residential pier and grade beams[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: residential pier and grade beams
- From: "Robert Shaffer" <rkdn(--nospam--at)cruzio.com>
- Date: Thu, 8 Jun 2000 12:37:12 -0700
I am designing a foundation for a hillside residence and I am curious as to the requirements for transverse reinforcing in my c.i.p. piers in bored holes. Section 1809.5.2.2 requires that transverse reinforcement per 1921.4 be provided in c.i.p. concrete piers in zones 3 and 4. I am told that standard practice in the area is to only provide nominal hoops at large spacing ( # 3 @ 12 to 24"o.c. ) over the length of the pier ( 8' to 15' depth max). Section 19184.108.40.206 would provide for a maximum hoop spacing of 3.75" ( 6*Db for #5 vert's ) where the more stringent(?) requirements do not apply. I see that the 1999 Blue Book provides for some steel volume relief, but not spacing. Surface soil creep ( 2 to 4' of depth ) is the primary contributor for flexural loads and the retaining walls are supported on very wide footings which allow for staggered placement of piers. My largest axial load may get up to 15 kips . So my questions are:
1. Am I understanding the transverse reinforcing requirement correctly ? ( Hoops at 3.75"o.c. )
2. I remember seeing a design several years ago that used a welded wire fabric cage around the vertical rebar, is this a good method considering that the axial loads are minimal ?
This requirement is also in 1994 UBC.
Robert Shaffer, P.E.
Santa Cruz, CA
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