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Thesis 2005

Thesis 2005. Cira Centre – Philadelphia. Structural Redesign of Lateral Force Resisting System. Andrew Kauffman Structural Option. Presentation Outline. Introduction Building Description Structural System Problem Statement Solution Overview Structural Redesign

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Thesis 2005

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  1. Thesis 2005 Cira Centre – Philadelphia Structural Redesign of Lateral Force Resisting System Andrew Kauffman Structural Option

  2. Presentation Outline • Introduction • Building Description • Structural System • Problem Statement • Solution Overview • Structural Redesign • Mechanical Redesign • Conclusion

  3. INTRODUCTION

  4. Introduction • Adjacent to 30th Street Train Station - Philadelphia, PA • 291,000 s.f., 28 story high rise office building • Convention center, restaurants and retail space • Tallest building in Philadelphia, outside Center City • Scheduled for completion – October 2005 • Total Projected Cost – $200 million

  5. BUILDING DESCRIPTION

  6. Building Description– Project Team • Architects – Cesar Pelli and Assoc./Bower Lewis Thrower • General Contractor – Turner Construction Co. • Structural Engineer – Ingenium Inc. • Civil Engineer – Pennoni Assoc. • MEP Engineer – Jaros Baum and Bolles • Lighting Design - Cline Bettridge Bernstein • Acoustic Consultant - Cerami and Associates • Curtain Wall Consultant - Israel Berger and Associates

  7. Building Description-Architectural Features • 725,000 s.f. rentable space • Open plan office levels: 727,725 s.f. (average) • 9 ft. floor to ceiling heights • Pedestrian bridge connecting to 30th Street train station • Single point of entrance in main lobby, added security • Highly reflective glass curtain wall

  8. Building Description – Building Systems • Electrical – 13.2 KV primary voltage • 480Y/277 volt, 3 phase, 4 wire • Secondary system • Mechanical – Fan powered, VAV system • Includes 4 cooling towers located in top mezzanine • Conveying – 14 high speed traction elevators • Low-rise, mid-rise, high-rise Configuration

  9. STRUCTURAL SYSTEM

  10. Structural System – Overview • Steel frame super-structure • Composite floor system • Drilled pier foundation • Lateral System: Combination of • braced and moment frames

  11. Structural System – Floor System • Fully composite, 5 ¼ in. floor system, with LW concrete, metal • decking, 50 ksi steel framing members • W18x35 and W24x76 typical beams and girders, 30’x30’ bays, typ.

  12. Structural System – Vertical Framing • Drilled concrete piers with up to 21.5’ • penetration into bedrock • Large built-up column sizes including • W36x1202 wide flange members • and 829 lb/ft. built-up box sections • Forking Columns • Leaning Columns

  13. Structural System – North/South Building Section

  14. North/South Section

  15. Structural System - East/West Section

  16. East-West Section

  17. Structural System – Lateral System • East/West - Located in building core • Combination of braced frames and moment connections

  18. Structural System – Lateral System • East – West Direction • Along column lines C & D • Located in structural core • Exterior braced frames • Interior moment frames

  19. Structural System – Lateral System • North/South – Located in building core • Combination of braced frames and moment connections

  20. Structural System – Lateral System • North - South Lateral System • Along column lines 4 & 7 • Located in Structural Core • Exterior Moment Frames • Interior Braced Frames

  21. Structural System – Lateral System • North/South – Located along exterior frames • Only moment frames

  22. Structural System – Lateral System • North - South Lateral System • Along column lines 1 & 10 • All moment frames • Varying stiffness

  23. PROBLEM STATEMENT

  24. Problem Statement – Overview • Complicated Structure to Analyze • Varying Floor Geometry • Large built-up members • Complicated Lateral System • Combination of braced and moment frames • Lateral frames with varying stiffness

  25. Problem Statement – Lateral Load Assumptions • Lateral Loads used in actual design were • developed using a wind tunnel analysis • Wind Tunnel results yielded 65% of total shear • and 75% of the overturning moment, compared • to ASCE7-02, analytical method. • Strength considerations did not control the • original design of the building. • Torsional acceleration at corner offices was • the limiting factor that controlled the design

