Steel Joist Floor Systems Best Practices

Transcription

1 Steel Joist Floor Systems Best Practices APRIL 20, 2016 Copyright 2016 Steel Joist Institute. All Rights Reserved. Presented by: Michael A. West, P.E., F.ASCE David Samuelson, P.E.

2 Learning Objectives Identify Codes and Standards providing requirements and guidance for selecting joists and Joist Girders for steel joist supported floor systems. Review of where standard joists, constant shear joists (KCS joists), Special Joists for supporting non-uniform and concentrated loads, or CJ- Series Composite Joists may be advantageous. Discuss SJI publications that are available to assist the Structural Engineer to design steel joist floor systems for serviceability, for selecting appropriate UL fire resistance ratings, and for adapting joists for future building uses. 2

3 Learning Objectives Demonstrate SJI s future Floor Bay Analysis tool showing how this tool can optimize the layout and select optimal depths for non-composite K-Series, LH-Series, and DLH Series joists and Joist Girders as well as CJ-Series composite joists. Learn how the recent incorporation of SJI s Virtual Joist Girder tables within RAM Structural System, RISA, and SCIA Engineer facilitates the selection of Joist Girders within lateral load resisting frames. Learn how SJI s new Virtual Joist tables can yield a reasonable approximate joist effective moment of inertia and weight for joists with nonuniform loading, concentrated loads of varying magnitude, and / or externally applied local moments. 3

4 Successfully Using Steel Joists in Floor Construction A TOOL KIT Copyright 2016 Steel Joist Institute. All Rights Reserved. Presented by Michael A. West, P.E., F.ASCE

5 Outline Loads and Resistance Non-composite vs. Composite v. KCS-Series Joists Deck Lateral Load Resisting Frames w/ joists and JG Serviceability Deflection Vibration Fire Resistance Accommodating M-E-P Adaptability modifying joists & Joist Girders 5

6 Loads IBC Table TABLE MINIMUM UNIFORMLY DISTRIBUTED LIVE, L O AND MINIMUM CONCENTRATED LOADS LIVE LOADS OCCUPANCY OR USE 22. Office buildings UNIFORM (psf) CONCENTRATED (pounds) Corridors above first floor 80 2,000 Files and computer rooms Based on occupancy Based on occupancy Lobbies and 1 st flr. corridors 100 2,000 Offices 50 2, Schools Classrooms 40 1,000 Corridors above first floor 80 1,000 First floor corridors 100 1,000 6

7 IBC Concentrated LL Distributed over an area 2 ½ feet by 2 ½ feet: 2000/(2.5) 2 = 320 psf 1000/(2.5) 2 = 160 psf 7

8 43RD Edition Catalog Standard Specifications, 43 rd Edition K-Series LH-Series DLH-Series Joist Girders Load and Weight Tables SJI Code of Standard Practice 8

9 Composite Steel Joist Catalog Standard Specifications for Composite Steel Joists, First Edition CJ-Series How to specify and more 9

10 Composite Steel Joist Catalog Standard Specifications Responsibility of the Specifying Professional Design Guides Examples Code of Standard Practice for Composite Steel Joists -Composite Joist Floor Design Parameters Check List 10

11 Designating CJ-Series Joists 30CJ 2188/1168/ is the joist depth 2188 is the Total Factored Composite Design Load 1168 is the Total Factored Composite Live Load 420 is the Total Factored Composite Dead Load 11

12 Steel Decks in Floor Construction Form decks vs. Composite decks Profiles (and thicknesses) (Gage numbers) 1 Form Deck ( ) (26-20) 1-1/2 Form Deck ( ) (24-20) 2 Form Deck ( ) (24-20) 1-1/2 Composite Deck ( ) (22-16) 1-1/2 Comp. Deck Inverted ( ) ( ) 2 Composite Deck ( ) (22-16) 3 Composite Deck ( ) (22-16) 12

13 Framing Layout A Function of Loads and required resistance Slab thickness & deck profile & joist spacing & joist depth & structure depth & story height The combinations are nearly infinite! Stay tuned for SJI s Floor Bay Analysis Tools 13

14 AISC Design Guide No. 3 Serviceability Design Considerations for Steel Buildings 14

15 IBC 2015 & AISC Design Guide 3 AISC Design Guide 3 IBC Table Construction Live Snow/Wind Dead + Live* Floor Members L / L / 240 * For steel structural members, the dead load shall be taken as zero. Non-composite, across the bay Span/360, max. 1 inch for dead load Span/360, max. 1 inch for 50% live load 15

16 SJI Technical Digest No. 5 Vibration of Steel Joist Concrete Slab Floors 16

17 Acceptance Criteria Walking (3-9 Hz) Peak acceleration ratio Tolerance acceleration ratio 17

18 Vibration Walking Excitation Table TD 5 (DG 11) Recommended Live Loads for Vibration Analysis Activity Recommended Live Load (psf) Walking Paper Office 11 Walking Electronic Office 6 8 Walking Residence 6 Walking Assembly Area 0 Walking Shopping Mall 0 Dancing 12.5 Lively Concert 31 Sports Event 31 Rhythmic Activities 4.2 (For use in determining natural frequency) 18

