.). I would use #4 ties, and use the same spacing for the entire length of the grade beam, the grade beam span is not that long and the cost difference probably isn't worth your time to detail the different stop and start points for the reinforcing, let alone verify that it was placed correctly.
Top of Grade Beam:
I would hold the top of the grade beam down 12" from top of finished slab, this allows for piping etc to pass over the top of the grade beam. Also do you want to provide dowels from the grade beam to the slab-on-grade to help transfer the seismic force to the slab-on-grade from the grade beam.
I would increase the footing size to 48" x 48" minimum (if you have the room), give yourself some room to work. Also dowel the grade beam to the footing each side of the column (2-#4 L dowels each side of the column), so you have the footing and grade beam will tied together to help resist uplift, not just the column base plate anchor bolts..
Hope this helps.
In a message dated 6/4/2004 10:49:03 AM Pacific Standard Time, dennis.wish(--nospam--at)verizon.net writes:
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