IBC 2015 and Cold-Formed Steel Design Standards and Design Aids. Roger LaBoube Wei-Wen Yu Center for Cold-Formed Steel Structures

Transcription

1 IBC 2015 and Cold-Formed Steel Design Standards and Design Aids Roger LaBoube Wei-Wen Yu Center for Cold-Formed Steel Structures

2 AISI Specifications st edition th edition

3 1946 Specification 14 pages Six sections (General, Design Procedure, Allowable Design Stresses, Connections, Design of Braced Wall Studs, Tests) Two ASTM steels (A245 & A246) 25 to 33 ksi Safety factor = 1.85 for basic design stress Effective width for stiffened elements (reduced area) Q-factor for unstiffened elements (reduced stress) Only welded connections

4 2012 Specification More Significant Technical Changes Limit on corner radius in Chapter B Combined bending and torsion modified Brace strength and stiffness based on required strength Bolt bearing for slotted holes Combined shear and tension for screw connections PAF provisions Chapter F using an analytical model DSM: Holes, shear, inelastic reserve What is the impact on your design office?

5 A2.1 Applicable Steels A2.1.1 Steels with a Specified Minimum Elongation of 10 Percent or Greater A2.1.2 Steels with a Specified Minimum Elongation from 3 Percent to less than 10 Percent A2.1.3 Steels with a Specified Minimum Elongation Less Than 3 Percent CFSEI Tech Note ASTM Standards, G800 & G801

6 A2.3 Permitted Uses and Restrictions of Applicable Steels A2.3.1 Steels with a Specified Minimum Elongation of 10 Percent or Greater A2.3.2 Steels with a Specified Minimum Elongation from 3 Percent to less than 10 Percent A2.3.3 Steels with a Specified Minimum Elongation less than 3 Percent

7 A2.3.4 Steel Deck as Tensile Reinforcement for Composite Deck-Slabs For steels used in composite slabs for the condition where the steel deck acts as the tensile reinforcement of the slab, the following requirements shall be followed: (1) If the ductility of the steel measured over a two-inch (50-mm) gage length is ten percent or greater (2) If the ductility of the steel measured over a two-inch (50-mm) gage length is less than ten percent

8 B1.3 Corner Radius-to-Thickness Ratios The effective width provisions of Chapter B shall apply to sections with inside bend radiusto-thickness ratios no larger than 10. For inside bend radius-to-thickness ratios larger than 10, rational analysis is permitted. t R 1 R 2

9 B2.5 Uniformly Compressed Elements Restrained by Intermittent Connections The provisions of this section apply to Compressed elements of flexural members only. Limited to multiple flute built-up members having edge-stiffened cover plates

10 C2 Tension Members C2.1 Yielding of Gross Section T n = A g F y C2.2 Rupture of Net Section T n = A n F u Provisions previously in Appendix A

11 C3.1.1 Nominal Section Strength Same Φ and Ω for flexural members having stiffened, partially stiffened and unstiffened compression flanges. This results in no change in Ω Reduction in Φ (0.90) for stiffened and partially stiffened flange cross sections

12 C3.1.4 & C4.2 Distortional Buckling Strength Eliminated provisions for simplified provisions for cross sections with simple lips. Change in definition for: x of = x distance from the centroid of the flange to the shear center of the flange h xf = x distance from the centroid of the flange to the flange/web junction y of = y distance from the centroid of the flange to the shear center of the flange M 1 /M 2 now positive for reverse curvature

13 C3.6 Combined Bending and Torsional Loading Limited to singly or doubly symmetric sections subject to bending about an axis of symmetry and not subject to bi-axial bending. The torsional effect for other sections shall be considered using rational engineering analysis. R = 1 f f bending _ max bending + f torsion

14 D3.3 Bracing of Axially Loaded Compression Members Strength: P rb = 0.01 P ra P rb = Minimum required brace strength to brace a single compression member with an axial load P ra P ra = Required axial compressive strength of individual concentrically loaded compression member to be braced

15 D3.3 Bracing of Axially Loaded Compression Members Stiffness: ASD - β rb,1 = 2[4 (2 /n)] ( ΩP L b ra ) LRFD - β rb,1 = 2[4 (2 /n)] L b P φ ra P ra = Required axial compressive strength of individual concentrically loaded compression member to be braced

16 E2.4.1 Shear Strength of Top Arc Seam Sidelap Welds Strength equation for top arc seam welds provided the arc seam welds meet minimum spacing requirements along steel deck diaphragm side laps.

