Torched and Bent Anchor Rods
Torched and Bent Anchor Rods
(OP)
Concern:
On a current job site, several 1 inch anchor bolts/rods were poured into column pedestals out of plum. Construction workers decided to torch heat the anchors and bend the exposed 5 inches back to straight, with 17 inches imbedded in the concrete. The anchors have visible heat marks and some scortched threads. The concrete surface surrounding the anchors now has a glassy appearance. The anchors were bent to accept the base plates and are now being questioned by engineers as to how this heat treatment has affected steel properties. A tension load test has been requested, but not yet performed.
Quality Inspection has proven to be poor on the site and the contractor wants a, "The anchor bolts are okay, no fix is needed," type of an answer. However, this answer cannot be provided without additional information. If anyone has good material science knowledge or has been faced with a similar problem, your comments on this subject would be greatly appreciated.
On a current job site, several 1 inch anchor bolts/rods were poured into column pedestals out of plum. Construction workers decided to torch heat the anchors and bend the exposed 5 inches back to straight, with 17 inches imbedded in the concrete. The anchors have visible heat marks and some scortched threads. The concrete surface surrounding the anchors now has a glassy appearance. The anchors were bent to accept the base plates and are now being questioned by engineers as to how this heat treatment has affected steel properties. A tension load test has been requested, but not yet performed.
Quality Inspection has proven to be poor on the site and the contractor wants a, "The anchor bolts are okay, no fix is needed," type of an answer. However, this answer cannot be provided without additional information. If anyone has good material science knowledge or has been faced with a similar problem, your comments on this subject would be greatly appreciated.
RE: Torched and Bent Anchor Rods
As a side note, I would also say that if you do want to do the work, and I can't think of a quick and simple solutions, make sure the contractor pays you for this additional service.
RE: Torched and Bent Anchor Rods
Second, what steel grade is involved? If they are anything other than plain mild steel, I would reject them on principle, since the final product will not be of the quality specified.
If the bolts are really needed (ie any horizontal load is too much to be taken in friction under the column, or there is significant tension/moment at the base) then I would again agree with dougantholz.
That is, the only basis on which I would be inclined to grudgingly accept the bent bolts is if they are plain mild steel and are there mostly for show. (But I wouldn't have expected 'nominal' bolts to be as big as 1 inch dia.)
A tension test might well be unsuitable anyway - how will you verify that the ultimate load capacity of the bolts is still adequate without risking failure of the bolts during test?
Then another entirely different aspect is - has the concrete at the footing surface been sufficiently overheated as to reduce its capacity to resist the shear loads in the bolts?
RE: Torched and Bent Anchor Rods
RE: Torched and Bent Anchor Rods
If the bolts were quenched and tempered then they should be replaced - no testing required!
If the anchor bolts are notch-tough steel - REPLACE!
If the anchor bolts were HSLA (high strength low alloy steel) - the heating will cause the grains to grow hence reducing its' strength - I would probally have these replaced.
I would expect that the concrete holding the bolts would also be weaked. Concrete holds a significant amount of water tand this heating would have remove this.
Overall, if in doubt, remove the achor bolts drill and grout new bolts.
RE: Torched and Bent Anchor Rods
The bolts have been bent to approximately 30 degrees. The contractor is asking to cold bend them back. This seems acceptable as long they verify there has not been any plastic deformation (necking) of the bolts.
Any feed back?
RE: Torched and Bent Anchor Rods
For martenstic plain-carbon steels with more than 0.2% carbon tempering produces Cernentite, Fe3C. The heat cycle determines the grain structure. The quenching controls the hardness.
From the limited test you are proposing, you are trying to derive the proof stresses, yield strength and acceptability of field altering the specified design fastener. The variation of the proof stress, plastic deformation and heat treat temperatures is explained in terms of the relative dominance of three important factors: namely, (a) internal stress, (b) lattice-expansion or work-hardening, and (c) crystal reorientation. There are many factors your test is omitting; i.e. crack initiation, variation of Poisson's ratio with plastic deformation, micro-hardness, internal stress and crystal reorientation. Additionally the tests you propose are not a significant number of test specimens (considering the variance of installation) to have a high confidence of the results.
It appears the contractor is shoveling his incompetence and errors to your responsibility. I would recommend you decline the analysis as, “out of your expertise area” and request he provides his own Professional Engineering report to show they are acceptable. That reduces your legal responsibility.
With all that said, realizing the real world pressures, consider the factors above. Compare the results to the
Mechanical Properties
Proof Load (psi) 85,000
Yield Strength Min (psi) 92,000
Tensile Strength Min (psi) 120,000
consider hardness testing and NDT for cracking