19 Damping, β 19

20 Vibration Walking Excitation Table 3.1 Recommended Tolerance Accelerating Limits Occupancy Tolerance Acceleration Limit (a o /g)x100% Offices, Residences % Assembly Areas, Worship, Schools % Shopping Malls 1.5% 20

21 AISC Design Guide No. 11 Floor Vibrations Due to Human Activity 21

22 Fire-proofed vs. Unprotected A required class of construction is a function of Occupancy, and Height and area Fire rated construction can be achieved in joist/joist Girder construction, but it s costly and makes M-E-P installation and maintenance more difficult 22

23 Construction Classification IBC, Chapter 6 and Table 601 Type II, B Noncombustible materials Type II, B Fire-Resistance Ratings Primary structural frame 0 (zero) Floor construction and associated secondary members 0 (zero) 23

24 Height and Area Limits IBC, Chapter 5 and Table 503 for Type II, B Maximum height 55-feet Assembly (A-1 through A-5) Stories 2 (unlimited for A-5) Area 8,500 to 9,500 sq.ft. (unlimited for A-5), per story Business (B) Stories 3 Area 23,000 sq.ft. 24

25 Height and Area Limits, cont. IBC, Chapter 5 and Table 503 for Type II, B Educational (E) Stories 2 Area 14,500 sq.ft. Factory (F-1 and F-2) Stories 2 for F-1 and 3 for F-2 Area 15,500 sq.ft. for F-1 and 23,000 sq.ft. for F-2 25

26 Height and Area Limits, cont. IBC, Chapter 5 and Table 503 for Type II, B Mercantile (M) Stories 2 Area 12,500 sq.ft. Residential (R-1 and R-2), not incl. R-3 and R-4 Stories 4 for R-1 and R-2 Area 16,000 sq.ft. for R-1 and R-2 26

27 SJI Technical Digest No. 10 Design of Fire- Resistive Assemblies with Steel Joists Floors and Roofs Membrane and Spray- Applied Fire Resistive Materials 27

28 SJI Technical Digest No. 10 Appendix Tables for Floors and Roofs w/ UL Design Numbers Group D Concrete and Steel Floor Units Group G Concrete and Steel Joists 28

29 UL Design G501 29

30 AISC Design Guide No. 19 Fire Resistance of Structural Steel Framing 30

31 Accommodation of M-E-P Under the framing: Simpler Probably increases story height Need to consider structure depth vs. story ht. Through the framing: Requires greater attention to structure/m-e-p co-ordination, including turning the corner May limit duct sizes Joists as deep as possible X-bridging provisions (TD 2) And a hybrid (of course) 31

32 SJI Technical Digest No. 12 Evaluation and Modification of Open Web Steel Joists and Joist Girders 32

33 Modification of Joists and Joist Girders Modify to increase load capacity Modify for new concentrated loads Modify to shorten at headered openings 33

34 SJI Technical Digest No. 11 Design of Lateral Load Resisting Frames Using Steel Joists and Joist Girders 34

35 In Conclusion - Consider Loads and Resistance Serviceability Deflection Vibration Fire Resistance Accommodation of M-E-P Adaptability And using the SJI Floor Bay Analysis Tools 35

36 SJI Floor Design Tools Copyright 2016 Steel Joist Institute. All Rights Reserved. Presented by David Samuelson, P.E.

37 SJI Floor Design Tools SJI Floor Bay Analysis Tool SJI Virtual Joist Tables SJI Virtual Joist Girder Tables 37

38 SJI Floor Bay Analysis Tool 38

39 Joist Spans 39

40 Joist Girder Spans 40

41 Noncomposite or Composite 41

42 Standard K, LH, & DLH or Load / Load Joist 42

43 Loads, Deck & Concrete Criteria 43

44 Steel Deck Options 2 18 Gage 3 22 Gage 3 20 Gage 3 18 Gage 9/16 Form 28 Gage 9/16 Form 26 Gage 9/16 Form 24 Gage 9/16 Form 22 Gage 1 Form 26 Gage 1 Form 24 Gage 1 Form 22 Gage 1 Form 20 Gage 1.5 Form 22 Gage 1.5 Form 20 Gage 1.5 Form 18 Gage 44

45 Min. & Max. Joist / Joist Girder Depths, Deflection Criteria and Minimize X-Bridging 45

46 Deck, Concrete & Joist Summary 46

47 Bridging & Joist Girder Summary 47

48 Estimated and Actual Joist / Joist Girder Weights 48

49 User Defined Cost Data 49

50 Final Design 50

51 Design Run Comparisons 51

52 Run Data copied to Run Comparison 52

53 Composite Joist Comparison 53

54 Joist Depth must be entered for Composite Joists 54

55 Composite Joist Design 55

56 Copy Composite Joist Design to Run Comparison Table 56

57 Total Cost, $/sf for Noncomposite vs. Composite Joist Design 57

58 Future Release of SJI Floor Bay Analysis Tool May,

59 Classic Roof and Floor Framing Programs Standard SJI joists only managed as simple-span infill joists supporting vertical gravity loads. 59

