SEISMIC REHABILITATION OF AN EXISTING BRACED FRAME HOSPITAL BUILDING BY DIRECT REPLACEMENT OF BRACES

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SEISMIC REHABILITATION OF AN EXISTING BRACED
FRAME HOSPITAL BUILDING BY DIRECT REPLACEMENT OF
BRACES WITH BUCKLING-RESTRAINED BRACES


Presented by Cale Ash Degenkolb
Engineers Stacy Bartoletti Degenkolb Engineers

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Presentation Topics
Seismic Evaluation
Seismic Upgrade Design Development
Construction Documents
Construction Phase
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Presentation Topics
Seismic Evaluation
Seismic Upgrade Design Development
Construction Documents
Construction Phase
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VA Seattle Seismic Program
NT
NHCU
Seattle Campus
CC

• Bldg. 100
• Diagnostic Treatment (DT)
• Nursing Towers (NT)
• Central Core (CC)
• Nursing Home Care Unit (NHCU)
• Energy Plant

DT
Energy Plant
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Seismic Evaluation
DT Building Information

• Designed in 1980 using VA Handbook H-08-8
• Main hospital for campus
• 4 stories
• Stepped elevation
• 18 ft. story height
• Interstitial floors at 10 ft.

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Seismic Evaluation
Lateral System

• Braced Frames
• Moment Frames

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Seismic Evaluation
ASCE 31 Evaluation

• Tier 2 Full-building Evaluation
• Performance Objective
• Immediate Occupancy

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Seismic Evaluation
Evaluation Results Moment Frames

• Pre-Northridge Moment Frames
• Connections evaluated as force-controlled actions
• Capacity limited to flange weld strength
• Expected Performance
• Limited damage to moment frame connections
• Some welds may fracture
• Repairs would not disrupt hospital functions

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Seismic Evaluation
Evaluation Results Braced Frames

• Expected Performance
• Heavy damage to braced frames in design
  earthquake
• Brace connections fracture
• Column splices fail
• Proposed Upgrade Scheme
• Replace existing braces with Buckling-Restrained
  Braces
• Reduces demand on column splices and brace
  connections

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Presentation Topics
Seismic Evaluation
Seismic Upgrade Design Development
Construction Documents
Construction Phase
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Seismic Upgrade
Methodology

• Seismic upgrade designed using FEMA 356 and 2003
  IBC
• Size braces using 2003 IBC, verify design using
  FEMA 356
• Target Performance Level
• Immediate Occupancy / BSE-2
• FEMA 356 Analysis Procedure
• Nonlinear Static

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Seismic Upgrade
FEMA 356 Evaluation

• BRB Supplier Selection Process
• Manufacturer-specific properties
• Worked with VA to develop specifications RFQ
• Proposals considered from 3 domestic suppliers
• Selected BRB supplier participated in design
  process

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Seismic Upgrade
FEMA 356 Evaluation
IO, e1.4 LS, e2

• Consider both existing and full build-out cases
• Refine design through nonlinear static analyses
• Modify BRB nonlinear properties based on brace
  strength

Typical BRB Nonlinear Properties
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Nonlinear Static Evaluation Results
Existing Configuration
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Nonlinear Static Evaluation Results
Built-Out Configuration
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Seismic Upgrade
Final Brace Forces

• Performance-based approach resulted in final
  brace sizes reduced by up to 20
• Connection savings
• Column strengthening eliminated

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Presentation Topics
Seismic Evaluation
Seismic Upgrade Design Development
Construction Documents
Construction Phase
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Construction Documents
Verify Existing Conditions

• Original 1980 plans
• Site visits
• Structural steel shop drawings
• Scaled elevations of (E) frames
• Brace clear distance
• Gusset plate geometry
• Coordination with steel detailer

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Construction Documents
Connection Design

• BRB connection to existing gusset plates
• Field welds to gussets allow field tolerances
• Gusset strengthening new gussets required

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Construction Documents
Interstitial Floor Resupport

• Interstitial floor framed into braces

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Construction Documents
Braced Frame Elevations
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Presentation Topics
Seismic Evaluation
Seismic Upgrade Design Development
Construction Documents
Construction Phase
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Construction Photos
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Construction Photos
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Construction Photos
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Construction Photos
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Construction Photos
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Construction Photos
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Construction Photos
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SEISMIC REHABILITATION OF AN EXISTING BRACED
FRAME HOSPITAL BUILDING BY DIRECT REPLACEMENT OF
BRACES WITH BUCKLING-RESTRAINED BRACES


Presented by Cale Ash Degenkolb
Engineers Stacy Bartoletti Degenkolb Engineers