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One South Dearborn Chicago, Illinois
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PRESENTATION OUTLINE BUILDING INTRODUCTION Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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BUILDING INTRODUCTION
Project Team Owner Hines Interests Limited Partnership Architect DeStefano Keating Partners Limited Structural Engineer Halvorson Kaye Structural Engineers Mechanical Engineer Alvine & Associates, Inc. Construction Manager Turner Construction Company
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BUILDING INTRODUCTION
One South Dearborn 40 Stories 1 Million sq. ft. Modern High-Rise Commercial Office Building Ground Floor Retail Space 3-Story Lobby Floors 3-6 Parking (160 Vehicles) Floors 9-38 Offices Floors 2,7,8,39,40 Mechanical
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PRESENTATION OUTLINE EXISTING STRUCTURE Building Introduction
Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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EXISTING STRUCTURE Structural Design Codes One South Dearborn
Chicago Building Code One South Dearborn Composite Structural Design Concrete Core Perimeter Steel Floor Framing
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EXISTING STRUCTURE Floor System
Steel Framing With Composite Steel Deck 45’ Column-Free Spans Yellow – Shear Walls Green – Elevators Corners Are Cantilevered Typical Framing High-Rise Plan
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EXISTING STRUCTURE Foundation Enclosure Limited Underground Basement
Only The Core Descends Below Grade Belled & Rock Caissons Avoid Existing Caissons Previously On Site Enclosure Pre-Cast Cladding – 90 psf Supported On Perimeter Girders Glass Curtain Wall – 20 psf Supported From The Slab Edge
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EXISTING STRUCTURE Lateral System Reinforced Concrete Shear Wall Core
(2) Nonproportionate Shear Walls – N-S Direction (3) Proportionate Shear Walls – E-W Direction Provides All Lateral Strength & Stiffness Foundation Thru Level 26 Level 27 Thru P.H. Roof
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PRESENTATION OUTLINE PROBLEM STATEMENT Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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PROBLEM STATEMENT Local History & Material Tendencies
Influential Factors in Structural Design Regional Preferences Chicago Past 20 Years, Composite System Northeast All-Steel Structural Systems Southeast All-Concrete Structural Systems
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PROBLEM STATEMENT Concerns About Current System Resulting Issues
Differential Shortening Plumbness Of The Wall Phasing Of The Concrete & Steel Erection Resulting Issues Small Tolerances Increase In Schedule Duration Increase In Cost
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PRESENTATION OUTLINE PROPOSAL Building Introduction Existing Structure
Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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PROPOSAL The Existing System Was Chosen Due To The Owner’s Preferences. Uninterrupted Floor Space Perceptibility Of Lateral Motion Ability For Future Modifications Was This Really The Most Economical And Structurally Sound Choice When Compared To Other Conventional Systems?
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PROPOSAL Determine An Alternative Lateral System
Steel Braced Core and Outriggers Determine An Alternative Flooring System Post-Tensioned Concrete System Determine The Impact These Changes Have On The Construction Schedule And Cost.
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PRESENTATION OUTLINE STRUCTURAL REDESIGN Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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STRUCTURAL REDESIGN Lateral System Redesign
Steel Braced Core & Outriggers Several Iterations Of Different Configurations Concentrically Braced Frames w/ and w/o Outriggers Eccentrically Braced Frames w/ and w/o Outriggers Worst Case Loading From Wind & Seismic Loads WE Frames Concentrically Braced NS Frames Eccentrically Braced Freestanding Core Minimum Size Members By Code
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STRUCTURAL REDESIGN Outriggers By Adding A Level Of Outriggers
Link The Core To The Exterior Columns – Truss Increase The Effective Depth Of The Structure By Adding A Level Of Outriggers Increases Flexural Stiffness Reduces The Overturning Moment Tension In Windward Columns Compression In Leeward Columns
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STRUCTURAL REDESIGN Engage The Interior Columns Of The Building
Enhances The System’s Ability To Resist Overturning In Most Designs, The Gravity Columns Are Not Incorporated or Underutilized By The Outriggers Floor Framing Plan Redesigned To Utilize Interior Columns To Accommodate The Changed Core Constant Throughout Height Of Building NS – 30’ Bays & WE – 25’ Bays
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STRUCTURAL REDESIGN After Solving For Member Sizes
Relative Stiffnesses Were Found Torsional Eccentricity 5% Of The Length Of The Building Frames Redesign Under New Loading Condition Allowable Drift Chicago Building Code H/750 - NS H/600 – WE To Maintain The Allowable Drift By Code The Members Were Oversized Dramatically
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STRUCTURAL REDESIGN Drawbacks
Outriggers Interference w/ The Mechanical Space A Set Of (2) 900 ton Cooling Towers Had To Be Moved Ten Feet To Clear an Outrigger On The 39th Floor Diagonal Bracing Inherently Obstructive To The Architectural Plan Bracing Selected On Basis Of Allowing The Necessary Openings – e.g. Doors At The Expense Of Efficiently Resisting Lateral Loads
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STRUCTURAL REDESIGN Floor System Redesign
