Seismic Structural Considerations in Steel

Seismic Structural
Considerations
JCC Training

by
Paul W. McMullin, SE, PhD
October 15, 2009

The Paper Clip Test

© Dunn Associates Inc, 2009

Concept of Selected Deformation


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


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


Acceleration Record from Northridge

From the Strong Motion Database (SMDB, 2000a)


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


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


Changes: Code

Code limited approved filler
metals
Inspection requirements
tightened
Limited connection types
Quality control significantly
increased


Changes: Weld Access Hole


Connections: WUF-W


Connections: Extended Flange


Connections: Flange Cover Plate


Connections: Reduced Beam
Section


Connections: Bolted End Plate


Connections: SidePlate


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


Protected Zones: Dog Bone


Protected Zones:
Concentric Braced Frame


Protected Zones:
Eccentric Braced Frame


Connections

Bolted End Plate

Reduced Beam
Section (“Dog
Bone”)

SidePlate™


Reduced Beam Section Connection

Advantages
• Approved
• Reduces column-beam weld
stresses
Disadvantages
• Milling of beam flange
• 80%-90% reliable
• Looks odd


Reduced Beam Section Connection

Watch for:
• Protected Zone (nicks, arc
strikes, shot pins, welds)
• Smoothness of Cut
• Bracing just outside cut


SidePlate Connection

Advantages
• Approved- seismic &
progressive collapse
• Eliminates beam-column weld
• High reliability
• Looks strong
Disadvantages
• Licensing fee
• Flip columns in shop


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.

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


Step 3: Erect Column Trees & Full-Length Beams with six 7/8” A325 Bolts Each End



Watch for:
1) Joint Gap
2) Protected Zone (nicks, arc
strikes, shot pins, welds)
3) SidePlate attachments

1

3 2


SidePlate Protected Zone


SidePlate: WELDING OK


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


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

Seismic Structural Considerations in Steel

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