Saturday, September 17, 2011

RE: rebar vs anchor

I have anchored equipment both ways.  It is more of an issue of what works best for the millwrights installing the equipment.  Welding the equipment to an embed plate does not give you any adjustment, nor accommodation for tolerance.  Concrete will have a tolerance per ACI 117 of 3/4" in elevation. 
If you are talking about hooked rebar welded to a carbon steel embedded plate, you are correct.  It is very different.  Appendix D would only govern if you use a hooked plain round bar.  Rebar embedment is governed by Chapter 12. 
The only caution is to require weldable rebar (ASTM A 706).   ASTM A 615 rebar can be used, but I would urge great caution.  If you do not request the mill certs during the ordering process, you will not get them.  Welding of ASTM A 615 bar is determined by AWS D1.4.  If you use this approach, assume a CE of over 0.75.  This requires a maximum preheat of 500 degrees F depending on the bar size.    
Welded ASTM A 615 rebar can result in VERY brittle welds.   I have been able to remove welded ASTM A 615 rebar from carbon steel plates with a hammer very easily. 
And always require welding inspection by an AWS certified inspector.  The preheat is absolutely essential.   

Regards, Harold Sprague

Date: Sat, 17 Sep 2011 09:37:00 -0700
Subject: rebar vs anchor

Good morning,

Anchoring a piece of heavy equipment with high seismic pullout. 

I can use anchors through the baseplate, and use ACI318 Appendix D.  

I can also weld the baseplate to embedded plate with welded-on hooked rebars.  This case does not appear to be governed by Appendix D, and the results (embedment depths etc.) are quite different.

Your thoughts on this subject will be highly appreciated.

V. Steve Gordin SE
SGE Consulting Structural Engineers