Frank Burke Structural Option Sallie Mae HQ Reston, VA.
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Transcript of Frank Burke Structural Option Sallie Mae HQ Reston, VA.
Frank BurkeStructural Option
Sallie Mae HQReston, VA
Outline
•Introduction•Structural Overview
•Thesis Goals•Structural Depth
•CM Breadth•Mechanical Breadth
•Conclusion•Acknowledgements
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
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
Structural Overview
W27’s
W24’s
Central Core
Structural Overview
Thesis Goals
• To create a post-tensioning design that considers constructability and is simplistic
• Investigate the savings in post-tensioning
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
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
• Slab is 8” thick• Slab tendons are in bundles of 4 and spaced at 5’
Gravity Members
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
Penthouse
Slab tendons
Nonprestressed Area
Prestressed Beams
Regular Beams
8th Floor
8th Floor / Typical Floor
30” Beams
Columns from above
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
CM Breadth
• Downfalls of my post-tensioning design
– Heavier building– Larger Foundations– Longer schedule
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
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
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
Mechanical Breadth
Steel Ceiling SectionConcrete Ceiling
Section
Mechanical Breadth
Savings
Sheet metal 10400 LBS
Schedule 4 days
Total Cost $41,000
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
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
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
Questions
?
Introduction
Architect
▼ Boggs & Partners
Structural
▼ Cagley and Associates
MEP
▼ GHT Limited
Contractor
▼ Hitt Contracting Inc.
Typical Floor