Seismic Design Recommendations of FEMA 460

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Seismic Design Recommendations of FEMA 460

• Bob Bachman, Consulting Structural Engineer
• Andre Filiatrault, University at Buffalo
• Mike Mahoney, DHS/FEMA

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Background

• FEMA approached by State of Washington for
  guidance on racks in public retail facilities
• Concern after fatality from falling pallet
• Increased by Nisqually earthquake.
• Current industry standards outdated (94 NEHRP).
• Reports of failures in past earthquakes and in
  industry.
• FEMA contracted with BSSC to study and develop
  guidance (FEMA 460).
• Published in September 2005

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Who Developed FEMA 460 ?

• BSSC Storage Rack Task Group (11 members)
• Robert Bachman, RE Bachman Consulting Structural
  Engineer
• Victor Azzi, RMI Consultant
• Morrison Cain, Retail Industry Leaders
  Association
• Dan Clapp, Frazier and RMI Spec Committee
• Andre Filiatrault, State University of New York
  and MCEER
• Ron Gallagher, Gallagher and Associates
• Peter Higgins, Peter Higgins Consulting Engineers
• Josh Marrow, Simpson, Gumpertz and Hegger
• Joe Nicolletti, Retired from John Blume and
  Associates
• John Nofsinger, RMI Managing Director
• Maryann Phipps, Estructure

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Rack Project Task Group - Others Involved

• FEMA Representatives
• Michael Mahoney
• Robert Hanson
• Government Advisory Members
• Richard Eisner, California OES
• George Crawford, Washington EMD
• Jeffery Lusk, FEMA
• Chris Jonientz-Trisler, FEMA
• BSSC Staff and NEHRP Contact
• Bernard Murphy, BSSC
• John Gillengerten, Chair, NEHRP
  TS-8

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Cross-Aisle Collapse at the Santa Clarita Stores
Building Materials Area
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Cross-Aisle Collapse at the Santa Clarita Stores
Tile Area
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Cross-Aisle Collapse Note Shrink Wrapping
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Content Spillage Door and Window Area
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Content SpillageWood Trim and Moulding Area
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Content Spillage Paint Area
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Content Spillage Small Item Area
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SIGNIFICANT FINDINGS

• Current Seismic Rack Design Criteria based on
  early 1970s approach.. K 1.0 for moment frames
  and K 1.33 for braced frames. Equivalent to R
  5.7 and R 4.3 today
• 2003 NEHRP is R 6 and R 4
• 1997 UBC is R 5.6 and R 4.4
• No detailing requirements in RMI Specification
  no use of Oo
• No publicly available evaluation on the failures
• 2003 NEHRP For Racks in Public Areas I 1.5
• 2003 NEHRP - Minimum Force Vmin 0.14SDSI

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RMI SPECIFICATION

• Initially developed in early 1970s
• Included 1970s seismic criteria based on K1.0
  and
• K 1.33 No detailing requirements
• Updated routinely includes testing procedures
• Latest update 2002 edition ANSI 2004
• Currently based on 1994 NEHRP Provisions and Base
  Shear Equations (I.e. T 2/3 ) Old Soil Factors
• Has own 1994 NEHRP Maps Do not include Ev in
  load combinations.
• R 4 and 6 Ip 1.5 for racks in public
  accessible areas

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RACK BEHAVIOR

• Moment Frame Direction Connections highly
  nonlinear
• 1. Rotational Capacity 0.10 to 0.20
  radians
• 2. Nonlinear behavior occurs in the
  connection not the
• column or beam
• 3. Periods in Range of 1.5 to 2.5 seconds
• Braced Frame Direction Connections nonlinear
• 1. Limited nonlinear capacity
• 2. At high seismic loads pallet can
  slide reducing design loads

