PCI 6 th Edition

1. PCI 6th Edition Connection Design

2. Presentation Outline • Structural Steel Design • Limit State Weld Analysis • Strut – Tie Analysis for Concrete Corbels • Anchor Bolts • Connection Examples

3. Changes • New method to design headed studs (Headed Concrete Anchors - HCA) • Revised welding section • Stainless Materials • Limit State procedure presented • Revised Design Aids (moved to Chapter 11) • Structural Steel Design Section • Flexure, Shear, Torsion, Combined Loading • Stiffened Beam seats • Strut – Tie methodology is introduced • Complete Connection Examples

4. Structural Steel Design • Focus on AISC LRFD 3rd Edition • Flexural Strength • Shear Strength • Torsional Strength • Combined Interaction • Limit State Methods are carried through examples

5. Structural Steel Details • Built-up Members • Torsional Strength • Beam Seats

6. Steel Strength Design • Flexure fMp = f·Fy·Zs Where: fMp = Flexural Design Strength Fy = Yield Strength of Material Zs = Plastic Section Modulus

7. Steel Strength Design • Shear fVn = f(0.6·Fy)·Aw Where: fVp = Shear Design Strength Aw = Area subject to shear

8. Steel Strength Design • Torsion (Solid Sections) fTn = f(0.6·Fy)·a·h·t2 Where: fTp = Torsional Design Strength a= Torsional constant h= Height of section t= Thickness

9. Torsional Properties • Torsional Constant, a • Rectangular Sections

10. Steel Strength Design • Torsion (Hollow Sections) fTn = 2·f(0.6·Fy)·Ᾱ·t Where: fTp = Torsional Design Strength Ᾱ= Area enclosed by centerline of walls t= Wall thickness

11. Torsional Properties • Hollow Sections Ᾱ= w·d

12. Combined Loading Stress • Normal Stress • Bending Shear Stress • Torsion Shear Stress

13. Combined Loading • Stresses are added based on direction • Stress Limits based on Mohr’s circle analysis • Normal Stress Limits • Shear Stress Limits

14. Built-Up Section Example

15. Example

16. Tension Area Compression Area Tension = Compression Determine Neutral Axis Location, y

17. Either Tension or Compression Area x Distance between the Tension / Compression Areas Centroids Define Plastic Section Modulus, Zp

18. Determine Centroid Locations • Tension • Compression

19. Calculate Zp

20. Beam Seats • Stiffened Bearing • Triangular • Non-Triangular

21. Triangular Stiffeners • Design Strength fVn=f·Fy·z·b·t Where: fVn = Stiffener design strength f = Strength reduction factor = 0.9 b = Stiffener projection t = Stiffener thickness z = Stiffener shape factor

22. Stiffener Shape Factor

23. Thickness Limitation

24. Triangular Stiffener Example Given: A stiffened seat connection shown at right. Stiffener thickness, ts = 3/8 in. Fy = 36 ksi Problem: Determine the design shear resistance of the stiffener.

25. Shape Factor

26. Thickness Limitation

27. Design Strength

28. Weld Analysis • Elastic Procedure • Limit State (LRFD) Design introduced • Comparison of in-plane “C” shape • Elastic Vector Method - EVM • Instantaneous Center Method – ICM

29. Elastic Vector Method – (EVM) • Stress at each point calculated by mechanics of materials principals

30. Elastic Vector Method – (EVM) • Weld Area ( Aw ) based on effective throat • For a fillet weld: Where: a = Weld Size lw = Total length of weld

31. Instantaneous Center Method (ICM) • Deformation Compatibility Solution • Rotation about an Instantaneous Center

32. Instantaneous Center Method (ICM) • Increased capacity • More weld regions achieve ultimate strength • Utilizes element vs. load orientation • General solution form is a nonlinear integral • Solution techniques • Discrete Element Method • Tabular Method

33. ICM Nominal Strength • An elements capacity within the weld group is based on the product of 3 functions. • Strength • Angular Orientation • Deformation Compatibility

34. Strength, f Aw - Weld area based on effective throat

35. Angular Orientation, g Weld capacity increases as the angle of the force and weld axis approach 90o

36. Deformation Compatibility, h Where the ultimate element deformation Du is:

37. Element Force Where:r and q are functions of the unknown location of the instantaneous center, x and y

38. Equations of Statics

39. Tabulated Solution • AISC LRFD 3rd Edition, Tables 8-5 to 8-12 fVn = C·C1·D·l Where: D = number of 16ths of weld size C = tabulated value, includes f C1 = electrode strength factor l= weld length

40. Comparison of Methods • Page 6-47:

41. Corbel Design • Cantilever Beam Method • Strut – Tie Design Method • Design comparison • Results comparison of Cantilever Method to Strut – Tie Method • Embedded Steel Sections

42. Cantilever Beam Method Steps Step 1 – Determine maximum allowable shear Step 2 – Determine tension steel by cantilever Step 3 – Calculate effective shear friction coeff. Step 4 – Determine tension steel by shear friction Step 5 – Compare results against minimum Step 6 – Calculate shear steel requirements

43. Cantilever Beam Method • Primary Tension Reinforcement • Greater of Equation A or B • Tension steel development is critical both in the column and in the corbel

44. Cantilever Beam Method • Shear Steel • Steel distribution is within 2/3 of d

45. Cantilever Beam Method Steps Step 1 – Determine bearing area of plate Step 2 – Select statically determinate truss Step 3 – Calculate truss forces Step 4 – Design tension ties Step 5 – Design Critical nodes Step 6 – Design compression struts Step 7 – Detail Accordingly

46. Strut – Tie Analysis Steps Step 1 – Determine of bearing area of plate

47. Strut – Tie Analysis Steps Step 2 – Select statically determinate truss AC I provides guidelines for truss angles, struts, etc.

48. Strut – Tie Analysis Steps Step 3 – Determine of forces in the truss members Method of Joints or Method of Sections

49. Strut – Tie Analysis Steps Step 4 – Design of tension ties

50. Strut – Tie Analysis Steps Step 5 – Design of critical nodal zone where: βn = 1.0 in nodal zones bounded by structure or bearing areas = 0.8 in nodal zones anchoring one tie = 0.6 in nodal zones anchoring two or more ties