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Re: New Steel to Existing Concrete

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We run into this pretty often when making modifications at nuclear power plants.
At none of the plants where I've worked have we been able to completely avoid
this.  But there are some steps to reduce the impact:

Rebar detectors are available.  Some work on electric/magnetic fields & some use
ultrasonics.  Cost, accuracy, suitability, and user friendliness vary.  It is
difficult to get below about 7" of cover with any of them.  The
electric/magnetic field variety may not work at all depending upon background
fields due to electrical equipment.  After using the rebar scanner to identify
rebar locations, holes are drilled where we've hopefully missed the rebar.

You can also drill pilot holes and ground fault interrupters on the drills.
This will prevent cutting the bars before you've evaluated it.  Using the pilot
holes, you can identify rebar locations.  The pilot holes are generally only
about 1/4" in diameter.  These are easier to repair than the larger holes for
the anchors.

We generally recommend including a fairly large tolerance on the anchor
locations.  This allows for relocating the anchors if a rebar is detected
without having to redesign the baseplate or anchors.  The tolerance should
consider anchor restrictions concerning proximity to abandoned holes.  It's also
better to drill the concrete holes before drilling the baseplates (or you may
have to replace the baseplate, which seems to happen at least once per crew).

Another design option is to minimize the number of anchors.  We have gone to
much larger capacity anchors and thicker base plates in order to go from
4-anchor baseplates to 2-anchor baseplates.  The material cost increases can be
offset by the reduced installation costs.

You may also be able to tailor your design to avoid areas with congested rebar.

We also, pretty frequently, consider cutting the rebar before we issue the
design.

Jim Annett, PE
GPUN
609-971-4307
jannett(--nospam--at)gpu.com







Robert Rollo <rrollo(--nospam--at)TEAM-PSC.com> on 02/17/99 11:35:55 AM

Please respond to seaint(--nospam--at)seaint.org
                                                              
                                                              
                                                              
 To:      "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>           
                                                              
 cc:      (bcc: James H Annett)                               
                                                              
                                                              
                                                              
 Subject: New Steel to Existing Concrete                      
                                                              








every time we try to connect new steel beams to existing concrete columns or
beam, the driller will hit rebar despite all detailing and layout efforts to
the contrary.  obviously, upon hitting rebar, the contractor calls for
guidance, we attempt to determine adequacy of the member with interupted
reinforcing, etc. etc.

anyone have better solution to this age old delema ? short of don't connect
new steel to old concrete ?

am i missing something so obvious it is slapping me in the face?

can i prevent the phone calls next time ? or am i forced to accept this as a
universal constant ?

thanks in advance for any thoughts . . .

robert d. rollo, PE
Corporate Associate
rrollo(--nospam--at)team-psc.com
(806) 747-0161vox
(806) 747-7146 fax


Title: New Steel to Existing Concrete

every time we try to connect new steel beams to existing concrete columns or beam, the driller will hit rebar despite all detailing and layout efforts to the contrary.  obviously, upon hitting rebar, the contractor calls for guidance, we attempt to determine adequacy of the member with interupted reinforcing, etc. etc.

anyone have better solution to this age old delema ? short of don't connect new steel to old concrete ?

am i missing something so obvious it is slapping me in the face?

can i prevent the phone calls next time ? or am i forced to accept this as a universal constant ?

thanks in advance for any thoughts . . .

robert d. rollo, PE
Corporate Associate
rrollo(--nospam--at)team-psc.com
(806) 747-0161vox
(806) 747-7146 fax