Seismic Structural Considerations in Steel

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Training provided for Jacobsen Construction Company Superintendent, Project Engineer, and Project manager training. Covers history of steel moment frames, Northridge and subsequent changes, moment connections, and potential challenges.

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Seismic Structural Considerations in Steel

  1. 1. Seismic Structural Considerations JCC Training by Paul W. McMullin, SE, PhD October 15, 2009
  2. 2. The Paper Clip Test © Dunn Associates Inc, 2009
  3. 3. Concept of Selected Deformation © Dunn Associates Inc, 2009
  4. 4. Early Use of Moment Connections Flatiron Building, NYC • One of the first steel frame buildings • Portal frame moment connections at all wind girders. Early Steel Frames- all moment connected © Dunn Associates Inc, 2009
  5. 5. Construction Changes that led to Northridge Failures Fewer, but larger moment frames • Heavier connections Changed from Riveted to Welded construction Used lower toughness welding rod • Welds went down fast • Not permitted in pipelines Quality control problems © Dunn Associates Inc, 2009
  6. 6. Acceleration Record from Northridge From the Strong Motion Database (SMDB, 2000a) © Dunn Associates Inc, 2009
  7. 7. Northridge Earthquake Magnitude 6.7 Building Inventory • Estimated Economic Damage • Loss = $49.3 billion • 100 buildings with minor fractures • 100 buildings with major fractures • 30 buildings with major fractures in 90% of all connections © Dunn Associates Inc, 2009
  8. 8. Fracture Causes Welding • Low Toughness Weld Metal • Slag Inclusions • Lack of fusion Mismatched Yield Strengths Erroneous Joint Detailing Weld Constraint by Heavy Sections Slab Interaction with Column © Dunn Associates Inc, 2009
  9. 9. Changes: Code Code limited approved filler metals Inspection requirements tightened Limited connection types Quality control significantly increased © Dunn Associates Inc, 2009
  10. 10. Changes: Weld Access Hole © Dunn Associates Inc, 2009
  11. 11. Connections: WUF-W © Dunn Associates Inc, 2009
  12. 12. Connections: Extended Flange © Dunn Associates Inc, 2009
  13. 13. Connections: Flange Cover Plate © Dunn Associates Inc, 2009
  14. 14. Connections: Reduced Beam Section © Dunn Associates Inc, 2009
  15. 15. Connections: Bolted End Plate © Dunn Associates Inc, 2009
  16. 16. Connections: SidePlate © Dunn Associates Inc, 2009
  17. 17. Protected Zone Requirements No discontinuities in Get protected zone from protected zone drawings or engineer • Arc Strikes Mark protected zones with • Erection Aids bright paint after erection and • Air-arc Gouging after fire coating • Thermal Cutting Not permitted • Welded studs • Shot pins • Screws • Welds • Holes © Dunn Associates Inc, 2009
  18. 18. Protected Zones: Dog Bone © Dunn Associates Inc, 2009
  19. 19. Protected Zones: Concentric Braced Frame © Dunn Associates Inc, 2009
  20. 20. Protected Zones: Concentric Braced Frame © Dunn Associates Inc, 2009
  21. 21. Protected Zones: Eccentric Braced Frame © Dunn Associates Inc, 2009
  22. 22. Protected Zones: Eccentric Braced Frame © Dunn Associates Inc, 2009
  23. 23. Connections Bolted End Plate Reduced Beam Section (“Dog Bone”) SidePlate™ © Dunn Associates Inc, 2009
  24. 24. Reduced Beam Section Connection Advantages • Approved • Reduces column-beam weld stresses Disadvantages • Milling of beam flange • 80%-90% reliable • Looks odd © Dunn Associates Inc, 2009
  25. 25. Reduced Beam Section Connection Watch for: • Protected Zone (nicks, arc strikes, shot pins, welds) • Smoothness of Cut • Bracing just outside cut © Dunn Associates Inc, 2009
  26. 26. SidePlate Connection Advantages • Approved- seismic & progressive collapse • Eliminates beam-column weld • High reliability • Looks strong Disadvantages • Licensing fee • Flip columns in shop © Dunn Associates Inc, 2009
  27. 27. Step 1: Column Tree Assembly Rotate Column to Column1intoColumn Sub-Assembly (Not Shown Here). Bring inRotate Applyand andPosition Weld intoTack into Place Side Plates Weld 2Weld 2, toSide Plates Apply Bring in Sidewith to Bring in Temporary Plates Horiz. Other Alignment, Bring in Horizontal Shear Plates, Tack, CheckApply Other Dogs Welds 1 and 3 Apply Welds Apply 3, Tack NS/FS. Position Begin Plates, Shear Plates, After that, Column Sub-Assembly Complete. © Dunn Associates Inc, 2009
  28. 28. Step 2: Full-Length Beam Assembly Begin Full-Length Full-LengthTack & and into Position 5 Shown) Bring inFull-Length Beam Beam Weld Inverted As Rotate Beam Assembly Tack Apply Position Bring in Cover Plates, (Beam into Weld Erection Angle, Assembly Complete © Dunn Associates Inc, 2009
  29. 29. Step 3: Erect Column Trees & Full-Length Beams with six 7/8” A325 Bolts Each End © Dunn Associates Inc, 2009
  30. 30. SidePlate Connection © Dunn Associates Inc, 2009
  31. 31. SidePlate Connection Watch for: 1) Joint Gap 2) Protected Zone (nicks, arc strikes, shot pins, welds) 3) SidePlate attachments 1 3 2 © Dunn Associates Inc, 2009
  32. 32. SidePlate Protected Zone © Dunn Associates Inc, 2009
  33. 33. SidePlate: WELDING OK © Dunn Associates Inc, 2009
  34. 34. What keeps us from backtracking? Special Inspection Good Communication • Ensure done well • RFIs that are researched & • Ultrasonic propose solutions • Mag Particle ends • Notify us ahead of certain activities (pours, fire coating) Shop Drawings • Tell us about problems as soon • Complete as you know (even your screw- • Well detailed ups) • Contractor review Think/Plan Ahead Shop vs Field Welds • Catch problems • Define up-front • Give us time to determine a solution • Shop welds- faster, higher quality • Field welds- some pieces too big for shop © Dunn Associates Inc, 2009
  35. 35. Our Liability STRUCTURAL ENGINEER CONTRACTOR Becomes liable when: Becomes liable when: • Omit information • Deviate from approved plans • Don’t follow the State of the and specs Art (code is minimum) • Material/workmanship/Quality problems Regardless of who is liable, if there is a problem, we all get dragged into the mess © Dunn Associates Inc, 2009

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