From: "Silva John (sj)" <Silva(--nospam--at)hilti.com>
Date: Thu, 27 May 1999 12:25:25 -0500
Steve, you don't mention how you are going to anchor the tank.
Unless you are casting the baseplates into the pedestal, you should design
the local reinforcing to ensure effective transfer of anchorage loads into
the balance of the structure. This would include providing confinement
around the anchors to prevent splitting (your cages should do this), as well
as vertical hairpins looping around the anchor heads and extending into the
footing pad. Horizontal (or slightly angled) hairpins hooking around the
anchors near the concrete surface will take up shear loads directly from the
anchors (better yet, use hairpins in combination with shear lugs). This is
important particularly if your baseplates are arrayed near the perimeter of
the pedestal. Some guidelines for use of supplementary reinforcement to
improve anchorage performance can be found in the CEB Design Guide - Design
of Fastenings in Concrete, published by Thomas Telford, 1996 (ASCE sells
it). If the baseplates are going to be leveled and grouted, be sure to
check bending in the anchors, assuming a point of fixity 2-3 diameters below
the concrete surface. Finally, I would highly recommend that you make sure
that the anchors are not the weakest link in the load path for this thing.
Design it so that something else will yield (e.g., the baseplate) before the
anchors reach ultimate.
I know this isn't what you asked. If it's all old news, disregard.
Regards, J. Silva
> From: Vyacheslav Gordin[SMTP:scgordin(--nospam--at)hotmail.com]
> Reply To: seaint(--nospam--at)seaint.org
> Sent: Wednesday, May 26, 1999 8:11 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Reinforcement of massive pedestals
> I need to design a footing for a large vertical vessel in a highly
> seismically-active area. Soils are good, though, and allow the footing
> to be 20'x20'x36." The loads (including considerable weight and seismic
> shear and uplift/pullout) are applied through three baseplates @120
> connected to a 12'x12'x4'-6" pedestal centered on the footing. The
> height is dictated by the technological process.
> Within the contact areas I installed rebar cages similarly to short tied
> "columns." I also tied the tops of the three "columns" together with
> to resist considerable shear.
> Unsure about the reinforcement of the rest of the pedestal. Both the ACI
> 0.0018 and Caltrance's 0.0025 reinforcement ratios appear to be excessive.
> Any thoughts about how to reinforce the pedestal away from the areas of
> contact (apparenly, minimum reinforcement)?
> Steve Gordin, S.E.
> Irvine CA
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