cambering i beam

Date 01-08-2008 07:20 Edited 01-08-2008 15:43

Hello luckylogger, would you be cambering the beam the easy or the hard way? By that I am referring to whether you are trying to put camber into the beam by shrinking the bottom flange of the beam to camber it(hard way). Or are you trying to shrink it from the side, meaning you are trying to shrink the flange top & bottom on one side of the web only(easy way)? How much overall camber? Is this an A-36 material or A572 or some other sort of alloy? Is the camber that is required for the application a loaded or unloaded camber? I ask the question that way because if the requirement for camber is unsupported/loaded(meaning that you would have the ends of the beam setting on the floor or some other support and then measure a specific camber or would have the beam laying on it's side not having it's own weight supported to measure the camber? This would make a lot of difference in the amount of camber that would need to be applied in this particular instance. All of these factors should be considered to answer your question accurately. If you are looking at a lot of camber you may want to have the beam rolled by a fabricator that has that capability. If the beam is other than A-36 you may want to consider using some form of mechanical cambering system to avoid heat issues with the alloy or if using a heat/shrinking type application be very careful of maximum temperatures in the heat/quench regimen. With a little bit more information I believe there are folks on the forum here, as well as myself, who could supply you with, or direct you to, sources for performing the heat cambering you have asked about. Best regards, aevald
I probably should have thought of this first, go to the search function of the forum and type in "beam cambering" you will receive a number of postings with regard to your question, there are also some publications listed and possibly some outside sources given to help you with your question.

By swnorris (****)

Date 01-08-2008 17:45

Beams are typically heat cambered by standing the beam up on its flange and supporting it at each end, with the supports reasonably close to each end of the beam. Heat is placed in the beam web in the shape of a "V", and the heated area extends to include the flange. The length of the "V" is typically is at least half the depth of the beam, and the "V" width depends on the beam size, the beam length, the amount of camber, and the number of heated "V"s along the length of the beam. You might want to try a "V" at 15 feet, 30 feet, and 45 feet for starters, and if that doesn't produce the desired camber, you can add more "V"s between those points. If you add more "V"s, you might want to reduce their depth and width, but that will depend on how much camber you have prior to adding them. You have to be very careful not to heat too much of a "V" area because the beam web will start to buckle. Also, your heat should not exceed 1100 degrees F. The amount of camber can be checked by pulling a string from one end to the other of the beam and measuring the difference in the middle. The end result will be a beam that has NO LESS than the required camber, with a nice continuous curve. You can't just put a "V" in the center and camber the beam. Without a continuous curve, the beam will not serve the full intent of its design requirements.

By Bob Garner (***)

Date 01-08-2008 19:16

And for what it's worth, the camber of a beam is measured in the shop, not out on the job (if this work is covered by AISC - AISC Code of Standard Practice, Section 6.4.4). So if it's O.K. on the shop floor, the owner can't say otherwise.

By Bob Garner (***)

Date 01-08-2008 19:23

Also, in the old days, we used to call this heat shrinking. The V's that you are heating are actually shrinking - they try to expand as they are heated, the expansion is resisted by the remainder of the beam remaining cool, the heated segments then undergo some plastic deformation as their expansion is resisted, and they cool off with this plastic deformation remaining built-in, or you could say they shrunk, pulling the camber into the beam.

By 803056

Date 01-09-2008 04:04

You can induce both camber and sweep by heating the member and letting to cool just as explained in the previous responses. However, you can get the desired movement without heating the base metal more than 300 to 600 degrees above ambient. The hotter you heat it, the more movement will occur, but there are metallurgical concerns that have to be considered with many types of base metals. Less heat is usually better if it will produce the results you are looking for. In this case, the difference in the heated area versus the area not heated is what causes "heat shrinking" to work. So, you want to heat the area of interest as quickly as possible to maximize the difference in temperatures between the heated area and the unheated area. I often clamp angles or lay plates long the edges of the area to be heated and place wet rags on the opposite side to maximize the temperature difference.

There is no need to cool the heated area with water. It will cool by itself and the movement will happen. Don't get excited when the beam moves in the direction opposite to the direction you want it to go while heating it. It will come back as it cools. You may have to reapply the heat to adjacent areas multiple times to obtain the proper amount of camber (or sweep).

You can also use this technique to straighten members that have been dropped and accidentally bent.

