light gauge framing

huangyhg

light gauge framing
how do other engineers out there deal with light gauge framing?  do you design and detail everything or do you consider it a specialty item and require the gc to provide stamped shop drawings and calculations.  i would like to start treating all light gauge as specialty items.  on load bearing projects i would call out the depth and spacing of the stud but still require shop drawings and calculations for the gc.  for shearwalls i would show the design force at top of each wall.
any comments would be appreciated!
j
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depends how much light gage you have on the project. if it is just a few pieces such as a canopy soffit or a parapet wall, i will design and detail it myself but if it is a multi-story building, i would write a performance spec and require calcs and details from the light gage supplier. if you are bidding to the architect, make sure that you are all bidding on the same basis.
we have it as a performance spec also and get shops and cals to review.  
if you want to send the cfs design to a specialty engineer, just make sure you identify all the design loads and requirements.  it will be a great benefit to the project if you check stud depths early on and make sure the architect is providing enough space.  for instance, if you have 20-foot walls, don't let the architect specify a 6-inch stud for 140mph exp c.  
note what fasteners (or anything for that matter) are and are not acceptable, if any.  note deflection requirements and locations where slip connections are necessary.  
in general, try to check things first to be sure you aren't asking someone to do something unreasonable.  if a column or beam would need to be 6x6x3/8 if it were hss, don't ask the cold-formed guy to build it with 6-inch studs.  these things can be done but they are very hard to do when a little thought from the seor in the beginning would solve the problem.  if you have walls with wide or tall openings and you limit the fastener embedment to 3/4-inch because of post-tensioning, the specialty engineer may have big problems getting adequate connections.  it would be a benefit to the client to anticipate issues and provide for them as best you can without exceeding your scope.
show at least an outline on your plans so that the specialty engineer can understand your intent and where support have been designed for the cfs loads.
there are other things that could be listed but i think you get the point.
if it is to be erected on site, i design and call out all the   
speaking as someone who does both "engineer of record" stuff and cold formed steel shop drawings, i agree with what everyone is saying.  if you know what you are doing, and have the budget to do it, just design the cold formed framing (the cold formed subcontractors will love you--when the framing must be engineered after the bids are due, it is difficult for them to bid the job!).
but it is also very common to have the engineering done by the cold formed subcontractor's engineer.  however, in this case, like ucfse said, at least make sure everything works conceptually.  for example, if you have a window opening that is over 10' wide, and there is brick above the opening, it might make more sense to use a hot rolled tube across the window head and at each jamb.
daveatkins
i always design and detail the light gage myself when in comes to interior load-bearing walls, all exterior walls, headers, lintels, etc.
the only thing i don't do is light gage trusses.  i provide a performance spec, design loads, etc. for those and require shop drawings and calcs.
i'm in the same camp as mike when it comes to interior partition walls - the architect can handle that.
the main reason i want to start treating cfs as a specialty item is because i don't seem to have the time to design and detail all of the components that are required to have a well constructed assembly.  also as the ser i have a little knowledge about a lot of different construction materials and methods relative to the specialty engineer who does light gauge design more often and who probably keeps up with the latest trends in cfs better than me.  i really think in the end it should lead to a more economical structure.  for example if i where to design wood trusses they would be twice as expensive as the specialty engineer's design because i don't design wood trusses everyday.  when i design light gauge i am usually so pressed for time that i have to identify one or two conditions (worst) and use that design everywhere; where as the specialty engineer can design for more conditions and detail each more clearly than the fastener schedule and typical details i provide.  also there have been several jobs i have done where during my site visit i have discovered the contractor hasn't done anything that i specified and having to correct this delays the project and upsets the owner.  what happens on jobs that i never get to make a site visit?  at least with shop drawings  the contractor can't say my note or detail was unclear.
thanks for the comments!!!
we have started to do the cfs design.  even as eor you'll get dragged in if something happens regardless, at the end of the day it won't suffice to say i was relying on the other engineer.  it is a time consuming work for sure but when done a number of times fairly repetative work, job to job i mean so thats a good thing.  there's lots of help available re aisi, cssbi, and the manufacturers.  we also find that if we have done the design then when everybody starts agrueing over it, re money, then at the least we have our design in place.
i have great concerns about cfs and durability though.  my experience has been primarily with wind loads and exterior walls in high rise construction.  i've been watching four and five storey buildings going up were the cfs carries hollow core slab plus gravity loads, and the lateral loads.  some of these buildings are open for up to 5 months before walls or roofs go on with water pouring through the whole building.  i've walked into buildings were the bottom tracks are full of water.  every screw penetration, every cut is ungalavanized.  not a very redundant system in my mind.  having trouble getting my head around this issue.
i design and detail everything for load bearing cold-formed steel studs.  i performance spec the cold-formed steel roof trusses.