residential steel beam common practice

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residential steel beam common practice
i work in colorado.  when you use steel beam (ie. w10x), what maximum or maybe comfortable to work with length do you usually specify? sometimes i wonder if i should just continue the beam or stop it at a column and specify other smaller/bigger beam (with connection on top of the column).
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the longest span that i have used in residential work is an 18' simple span using a w12. the beams are not the problem, just size them as usual; full load allowable deflection is often the criteria that dictates beam size. coming up with (carpenter-friendly wooden) columns that can carry those loads is more of a challenge - i consider that to be the limiting factor.
due to bulk plane limitation i get a lot of projects where 2nd floor plan foot print is about 2' smaller than main floor.  so theoratically on this project i can use up to 70 continuous beam with 2 columns in the middle.  just wondering whether i should analyze it as 3 continuous span and put splicing locations or size them as simple span and size them individually. or 2 continuous span and 1 simple span.  i hope you understand my dilema  .
opinion: i would never size any beam in "typical" residential construction to be either 2 or 3 span continuous - at the construction level the understanding and quality control to make that happen (in a structurally correct way) is just not there.
suggest that you consider simple spans, but see if economics will allow using one beam size for all applications. in the field, getting various beam sizes mixed up and putting them in the wrong places is a very real possibility.
if you must use different sizes, one way to help minimize field errors is to try to use only one weight beam for each nominal beam height, ie. one size w8, one size w10, one size w12, etc.
i wouldn't go with a 70' continuous beam. transportation and erection are really your limiting concerns. for analysis try to model the actual in situ condition; after all you specify splice locations.
for residential, i would probably break a 70' foot span into three spans with shear splices.
when dealing with wood construction, especially residential, i call out contin. steel beams with caution.  sometimes, you have trouble getting the bottom flange bracing you need for cont. beams.  if i can get by with simple spans, that is the way i go.  you don't have the bottom flange bracing to worry about and you may be able to keep the crane off the job.
good point slide.  i just thought it would be nice to make it continous so i can make the size of beam smaller.  i thought about using 2 continuous span and 1 simple span.  but then i need 44' long beam.  is that too long for a residential?  then i began to think to design it as 3 continuous span and put the splicing at the 0 moment.  that would make maximum beam length roughly about 22'.  
the columns are going to be rectangular steel pipes.  i like to avoid wood/lvl column on heavy steel.  so if you have 3 simple spans, they still have to splice the beams right by the support right?  if they have to do this anyway, why not just design it as 1 continous beam (smaller   
rday.. thats what i meant. 70 ft with splices (longest   
i would make them all simple beams.  keep it simple.
well... if i make it continuous i will only need w 10x88.  if i make it simple than one beam i need up to w 12x96.
that's the trade-off you have to deal with and why you need to use your engineering judgment.  you're talking about a lot when you want a residential contractor to deal with the details associated with continuous steel beams and bracing and so forth.  sliderule gave some very good advice.