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EddyCurr
09-30-2011, 03:39 PM
When and how are holes made in steel beams used for modern commercial
building construction?

I have spent some time gazing up at the exposed beams and columns of
a facility. This has led me to wonder whether the holes for all the fasteners
are drilled on site (which hardly seems economic) or if they are pierced
off-site in some precision manner that makes allowances for the usual
construction tolerances.

.

bob308
09-30-2011, 03:52 PM
in the shops i worked they were laid out to the print and drilled with a magnetic drill. one shop had a machine trhat punched them after being programed from the print.

dalee100
09-30-2011, 03:57 PM
Hi,

Yep drilled off site in a fab shop. The clearance loads are fairly generously sized. They have specialized NC controlled drilling machines to locate the holes in the beams. Back in the day they used to punch the holes. But advances in machines and tooling allow drills to preform faster than punches.

dalee

duckman
09-30-2011, 04:03 PM
I've done repair work at a steel fab co. and there hyd. punch would do 1 1/4" holes in 1/2" plate after I readjusted the hyd. control, it used a 2 stage pump and the resident brain surgeon decided that he could make it faster, by the time he got done it wouldn't punch a 1/2" hole in 1/4" plate. :eek: :D

madmec
09-30-2011, 06:28 PM
Hi,

Yep drilled off site in a fab shop. The clearance loads are fairly generously sized. They have specialized NC controlled drilling machines to locate the holes in the beams. Back in the day they used to punch the holes. But advances in machines and tooling allow drills to preform faster than punches.

dalee

The reason for drilling holes is different, punched holes are prone to cracking due to overstressing the material and the scribe lines from the process.

Punching is still faster than drilling, but not allowed anymore.

Greets from germany

Thomas

Errol Groff
09-30-2011, 07:54 PM
I saw that being done on one of those "How Do They Do It" type shows. The holes were drilled by a gang drill that rode on a rail alongside the beam and the drills they use have an included angle of (I think) 150 degrees. The usual included angle is 118 degrees for general purpose drills. The reason for the 150 degree IA, they explained, was to minimize the burr on the back side ot the hole.

Strange the little factiods that get caught in memory!

Davo J
09-30-2011, 08:21 PM
Interesting Thomas and Errol, thanks for the explanations.

Dave

wierdscience
09-30-2011, 10:04 PM
One word - Plasma

http://www.youtube.com/watch?v=sDwup-rtCYM&feature=related

EddyCurr
10-01-2011, 12:25 AM
Thank you to all for the replies - very helpful.

As a supplemental question, when there are diagonal lateral support beams that
join a primary beam at some distance away from a column, I notice that the
web of the support beam approaches the main beam at, say, a 15-20 angle.
Instead of being attached directly to the primary beam, there is a rectangular
flange plate bolted flat to the primary beam and the support beam is welded
at an angle to the flange plate.

Am I right in supposing that the flange plate is welded to the support beam
during construction? Or are the fabricators able to add these flanges at the
correct angle and location offsite beforehand and still have it all fit together
like an erector set when the ironworkers assemble it ?

.

EddyCurr
10-01-2011, 12:32 AM
One word - Plasma

http://www.youtube.com/watch?v=sDwup-rtCYM&feature=relatedVery nice.

That sure has to be an improvement over the cutting time and maintenance
required for annular cutters, drills or other similar tooling ! If what appears to
be a routine for establishing the Z-axis position for each hole could be
shortened or eliminated, making such holes would be close to instantaneous.

.

djc
10-01-2011, 01:39 AM
Am I right in supposing that the flange plate is welded to the support beam during construction?

On the drilling question, have a look at

http://www.avenger.oceanmachinery.com/

The site also contains very interesting stuff on sharpening the drills.

Flange plates are welded on at fabricators.

Speaking from a UK perspective, all steel frames are modelled in 3D, common system is Tekla (http://www.tekla.com/uk/products/steel-detailing/Pages/Default.aspx). This produces all members, which are further broken down into each element of the member (main beam and endplates in simplest form). This is shown on a fabrication drawing, which is fed into the fabricator's production schedule and the different 'lines' (plate cutting - laser for thin, oxy for thick, beam, machining) of the production process coordinated so all parts end up with a welder somewhere at the fabricators to glue them together. They then go to the paint shop.

Steel erectors are usually a subcontractor to the fabricator and are paid on a piecework basis. This is how their programme/schedule is discussed - number of pieces per day required. This determines number of erection gangs and number of cranes required. Anything that doesn't fit, they leave behind for a snagging gang who are in a separate commercial relationship with the fabricator.

If there is on-site welding to do, it generally means the fabricator has screwed up (or the designer has changed something). Anything that is site welded is usually die-pen tested and then has to be site painted.

EddyCurr
10-01-2011, 02:28 AM
Thank you,

Having everything, including paint, done at the fabricator's is the way one
would want it done in a perfect world. This must raise the standard
required of the foundation contractors by some orders of magnitude over
what once was tolerated in industry.

Has end-to-end technology now pretty much eliminated any pucker factor?

I remember a situation in the late '70's during a period of steel allocation and
very extended lead times in the Canadian steel industry when a keying
error by a telex operator during the ordering process led to the rolling
of a sizable plate of incorrect dimension in central Canada that was required
by a bridge fabricator in western Canada working to a tight schedule.


On the drilling question, have a look at

http://www.avenger.oceanmachinery.com/

The site also contains very interesting stuff on sharpening the drills.
In the following video, a test results in 500 holes in 66 min. They estimate
they are producing a hole every eight seconds (3,960/500). The cobalt
drill bit is claimed to be still sharp after 500 holes.


Drill Bit Test for Structural Steel Drill Bits (http://www.youtube.com/watch?v=-KildMNztMc)
A better result than I would have guessed. I wonder (rhetorically) what the
cost/performance comparison is between drilling and plasma procedures ?

.

RussZHC
10-01-2011, 02:37 AM
EddyCurr:

don't know the answer to your question (answered by djc, neat!) but if you want to see perhaps the most complicated structure in that regard:

http://en.beijing2008.cn/99/29/column212042999.shtml

there is a bit of an animation there about the Beijing National Stadium (Bird's Nest) and IIRC they built sort of "sub-sections" and then fastened together on site [there was a Discovery channel feature back around 2008 at the time of the Olympics...if you ever get a chance to see it, well worth while]