Read D-Insights-CFS-Allen-Jan-08.pdf text version

InSIghtS

new trends, new techniques and current industry issues

Cold-Formed Steel

Trends, Techniques, and Resources

By Don Allen, P.E., SECB As the demand for non-combustible, costeffective construction solutions for mid-rise projects continues to grow, engineers and designers are becoming increasingly innovative with cold-formed steel framing (CFSF), and other structural products and combinations of materials. Engineers, architects, and builders are stretching the limits of loadbearing CFSF construction, designing 7 to 10 stories in some cases. Mixed systems (CFSF combined with precast concrete, engineered lumber, structural steel, composite concrete deck, and other systems) are also showing up in construction projects across the country. While no single, specific system is currently saturating the market in any particular region, several options are being used that make sense in different wind, seismic, and loading zones. These include: · Bearing CFSF walls with hollowcore precast plank floors (most recently addressed in STRUCTURE® magazine, August 2006 and July 2007). · Bearing CFSF walls with either proprietary or generic composite deck with poured concrete. (Figure 1)

Figure 2: Engineeredtlumber (plywood or gh OSB) on CFSF.ri py

R T S

C U

a

m

­ Cement-based decking, which consists of cement with fiber or other reinforcement, capable of spanning 24 inches between joists and maintaining a non-combustible rating. (Figure 3) ­ Pan deck and poured gypsum: typically a leveling type compound, that may or may not include gypsum between levels at the bearing walls. (Figure 4) ­ Pan deck and poured concrete: often less than 2½ inches total thickness. (Figure 4) · Shearwalls in conjunction with the above systems: ­ Strap bracing in tension-only systems. ­ Sheathing-braced systems, using engineered lumber (plywood or oriented strand board), sheet steel, gypsum, and proprietary sheathing. ­ Boundary elements made from proprietary materials or structural steel, to go with one of the above systems. (Figure 5, page 66)

Co

U T

i z

a g

Institute (AISI) codes and standards, and an update of the 2002 AISI Cold-Formed Steel Framing Design Guide. The design guide is ® one of the most popular documents among specifying engineers, since it gives step-bystep design examples for using CFSF and designing members, connections, and bracing for typical applications. In addition, the Cold-Formed Steel Engineers Institute (CFSEI), the new name for the former Light Gauge Steel Engineers Association, has ramped up their production of technical documents. During 2007, CFSEI published Technical Notes on Specifying and Using ASTM Standards, Coastal Corrosion Protection of CFSF, and Use of the "Tests for Special Cases" (Chapter F) of the AISI North American Specification to define and calculate capacities and safety factors for members, connections, and assemblies using CFSF. This note has already yielded several comments about the more realistic (lower) factor of safety that can be derived for pins and other connectors by following the example that is presented. The CFSEI has also updated their Technical Note on Durability of CFS Members.

E R

e n

Figure 4: Pan deck and poured gypsum or concrete.

Figure 1: Composite poured concrete on ColdFormed Steel Framing.

· Bearing CFSF walls with engineered lumber floor systems. · Bearing CFSF walls with CFSF joists and one of the following topping systems: ­ Where permitted, fire retardant treated plywood (FRTW). Note that while there are no longer corrosion issues with FRTW, there are still some corrosion issues with some of the new pressure-treated preservatives for prevention of termites, mold, and other organic growths and wood-consuming organisms. (Figure 2)

Figure 3: Cement-based flooring: proprietary product from USG called Fortacrete. Courtesy of USG.

With all of this innovation, engineers have shown a renewed interest in CFSF details, codes and standards, and information. Recently released documents include a compilation of standards relating to CFSF (ASTM International: keyword FRAMING07), 2007 versions of the American Iron and Steel

Upcoming Technical Notes include: a guide to the available software for CFSF design; Corrosion Protection of Screws; specifying the appropriate sheet steel for CFS members (a specifier and user introduction to ASTM A1003); and an update of the old LGSEA Fastener Corrosion technical note. The firstever CFSEI design guide on CFSF Lateral System is currently going through the technical review process, and should be out in early 2008. (Figure 6, page 66) Furthermore, the Steel Stud Manufacturers Association (SSMA) has updated their tables for their new Product Technical Information Catalog, and will release the catalog pending approval of their new Evaluation Service Report. SSMA will also be providing updates to their tech notes and some of their details, which will be available for free download at www.ssma.com. continued on next page