60 SJI s Virtual Joist and Virtual Joist Girder Load Tables Standard programs such as RAM Structural System, RISAFLOOR, SCIA, etc. do an excellent job of selecting Standard SJI joists. 60

61 Standard Joists Selected Based on Span and Uniform Loading RAM Structural System Partial Framing Plan 61

62 Classic Roof and Floor Framing Programs Standard joist designations and definition do not address concentrated loads, end moments, negative moments or axial loads. 62

63 Steel Joist \ Joist Girder Stiffness not Included in Structural Model Quote from STAAD-PRO Technical Reference Manual 63

64 What are Virtual Joist / Virtual Joist Girder Tables Virtual Joists and Virtual Joist Girders are a set of pseudo section properties based on commonly available joist chord pairs. The major axis moment of inertia (I xx ) is based directly on a pair of double angle joist chords and pre-adjusted for approximate deflection contribution from web strain. Allows joists and Joist Girders to be checked for flexure, shear, axial, and combined forces by treating them as doubly symmetric I shaped beam sections. Can be inserted into stiffness based structural analysis programs such as RAM, RISAFLOOR, SCIA, etc. 64

65 What are Virtual Joist / Virtual Joist Girder Tables Virtual joist and Virtual Joist Girder tables allow joist member stiffness to be accounted for in the overall building model. Once the building model is completed, standard SJI joist and Joist Girder designations are called out on the plans. 65

66 SDSM&T Comparison Study of VJ and VJG Tables 66

67 Joist Girder Frame Model 5'-0" = 120'-0" P P P WIND = 1000 plf 23'-6" G3 G4 P : DL = 2.4 kips G3 LL = 4.0 kips TL = 6.4 kips 1 2 WL = 7.0 kips 3 4 WIND = 1000 plf FRAME GRID LINE B & E VJ / VJG Tables permit easy determination of required effective I xx for joist /Joist Girders in the structural model. 67

68 Virtual Joist Girder Reporting Loads Note: Please contact the Project Structural Engineer of Record if the final effective Joist Girder Moment of Inertia (I xx ) varies from the tabulated target value by more than 10%. 68

69 Virtual Joist / Virtual Joist Girders SCIA Screen Shot 69

70 Joist and Girder Designations displayed in VJG Format RAM Steel Partial Framing Plan 70

71 RISAFLOOR Draw Virtual Joist Girders 71

72 Virtual Joist Girder 72

73 RISAFLOOR- Draw Virtual Joists 73

74 Virtual Joists 74

75 RISAFLOOR 75

76 RISAFLOOR Weight Takeoff 76

77 RISAFLOOR VJ / VJG Moment of Inertia 77

78 RISAFLOOR VJ / VJG Moment of Inertia Min I zz effective = 134 in 4 78

79 SCIA Virtual Joist Designation 79

80 SCIA Special Joist Designation 80

81 SCIA VJG Designation 81

82 How should a Virtual Joist or Virtual Joist Girder be Specified on the Structural Drawings? It is important to specify all joists and Joist Girders using conventional SJI designation nomenclature. ASD 28K7 Joist 185/100 Uniform Load (PLF) 50 Span Standard Joist Designation ASD 28 K 7 Allowable Strength Design Joist Depth in inches Joist Series Chord Size 82

83 How should a Virtual Joist or Virtual Joist Girder be Specified on the Structural Drawings? Joist Space 11.9K 11.9K 11.9K 11.9K 11.9K 11.9K 11.9K Joist Girder Span (C.L. of column to C.L. of column) Allowable Strength Design Standard Joist Girder Designation ASD 44G 8N 11.9K Depth of Number Girder in of Joist inches Spaces Load in Kips at Each Panel Point 83

84 SCIA Standard SJI Joist Designations Shown on Structure Labels in Structure 84

85 Conclusions SJI s Virtual Joists permit the determination of joist weight and effective I xx for complex load cases. Recent incorporation of SJI s Virtual Joist Girder Tables within RAM Structural System, RISAFLOOR, and SCIA Engineer allows one to readily determine Joist Girder weights and effective moments of inertia in a lateral load resisting frame. Utilizing SJI s Virtual Joist / Virtual Joist Girder Tables, one can now determine the estimated weight and cost for complex loaded Special joists and non-symmetrically loaded Joist Girders. 85

86 Conclusions SJI s Floor Bay Analysis Tool facilitates the calculation of estimated total floor costs for K, LH, DLH and CJ-Series composite joists. Current codes, specifications, design guides, and design tools make the design of joists and Joist Girders more efficient than ever before. 86

87 Future SJI Webinars on VJ / VJG Tables May 18, 2016 RAM Structural System June 1, 2016 SCIA Engineer June 15, 2016 RISAFLOOR 87

88 THANK YOU Copyright 2016 Steel Joist Institute. All Rights Reserved. 88