huangyhg

structural steel beams
we have contracted with a builder for light weight residential steel framing to build a 50 ft x 60 ft two story residence. the residence will have a 4/12 pitch hip roof with conventional 25 yr fiberglass shingles. our builder is telling us that we require a w-10 x 33 beam in the top of second floor interior walls running the 60 foot length of the house to support roof load and wind load (100 mph) for the roof. the beam load by his design is them brought down through the 6" steel frame exterior walls to the foundation system which are also steel w-10 x 33 beams on the 50 ft side and w-10 x 39 beams on the 60 ft side. this design seems to me to be a bit overstated if the interior wall system is correctly engineered. short of paying twice for structural engineering, can anyone offer some advice or suggestions based upon this very limited parameter? thanks!
the beam sizes don't seem excessive at all, given the spans and loads involved. if you have any doubts, have the structure checked by a licrnsed engineer. i recently worked on a job where the owner (having more money than brains) arbitrarily extended his garage ten feet to accomodate his limo; the resulting structure was on the same scale as yours, and the w10 x 39 beams originally specified no longer worked.
the beam appears normal for a red iron steel framing with nonload bearing filler walls. typically the framing packages are engineer stamped for your locality loadings. i have check many beams to see if they were strong enough, never if they could be smaller.
but, you left many details out. what direction do the trusses run, what is the overhang, what is the intermedate beams support distances, is the steel a36 or 50 ect...
the loads are gravity (down) and wind load (uplift). the typical gravity loads are ~40 psf (20 dl + 10 top cord +10 bottom cord). if the trusses run the 50 ft span the uplift is calculate to be -11.4 psf for a one ft overhang. a center interior beam would typically be designer to carry 12 1/2 ft tribiary load on each side, totalling 25 ft per linear foot. this give a load of dl=1000 pounds/lft ll=-285 pounds/lft.

the design process for a beam can be summarised as follows
a) determination of all forces and moments on critical
section
b) selection of ub or uc
c) classification of section
d) check shear strength; if unsatisfactory return to (b)
e) check bending capacity; if unsatisfactory return to (b)
f) check deflection; if unsatisfactory return to (b)
g) check web bearing and buckling at supports or
concentrated load; if unsatisfactory provide web stiffener
h) check lateral torsional buckling; if unsatisfactory
return to (b) or provide lateral restraints
i) summarise results
hope this helps
cheers

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