Gerber Beam
Gerber Beam
(OP)
I am a little confused about the different load combinations to check for a gerber system. Is the load combination LL+DL whole length, DL whole length +1/2LL on cantilever and DL whole length +1/2LL middle?
Why 1/2LL? Obviously LL+DL whole length would govern.
My other question is how to choose the length of the cantilevered portion?
Why 1/2LL? Obviously LL+DL whole length would govern.
My other question is how to choose the length of the cantilevered portion?






RE: Gerber Beam
RE: Gerber Beam
RE: Gerber Beam
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: Gerber Beam
RE: Gerber Beam
Thanks.
RE: Gerber Beam
RE: Gerber Beam
RE: Gerber Beam
Presumably the same way that I don't know.
It's been said before, but this forum is on the WWW, not the USWW.
RE: Gerber Beam
RE: Gerber Beam
Going by slickdeals, I have designed many cantilever/span systems.
I always designed for the worst checkerboard loading for my own comfort; which, meant three cases for the cantilever beam, LL on the drop in span only, LL on the drop in and the cantilevers that support it (bottom flange compression case), and full LL over the length.
There were no special code requirements when I designed those, but I would not have done less, even if permitted by code.
Confirmed, it is cantilever/span.
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Gerber Beam
While the term might be common in Canada, it is not so in the US and perhaps other areas, as noted by the responses. I have seen several different terms over the years to describe the beam you are dealing with...infill beam, connector beam, slot beam...
Unless your code dictates otherwise, this beam section should be subjected to the same loads as the other sections...DL+LL
The length of the cantilevered section is chosen at the point of moment inflection and where shear is moderate, but not maximum (commonly less than or up to 1/4 of span)
RE: Gerber Beam
Thanks slickdeals, now I know what you are talking about.
RE: Gerber Beam
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Gerber Beam
RE: Gerber Beam
He is calling all engineers pigs. muhahaha, good job Rowing, keep on rowing.
RE: Gerber Beam
RE: Gerber Beam
RE: Gerber Beam
RE: Gerber Beam
Article 4.1.6.3 of the NBC is attached. Usually Gerber beams are used for flat roofs of large, box type buildings.
A few years ago, the NBC required 100% of snow load to be considered on any area and 0% on the remainder. This was deemed to be unrealistic for snow load on a flat roof, so about twenty years ago, it was changed to 50% on the remainder.
If 100% of the snow load is placed on cantilevers and drop-in spans and 0% on the continuous spans, there would be negative moment across the entire span. This was deemed to be an improbable condition on a large, flat roof so the code was changed to what you see attached.
BA
RE: Gerber Beam
is a just a term used for framing systems, usually roofs of industrial buildings - in my experience - and is about optimizing steel (ie. using cantilevers and 'drop-in' beams). Typically used with OWSJ. It is common in Canada. The CISC (AISC) likely has publications and guidelines with regard to the gerber system. I believe that the CISC has a set of seminars coming up for industrial buildings.
RE: Gerber Beam
I find it quite amusing that you use a vaguely known engineering term for a beam system that you don't know how to design, while acting extremely condescending to those whom have never heard of it. A little humility goes a long way, even for geniuses.
RE: Gerber Beam
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Gerber Beam
Didn't realize you were such an old codger. These links will provide all you want to know about the Gerber System but were afraid to ask:
http:/
BA
RE: Gerber Beam
You know, I learned years ago that the more you know, the less you know.
From what I hear here, I guess the term is applied in bridge construction and steel/glulam link-span systems?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Gerber Beam
RE: Gerber Beam
Michael.
Timing has a lot to do with the outcome of a rain dance.
RE: Gerber Beam
you are correct.. many of us on this forum appreciate the experience of the elder statesmen on this forum..
RE: Gerber Beam
RE: Gerber Beam
Not in the bridge construction I've been involved with. We call 'em "drop-in sections".
Then again I can't remember the names for any of the truss systems, so I probably don't count as an engineer anyway--but at least I know which terms I've heard before, and "Gerber" ain't one of them.
Hg
Eng-Tips policies: FAQ731-376: Eng-Tips.com Forum Policies
RE: Gerber Beam
As others have pointed out, you do indeed need to consider partial loading on the gerber system per your local Code.
Typically, I've found that cantilevers on the order of 15-20% of the interior span work well.
Unless you're designing an element that repeats in large numbers, I've found that the optimization of the member sizes is not that important. In my market, contractors simply like the beam-over-column detail for steel. Of course, they like it a little less when I make them brace the bottom flange at the columns which is very important.
Older versions of the wood design manuals (Canada & US) provide information on the Gerber systems, including recommendations regarding the cantilever dimension.
RE: Gerber Beam
On April 23, 1988 an 80' x 80' section of the Save On Foods store in the Station Square Development in Burnaby, BC collapsed on opening day. The opening was attended by a number of senior citizens. There was one photographer who managed to take a few amazing photographs considering that the roof was in the process of collapsing above him.
A comprehensive report was written about the reasons for the failure. The main reason attributed to the collapse was the lack of lateral bracing of the bottom flange of the cantilevered beam where it passed over the column. Other factors were the underestimate of dead load and the overestimate of yield strength of the beam. The report puts the entire blame on the engineers responsible for design and inspection.
The photographs suggest to me that several joists were not welded to the top of the beam. This, however is not mentioned in the report and has not subsequently been acknowledged by anyone who assisted with the preparation of the report.
Page 1 of the attachment shows the collapsed area after the event. Page 2 shows the failure in progress.
BA
RE: Gerber Beam
BA
RE: Gerber Beam
RE: Gerber Beam
The beam which failed was a W24x76. It had been identified, along with one other beam as requiring remedial measures. A mill certificate indicated a yield strength of 55,700 psi. The design strength was 44,000. The engineers concluded that remedial work was not required after all as the beam was 26% stronger than their design had assumed.
The report stated that the mill certificate was based on coupon tests taken from the web of the beam. The strength of the web is always greater than that of the flange, so that decision was criticized.
Elsewhere in the building, beams were of different sizes and different spans.
BA
RE: Gerber Beam
I have only been around for a decade, and spent another 8 years in the building/contracting trade (where I feel I picked up a tremendous amount of valuable experience).
It seems to me that there are two kinds of "older guys" in the profession.
There are guys that I can't believe have worked 35 years and can't answer very simple questions in areas in which they are supposed experts.
Those, like you guys seem to be, that seem to be full of insight.
The former, I believe, mastered nothing more than how stay in a job for 35 years.
I don't think those types would bother logging onto any forums.
RE: Gerber Beam
Michael.
Timing has a lot to do with the outcome of a rain dance.