frank burke structural option sallie mae hq reston, va
TRANSCRIPT
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Frank BurkeStructural Option
Sallie Mae HQReston, VA
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Outline
•Introduction•Structural Overview
•Thesis Goals•Structural Depth
•CM Breadth•Mechanical Breadth
•Conclusion•Acknowledgements
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Introduction
• Project cost: 41 million • Design-Bid-Build• April 2003- September 2004
• 9 story Office Building– 22,000 SF/Floor
• 5 story Parking Garage– 75,000 SF/Floor
• Glass and Precast Facade
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Structural Overview
• Parking Garage1. Below grade2. 10’ high stories3. 28’ x 28’ bays4. Two-way concrete slab5. 9” & 10” elevated slabs6. Square Footings
• Office Structure1. Above Grade2. 14’ Stories3. 42’(+) x 28’ Bays4. Steel Framing5. 3 ¼” lightweight concrete over 2”
deep x 18 gage composite metal deck
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Structural Overview
W27’s
W24’s
Central Core
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Structural Overview
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Thesis Goals
• To create a post-tensioning design that considers constructability and is simplistic
• Investigate the savings in post-tensioning
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Design Considerations• Type of System?
One-way slab
• Type of Concrete? 6000psi Normal Weight Concrete
• Unbonded or bonded tendons? Unbonded Tendons
• Design Class U, T or C? Slab = Class U Beams = Class T
• Roof Structure? Original Steel Framing
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Vertical Members
• Columns:– 20” x 20” – 24” x 24”– 24” x 30”
• Shearwalls are 12” thick and are located in the elevator core and stairwells
Column Pedestal Detail
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• Slab is 8” thick• Slab tendons are in bundles of 4 and spaced at 5’
Gravity Members
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Gravity Members• Prestressed beams are 26” and 30” deep• The majority of beam tendons are in bundles of four• 4” cover at midspan & supports / 6” cover at anchorage
zones
Midspan
Supports
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Penthouse
Slab tendons
Nonprestressed Area
Prestressed Beams
Regular Beams
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8th Floor
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8th Floor / Typical Floor
30” Beams
Columns from above
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CM Breadth
• Benefits of my post-tensioning design
– The PT strands can be placed quickly– Jacking can occur from one side– Facade can be reduced by 6”per floor
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CM Breadth
• Downfalls of my post-tensioning design
– Heavier building– Larger Foundations– Longer schedule
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CM Breadth
Specific Task Working Days Needed
Construct Columns and Walls 4
Form Slab, Beams 3
Place Rebar 2
Place PT Strands 2
Pour Slab, Beams 2
Cure Slab, Beams 3
Stress PT Strands 2
Construct 8 floors 72
• Schedule
Construct 1 floor 9
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CM BreadthFloors $1,013,200
Columns $481,600
Walls $264,800
Formwork $946,200
General Conditions Increase $50,000
Foundation Increase $188,400
Facade Savings -$152,600
Cost Index .91
Total $2,540,356
SF analyzed 166,000
Price/SF $15.30/SF
PT Concrete Steel
$15.30/SF $17.79/SF
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Mechanical Breadth
• Post-tensioning allows savings in ceiling depth
• Mechanical ducts can be enlarged from 12” to 18” in depth to be more efficient and save sheet metal cost
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Mechanical Breadth
Steel Ceiling SectionConcrete Ceiling
Section
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Mechanical Breadth
Savings
Sheet metal 10400 LBS
Schedule 4 days
Total Cost $41,000
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Conclusions
Lead- in- time
Constructability
Safety
Cost / Weight
Foundation
Gravity System
Lateral System
Mechanical System
Fire Rating
Vibration
Deflection
Acoustics
Alterations
Overall Cost
Concrete Steel LegendGood
Bad
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Conclusions
• Sallie Mae is solely a headquarters building; no tenants
• If Sallie Mae had renters, depending on the lead-in-time, steel or concrete might be the better alternative
• However; due to the facade savings post-tensioning is the cheaper system
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Acknowledgements
Cagley and Associates / Frank Malits
Professor Boothby, Professor Parfitt, Professor Hanagan, Professor Ling, Professor Lepage
Structural Mentors
Bryan Quinn, Lourdes Diaz
Family and Friends
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Questions
?
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Introduction
Architect
▼ Boggs & Partners
Structural
▼ Cagley and Associates
MEP
▼ GHT Limited
Contractor
▼ Hitt Contracting Inc.
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Typical Floor