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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
ConsiderationsJCC Training
Seismic Structural
ConsiderationsJCC Training
byPaul W. McMullin, SE, PhD
October 15, 2009
© Dunn Associates Inc, 2009
The Paper Clip Test
© Dunn Associates Inc, 2009
Concept of Selected Deformation
© Dunn Associates Inc, 2009
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
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
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
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
Acceleration Record from Northridge
From the Strong Motion Database (SMDB, 2000a)
© Dunn Associates Inc, 2009
Northridge Earthquake
Magnitude 6.7• Estimated Economic
• Loss = $49.3 billion
Magnitude 6.7• Estimated Economic
• Loss = $49.3 billion
Building Inventory Damage• 100 buildings with minor
fractures
• 100 buildings with major fractures
• 30 buildings with major fractures in 90% of all connections
Building Inventory Damage• 100 buildings with minor
fractures
• 100 buildings with major fractures
• 30 buildings with major fractures in 90% of all connections
© Dunn Associates Inc, 2009
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
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
Changes: Code
Code limited approved filler metals
Inspection requirements tightened
Limited connection types
Quality control significantly increased
Code limited approved filler metals
Inspection requirements tightened
Limited connection types
Quality control significantly increased
© Dunn Associates Inc, 2009
Changes: Weld Access Hole
© Dunn Associates Inc, 2009
Connections: WUF-W
© Dunn Associates Inc, 2009
Connections: Extended Flange
© Dunn Associates Inc, 2009
Connections: Flange Cover Plate
© Dunn Associates Inc, 2009
Connections: Reduced Beam
Section
© Dunn Associates Inc, 2009
Connections: Bolted End Plate
© Dunn Associates Inc, 2009
Connections: SidePlate
© Dunn Associates Inc, 2009
Protected Zone Requirements
No discontinuities in protected zone• Arc Strikes• Erection Aids• Air-arc Gouging• Thermal Cutting
Not permitted• Welded studs• Shot pins• Screws• Welds• Holes
No discontinuities in protected zone• Arc Strikes• Erection Aids• Air-arc Gouging• Thermal Cutting
Not permitted• Welded studs• Shot pins• Screws• Welds• Holes
Get protected zone from drawings or engineer
Mark protected zones with bright paint after erection and after fire coating
Get protected zone from drawings or engineer
Mark protected zones with bright paint after erection and after fire coating
© Dunn Associates Inc, 2009
Protected Zones: Dog Bone
© Dunn Associates Inc, 2009
Protected Zones: Concentric Braced Frame
© Dunn Associates Inc, 2009
Protected Zones: Concentric Braced Frame
© Dunn Associates Inc, 2009
Protected Zones:Eccentric Braced Frame
© Dunn Associates Inc, 2009
Protected Zones:Eccentric Braced Frame
© Dunn Associates Inc, 2009
Connections
Bolted End Plate
Reduced Beam Section (“Dog Bone”)
SidePlate™
Bolted End Plate
Reduced Beam Section (“Dog Bone”)
SidePlate™
© Dunn Associates Inc, 2009
Reduced Beam Section Connection
Advantages• Approved
• Reduces column-beam weld stresses
Disadvantages• Milling of beam flange
• 80%-90% reliable
• Looks odd
Advantages• Approved
• Reduces column-beam weld stresses
Disadvantages• Milling of beam flange
• 80%-90% reliable
• Looks odd
© Dunn Associates Inc, 2009
Reduced Beam Section Connection
Watch for:• Protected Zone (nicks, arc
strikes, shot pins, welds)
• Smoothness of Cut
• Bracing just outside cut
Watch for:• Protected Zone (nicks, arc
strikes, shot pins, welds)
• Smoothness of Cut
• Bracing just outside cut
© Dunn Associates Inc, 2009
SidePlate Connection
Advantages• Approved- seismic &
progressive collapse
• Eliminates beam-column weld
• High reliability
• Looks strong
Disadvantages• Licensing fee
• Flip columns in shop
Advantages• Approved- seismic &
progressive collapse
• Eliminates beam-column weld
• High reliability
• Looks strong
Disadvantages• Licensing fee
• Flip columns in shop
© Dunn Associates Inc, 2009
Begin with Column Sub-Assembly
Step 1: Column Tree Assembly
Bring in Side Plates, Tack Weld into PositionBring in Horizontal Shear Plates, Tack, Check Alignment, Apply Welds 1 and 3Rotate Column into Position to Apply Other PlatesBring in Side Plates and Horiz. Shear Plates, Tack into PlaceApply Welds 1 and 3, Bring in Temporary DogsApply Weld 2, NS/FS. Rotate Column to Apply Weld 2 to Other Side Plates (Not Shown Here). After that, Column Sub-Assembly Complete.
© Dunn Associates Inc, 2009
Begin Full-Length Beam Assembly (Beam Inverted As Shown)
Step 2: Full-Length Beam Assembly
Bring in Cover Plates, Tack into PositionRotate Full-Length Beam and Apply Weld 5Full-Length Beam Assembly Complete Bring in Erection Angle, Tack & Weld into Position
© Dunn Associates Inc, 2009
Step 3: Erect Column Trees & Full-Length Beams with six 7/8” A325 Bolts Each End
© Dunn Associates Inc, 2009
SidePlate Connection
© Dunn Associates Inc, 2009
SidePlate Connection
Watch for:1) Joint Gap
2) Protected Zone (nicks, arc strikes, shot pins, welds)
3) SidePlate attachments
Watch for:1) Joint Gap
2) Protected Zone (nicks, arc strikes, shot pins, welds)
3) SidePlate attachments
1
3 2
© Dunn Associates Inc, 2009
SidePlate Protected Zone
© Dunn Associates Inc, 2009
SidePlate: WELDING OK
© Dunn Associates Inc, 2009
What keeps us from backtracking?
Special Inspection• Ensure done well• Ultrasonic• Mag Particle ends
Shop Drawings• Complete• Well detailed• Contractor review
Shop vs Field Welds• Define up-front• Shop welds- faster, higher
quality• Field welds- some pieces too
big for shop
Special Inspection• Ensure done well• Ultrasonic• Mag Particle ends
Shop Drawings• Complete• Well detailed• Contractor review
Shop vs Field Welds• Define up-front• Shop welds- faster, higher
quality• Field welds- some pieces too
big for shop
Good Communication• RFIs that are researched &
propose solutions• Notify us ahead of certain
activities (pours, fire coating)• Tell us about problems as soon
as you know (even your screw-ups)
Think/Plan Ahead• Catch problems• Give us time to determine a
solution
Good Communication• RFIs that are researched &
propose solutions• Notify us ahead of certain
activities (pours, fire coating)• Tell us about problems as soon
as you know (even your screw-ups)
Think/Plan Ahead• Catch problems• Give us time to determine a
solution
© Dunn Associates Inc, 2009
Our Liability
STRUCTURAL ENGINEER
Becomes liable when:• Omit information
• Don’t follow the State of the
Art (code is minimum)
STRUCTURAL ENGINEER
Becomes liable when:• Omit information
• Don’t follow the State of the
Art (code is minimum)
CONTRACTOR
Becomes liable when:• Deviate from approved plans
and specs
• Material/workmanship/Quality problems
CONTRACTOR
Becomes liable when:• Deviate from approved plans
and specs
• Material/workmanship/Quality problems
Regardless of who is liable, if there is a problem, we all get
dragged into the mess