huangyhg

weight of steel structures per area of building
i wanted to make a little survey on the amount of steel used in your designs, for example, your latest housing building, commercial buildings, warehouses, etc., in terms of weight of the structure per area of it. some of my clients tell me that i use too much steel, and that they have "other" engineers that will provide lighter structures. are there really rules of thumbs for this?
thanks!
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i design the framing to resist the code prescribed live loads and lateral loads in addition to whatever other live loads exist due to special functions and the dead loads imposed on the framing. based on recommendations heard at aisc seminars, i use as many common beams sizes as possible to reduce the number of different connection types and to create as many repeatable fabricated components as possible. mass production reduces costs. about 8 years ago, a client (architect) accused me of overdesigning a single story commercial building. the client said, "you must have stock in w14x22 beams because you used them everywhere." that wasn't true because there were larger and smaller beam sizes used, but i did use that particular beam size in several places where a shallower beam with lesser weight per foot might have worked. also, the architect complained that i used w8x21 columns everywhere and the footings were too big. again, not true, but i did use a common column and footing size alot for similar reasons i used a common beam size. i told the architect that they could have the framing and foundation redesigned and if the other designer could create a design less expensive than mine, i would refund my design fee. they took me up on my offer. the structure was redesigned and cost estimates were made on that design. my design was less expensive by about 15%. i got my design fee and a longtime client, even though the client paid the other engineer, too. maybe i was lucky but since then, i have not heard comments that i overdesign from anyone and i have not changed the way i design. i don't know about a rule of thumb because each building is different. the means cost estimating handbooks might have some kind of rules of thumb, but i'm not aware of them. developers use rules of thumb to lock into a gmp for their clients. if you work for developers, they might be the ones complaining because it's my experience they underbid stuff anyway.
depending on your locale, you might be looking at 3 psf for joists and deck, another 1 psf for beams and 1 psf for columns. add maybe 1/2 psf for misc... i did a large cargo terminal building with 40' clear height inside... 400,000 sq.ft. weight was about 8 psf including girts, etc.
dik
i think your clients probably have gotten information from a fabricator for an existing building and are comparing it to one you did. you might have overdesigned it or they might have underdesigned theirs, or they may be comparing apples and oranges. i would ask them to provide the documentation of the building they are comparing yours with and not feel obligated to provide an answer until then.
but be nice about it.
use reinforced concrete, rebars are less than 3% of the section weight. compare to steel buildings that are fireproofed.
choosing the material and structural system for a given building is a bit of an art - perhaps these clients would prefer wood on the lighter buildings and concrete on the heavier, if it's simply their dislike of steel.
if, instead, it's an attempt to get you to skimp on structure, first make sure you're on the right track (pay another local engineer to backcheck you, or ask the client for another building to review yourself). if you've checked your loads and designed the building with a level of conservatism you are comfortable with, you have to just take the chance of losing those clients to another engineer. they may heckle him in turn to lighten the steel.
what i really suspect is, as haynewp said, they're comparing apples and oranges. trying to estimate the average amount of steel in a given type of building is very difficult, it is so dependent on the architectural design, the loads and the systems used.
good luck.
thanks for all of the valuable comments. i'm very carefull abou the comments my clients make, because ussually they are comparing apples with oranges.....but this time they were comparing the same kind of building, an office building. i try to use simple designs, with regular patterns, repeating beams and columns in order to make fabrication easier. i got a 8 psf design, considering a deck on top the the beams (4 story building). my client told me that he got a 6 psf design on a similar building, i think in archiving that the other enginer might have gone over the code limits on several issues (my client did'nt give me much information, so he might have been bluffing in order to put some pressure....) or perhaps making a very hard to build structure for a very simple project.
it's good to keep in mind that least weight does not always mean most economical. the steel material only accounts for about one-third of the total framing cost. two-thirds of the cost goes into fabrication, erection, and other labor costs. like archeng59, i often add steel tonnage in order to have a more repetetive building that cuts down the labor costs.

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