Underlying Concepts in Seismic Design Codes: Application to Steel Building Structures

1. Underlying Concepts in Seismic Design Codes: Application to Steel Building Structures

2. 2 Outline Seismic Loadings Codes - Historical Development - Intent of Seismic Performance Factors Seismic Materials Codes Ductility vs. Strength Ductility Design - Examples of Code Implementation (SMF, BFs) Capacity Design - Examples of Code Implementation (SMF, BFs) Summary

3. 3 Historical Development of Seismic Loadings Codes

4. 4 Basic Load Combinations (ASCE 7) E: Probably the Most Mysterious “Load”

5. 5 Seismic Loadings: Historical Perspective

6. 6 Design Base Shear: Historical Perspective

7. 7 Seismic Design Philosophy

8. 8 Earthquake Observation

9. 9 Building Standard Law (BSL) of Japan

10. 10 Building Standard Law (BSL) of Japan Level 2 Earthquake (PGA = 0.34?0.4 g) for Safety Consideration Level 1 Earthquake (PGA = 0.07?0.1 g) for Serviceability Consideration

11. 11 BSL Level 1? Serviceability Design

12. 12 BSL Level 2?Safety Design

13. 13 US Approach?up to 1985 UBC

14. 14 1988 UBC

15. 15 Comparison of BSL and UBC Drift Limits

16. 16 Implication of UBC Drift Limit

17. 17 1997 UBC

18. 18 ASCE 7-05

19. 19 Performance-Based Design Two-Level Seismic Design Including Seismic Serviceability Check Is Back Again!

20. 20 Tall Buildings PBD Guidelines Still Use Capacity Design Principles Require Nonlinear Time-History Analysis Check at Least Two Seismic Hazard Levels

21. 21 Los Angeles Tall Buildings Structural Design Council

22. 22 Pacific Earthquake Engineering Research Center Definition of Tal Buildings Not Height Dependent Period > 1 Second Significant Higher Mode Effects Significant Story Drift Component due to Chord (Column, Shear Wall) Deformation

23. 23 Pacific Earthquake Engineering Research Center

24. 24 Seismic Serviceability Design

25. 25 Design Basis Earthquake (ASCE 7)

26. 26 “1g” Building

27. 27

28. 28 Ductility Factor

29. 29 Newmark-Hall Ductility Reduction Rule

30. 30 Multistory Frames

31. 31 BSL Level 2?Safety Design

32. 32 US Approach

33. 33 Simplicity Nonlinear Analysis not Required Ultimate Structural Strength not Known Empirical Seismic Performance Factors (R, Cd, and ?o) Design Focuses on Life Safety at One Design Earthquake (475-year) Level The Design Procedure Serves Well in General

34. 34 Seismic Design Concept 1?Ductility Design A Reduced Design Seismic Force Can Be Used IF Sufficient Ductility Is Built into the Structure But Only Certain Elements Are Strategically Designated to Serve as Structural Fuse, i.e., Deformation-Controlled Elements (DCE)

35. 35 Example (SCBF)

36. 36 Example (EBF)

37. 37 Example (SMF)

38. 38 Seismic Design Concept 2?Capacity Design Remaining Part of the Structure Is Designed to Remain Elastic, i.e., Design These Elements as Force-Controlled Elements (FCE).

39. 39 Two Key Concepts in AISC Seismic Provisions Ductility Design Requirements + Capacity Design Requirements

40. 40 2005 AISC Seismic Provisions Moment Frames (Sections 9, 10, 11) Special Truss Moment Frames (Section 12) Concentrically Braced Frames (Sections 13,14) Eccentrically Braced Frames (Section 15) Buckling-Restrained Braced Frames (Section 16) Special Plate-Shear Walls (Section 17)

41. 41 2010 AISC Seismic Provisions Section A: General Requirements Section B: General Design Requirements Section C: Analysis Section D: General Member and Connection Design Requirements Section E: Moment-Frame Systems Section F: Braced-Frame and Shear-Wall Systems Sections G, H: Composite Systems etc.

