Weitere ähnliche Inhalte Ähnlich wie Seismic Structural Considerations in Steel (7) Kürzlich hochgeladen (20) 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. 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
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. 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. Changes: Code
Code limited approved filler
metals
Inspection requirements
tightened
Limited connection types
Quality control significantly
increased
© Dunn Associates Inc, 2009
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
23. Connections
Bolted End Plate
Reduced Beam
Section (“Dog
Bone”)
SidePlate™
© Dunn Associates Inc, 2009
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. 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. 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. 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. 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. Step 3: Erect Column Trees & Full-Length Beams with six 7/8” A325 Bolts Each End
© Dunn Associates Inc, 2009
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
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. 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