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TESTING

• 1980 Blume Shake Table and Component Tests
• 1. Shake Table Tests
• 2. Component Tests
• 3. Calibrate to the UBC at elastic level
  (1/2 El Centro)
• 4. No explicit thoughts how much higher
  levels should
• be able to handle without collapse
• Recent Tests by Filiatrault Home Depot and
  Interlake
• RMI Component Cyclic Testing Remove minimum

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FEMA 460

• Chapter 1 Introduction
• Chapter 2 Damage in Recent Earthquakes
• Chapter 3 Codes/Standards for Storage Racks
• Chapter 4 Current Seismic Design Practices
• Chapter 5 Performance Expectations
• Chapter 6 Suggested Improvements to Design
  Practices
• Chapter 7 - Guidelines for Specifying, Procuring
  and Installing
• Chapter 8 - Suggestions for Securing Contents
• Chapter 9 - Suggestions for Installation,
  Operation, Inspection and Maintenance
• Chapter 10 - Suggestions for QA Programs
• Chapter 11 - Review of Past Research
• Chapter 12 Inspection of Racks and Contents
  after Earthquakes
• Chapter 13 Summary and Recommendations
• Chapter 14 - References and Bibliography

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FEMA 460 Suggested Down Aisle Evaluation Approach

• Developed simple displacement-based seismic
  design procedure to verify collapse prevention of
  storage racks in their down-aisle direction under
  MCE ground motions
• Derived simplified expressions for down-aisle
  fundamental period, base shear and top lateral
  displacement of storage racks
• Approach based on observation that at higher
  levels of earthquake ground motion, racks tend to
  respond as nonlinear SDOF systems in the down
  aisle direction

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Down Aisle Moment Connection BehaviorNonlinear
Behavior in Connection !
Mc
kc
q
Mc kc q
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Proposed Displacement-Based Procedure to
Evaluate Collapse Margin

• Step 1
• Assume experimental connection curve for
  particular type of beam-to-upright connector
  considered is available
• Step 2
• Compute fundamental period

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Proposed Displacement-Based Procedure to Verify
Collapse Margin

• Step 3
• Compute maximum first order displacement demand
  at effective height of rack for MCE ground motion
  using equation from 2003 NEHRP Provisions
• Step 4
• Compute maximum displacement demand Dmax by
  adjusting D for second order effects

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Proposed Displacement-Based Procedure for
Collapse Prevention

• Step 3
• Compute maximum first order displacement demand
  at effective height of rack for MCE ground motion
  using equation from 2003 NEHRP Provisions
• Step 4
• Compute maximum displacement demand Dmax by
  adjusting D for second order effects

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Proposed Displacement-Based Procedure to
Evaluate Collapse Margin

• Step 5
• Determine maximum rotational demand in
  connectors
• Step 6
• Check whether maximum rotational demand is less
  than maximum rotational capacity. If not, modify
  design and repeat Step 1

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Displacement Based Approach Summary

• A displacement-based procedure to evaluate
  displacement demand and capacity in down-aisle
  direction of pallet-type steel storage racks
  under MCE ground motions consistent with
  performance objectives of US building codes is
  proposed in FEMA 460
• A simple analytical model captures the down-aisle
  seismic behavior of rack structures
• Predictive capabilities of model verified through
  shake table testing of full-scale pallet-type
  steel storage racks at the University at Buffalo
• Experimental connection curves for of
  beam-to-upright connectors must be developed
• Alternate way of estimating demand which
  correlates well with the displacement procedure
  is being proposed for next addition of the RMI
  specification.

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Acknowledgements

• Performance-based design procedure and analytical
  model developed as part of FEMA-460 Project
  Seismic Considerations for Pallet-Type Steel
  Storage Racks and their Contents in Areas
  Accessible to the Public
• Funded by Federal Management Agency (FEMA)
  through National Institute of Building Sciences,
  Building Seismic Safety Council (BSSC).
• FEMA 460 available at www.bssconline.org and from
  FEMA by calling 1-800-480-2520.