METAL STUD QUESTION

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Author Message Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 694 Registered: 05-2003 Posted on Thursday, July 16, 2009 - 06:27 pm:    WE TYPICALLY CALL FOR 20 GAGE METAL TOP AND BOTTOM TRACK (RUNNERS) ON NON-BRG PARTITIONS, HOWEVER WE HAVE BEEN CHALLENGED TO EXPLAIN WHY ON A CURRENT JOB OUT FOR BID. ANYONE HAVE SOME AMMO WE CAN USE IN OUR ARGUMENT TO RETAIN THIS GAGE TRACK? THE METAL STUDS ARE STANDARD 25 GAGE ERECTED BETWEEN CONCRETE SLABS FOR A HOTEL PROJECT. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 177 Registered: 10-2007 Posted on Friday, July 17, 2009 - 12:10 am:    I assume we are talking about interior partitions. I would be more likely to question the 25 gage studs. Is your accoustical consultant comfortable with these light studs? Having a heavier track than the studs could may be needed in order to resist the forces applied perpendicular to the wall. You should have an engineer check the bending on the legs of the top track to resist these forces. The larger the allowance for provision for slab deflection the heavier gage should be used. In addition a heavier gage track might allow the fasteners to the slab to be spaced further apart. This could be a consideration if you have post tensioned slabs. Rich Gonser AIA CSI CCCA Senior Member Username: gonserarch Post Number: 8 Registered: 10-2003 Posted on Friday, July 17, 2009 - 12:32 am:    Acoustical engineers prefer the lightest gauge stud possible. It reduces the vibration transmitted between units. I for one do not like 25 gauge studs. They are extremely flimsy and subject to trade damage that gets covered up far too quickly. I agree with Mark about the track being subject to the horizontal forces. Once you have the top of the stud cut down an inch for the slip track, your bearing point is now separated from the slab and direct shear forces. Bending and stretching can occur. It doesn't matter, but you also didn't state what the stud depth is. I was just curious. I hope very little is hung on these walls. Lynn Javoroski CSI CCS LEED® AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 903 Registered: 07-2002 Posted on Friday, July 17, 2009 - 09:12 am:    For the last 5 years or so, we have specified studs using a metal thickness instead of a gage. Thus we specify .033 inch, since 20 gage actually has 2 different thicknesses that can be used. You can always tell the contractor to use the "dimpled" studs instead. They are thinner and stronger as I understand it. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 178 Registered: 10-2007 Posted on Friday, July 17, 2009 - 10:19 am:    Lynn is right that the proper specification for cold formed sections designates the material thickness. The Steel Stud manufacturers Association can provide you with information on how to designate these members. www.ssma.com Dimpled studs can provide extra bending strength by suppressing certain buckling failure modes. They will not improve the stiffness. It is unclear that there are any advantage for using dimpled sections for the track. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 229 Registered: 01-2008 Posted on Friday, July 17, 2009 - 11:32 am:    Jerome, We specify the minimum thickness (mils) of the top and bottom track be the same as the studs. We abandoned specifying gage and delegate the engineering and selection to the contractor. Indicated stud spacing are maximums. Where gage indicated, they are minimums but may increase to comply with performance requirements. Regardless whether the line studs are 25 gage (18 mils) or 22 gage (27 mils) or 20 drywall gage (30 mils) we specify and detail two 20 gage (30 mil) studs at each interior door jamb and borrowed lite jamb. 25 gage at 16" and 24" centers is not adequate for a lot of the wall heights we have in our projects. Increasing gage and decreacing spacing and increasing stud size are possible, used singly or in combination. We also include the PSF and deflections of L/120 or L/240 for interor partition walls. We bump up the PSF and L/ for walls supporting wall mounted casework. Assebmiles with tiling or other hard surface are L/360. For lobbies, corridors, and elevator lobbies we increase loading to 10 psf and deflection to L/360. We require the contractor to notify us if increase in stud size is necessary. Not flange but depth. Acoustical consultant has a lot to say about gage and ours prefers light gage 25 gage or 18 mils. Wayne J. Peter Jordan Senior Member Username: jpjordan Post Number: 343 Registered: 05-2004 Posted on Saturday, July 18, 2009 - 01:43 pm:    In my experience, there is not too much problem getting the metal stud installer to take on the engineering for