Post-Tensioned Concrete System Wide Shallow PT Concrete Strips Allows Long Spans 3 Span Design Oriented In The West-East Direction
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STRUCTURAL REDESIGN Band Beam & Slab System Unbonded Tendon System
Thickening Of The Slab Along The Column Line Allows Additional Drape Unbonded Tendon System Tendons Are Not Grouted Free To Move Independently Of The Concrete Easily Fixed To Different Profiles Easily Displaced Around Holes
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STRUCTURAL REDESIGN ADAPT-PT Design 3-Span Condition
Core Strip Column Strip End Strip Analyzed With Different Gravity Loads Typical, Mechanical, Parking & Level 2
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STRUCTURAL REDESIGN For Typical Office Loading Band Beam
96” Wide 11” Deep 6” Slab Spans 45’, Then 50’, Then 45’ Tendons ½” Diameter 27K – Final Effective Force 35 Tendons For Typical Design Strip Spacing Cannot Exceed 8x Slab Thickness or 5’ Mild Reinforcement Required Meet Factored Ultimate Conditions
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STRUCTURAL REDESIGN Partial Parabola Drape
Tendons Positioned Straight Over The Supports Adjusting Drapes & Jacking Forces Allowable Compressive & Tensile Stresses
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STRUCTURAL REDESIGN Deflections Will Not Be Discussed
Allowable By Chicago Building Code L/360 45’ Span = 1.5” 50’ Span = 1.67” Will Not Be Discussed Reinforced Concrete Shear Wall Core Reanalyzed With Worst Case Wind & Seismic Loading Including 5% Torsional Eccentricity Column Design Analyzed With PCA Column Worst Case Moments & Axial Loading SPAN DL DL+PT DL+PT+CREEP LL TOTAL 45’ 0.38” -0.02” -0.05” 0.34” 0.29” 50’ -0.09” -0.28” 0.06”
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PRESENTATION OUTLINE FINAL CONCLUSIONS Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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FINAL CONCLUSIONS Structural Redesign Criteria Maintain
Perceptibility of Lateral Motion Uninterrupted Floor Space Ability For Future Modifications Maintain Square Footage Exterior Aesthetics Story Height Architectural Layout of The Building Cost of The Structural System Duration of The Structural System
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FINAL CONCLUSIONS Perceptibility of Lateral Motion
Steel Braced Core Made Comparatively Stiff Damping In The Range of 1% Reinforced Concrete Core Damping In The Range of 1.5% to 2% Uninterrupted Floor Space Ability For Future Modifications Post-Tensioned Concrete Limited To Minor Modifications Flooring Depths
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FINAL CONCLUSIONS Cost Comparison
All-Steel Structure (18% Decrease) $3.32 Million All-Concrete Structure (36% Increase) $7.87 Million The All-Steel Structural System Is Significantly Less Expensive Than The Other Systems
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FINAL CONCLUSIONS Schedule Comparison
Existing Duration: March 15, 2004 to February 10, 2005 All-Steel Structure (10% Decrease) 4 weeks All-Concrete Structure (35% Increase) 10 weeks The All-Steel Structural System Has A More Efficient Assembly Than The Other Systems
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PRESENTATION OUTLINE RECOMMENDATIONS Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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RECOMMENDATIONS The All-Steel Structure Had A Lower Expenditure And Shorter Construction Phase The Composite Structure Is The Better Solution Composite Structure Made The Best Use Of The Materials And Their Respective Benefits Concrete Lateral Drift Control Steel Long Spans & Flexibility For Future Modifications
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PRESENTATION OUTLINE MECHANICAL STUDY Building Introduction
Existing Structure Problem Statement Proposal Structural Redesign Final Conclusions Recommendations Mechanical Study
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MECHANICAL STUDY Existing Mechanical (2) 1500 Ton Chillers
7th Floor (4) 900 Ton Cooling Towers 39th Floor (4) 162,000 cfm Air Handling Units (2) 7th Floor (2) 39th Floor 25,000 cfm Air Handling Unit Lobby
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MECHANICAL STUDY Try To Lower Building Operating Costs and The Capital Cost of The Cooling Equipment Thermal Energy Storage Partial-Storage Load-Leveling Chillers Run At Full Capacity For 24 Hours Demand-Limiting Chillers Run At Reduced Capacity During On-Peak Hours Load-Leveling Demand-Limiting
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MECHANICAL STUDY Chicago, Illinois Worst Design Month – July
On-Peak 12 hours – 6AM to 6PM 5.75¢/kwh Off-Peak 12 Hours – 6PM to 6AM 2.49¢/kwh Worst Design Month – July Total Building Load – Ton-hrs Peak Load – 2670 Tons Ice Storage 25% Ethylene Glycol Running Thru The Pipes
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MECHANICAL STUDY Load-Leveling Demand-Limiting Chillers Storage Tanks
(2) 760 Ton (Derated) Storage Tanks 19 Units Monthly Savings $1, (23% Savings) Demand-Limiting 962 Ton 540 Ton (Derated) 24 Units $1, (29% Savings) Equipment Cost Greater Than Load-Leveling
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MECHANICAL STUDY Structural Impact Storage Tanks – 391psf
Original Design – 250 psf Redesign 7th Floor Post-Tensioned Concrete Floor 4” Deeper In The Band Beams Additional $7,956 Steel Floor Framing 26 Tons Steel Added Additional $423,330
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ACKNOWLEDGEMENTS Penn State AE Faculty Professional Contacts
AE Class of 2005 Professional Contacts Penn State AE Faculty My Family Special Thanks To: Thesis Hard At Work
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QUESTIONS What Would You Say, You Did Here? Look! I Already Told You. I Deal With The Customers So The Engineers Don’t Have To. I HAVE PEOPLE SKILLS!!! ?
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