Buckling Restrained Braced Frame Application for a Power Plant Boiler Building

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Buckling Restrained Braced Frame Application for
a Power PlantBoiler Building

• Harold O. Sprague, Jr., P.E.Project Manager

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Introduction Harold O. Sprague, PE

• Former Iron Worker
• Professional Engineer 29 years ago
• ICC Structural Steel Special Inspector
• Building Code Development
• BSSC, ASCE 7 STC, Blast Committee
• FEMA Urban Search Rescue Structures Specialist
• Adjunct Prof. of Engr. University of Missouri -
  KC
• Black Veatch - Engineer, RD, Blast Seismic

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Agenda

• Project background
• The problem
• Code Acceptance of BRBs
• Dynamic Analysis
• BRB Manufactures Features
• Lessons Learned
• Cost of BRBF vs. OCBF

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Acknowledgements

• Jones, Dan, P.E. Black Veatch structural
  engineer
• Kohns, Larry, P.E. - Black Veatch structural
  engineer
• Petersen, Mark, P.E., G.E. Black Veatch
  geotechnical engineer
• Zheng, Wei, Ph.D., P.E. - Black Veatch
  geotechnical engineer
• Wiley, Alan, P.E. Black Veatch lead
  structural analysis
• Hart, Tom, P.E., R.G. Black Veatch
  geotechnical engineer
• Brainard, Ray - Black Veatch geotechnical
  engineer
• Powell, Steven D., S.E. Star Seismic LLC
• Hashash, Youssef, PhD, P.E., professor at the
  University of Illinois
• Whittaker, Andrew, PhD, S.E., professor at
  SUNY-Buffalo
• Power, Maury Geomatrix geotechnical engineer

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Plum Point Energy Station Project

• 665 MW Coal Fired electric generation facility
• Osceola, Arkansas (Northeast Arkansas)
• Greenfield site
• State of the art emission controls
• Construction Start April 2006
• Commercial Operation Summer 2010

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Plum Point - Generation Building Elevation
Boiler
Coal Silos
Air Quality Control System
Turbine
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Boiler Building
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Plum Point Project Location
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Seismicity in the United States
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New Madrid Quakes 1811 - 1812

• December 16, 1811 2 shocks Magnitude 8.5
• January 23, 1812 Magnitude 8.4
• February 7, 1812 Magnitude 8.0
• Felt in Boston
• Damage in Charleston, SC
• Jared Brooks,
• Louisville, KY 1,872 events

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New Madrid Quakes

• Buildings damaged over an area size of Texas
• Eight shocks felt in Montreal, Canada (1200 miles
  away)
• 2 million square miles, over half the U.S. was
  shaken largest area ever known to be affected
  by an earthquake

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New Madrid Seismic Activity
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Seismic Design Conditions for Plum Point

• Mapped Ground Motion
• Ss 2.60g
• Mapped Ground Motion
• S1 0.67g
• Site Class F
• Site Specific Response Spectra required

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Choosing a Framing System

• Large seismic demands at Plum Point site
  suggested rethinking our framing system
• Typically use conventional braced frame (OCBF).
• Estimated steel for Generation Building using
  OCBF 18,000 tons

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The Problem?

• Conventional concentric braced frames result in
  stiff structures
• Stiff structures result in large inertial seismic
  forces in structure, components, and in
  foundations

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Ground Motion
Flexible Structure
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Ground Motion
Rigid Structure
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The Problem

• Concentric bracing is designed for two possible
  failure modes
• Tension Stress
• Compression Buckling
• Compression buckling controls design and
  therefore create a stiff structure.

Show John Hancock tower or heavy braced building
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The Solution Buckling Restrained Braced
Frame
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Conventional Brace Behavior
BRB Behavior
Core
Outer casing
De-Coupled Stress and Buckling (Mechanics
Definition)
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BRB Basics
Steel Casing (Tube)
Yielding Core
End Connections
Restraining Mechanism (Concrete Grout)
Debonded Gap
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The Solution

• Provides much more ductile structure reducing
  seismic demand
• Reduces member sizes, connection sizes, and size
  of foundation (and number of piles).

