If you have ever performed a tension test on a A325 bolt that has been welded upon then you will quickly understand why you do not weld them. Especially after they have been installed and fully tensioned. when I come time for me to fix someone elses crap as i do way too regularly, I actually weld upon the head of the A325 bolts both hex and domed head (TCB style bolts) to relieve the tension on the bolt so that they can quickly be removed from the "iron" with little more then a hard tug on a spud wrench or an electric imapct of the 1/2 to 3/4 inch variety. This saves the need for a torch to heat the bolts which takes much longer and is a bit unfriendly to the painted or primed surface. Since I deplore looking at work that appears all burned up such as paint finishes, and I don't want to spend the time repairing finish; this method works awesome. The bolts get loose, I correct the problem oftimes just plumb and align; new bolts go in, tension them up and I am down the road with the superintendent shaking their heads as it was completed with little effort. Point is heat like directly welding on A325 bolts is not good. In LA a few years back we erected some canopies made of structural steel over walkways of a mall that had direct tension connections for tension columns carrying a larger lower element below. Columns attached to bottom flange of beams spaning walkways above. Engineer had spec'd A325 bolts to be welded to bottom flange at bolt head for erection purposes. Welding performed per requirements and was fully compliant with plans. Hung the iron, tensioned the bolts and left for the day. The next morning the whole lower element (about 6000lbs) was laying on the concrete walkway. Must have made one hell of a noise that night when it came down. A look at the bolt head (TCB) post to failure revealed some very interesting fracture lines. The steel erector immediately de-erected the remaining portions of the canopy that had connections with bolts that had been welded in like fashion. We cut off the welded bolts and erected it again with new bolts and no welding. More hassle for sure but nobody was dead out of the deal.
Welding A307 bolts with direction of the engineer? Sure thing. If you have ever had to puddle weld an anchor bolt to a column baseplate then you know the drill. Preheat to burn off galvanizing and/or zinc plating little wirebrush action and let er rip with the low-hy. Saves the butt of the concrete guy who screwed up anchor bolt placement. Here in western Colorado, everything I work on has some of this action to correct anchor bolt locations. Procedure is torch slot baseplate of column, fabricate weld washer as required with drilled/ punched hole for anchor bolt to project through (now too short owing to weld washer thickness for full engagement of nut), preheat and remove plating on anchor bolt, plug weld/fillet weld remaing stub of anchor bolt to baseplate. Works good as long as plumb and align of building is complete prior to final welding. Last building mess I fixed for the local hack and whack erection company who preceeded me, had 143 anchor bolts repaired just this way. Everyone, welded A307 anchor bolts to column baseplates.
DO NOT PERFORM THIS REPAIR AS OUTLINED TO ANY ANCHOR BOLT THAT INSTALLED INTO CONCRETE WITH EITHER EPOXY OR ACRYLIC ADHESIVE AS IS COMMONLY DONE. WELDING HEAT WILL INSTANTLY DESTROY THE INTEGRITY OF THE ADHESIVE. SOON AFTER APPLYING HEAT TO ADHESIVE ANCHORS IN CONCRETE YOU MAY NOTICE A RAPID ACCELERATION OF THE COLUMN TOWARD EARTH IF NOT PRPOPERLY BRACED!!!!
A LITTLE OFF THE TOPIC? SURE IS! BUT EVERYONE HERE KNOWS HOW EASILY SPECIFIC INFORMATION PERTAINING TO A PARTICULAR SET OF CIRCUMSTANCES GETS QUICKLY DISTORTED SO THAT IT IS VIEWED AS TO SUITABLE FOR GLOBAL APPLICATION IN ALL SITUATIONS.
XPERTFAB
Chet,
HS bolts get a quick "No" answer if you ask the mfg of the bolt about it. I asked the bolt mfg (because the higher ups wanted to know why we couldn't weld) about tacking the head of a bolt to keep it from turning and they don't like the idea of any heat being applied as all of the other replies have stated already. I even posed this question to the AISC who didn't really answer my question at all, other than to say that it was a bad idea.
If the clip angles are being welded with fillet welds to make up the designed end reactions, it seems seal welding the bolts are a mute point regardless of the grade. I don't think that enginners like to try and calculate bolts and weld in the same joint, so it is either welded or bolted, but not both.