Financials

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Seismic Retrofit of a Hospital Building Using
Dampers
Bob Glasgow, MS, SE Amir Gilani, PhD, SE Kit
Miyamoto, MS, SE
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Introduction

• Hospital Building South of Los Angeles
• Steel MRF with Pre-Northridge Beam-Column
  Connections
• FEMA 356 Guidelines Evaluation
• Non-ductile Connections
• Small Column Sizes
• Seismic Retrofit
• FVDs
• Minimize Operational Interruption

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Building Description

• Constructed in the 1970s, 40 ft Tall
• Three Stories Partial Basement
• 282ft x 75 ft, Rectangular Floor Plan
• Building Weight 3,100 kips

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Photograph of the Building
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Framing

• Gravity
• 3 ¼ in. LWC over 3 in. Metal Deck
• Steel Beams and Columns
• Lateral
• Perimeter MRF, Longitudinal
• MRF all Bays, Transverse
• Foundation
• Pre-stressed Concrete Square Piles

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Floor Framing
8.5 two-way slab
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Performance Evaluation

• Performance Objectives
• LS at DBE
• CP at MCE
• Design Criteria
• PH Rotations less than 0.5 Radian
• More Strict than FEMA 356 351 (OSHPD
  Requirement)
• Story Drift Ratios less than 1
• First Floor Displacement lt 1.5 in. to Avoid
  Pounding Against the Adjacent Single Story
  Buildings

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Seismic Demand

• Soil type SD
• DBE RS
• Ss 0.9g
• S1 0.5g

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Seismic Evaluation

• Performance Based Earthquake Engineering (PBEE)
  Methodology
• Analysis Procedure
• Modal
• Nonlinear Static (Pushover)
• Nonlinear Dynamic (Response History)

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Analytical Model
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Dynamic Analysis

• Consider Two Cases
• Column Bases Fixed Pinned
• Observations
• No Torsional Coupling Most Mass Participate in
  First Mode
• Thus
• Use Separate 2D Models for Evaluation

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Evaluation of the Existing Building

• Linear Dynamic Analysis
• Pinned Base Models
• Large Drifts First Story, Could Lead to Soft
  Story Behavior
• All Models
• Drifts of Existing Building too Large, Would Lead
  to Large Demand on Steel Members

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NSP-Pushover Analysis

• 2-D Models
• Pinned and Fixed Base
• FEMA 356 PHs
• 0.5 Radian Limit

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Longitudinal Response
Fixed Based Model
Pinned Based Model
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Transverse Response
Fixed Based Model Pinned Base Model
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Existing Building Evaluation

• Many PHs Exceed the 0.5 Radian Limit
• Hinging in Columns
• Response is Unacceptable

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Proposed Conventional Retrofit

• All Columns
• Weld Full-length Cover Plates to Columns
• All Connections
• Add Continuity Plates
• Reinforce Panel Zone

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Drawbacks of Conventional Retrofit

• Cost
• Total Disturbance of Occupancy, Business
  Interruption
• Time to Perform Retrofit

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State-of-the-Art Retrofit

• Reduce Seismic Demand by Increasing Supplemental
  Damping
• Minor Occupancy Interruption
• Repair of Selected Columns
• Cost-effective
• Use Fluid Viscous Dampers

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FVDs

• Force Nearly Out-of-Phase with Elastic Forces
• Easily Installed
• Reliable
• Used Previously for New and Retrofitted Steel
  Framed MRFs
• Add 4 Units Each Floor Each Direction

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Proposed FVD Installation
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Retrofitted Model
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Evaluation of Retrofitted Model

• NL Response (Time) History Analysis
• Pushover Analysis at the Target Roof Displacement
  to Check Existing Frame Elements

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Roof Displacement Response
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Existing Building Response in Longitudinal
Direction
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Damped Response in Longitudinal Direction
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Pushover Response, Retrofitted Model
Note all PH Rotations lt0.5 Radian
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Performance Evaluation

• Three Objectives
• Maximum Story Drift Ratio 0.9 lt1
• Small PH Rotations
• First Story Displacement 1.3 in lt1.5 in
• All Performance Goals are met

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Components of Seismic Input Energy
Input Dampers Inherent Viscous
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Conclusions

• Evaluation
• PBEE Used to Assess Performance Retrofit
• FEMA 356 NL Procedures
• Proposed Retrofit
• Add FVDs Reduce Seismic Demand Significantly
• Minimize Business Interruption