Frank Burke Structural Option Sallie Mae HQ Reston, VA

Outline Introduction Structural Overview Thesis Goals Structural Depth CM Breadth Mechanical Breadth Conclusion Acknowledgements

Introduction Project cost: 41 million Design-Bid-Build April September story Office Building –22,000 SF/Floor 5 story Parking Garage –75,000 SF/Floor Glass and Precast Facade

Structural Overview Parking Garage 1.Below grade 2.10’ high stories 3.28’ x 28’ bays 4.Two-way concrete slab 5.9” & 10” elevated slabs 6.Square Footings Office Structure 1.Above Grade 2.14’ Stories 3.42’(+) x 28’ Bays 4.Steel Framing 5.3 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

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

8 th Floor

8 th 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 TaskWorking Days Needed Construct Columns and Walls4 Form Slab, Beams3 Place Rebar2 Place PT Strands2 Pour Slab, Beams2 Cure Slab, Beams3 Stress PT Strands2 Construct 8 floors72 Schedule Construct 1 floor9

CM Breadth Floors$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 analyzed166,000 Price/SF$15.30/SF PT ConcreteSteel $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 metal10400 LBS Schedule4 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 ConcreteSteel Legend Good 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