  26. SOLUTION OVERVIEW

  27. Solution Overview – Lateral System Redesign • Develop wind and seismic loads based on ASCE7-02 • Redesign Lateral System based on these loads. • Compare cost of redesign to cost of original structure

  28. Solution Overview – Design Goals • Gain a better understanding of lateral force • resisting system design for steel buildings • Investigate alternative lateral system configurations • Meet the design criteria of IBC 2003. • Limit interstory drift • Limit overall building drift to L/400 criteria • Achieve an economically feasible design • Optimization of original design was not a goal

  29. Solution Overview - Procedure • Develop wind loads using Analytical Procedure • Model 2-D lateral frames using GT Struddle • Determine relative stiffness based on virtual loads • Distribute loads based on stiffness and torsion analysis • Analyze frames for deflection and interstory drift • Redesign lateral frames based on drift criteria - iterative • Compare cost of redesign to original structural system

  30. Solution Overview – Mechanical Breadth Study • Analyze feasibility of adding enthalpy wheels to the original • mechanical system. • Goal: Utilize the properties of building exhaust to save $$$

  31. STRUCTURAL REDESIGN

  32. Structural Redesign – Stiffness Analysis • Created model of each lateral frame in GT Struddle • 100k virtual load at top of each frame to measure relative stiffness

  33. Structural Redesign – East/West Lateral Frames Column Lines C & D • Equal Stiffness • Distribute half of total story load to • each frame • Equal distance from center of plan • Torsion had minimal effect in this • direction

  34. Structural Redesign – Load Distribution

  35. Structural Redesign - Results • Total Deflection: 13.25” • L/400 = 13.08” • Acceptable based on • occupancy comfort

  36. Structural Redesign – North/South Direction • Modeled lateral frames along Column Lines 1,4,7,10 • Applied Virtual Load at levels 28,20,10

  37. Structural Redesign – North/South Direction CL 1 CL 4/CL 7 CL 10

  38. Structural Redesign – North/South Direction • Relative stiffness varied with height. • Applied uniform 10 kip load to verify stiffness • Plotted results and fit equation • Solved equation for stiffness in terms of height

  39. Performed torsion analysis at each level based on center of rigidity Included 5% eccentricity per code, and determined loads on frames Structural Redesign – North/South Direction

  40. Applied load to models in GT Struddle and analyzed results Structural Redesign – North/South Direction

  41. Each lateral frame deflected equal amounts. All frames deflected well over the L/400 limit. Structural Redesign – Results 19.92” 19.99” 17.16”

  42. Structural Redesign – Solution • Alleviate interstory drift problems • Limit overall building drift to 12” • Started with exterior frames

  43. Analyzed several bracing configurations using iterative procedure. Eliminated interstory drift problems, limited total drift to 12” Structural Redesign – North/South Direction

  44. Structural Redesign – North/South Direction • Used same procedure for interior lateral • frames along column lines 4 & 7 • Could not limit drift to 12”

  45. Increased stiffness of exterior lateral frames W14x145 bracing members Additional chevron braces to these frames Limited total drift to 9” Changed bracing of interior frames W14x159 bracing members Increased stiffness of girders to W33x221 Reapplied stiffness analysis and torsion calculations Calculated new story loads Structural Redesign – North/South Direction

  46. Results

  47. Used R.S. Means to estimate total cost of original structure 20% total building cost = $ 40 million Structural Redesign – Cost Analysis • Performed take-off to calculate cost of lateral system redesign • Compared additional cost to overall structural cost • Cost Increase = 0.6% Structure Cost • Cost Increase = 0.1% Structure Cost

  48. Mechanical Redesign

  49. Fan powered VAV system Supply Air: 80% return, 20% outdoor air Exhaust: based on 150 cfm/toilet, 20 cfm/sink Typical Air Handler Size: 23,500 Mechanical System Redesign System Description Procedure • Use ASHRAE Bin data to analyze a full year cycle • Based on 2 design condition: on peak – business hours, • off peak – evenings and weekends • Calculated total building load with/without use of enthalpy wheel • Compared loads and calculate savings

  50. Mechanical System Redesign – Typical Floor • Total Savings = Sensible Load savings + Latent Load savings • Enthalpy wheels turned off when no energy is saved • Additional energy can be saved by modulating wheel

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