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RE: Masonry lap Splice

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I recently had a bad experience with the required lap splice for masonry
rebar in the 2000 IBC. I had designed a building under the 1997 UBC and had
used #6 bars each face adjacent to wall openings with 12" block (due to a
tall story height). Prior to issue for construction, the local jurisdiction
adopted the 2000 IBC, so I incorporated the IBC splice length requirements. 

The splice for a #6 bar at 2" clear became 8'-2". During construction the
masonry subcontractor strongly objected to the design and said he had never
seen such a splice length in masonry work. I agreed but said I was
restricted since it is a code requirement. I spoke with NCMA and they said
it was based on their research - they are doing more research to try to
improve on this. They said that ACI 530-02 shows this splice length just for
strength design but not for allowable stress design - but the next ACI 530
will likely require it for both. (How does the rebar know which way it was
designed??) 

For a #5 bar at 2" clear, the splice length would be half as much. There is
a 1.4 factor for bars greater than #5 and the splice length varies with the
square of the bar diameter. Thus, in the future I will try to limit my
designs to #5 bars, or at least not use larger bars near the CMU face, due
to the lap splice limitations. 


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

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