17 E3.3.1 Bearing Strength Without Consideration of Bolt Hole Deformation Strength: P n = C m f d t F u Thickness of Connected Part, t, in. (mm) t < (0.61 t < 4.76) Table E Bearing Factor, C Connections with Standard Holes Ratio of Fastener Diameter to Member Thickness, d/t C Connections with Oversized or Short-Slotted Holes Ratio of Fastener Diameter to Member Thickness, d/t d/t < d/t < d/t (d/t) 7 d/t /(d/t) d/t > d/t > C

18 Table E Modification Factor, m f Type of Bearing Connection m f Single Shear and Outside Sheets of Double Shear Connection Using Standard Holes with Washers under Both Bolt Head and Nut 1.00 Single Shear and Outside Sheets of Double Shear Connection Using Standard Holes without Washers under both Bolt Head and Nut, or with only One Washer Single Shear and Outside Sheets of Double Shear Connection Using Oversized or Short-Slotted Holes Parallel to the Applied Load without Washers under both Bolt Head and Nut, or with only One Washer Single Shear and Outside Sheets of Double Shear Connection Using Short-Slotted Holes Perpendicular to the Applied Load without Washers under both Bolt Head and Nut, or with only One Washer Inside Sheet of Double Shear Connection Using Standard Holes with or without Washers Inside Sheet of Double Shear Connection Using Oversized or Short- Slotted Holes Parallel to the Applied Load with or without Washers Inside Sheet of Double Shear Connection Using Short-Slotted Holes Perpendicular to the Applied Load with or without Washers

19 E3.4 Shear and Tension in Bolts P n = A b F n Ω = 2.00 φ = 0.75 (Eq. E3.4-1) F n is consistent with AISC

20 TABLE E3.4-1 Nominal Tensile and Shear Strengths for Bolts Nominal Tensile Strength Fnt, ksi (MPa) Nominal Shear Strength Fnv, ksi (MPa) a) A307 Bolts, Grade A 1/4 in. (6.4 mm) d <1/2 in. (12.7 mm) A307 Bolts, Grade A d 1/2 in (12.7 mm) 40 (280) 27 (188) b) 45 (310) 27 (188) b) A325 bolts, when threads are not excluded from shear planes 90 (620) 54 (372) A325 bolts, when threads are excluded from shear planes 90 (620) 68 (457) A354 Grade BD Bolts 1/4 in. (6.4 mm) d < 1/2 in. (12.7 mm), when threads are not excluded from shear planes A354 Grade BD Bolts 1/4 in. (6.4 mm) d < 1/2 in. (12.7 mm), when threads are excluded from shear planes A449 Bolts 1/4 in. (6.4 mm) d < 1/2 in. (12.7 mm), when threads are not excluded from shear planes A449 Bolts 1/4 in. (6.4 mm) d < 1/2 in. (12.7 mm), when threads are excluded from shear planes 101 (700) 68 (457) 101 (700) 84 (579) 81 (560) 54 (372) 81 (560) 68 (457) A490 Bolts, when threads are not excluded from shear planes 113 (780) 68 (457) A490 Bolts, when threads are excluded from shear planes 113 (780) 84 (579) Threaded parts when threads are not excluded from shear planes 0.75 Fu Fu Threaded parts when threads are excluded from shear planes 0.75 Fu Fu Notes: a) For end loaded connections with a fastener pattern length greater than 38 in. (965 mm), F nv shall be reduced to 83.3% of the tabulated values. Fastener pattern length is the maximum distance parallel to the line of force between the centerline of the bolts connecting two parts with one faying surface. b) Threads permitted in shear planes.

21 E4.4 Tension For screws that carry tension, the head of the screw or washer, if a washer is provided, shall have a diameter d h or d w not less than 5/16 in. The nominal washer thickness shall be at least in. for t 1 greater than in. and at least in. for t 1 equal to or less than in. The washer shall be at least in. thick when 5/8 in. < d w 3/4 in.

22 E4.4.2 Pull-Over Strength (b) For a round head, a hex head, or hex washer head screw without an independent washer beneath the screw head: d w = d h but not larger than ½ 3/4 in. (c) For a domed (non-solid and either independent or integral) washer beneath the screw head, d w can not exceed 5/8 3/4 in.

23 E4.5 Combined Shear and Tension E4.5.1 E4.5.2 E4.5.3 Combined Shear and Pull-Over Combined Shear and Pull-Out (new) Combined Shear and Tension in Screw (new)

24 E4.5.2 Combined Shear and Pull-Out ASD: Q P ns + T P not 1.15 Ω Shear Strength: P ns = 4.2(t Tension Strength: P not = Ω = 2.55 Similar equation for LRFD 3 1/2 2d) Fu2 0.85t c df u2

25 E4.5.2 Combined Shear and Pull-Out Equation valid for connections that meet the following limits: (1) in. t in. (2) No. 8, 10, 12, or 14 self-drilling screws with or without washers (3) F u2 121 ksi (4) 1.0 F u /F y 1.62.