the exterior non-load-bearing metal framing; however, getting them to take on engineering responsibility for the interior studs is a big problem. In the Houston area, Contractors are generally resisting taking on responsibility for "delegated design". While they may want the architect to have a "performance" specification, what they usually mean is a nonporoprietary specification. What they don't realize is that having a true performance specification permits them some additional pricing flexibility. I have a hunch that it is what they are comfortable doing. A Contractor who does a lot of exterior wall construction of non-load-bearing metal framing or tilt-wall may be very comfortable taking on this responsibility or have a sub who does this well. On the other hand, I was involved in a project recently in which the general had the drywall stud guy bid on the exterior metal studs (in a near-hurricane wind load area). This guy just did what he always did without really looking at the Drawings or the Specifications. The Architect and Engineer worked with the sub so there was not a big cost impact, but the general did some "designer bashing" because the Drawings and Specifications were not absolutely perfectly coordinated. Incidentally, if you have masonry veneer, you may want to establish a minimum (not an absolute) flange width. To withstand the windload at a particular stud depth, it may be possible to increase the flange width instead of going to a heaver sheet metal thickness. Randy Cox Senior Member Username: randy_cox Post Number: 60 Registered: 04-2004 Posted on Monday, July 20, 2009 - 08:36 am:    In my past life experience, working for a GC, the problem with delegated design is that the bids have to be based on something, and no-one is willing to pay for engineering unless they have the job. Delegated design can't be accurately bid unless the designer indicates something for the base price or it's something the sub has seen and done before. I would guess that enough subs have experience with determining exterior stud requirements to make that a competitive bidding environment, but those subs aren't sure what the performance specs will mean for interior stud design. Gerard Sanchis (Unregistered Guest) Unregistered guest Posted on Monday, August 03, 2009 - 06:09 pm:    Let's not forget heavy acoustical doors (2-1/4-inch thick) on cam hinges. They require either steel tubes anchored to floor and structure above, or equivalent studs (14 gage) welded face to face. 20 gage studs will not do in this case. Also stair and elavator shafts will need to resist more than 5 psf prescribed by code. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1075 Registered: 03-2002 Posted on Tuesday, August 04, 2009 - 08:21 am:    We don't call for engineering of interior framing except for particular cases: openings over 6 feet wide, large soffits hanging from structure, and very tall walls. For school work, we use 33 mil studs for everything. Another tidbit: if you are installing cementitious backer board, you have to use thicker studs per manufacturer requirements--min 33 mil. James M. Sandoz, AIA, CSI, CCS, LEED AP Senior Member Username: jsandoz Post Number: 54 Registered: 06-2005 Posted on Tuesday, August 04, 2009 - 08:49 am:    John, where did you find the requirement that 33 mil studs need to be used with cementitious backer board? Was it from a particular framing manufacturer or manufacturer of the backer board or another source. I would like to be able to cite that source when I am questioned as to why I am specifying 33 mil studs. Dale Roberts CSI, CCPR, CTC Senior Member Username: dale_roberts_csi Post Number: 71 Registered: 10-2005 Posted on Tuesday, August 04, 2009 - 12:19 pm:    TCNA W244C-09, (cement backerboard detail) Metal studs need to be 20 gauge or heavier. Maximum 16” O.C. Minimum stud depth of 3-1/2”. Custom Building Products Recommends 20 mil gauge Studs for WonderBoard CBU Wayne Yancey Senior Member Username: wayne_yancey Post Number: 242 Registered: 01-2008 Posted on Tuesday, August 04, 2009 - 12:35 pm:    20 gage would be 30 mil or 0.0312" SSMA lists two 20 gage studs: 20 drywall = 30 mils, and 20 structural - 33 mils I think 20 drywall is what TCNA means as the minimum but that is only my interpretation. Thicker may be better. I recommend adding maximum deflection of L/360 for rigid finish materials including ceramic tile, stone, and mirrors. I have not seen a 20 mil stud. 18 mils is equivalene to 25 gage. Minimum thicknesses (mils) per SSMA are 18, 27, 30, 33, 43, 54, 68, 97, and 110. Dale Roberts CSI, CCPR, CTC Senior Member Username: dale_roberts_csi Post Number: 72 Registered: 10-2005 Posted on Tuesday, August 04, 2009 - 12:42 pm:    you are correct that should have been 20 gauge stud Dale Roberts CSI, CCPR, CTC Senior Member Username: dale_roberts_csi Post Number: 73 Registered: 10-2005 Posted on Tuesday, August 04, 2009 - 12:49 pm:    The MIA (Marble Institute of America) for direct adhered stone installation, recommends walls and partitions constructed of metal studs should be designed to maximum deflection of L/720 for conditions utilizing thin-set mortar installation methods. Although if you push them they do say L/680 is probably fine in most instances depending on the span. For an anchored stone installation they do recommend 16 gauge studs. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 188 Registered: 12-2006 Posted on Tuesday, August 04, 2009 - 01:24 pm:    For our hospital work we usually have to provide a complete design, including stud size, metal thickness, spacing and supporting calcs. This often results in a wall type schedule with numerous variations. More than once the GC has come back to us with a no cost substitution of 6 inch, 16 gauge, 16 inches on center across the board. Their reasoning is that that cuts on site supervision time down to just getting the wall in the right place, and pricing and keeping track of just one kind of stud. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 243 Registered: 01-2008 Posted on Tuesday, August 04, 2009 - 01:32 pm:    Steve, This is good concept to idiot-proof the layout and installation. Hospital work usually has LOTS of critical clear dimensions. Does the GC take into account these conditions where the may occur when substituting 6" for 3 5/8" or 4"? OR Does your firm practice some DIMENSION RISK MANAGEMENT and increase the critical dimensions by 2 inches in anticipation of the substitution or plain screw-ups. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 189 Registered: 12-2006 Posted on Tuesday, August 04, 2009 - 01:59 pm:    Yes, there can be big pieces of hospital layout that can be virtual closed dimension strings, so we have to take advantage of every opportunity to create some wiggle room in the dimensions. We do not practice an ALL-CAPS dimension risk management, but our drawings assume a 6 inch stud, we carefully model all of the tight areas and we have a lot of combined experience and remember all of the trivia battlegrounds(one state measures clear door width from face of exit device to opposite stop, the next state from face of door to opposite stop). The out of the blue dimension bust I deal with more than I ever would have expected is out of alignment, out of plumb, steel columns. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 184 Registered: 10-2007 Posted on Tuesday, August 04, 2009 - 03:40 pm:    Given all of the things that go in a hospital it probably makes sense to start with 6" studs. With full height walls and the heavy loads on some of these walls it can be difficult to make a 4" stud figure. In some cases a 4" wall might require the use of steel tubes while a 6" wall could resist the same loads using cold formed sections. When the deflection criteria is specified in the form L/N, where N is some number typically between 120 to 600, what you are really controlling is the slope of the member at the support. In many cases you are not concerned about the slope but rather you are concerned about the curvature, absolute deflection, or natural frequency. Thus take these numbers with a grain of salt. What they really mean is that for common spans if the members met this criteria that they have not had problems. If you have problems with out of plumb steel columns are you talking about steel columns that do not comply with standard industry tolerances or situations where the designers assumed perfectly located columns. My belief is that BIM models are not able to easily model the impact of normal construction tolerances. Steven Bruneel, AIA, CSI-CDT, LEED-AP Senior Member Username: redseca2 Post Number: 190 Registered: 12-2006 Posted on Tuesday, August 04, 2009 - 05:25 pm:    Mark, 6-inch studs; Yes they are pretty much the norm; our clients do not want rooms formed with entirely different assemblies on each side so that casework on one wall is fine but you shan't put it on the wall opposite. We tend to be busy enough with the fire resistive design criteria and acoustical criteria as it is. Problems with out-of-plumb steel: I was speaking of projects where a "perfect storm" of construction errors go beyond the allowable tolerances and were not discovered (or made part of the Owner-Architect-Contractor discussion) until going back and fixing the steel was no longer feasible. Problems have included: 1. Simply putting the column base in the wrong place. 2. Ignoring the structural engineers instructions on the sequence of welding.