Heated and Bent Anchor Rods

[NWK]

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.

 

[Ron]

Rebar has variable chemical properties that can change the metallurgical character on heating. Rebar is typically only required to meet a tensile strength requirement (and elongation).

For 1" diameter material, pre-heat and post-heat could be required to properly accomodate the heating for straightening.

Rebar is a generally a mixture of many different kinds of scrap steel, thus the variable properties.

An in-place load test would be appropriate.

 

[NWK]

The designer has informed me that the unfactored loads on each anchor rod is 21 kips. The anchor bolts are Quenched and Tempered and apply to ASTM A449. Many anchor rods throughout the project have been tampered with, but in this particular case they are imbedded in an incorrectly formed pedestal without proper edge distance. The footing will be removed and rebuilt for sure. Because it is being removed, it was suggested to perform the load test on these bolts. The allowable load on each rod is 31 kips. Therefore, it was suggested to test them to 26 kips, the average. If it reaches this level, the test will be stopped. If it snaps prior to this, the heating and bending had ill effect. Most likely, due to unproper edge distance, the concrete will fail prior to the anchor. This is a large steel framed-structure designed with shear lags in the perimeter columns. This is new terminology to me, being a young engineer, but the structure is a large open hanger-type building.

 

[Ron]

Heating a quenched and tempered steel can severely anneal it, changing its properties.

After you get results, please post and let us know how it turned out.

 

[Ron]

Heating a quenched and tempered steel can severely anneal it, changing its properties. My apologies for reading your question as "rebar" rather than a threaded rod.

After you get results, please post and let us know how it turned out.