rational design of embedments and anchors in concrete
rational design of embedments and anchors in concrete
(OP)
What is the rational approach to be used in designing embedded steel components, say for example a bracket attached to a reinforced concrete column, or a non standard anchor bolt made of mild steel rebar, attached to a column subjected to wind uplift.
Thanks in advance
Thanks in advance





RE: rational design of embedments and anchors in concrete
RE: rational design of embedments and anchors in concrete
RE: rational design of embedments and anchors in concrete
Back to Ron, do you have any reference in mind?. Some engineers tend to rely on ACI-based anchorage lengths in designing embedded rods designed for rods, something like 50times the rod diameters. I have also heard of this cone idea but dont know how to implement it.
Thanks once more and again
RE: rational design of embedments and anchors in concrete
For wedge anchors and the second check on the epoxy anchor, you compute the tensile-shear failure area based on the area of a truncated cone with height (depth) equal to the fastener length, and having a base diameter of about 50 percent of the fastener length. This is a conservative approach, as the failure cone is usually about the same diameter as the fastener length. I have no basis for this other than it is consistent with the angle used in shear testing for epoxy bond.
Hope this is helpful.
Ron
RE: rational design of embedments and anchors in concrete
It offers great explanations and equations concerning the tensile/shear cone design method.
RE: rational design of embedments and anchors in concrete
RE: rational design of embedments and anchors in concrete
RE: rational design of embedments and anchors in concrete
FYI these anchor plates are typically 1"x12"x1" and are pinned into the vault floor steel.
The concrete usually a minimum of 3'x3'x3' and extends down to catch the floor rebar. The anchor itself has horizontal cage type rebar every 4" in vertical height. The anchor plates have a minimum of 4" of concrete to the edge of the anchor, and a minimum of 8" clearance from the exterior of the pipe insulation, and can be up to 20 " from the pipe center line. We still see the splitting occur. Of course as corrosion attacks the first few inches of the embedded plates, the splits more severe.
Was wondering if we should consider a cork layer to prevent the expanding steel from stressing the concrete itself. This would only be used in the first 12" to allow the lower and cooler steel to bind to the concrete. Just thinking out loud along the lines of some type of expansion joint as the answer.
RE: rational design of embedments and anchors in concrete
The 1x12x1 anchor? Is this a BAR 1x1x12" long? Are these the anchors that hold the heated pipe? Are they hooked into the pedestal?
I didn't know that corrosion is a part of the problem. Could the cracking be from the expansion by products of corrosion?
Is it possible to have galvanized anchorages? There is no lateral oblation with cork and it would serve as a stress reliever and may force the expansion into the mass of the concrete where it may be resisted; the steel sleeves would serve the same purpose and these could be anchored into the concrete mass with better heat dissipation (The joint between the sleeve and the anchor may allow corrosive material to enter via capillary action). If there is corrosion, then the cork may also serve as a vehicle to cause additional corrosion. It is possible to use a foam sleeve and melt the foam after casting and filling the void with a high temperature epoxy material.
If the thermal expansion stresses are as large as they appear, you might be better served to create a crack path so that it is not 'random' and deal with it. Sort of a thermal expansion joint.
RE: rational design of embedments and anchors in concrete
Corrosion can be an issue, but I think that the majority of the problems revolve around the differential expansion of the steel plates vs. the concrete in the anchor.
Deeply appreciate your input on this subject. Thank you
RE: rational design of embedments and anchors in concrete
Further, the heat transferred by the plate into the concrete creates stress concentrations that are not easily attenuated by the concrete, particularly at those plate corners.
A round penetration cross section would better serve both issues. A "finned" pipe support (using radial fins, not longitudinal ones) would dissipate a lot of heat before allowing it to get to the concrete. If your connection between the pipe and the support were bolted or pinned, even more isolation would be gained. Further, vibrations from the pipe, if there are any, could be attenuated and you would not have such a rigid connection between the concrete and pipe that creates other loading problems.
If you did an infrared thermography scan of both conditions, you would see a significant positive difference in the "non-rigid" approach.
RE: rational design of embedments and anchors in concrete
The load transfers at the bolt head and this causes cracks to start from the head and propogate up and out in a cone. At some intermediate stage there is likely to be a fully cracked cone around the head with an active cracking zone at the crack tips. When this cone reaches the surface it pulls out, but at no stage can you say there is a failure cone with a uniform stress over its surface.
There is an excellent CEB publication on the subject. I will try to find the title and post it next time I'm on.
I have used reinforcing bar threaded on one end as anchor bolts to overcome these problems. So long as the load is axial I can't see why normal development lengths as calculated for reinforcing bar can't be used.
RE: rational design of embedments and anchors in concrete
CEB Bulletin No. 233
Title:
Design of Fastenings in Concrete - Design Guide - Parts 1 to 3
No.:
233
Year:
1997
Pages:
83
ISBN:
0-7277-2558-0
RE: rational design of embedments and anchors in concrete
State of the Art Report - (printed revised hardbound edition of Bulletins 206 and 207, Telford, London, 1994; ISBN 0-7277-1937-8; 249 pages) Order directly from Thomas Telford Ltd.http://www.t-telford.co.uk