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BRB Evolution

• BRB technology developed in Japan in mid 1980s
• U.S. started research and testing in 1999
• 2003 National Earthquake Hazards Reduction
  Program Recommended Provisions for Seismic
  Regulations for New Buildings and Other
  Structures
• AC238 - Acceptance Criteria For
  Buckling-restrained Braced Frame Subassemblages

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Code Acceptance of BRBs

• AISC 341-05 Seismic Provisions Manual 2005.
  Developed BRB testing and design requirements.
• ASCE 7-05 Standard for Design Loads for
  Buildings and Other Structures. First building
  design standard to accept the BRBF system.
• IBC 2006 International Building Code 2006
  recognized BRBFs as an approved structural
  system.
• Arkansas Building Code 2002 (based on IBC 2000
  with supplements)
• Arkansas granted a deviation request to use
  portions of IBC 2006

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Design Requirements for BRBFs

• Seismic Design Coefficients (ASCE 7-05)
• Response Modification Factor (R value) 7
  Highly ductile system. Reduce forces by factor
  of seven.
• Deflection Amplification Factor (Cd) 5.5
  Multiplier to obtain your design story drift.
• System Overstrength Factor (Oo) 2.0
  Collector element design.

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Site Specific Seismic Hazard
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Plum Point Site
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BRB Manufacturers BRB Features
Only major manufacturers in this market

• Nippon Steel
• CoreBrace
• Star Seismic

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BRB Manufacturers BRB Features
Nippon Steel

• Founded in 1970 (Japanese Company)
• Originator of BRB in mid 1980s Professor Wada
  of Tokyo Institute of Technology worked with
  Nippon.
• First BRBF built in Japan in 1988 using Nippons
  braces.
• Un-Bonded Brace is trademark name for their
  BRB.
• Core has a cruciform shape. Casing is a steel
  tube.
• End connection is a standard bolted connection
  with splice plates on all four legs of the core.

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BRB Manufacturers BRB Features
CoreBrace

• Founded in 2002 Located in Utah. Parent
  company is SME Steel.
• CoreBrace is trademark name for their BRB
• Core has a cruciform shape. Casing is a steel
  tube.
• Two end connection options
• - Standard bolted connection (similar to
  Nippons)
• - Modified bolted connection splice plates
  are welded on in the shop, so uses half the bolts
  compared to standard.

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BRB Manufacturers BRB Features
Star Seismic

• Founded in 2002 Located in Utah.
• 3rd Generation BRB, PowerCat is trademark
  name for their BRB.
• Fabricated in Salina, Kansas.
• Core is a flat plate. Casing is a steel tube.
• For large braces (gt800 kips) ganged smaller
  braces
• Two end connection options
• - True Pin connection single round pin
• - Welded connection easier to align than
  single pin.

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BRB Manufacturers BRB Features
Star Seismic - continued

• True pin connection is Star Seismic feature
• Allows rotation, more predictable behavior
• Reduces installation labor.

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BRB Manufacturers BRB Features
Star Seismic - continued

• Another benefit of the true pin connection is it
  allows for a much more compact connection.
  Advantages to a compact connection
• Allows for a longer brace. Longer brace provides
  a more flexible and ductile structure.
• Eliminates stiffeners in the gusset. A major
  cost benefit on a seismic job.
• Uses up less space, so more room for utilities
  and less interferences.

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BRB Manufacturers BRB Features
Star Seismic - continued

• Disadvantage to the single pin connection is
  tight tolerances.
• Erection tolerance is only 1/32
• Almost impossible for shop to fabricate your
  structure to these tolerances.
• Heavy boiler steel would need more erection
  tolerance

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BRB Manufacturers BRB Features
Star Seismic - continued

• Eccentric Pin feature
• Initially developed for the Plum Point project to
  overcome tolerance issues of their standard
  single pin.
• Two outside portions of the pin are concentric.
  The center is offset to provide chosen erection
  tolerance.
• Plum Point chose a tolerance of 3/16 since it
  matched tolerance of oversize hole for 7/8 bolt.

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BRB Manufacturers BRB Features
Star Seismic - continued

• Collar feature
• Provides support for the unbraced core where it
  leaves the encasement to connect to the gusset.
• Forces all external moments (from wind and
  seismic movement) to the outside casing (steel
  tube)
• Collar in combination with compact connection
  eliminates need for gusset stiffeners.

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Lessons Learned BRB Erection

• Due to clevis type single pin connection, the
  brace and upper connecting beam should be erected
  together.

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454 kip (Service load) BRB, L 40
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Equivalent OCB for 454 kip BRB, L 40 (W14x398)
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Cost of BRBF vs OCBF

• The following cost comparison is for a BRBF
  versus an OCBF for the Plum Point Generation
  Building.
• BRBF design per IBC 2006
• OCBF design per Arkansas Bldg Code 2002

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Cost of BRBF vs OCBF

• If looking at the brace components only (brace
  and gussets), the average net savings using BRB
  over OCB for Plum Point
• 2068 average per brace
• 565 braces x 2068 1,168,000

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Cost of BRBF vs OCBF

• Total net savings if using BRB over OCB for Plum
  Point

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Questions?