huangyhg

truss vs. beam
this is a quick one. i have a long span beam carrying brick. i can't change any of the design parameters so this is a price question:
does anyone have a feel for the cost of a shop built truss (in cost per pound of steel) that i could compare with a plain steel beam?
i am looking at a w40x290 vs a truss with hss8x8x1/2 chords with hss6x4x3/8 webs. i need to account for the welds and gusset plates in my cost analysis.
the cost of steel is constant for the majority of standard sections, it depends on how much steel is required.
the main variation of cost is the fabrication. a truss will attract a much higher labour cost than a plain cut beam. my thoughts are that a plain beam would be cheaper.
my gut feel is that the costs will be similar. the w40 will be heavier, but the truss will have more fabrication costs. means 2001 estimating guides lists a w36 x 300 (their largest beam listed) as $200/ft. the w40 would probably cost the same. they didn't have any information on trusses.
a couple of additional costs to consider. if the span is too long, the
nice point about splicing in the field. dimension will be controlled by traffic regulations. weight of each piece will be controlled by the truck capacity and one additional factor. crane capacity and the closest location where it can be placed during lifting. for long spans, lifting the piece furthest from the crane (long moment arm), the capacity reduces considerably. this, in my opinion, can be considered means and methods so engineer need only provide enough info on limits and have the contractors do the math. engineer to review when shop drawings come in.
just curious thats a large beam for brick support, no 'loose lintel' that one. how much brick are you supporting and what is the span of the beam?
the beam has a 56' span with 7' of brick. its a canopy so no reductions are possible. it also is a girder so it has to support the transverse beams as well. i am trying desperatly to get a column or two in the middle.
use wideflange beam. the price of the tubes is higher than regular steel plus you will save a ton in labor for fabricating the truss.
i am with jedclampett. my personal 'rule of thumb' is that a truss is more economical over spans of about 16m (52')with respect to a beam. yours is a border-line case so i don't expect much change in cost. but rules of thumb are just like that - to be proved wrong.
consideration for the truss costs is dependent somewhat on depth/span requirements. however, my experience has been that trusses of this nature (midwest--nothern ohio locations) cost between $0.90 and $ 1.20 per pound, fabricated. assuming no significant fabrication on the w40 section, i would anticipate a cost of $0.40 to $0.50 for it, from a structural shop. you can probably contact a fabricator in your area to determine thesee cost parameters more closesly for your specific case.
easier to pre-camber a truss, deflection limits on masonry are rather stiff .... lousy pun. precamber for all other loads, masonry last.

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