42. 42 Sample Section (§13 on SCBF)

43. 43 Ductility vs. Capacity Design

44. 44 Ductility Design Concept

45. 45 Target Yield Mechanism

46. 46 2010 AISC Seismic Provisions Definition of Highly Ductile Members and Moderately Ductile Members Seismic Compactness Requirement Lateral Bracing Requirement

47. 47 Ductility Requirements Code Implementation Example 1: Special Moment Frame (SMF) Design

48. 48 RBS Moment Connection

49. 49 RBS Moment Connection

50. 50 BFP Moment Connection

51. 51 Dynamic Testing of Pre-Northridge Moment Connection

52. 52 Local Buckling Control

53. 53 Local Buckling Control (2005 SP)

54. 54 Local Buckling Control (2010 SP)

55. 55 Lateral-Torsional Buckling

56. 56 Lateral-Torsional Buckling

57. 57 Lateral-Torsional Buckling

58. 58 Panel Zone

59. 59 Protected Zone (AISC SP §9.3)

60. 60 Ductility Requirements Code Implementation Example 2: Special Concentrically Braced Frame (SCBF) Design

61. 61 Target Yield Mechanism

62. 62 Bracing Ductility Requirements Bracing Buckling (SP §13.2a)

63. 63 Bracing Ductility Requirements Local Buckling (SP §8.2b): Seismically Compact

64. 64 Gusset “2t” Requirement

65. 65 Gusset “2t” Requirement

66. 66 Ductility Requirements Code Implementation Example 3: Eccentrically Braced Frame (EBF) Design

67. 67 EBF Configuration

68. 68 Link Ductility Requirement

69. 69 Link Ductility Requirements Link Deformation Capacity Depends on ? (Seismic) Compactness ? Length ? Link Stiffeners

70. 70 Link Length Effect

71. 71 Link Web Stiffeners (AISC SP §15.2c)

72. 72 Capacity Design Concept

73. 73 Ductility vs. Capacity Design

74. 74 ASCE 7 Seismic Performance Factors 3 System Factors: R, Cd, and ?o

75. 75 Capacity Design Seismic Forces

76. 76 Seismic Load Combinations (IBC) §16.5.2.1 Basic Seismic Load Combination: 1.2D + f1L + f2S + 1.0E §1605.4 Special Seismic Load Combination: 1.2D + f1L + 1.0Em

77. 77 Internal Force Distribution At Seismic Force Level II (Basic Seismic Load Combination)?Use Elastic Structural Analysis to Determine Internal Force Distribution At Seismic Force Level III (Special Seismic Load Combination)?Internal Force Re-distribution Occurs due to Nonlinear Response

78. 78 Example

79. 79 Capacity Design Think beyond Elastic Response Mentality Use Expected Material Strength to Estimate Maximum Force Developed in Structural Fuse (Note: Structural Fuse Material Strength too High Is not Desirable for Seismic Design) Two Methods to Calculate Seismic Force Level III for Capacity Design ?Local Approach ?Global Approach

80. 80 Expected Material Strength AISC SP §6.2 Expected Yield Stress,

81. 81 Method 1?”Local” Approach When the Structural Fuse Is Next to Force-Controlled Element Apply Statics at “Local” Level Seismic Force Level II not Needed An Upper-Bound Estimate of Seismic Force Level III

82. 82 Example 1: SCBF Bracing Connection Bracing is Structural Fuse AISC SP §13.3 Bracing Connection Design

83. 83 Example 1: SCBF Beam Design AISC SP §13.4a Beam Design for V-Type Bracing

84. 84 Example 1: SCBF Beam Design

85. 85 Example 2: EBF Column Design Links Are Structural Fuse AISC SP §15.8 for Column Design

86. 86 Example 2: EBF Brace Design Links Are Structural Fuse AISC SP §15.6 for Beam/Bracing Design

87. 87 Example 3: SMF AISC 358-05

88. 88 Example 3: SMF Strong Column-Weak Beam Condition (AISC SP §9.6):

89. 89 Method 2?”Global” Approach An Approximate (or “Lazy”) Method: ?o ? (Seismic Force Level II) Use It When Method 1 Cannot Be Applied Easily Usually Applied at the “Global” (or System) Level Can Be Dangerous If Not Properly Applied

90. 90 Example 1?SCBF

91. 91 SCBF: 2010 AISC SP Case 1 All Tensile Braces: T = Ry Fy Ag All Compressive Braces: P = min{Ry Fy Ag, 1.14FcreAg} Case 2 All Tensile Braces: T = Ry Fy Ag All Compressive Braces: 30% of P in Case 1

92. 92 Example 1?SCBF Column Design

93. 93 Example 2?SCBF Column Design

94. 94 Example 2?SCBF Column Design

95. 95 Summary Seismic Provisions Trade Strength with Ductility AISC Seismic Provisions Centered on Two Concepts. A Target Yield Mechanism Is Aimed for Each Lateral Force-Resisting System Deformation-Controlled Elements (Structural Fuse): ?Design for Reduced Seismic Forces ?Ductility Design Is Relatively Straightforward Force-Controlled Element: ?Design for Amplified Seismic Forces ?Use Either “Local” or “Global” Approach ?Capacity Design Requires Good Judgment and Experience