Bond strength of concrete to new galvanized smooth round steel pipe

[ajk1]

Is there any data on the allowable bond stress of concrete to hot dip galvanized smooth steel pipe? The galvanized steel pipe diameter is about 150 mm (6"±). The application is an uplift force to a vertical steel pipe, extending down into the ground and encased in concrete below grade. There are allowable (unfactored) bond stresses on plain round rebars, in old building codes, but they are not for galvanized surfaces, nor are they for such large diameter elements as pipes. I would expect that the galvanizing would much reduce the allowable bond strength, as would the diameter.

 

[Tmoose]

What are the allowable bond stresses in those old codes?

Is the pipe used as a pipe, or a column/post?
Is it open at the top, within a foot or so above grade?
If there is no product inside I'd think about "toe-nail"ing it with anchors drilled at an angle.

How much is the uplift force?

I'm guessing It's probably too late to weld some features on the pipe before the concrete is poured.

A buddy lived and worked in big city in Egypt for a few years back in the late 70s/early 80s. On a visit home He commented on their common use of smooth rebar in new construction, and that building failures were not unheard of.

 

[Ron]

Partial embedment of galvanized steel in concrete is not a good idea. The chemistry of the concrete and the galvanizing will react. As for bond strength, it will be relatively good at first, but as the chemical reaction continues, "salts" are produced which will reduce the bond interface. I would not depend on it. Provide a shear key instead.

 

[ajk1]

To Ron - ok, I will convey that to my colleague whose job it is. For my interest though, I know that galvanized bars are successfully routinely used in reinforced concrete. This is done in Bermuda I know because the head of the company I previously worked for had spent 10 years as chief of public works in Bermuda and he told us that. So to be clear, are you saying that it becomes a problem only when there is partial embedment?

To Tmoose - for plain bars up to 1.375" diameter, the allowable stress in the 1963 ACI code was 1/2 x 4.8 x (f'c)^0.5 / bar diameter, but not to exceed 160 psi. For 5000 psi concrete and a 1.375" diameter plain bar, this works out to be 123 psi allowable working strength design bond stress. However cannot use this formula for a 5" diameter pipe because the formula is limited to bars not exceeding 1.374" diameter.

Using current Code, I don't think they give a development length for plain bars, but halving the value for deformed bars (as was done in the old ACI 1963 Code), and translating it from LSD to WSD, it works out to 127 psi.

It is not open at the top; it is a post; it does have end anchorage but the design also assumed a bond strength with the concrete and summed the two to get total uplift resistance.

Anyway, we are getting away from my question: "what is the allowable bond strength to plain galvanized steel pipe". I take it so far that no one knows the answer, and based on Ron's response we should not rely on that bond anyway.

Thanks

 

[oldrunner]

Just wouldn't do it.