26 E4.5.3 Combined Shear and Tension in Screws ASD: T P ts + Q P ss 1.3 Ω P ts and P ss = Nominal tension and shear strength of screw as reported by manufacturer or determined by independent laboratory testing Ω = 3.0 Similar equation for LRFD CFSEI Tech Note F701 screw strength

27 E5 Power Actuated Fasteners Geometric variables

28 E5 Power Actuated Fasteners The provisions apply to power actuated fasteners (PAFs) that are driven into steel substrates. The thickness of the substrate not in contact with PAF head shall be limited to a maximum of 0.75 in. The thickness of the substrate in contact with PAF head shall be limited to a maximum of 0.06 in. The washer diameter shall not exceed 0.6 in. in computations, although the actual diameter may be larger. Power-actuated fastener diameter shall be limited to a range of 0.11 in. to 0.21 in.

29 E5 Power Actuated Fasteners For diaphragm applications, the provisions of Section D5 shall be used. Alternatively, the available strengths for any particular application are permitted to be determined through independent laboratory testing, with the resistance factors, Φ, and safety factors,ω, determined in accordance with Chapter F. The values of P ntp and P nsp are permitted to be reported by the manufacturer. May continue to use ICC-ES or IAPMO Reports

30 E6 Rupture Provisions now also applicable for screws and PAFs. Table E6-1 Safety Factors and Resistance Factors for Rupture Connection Type Ω (ASD) φ (LRFD) φ u (LSD) Welds Bolts Screws and Power Actuated Fasteners

31 E6.2 Tension Rupture T n = F u A e A e = Effective net area subject to tension = U sl A nt U st = 0.9 removed for staggered holes when computing A nt

32 Table E6.2-1 Shear Lag Factors for Connections to Tension Members Description of Element (1) For flat sheet connections not having staggered hole patterns (a) For multiple connectors in the line parallel to the force (b) For a single connector, or a single row of connectors perpendicular to the force (i) For single shear and outside sheets of double shear connections with washers provided under the bolt head and the nut (ii) For single shear and outside sheets of double shear connections when washers are not provided or only one washer is provided under either the bolt head or the nut (iii) For inside sheets of double shear connections with or without washers (2) For flat sheet connections having staggered hole patterns U sl = 1.0 Shear Lag Factor, Usl U sl = 3.33 d/s 1.0 U sl = 2.5 d/s 1.0 U sl = 4.15 d/s 1.0 U sl = 1.0

33 Table E6.2-1 Shear Lag Factors for Connections to Tension Members (3) For other than flat sheet connections (a) When load is transmitted only by transverse welds (b) When load is transmitted directly to all the cross- sectional elements (c) For connections of angle members not meeting (a) or (b) above (d) For connections of channel members not meeting (a) or (b) above U sl = 1.0 and A nt = Area of the directly connected elements U sl = 1.0 U sl = x L 0.9 but U sl shall not be less than 0.4 U sl = x L 0.9 but U sl shall not be less than 0.5

34 F1.1 Load and Resistance Factor Design and Limit States Design Structural performance that is required to be established by: Tests in accordance with A1.2(a) or Rational engineering analysis with verification tests in accordance with A1.2(b)

35 APPENDIX 1: Design of Cold-Formed Steel Structural Members Using the Direct Strength Method Design provisions added for evaluating Shear alone and combined bending and shear Web holes for both columns and beams Inelastic strength for flexural members

36 AISI 2012 Updates: Framing Standards The More Significant Changes

37 North American Cold-Formed Steel Framing Standards AISI S200-12, General Provisions AISI S201-12, Product Data AISI S202-11, Standard Code of Standard Practice for Cold- Formed Steel Structural Framing AISI S (2012), Floor and Roof System Design AISI S211-12, Wall Stud Design AISI S (2012), Header Design AISI S213-07/S1-09 (2012), Lateral Design AISI S214-12, Truss Design AISI S220-11, Nonstructural Members AISI S (2012), Prescriptive Method for One and Two Family Dwellings

38 S200-12, North American Cold-Formed Steel Framing-General Provisions, and S201-12, North American Cold-Formed Steel Framing-Product Standard Reorganized as a code synchronization effort to eliminate duplications and redundancy, as well as to clear any ambiguities among AISI and ASTM standards, and building codes Reorganization due to the development of a new AISI S220, North American Cold-Formed Steel Framing Standard Nonstructural Members

39 AISI S211, North American Cold- Formed Steel Framing Standard- Wall Stud Design Includes updates of the referenced standards, and deletions of the provisions related to nonstructural members.

