I am sometimes surprised by the response of engineers to some types of
situations. We have material standards, design standards and safety factors
that are sometimes acknowledged to be outrageous but make design easier to
accomplish in many conditions (okay, the opposite can also be true).
Frequently, it is easier and less expensive of engineering time to simply
specify the maximum requirement (e.g. full strength and over-the-shoulder
inspection) but it is not necessarily efficient of owner's resources (e.g.
total time, materials, money).
The design standards do not distinguish between shop or field welding. The
work should be done to the required quality. In this case, the work is an
interior retrofit and one assumes that there will be a controlled
environment, so that is removed as a variable.
So, my following comments/questions are simplistic but intended to elicit
those experiences that have caused what I perceive as overly cautious
attitudes.
I have given my suggestion at the end - feel free to take a shot at it.
> From: "Mike Hokama" <m_hokama@sbcglobal.net>
> wide flange beam approximately 55' long inside of an existing restaurant =
> and the contractor is asking about whether it is possible to bring the =
> beam inside the building in sections and then welding it together. Is =
> there any problem with doing that provided the welds are full =
> penetration?
> Mike H
The work is inside and the contractor is asking a question. Mike has
determined that the beam should be welded and that the welds must be full
strength. We are starting from a point of limited terms of reference. We do
not know what the beam supports.
> From: Daryl Richardson <h.d.richardson@shaw.ca>
>
> I don't like this but I have done it in the past.
Surely this is not driven by anything other than mistrust of the welder's
ability and expectations of the contractor's greed. There are limited
conditions where it is inappropriate to use full section welds.
> I would locate the weld at a point of low moment
Why limit locations? Of course, such a condition would be automatic where
the beam selection is controlled by service conditions or unbraced length
(hmmmm, there's a thesis topic in that point). Otherwise, I assume this is
simply to provide additional safety.
> or have someone specializing in welding inspection do a full inspection of the
> weld.
Inspection is practical. What level of inspection would you specify? The
weld standards provide very limited guidance on this point.
> By low moment I mean low relative to the full moment capacity of the beam.
Why? Do you not trust that a properly executed weld will actually be
stronger than the parent material, especially with the added level of safety
inherent in the connection strength design requirements?
I note that you did not restate that the welds had to be full strength.
> H. Daryl Richardson
> From: "Micayas, Julius" <jmicayas@riverconsulting.com>
> and a full penetration of weld will work.
Why not a well done weld that is adequate+? Is this the short answer or the
essential answer?
> Engr. Julius Micayas
> From: "Thor Tandy" <vicpeng@telus.net>
>
> FWIW I try to avoid site welding wherever possible. Unless you can get =
> a competent site inspector who will take responsibility for the =
> workmanship, quality usually nowhere near shop fabrication quality.
>
> I suggest designing bolted splices that can be prepared in the shop.
On the surface, this is the best answer and the worst answer. It's not clear
if the shop preparation would include any welding or other fittings or just
holes.
I disagree on the quality point. You can get adequate quality in the field
and inadequate quality in a shop. The objective is not perfection.
Best because there are cost efficiencies to avoiding site welding (e.g. no
need to bring a welder/inspector to site if you don't otherwise need one).
Worst because it implies that (field) welding is not an appropriate option
and that bolting has no trade-off conditions.
Of course shop preparation tends to be less expensive than field work and
should be maximized for either case. Also, I recognize that Thor is in a
shaky part of the world where welds are viewed with a suspicious eye.
> Thor A. Tandy P.Eng, MIStructE, Struct Eng=20
> From: "Steve Gordin" <sgordin@sgeconsulting.com>
>
> At 1/3 of the span the "low" moment will be at about 90% of the maximum, not
> too much of relief. Even if the the beam does not carry any noteworthy
> load, the flanges will be about 3/4" thick . Imagine welding in the open
> air...
I'm imagining ... I wonder what Harold's previous life experiences might add
to this point.
> I would agree with Thor (unless the beam is exposed). If it is, I would
> specify the best firms available for welding, inspection, and TESTING.
Are we retro-fitting Fort Knox? Can we knock the expectations down to the
top of the first standard deviation?
> Steve Gordin SE
> From: "Alex C. Nacionales" <anacionales@insightts.net>
> To be conservative for added safety. I would also recommend that =
> it should be bolted as well including ultrasonic weld testing.
Bolted for ... fit-up/erection purposes?
Ulrasonic testing ... would you require this if it were spliced in the shop?
> Alex C. Nacionales
> From: "y.hamida" <y.hamida@scs-net.org>
> on site welding for long beam not prefer
> try to weld end plates at the boints
> where the moments are minimum at shop ,
> and join the parts together by bolts at site .
You took the words from my mouth. Additionally. this would probably use
simple fillet welds instead of full strength - possibly more welds but
probably smaller sizes. The volume of consumables may still be less - less
electricity, less heat, less rod/wire, less time.
As Steve noted, intermediate points of a segmented simple span beam do not
provide much reduction from maximum moment. So, location is not really an
issue from a strength perspective.
> Dr.hamida - syria
Regards
Paul
--
Paul Ransom, P.Eng.
ph 905 639-9628
cell 905 802-3707
fax 905 639-3866
ad026@hwcn.org
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