STRUCTURE magazine

65 January 2008

STRUCTURAL STEEL BEAM

JOIST COLLECTOR

Other issues currently being discussed PLAN VIEW A-A 1000T150-54 RIM within the industry include methods for less STRUCTURAL JOIST COLLECTOR PLAN BEAM A-A (24) #12 STEEL VIEW C expensive bracing of axially loaded members, LOF (16) #12 SCREWS AT SPLICE (24) #12 SCREWS especially since more multi-story structures AT C 1-2" O.C. LOF (16) #12 SCREWS AT 1-2" SCREWS AT are being built with some wall axial loads O.C. in :" SPLICE :" 1- A-A PLAN VIEW2" O.C. 1000T150-54 STRUCTURAL :" :" excess of 10 kips per foot! Issues such1-2"end as O.C. RIM JOIST #12 (24) STEEL BEAM C 1000T150-54 LOF COLLECTOR STRUCTURAL (16) #12 bearing on concrete, in-line framing, uplift SCREWS AT RIM JOIST SPLICE 1-2" O.C. STEEL BEAM SCREWS AT anchorage for both wind and shearwalls, and COLLECTOR 1-2" O.C. :" :" connection detailing, are all being considered 1000T150-54 STRUCTURAL RIM JOIST STEEL BEAM A A for updated technical information. The steel COLLECTOR industry also has free services available for A A 800S162-54 engineers, specifiers and builders, includSTUD SPLICE 800S162-54 A A ing the steel hotline (800-79-STEEL) and SHEAR WALL STUD SPLICE for corrosion issues, the Galvinfo Center STRUCTURAL 800S162-54 SHEAR WALL STEEL (www.galvinfo.com). All completed TechniSTRUCTURAL STUD SPLICE COLUMN SHEAR WALL cal Notes and AISI standards listed STEEL in this t STRUCTURAL COLUMN ELEVATION AT SECOND article are available for purchase (and some igh STEEL y FLOOR rCOLLECTOR ELEVATION AT SECOND COLUMN for download) at www.cfsei.org. Cop 4A SCALE:FLOOR COLLECTOR 1" = 1'-0" ELEVATION AT SECOND

SHEAR WALL SHEAR 1000T150-54 WALL RIM JOIST 1000T150-54 COLLECTOR RIM JOISTSHEAR COLLECTOR WALL

1000T150-54 RIM JOIST COLLECTOR

4A

SCALE: 1" = 1'-0"

Figure 6: Draft detail from CFSEI Lateral Design Guide.

Figure 5: Boundary elements of structural steel or proprietary members.

R T S

C U

4A

SCALE: 1" = 1'-0"

FLOOR COLLECTOR

Don Allen, P.E., SECB, is the Secretary of the Cold-Formed Steel Engineers Institute, Technical Director of the Steel Stud Manufacturers Association, and Director of Engineering for the Steel Framing Alliance. Allen has a particular interest in the role of structural materials in sustainable construction, and is a member of the ASCE SEI Committee on Sustainability. He may be reached at [email protected]

U T

4B 4B

2 ROWS OF #10 SCREWS 2 AT 3" O.C. ROWS OF #10 SCREWS OR 1 ROW AT 3"1-2" O.C. AT O.C. 2 ROWS OF OR 1 ROW 2-SIDED SCREWS AT 1-2" #103" O.C. O.C. AT SHEAR WALL OR 2-SIDED 1 ROW AT 1-2" O.C. SHEAR WALL

2-SIDED SHEAR WALL

SCALE: 1" = 1'-0" SECTION

SCALE: 1" = 1'-0" SECTION 4B SCALE: 1" = 1'-0"

E R

FLOOR SHEATHING

FLOOR SHEATHING FLOOR SHEATHING

®

1000S162-54 FLOOR JOISTS 1000S162-54 FLOOR JOISTS 350T125-54 TOP1000S162-54 TRACK 350T125-54 JOISTS FLOOR TOP TRACK

350T125-54 TOP TRACK

SECTION

m

ADVERTISEMENT ­ For Advertiser Information, visit www.structuremag.org

a

a g

i z

e n

STRUCTURE magazine

66

January 2008

Information

2 pages

Find more like this

Report File (DMCA)

Our content is added by our users. We aim to remove reported files within 1 working day. Please use this link to notify us:

Report this file as copyright or inappropriate

298505


You might also be interested in

BETA
detcdrom.qxd
c01.012_044
2006_IBC_Update.vp
GRBT055-Com.tex