Good luck - Al

By qcmike

Date 02-01-2008 21:48

Lots of good ideas. If it is code work such as D1.1, D1.5, it clearly explains what temperatures and cooling options. Not to hurt anyones feelings, I don't remember the wet rag section. So just make sure you follow your code. Or, I bet the wet rags works fine, but you may get some quenching effects creating a brittle condition. Our codes allow artificial cooling only after the steel has air cooled to 600F. After that you can only cool by directing compressed air at the heated areas. Leave the water hose alone.

One time a junior guy decided to camber some light i beams on his own. He heated them cherry red, guess what. We had to throw them away. Steel at maximum temp. is a very dark dark red if noticeable at all. You should always use temperature indicating crayons.

The maximum heat for regular A36/A572 steel is 1200 degrees. Above that an inspector may reject the steel. Costly, but above 1200 you change the grain structure of the steel therefore reducing its yield and fatigue strenght. Not a good thing.

We use truncated triangles 10" wide at the flange and 2" on the bottom. Heat on both sides in a coordinated manner from the top flange to the web. I need to share it is never an exact science. Steels change, employees change. If we are looking for a 3" camber on a W36 X 135 or so we start with 5-8 v-heats evenly spaced. Usually it's light but we can tweak the camber from there. It's not easy to take excessive camber out and keep the arc smooth.

Good luck,

qcmike

By XPERTFAB (**)

Date 02-11-2008 06:54 Edited 02-11-2008 06:57

As it now at this time in history very important to speak as to be understood by the lowest common denominator within the shop or field personnel so as not offend them, how cool would it be to actually have someone make a video of this important process for all to enjoy and benefit from. Currently, when I point out to others that they can read on this forum some highly useful information on this very subject; I get strong protest from those who will not read little more than a cereal box yet are charged with the responsibility in performing this work.
The information like is carefully explained in this thread is a certainly source of ongoing profit to someone who has the abilities and time to put this on video. Just food for thought.

This discussion is really important as I have recently seen a large bridge repair on a major highway which after being heavily dmaged by a large falling boulder, was repaired by a concerted effort of applied heat. When you drove past the project on the detour section you could sometimes see the actual work in progress. Good looking inspector guy watching as crews heated bent steel elements to straighten them. Really cool to see the contrast between the evening sky and the bright red torch heated steel. Now when I cross over that section of the now repaired road I am inexplicably and unconsiously compelled to increasing my vehicle speed. Strange phenomena for sure!

BTW My thanks to all who have inputted here! The careless work in the heating of steel has long been a personal pieve of mine. It is good to see that there are others who have voice on this subject also.

By Joseph P. Kane (****)

Date 02-11-2008 11:54

XPERTFAB

If you saw "bright red heated steel," they definitely overheated it, and probably destroyed it. This might look interesting, but it is definitely a bad example of how to do it.

By XPERTFAB (**)

Date 02-12-2008 17:30

Yup! I would completely agree with you! The point is all of this is that ignorance continues even though there is a tremendous amount of readily accessible information on the subject. Laziness and lack of desire to excell in your trade seems to certainly be the prevalent tone in the field work performed in my area. Sad it is that vast libraries of knowledge seem to go more frequently unused these days when distractions such as TV and IPODS are so good at "sucking you in and eating up your time." I've got a teenger who is fortunate enough to be able to have access to all the shop fabrication equipment any person could want. However, he has little to no interest nor do his friends in anything other than computers, IPODS, video games and oh Yes! the cell phone.
I work with guys that despite the fact they make their living with the skills and knowledge of the welding trade, could care less about putting even the smallest amount of effort to expand that knowledge. So the things like I witnessed on that bridge repair continue throughout the world owing to a level of ignorance and indifference to doing the job right. You would have to exercise some intiative to gain the skills and knowledge to be talented at your craft. Seems outside of discussions amongst a few in forums like these, relative little effort is put forth by the masses to become more learned in the skills of this trade. Thank God for those that are like yourself and the others here who are interested and concerned enough to share knowledge important to the physical construction of the world we live in. Maybe someday when people figure out that the "information age" is not as profitable as they thought it once was, then they as educators will reconsider their mistakes in removing the "blue collar" experience from the vocational training offered in high schools througout the US. Thanks again for all you input on the various forum topics you add comment too!

By HgTX

Date 02-01-2008 22:56

There's some related discussion here:

http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=10596

Hg