40 AISI S214, North American Cold- Formed Steel Framing Standard- Truss Design The major change of this standard is related to the provisions of truss responsibilities. Responsibilities provisions were extracted from AISI S202, Code of Standard Practice for Cold-Formed Steel Structural Framing, and added to AISI S214.

41 AISI S220, North American Cold- Formed Steel Framing Standard- Nonstructural Members New standard addresses the design, installation, and testing analysis of nonstructural members. A member in a steel-framed system that is not a part of the gravity load resisting system, lateral force resisting system or building envelope. Design approach utilizes the design provisions of AISI S100 but with adjusted safety and resistance factors, Ω N =0.9Ω; and φ N =1.1φ (consequence of failure is less severe historically 1.5 has been used)

42 Design Aids and Other Standards Other Standards S110, Standard for Seismic Design of Cold-Formed Steel Structural Systems - Special Bolted Moment Frames S310, North American Standard for the Design of Profiled Steel Diaphragm Panels D100, Cold-Formed Steel Design Manual Design Guides: D110, Cold-Formed Steel Framing Design Guide D111, Design Guide for Cold-Formed Steel Purlin Roof Framing Systems D112, Brick Veneer Cold-Formed Steel Framing Design Guide

43 Free Downloads! Current AISI Standards available as a free download: S200 Framing Standard Series S310 Diaphragm Design Standard S900 Test Standard Series

44 CFSEI Mission To enable and encourage the efficient design of safe and cost effective cold-formed steel framed structures. Mission fulfilled by: Webinars Annual Expo Answer questions by phone, , and website STEEL ( ) Ask an Expert on CFSEI website, Technical Notes on Cold-Formed Steel Construction (Tech Notes)

45 CFSEI Tech Notes Available Tech Notes = 45+ General Component Assemblies (Trusses and Wall Panels) Durability and Corrosion Protection Fasteners and Connection Hardware Floor and Joist Systems Lateral Systems Wall Systems Thermal, Fire, and Acoustic

46 Cold-Formed Steel Framing Design Guide D110 Curtain Wall Design

47 Deflection Track Design (Per Wall Stud Standard)

48 D110 Curtain Wall Design Using mullions: Strip Windows

49 D110 Curtain Wall Design Punched Windows: Strip Windows

50 Strip Windows Design Considerations:

51 D110 Floor Joist and Axial Loaded Studs

52 Bridging and Brace Design The Wall Stud Standard stipulates that for combined bending and axial loads, each brace shall be designed for the combined brace force determined by Section D3.2.1 of the Specification (torsional behavior) and 2% of the stud axial load (flexural buckling behavior). A brace stiffness requirement is not stipulated.

53 Bridging Channel Design (Per AISI Specification) The bridging channel will be subjected to axial load and both major and minor axis bending moment. The capacity of the bridging channel must be checked using the AISI Specification C5.2.1.

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56 Brace Design Bridging Anchorage Using flat strap X-bracing or other means of load transfer.

57 Brace Force Resolution

58 Brace Force Resolution 58

59 Scope: Wood & Steel sheathing only No gypsum No fiberboard No proprietary materials No Diaphragms No X bracing AISI D113 to be updated by the end of the year 1-59

60 Type I Shear Wall: Wood Sheathed 3-60

61 Type I Shear Wall SWDG Page

62 Structure for all Examples SWDG Page 14: Figure

63 Structure for all Examples: at Roof SWDG Page 15: Figure 5, top half (ROOF) 3-63

64 Structure for all Examples: at 2 nd Floor SWDG Page 15: Fig. 5, 2 nd Floor 3-64

65 Calculation of Force on Walls Diaphragm assumed flexible. Can assume flexibility from section of ASCE Flexible Diaphragm Condition. Diaphragms constructed of untopped steel decking or wood structural panels are permitted to be idealized as flexible in structures in which the vertical elements are steel or composite shear walls. 3-65

66 24th Short Course on Cold-Formed Steel Structures October 27-29, 2015 in St. Louis, Missouri Earn 24 hours of continuing education, 2.4 CEU credits. Take-home a copy of the AISI specification AISI commentary AISI design manual Text Cold-Formed Steel Design, 4 th edition Lecture notes Wei-Wen Yu Center for Cold-Formed Steel Structures 1-66

67 Wei-Wen Yu Center for Cold-Formed Steel Structure

68 Questions?