Seismic Structural Considerations in Steel

Seismic Structural

ConsiderationsJCC Training

Seismic Structural

ConsiderationsJCC Training

byPaul W. McMullin, SE, PhD

October 15, 2009

© Dunn Associates Inc, 2009

The Paper Clip Test


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

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

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• 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


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


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


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 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


Protected Zones: Dog Bone


Protected Zones: Concentric Braced Frame


Protected Zones: Concentric Braced Frame


Protected Zones:Eccentric Braced Frame


Protected Zones:Eccentric Braced Frame


Connections

Bolted End Plate

Reduced Beam Section (“Dog Bone”)

SidePlate™

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

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

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

Advantages• Approved- seismic &

progressive collapse

• Eliminates beam-column weld

• High reliability

• Looks strong

Disadvantages• Licensing fee

• Flip columns in shop


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.


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


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

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• 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


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

Design

Seismic Structural Considerations in Steel