Post on 21-Aug-2020
Thesis 2005Cira Centre – Philadelphia
Structural Redesign ofLateral Force Resisting System
Andrew KauffmanStructural Option
Presentation Outline
Introduction
Building Description
Structural System
Problem Statement
Solution Overview
Structural Redesign
Mechanical Redesign
Conclusion
INTRODUCTION
IntroductionAdjacent to 30th Street Train Station - Philadelphia, PA291,000 s.f., 28 story high rise office buildingConvention center, restaurants and retail spaceTallest building in Philadelphia, outside Center CityScheduled for completion – October 2005Total Projected Cost – $200 million
BUILDING DESCRIPTION
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
Building Description- Architectural Features725,000 s.f. rentable spaceOpen plan office levels: 727,725 s.f. (average)9 ft. floor to ceiling heightsPedestrian bridge connecting to 30th Street train stationSingle point of entrance in main lobby, added securityHighly reflective glass curtain wall
Building Description – Building Systems
Electrical – 13.2 KV primary voltage 480Y/277 volt, 3 phase, 4 wire Secondary system
Mechanical – Fan powered, VAV systemIncludes 4 cooling towers located in top mezzanine
Conveying – 14 high speed traction elevatorsLow-rise, mid-rise, high-rise Configuration
STRUCTURAL SYSTEM
Structural System – Overview
Steel frame super-structure
Composite floor system
Drilled pier foundation
Lateral System: Combination of braced and moment frames
Structural System – Floor SystemFully composite, 5 ¼ in. floor system, with LW concrete, metaldecking, 50 ksi steel framing membersW18x35 and W24x76 typical beams and girders, 30’x30’ bays, typ.
1 3 4 5 6 8
D
C
B
A
2 7 9 10
E
F
7'-11" 30'
12'-6
"30
'
7'-8"
12'-6
"30
'30
'
30' 30' 30' 30' 30' 30'
N
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
Structural System – North/South Building Section
1 3 4 5 6 8
D
C
B
A
2 7 9 10
E
F
7'-11" 30'
12'-6
"30
'
7'-8"
12'-6
"30
'30
'
30' 30' 30' 30' 30' 30'
N
North/South Section
Structural System - East/West Section
1 3 4 5 6 8
D
C
B
A
2 7 9 10
E
F
7'-11" 30'
12'-6
"30
'
7'-8"
12'-6
"30
'30
'
30' 30' 30' 30' 30' 30'
N
East-West Section
MECHROOM
MACHROOM
MACHROOM
CONFERENCE
Structural System – Lateral SystemEast/West - Located in building core
Combination of braced frames and moment connections
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural System – Lateral System
East – West Direction
Along column lines C & D
Located in structural core
Exterior braced frames
Interior moment frames
Structural System – Lateral SystemNorth/South – Located in building core
Combination of braced frames and moment connections
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural System – Lateral System
North - South Lateral System
Along column lines 4 & 7
Located in Structural Core
Exterior Moment Frames
Interior Braced Frames
Structural System – Lateral System
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
North/South – Located along exterior frames
Only moment frames
Structural System – Lateral System
234567891011121314151617181920
22232425262728
21
North - South Lateral SystemAlong column lines 1 & 10
All moment frames
Varying stiffness
PROBLEM STATEMENT
Problem Statement – Overview
Complicated Structure to Analyze
• Varying Floor Geometry
• Large built-up members
Complicated Lateral System1. Combination of braced and moment frames
2. Lateral frames with varying stiffness
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 wasthe limiting factor that controlled the design
SOLUTION OVERVIEW
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
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
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
Solution Overview – Mechanical Breadth StudyAnalyze feasibility of adding enthalpy wheels to the original mechanical system.
Goal: Utilize the properties of building exhaust to save $$$
STRUCTURAL REDESIGN
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
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural Redesign – East/West Lateral Frames
Equal Stiffness
Distribute half of total story load to each frame
Equal distance from center of plan
Torsion had minimal effect in this direction
Column Lines C & D
Structural Redesign – Load Distribution
Structural Redesign - Results
Total Deflection: 13.25”
L/400 = 13.08”
Acceptable based on occupancy comfort
Structural Redesign – North/South Direction
Modeled lateral frames along Column Lines 1,4,7,10
Applied Virtual Load at levels 28,20,10
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural Redesign – North/South Direction
CL 1 CL 4/CL 7 CL 10
Relative stiffness varied with height.Applied uniform 10 kip load to verify stiffnessPlotted results and fit equationSolved equation for stiffness in terms of height
Structural Redesign – North/South Direction
Relative Lateral Frame Stiffness
y = 23584x - 2049.3
y = 2088.6x - 122.41
y = -3839.6x + 1640.3
0
50
100
150
200
250
300
350
400
0 0.1 0.2 0.3 0.4 0.5
K - Relative Stiffness
Build
ing
Heig
ht (f
t.) CL4CL10CL1Linear (CL1)Linear (CL10)Linear (CL4)
Structural Redesign – North/South Direction
Performed torsion analysis at each level based on center of rigidity
Included 5% eccentricity per code, and determined loads on frames
1 3 4 5 6 7
D
C
B
A
2 7 8 10
E
F
N
Level 20
Centre of
Rigidty
390 PSF
21'
1,900 Ft. Kips
90 Kips
Structural Redesign – North/South Direction
Applied load to models in GT Struddle and analyzed results
Structural Redesign – ResultsEach lateral frame deflected equal amounts.All frames deflected well over the L/400 limit.
19.99”17.16”
19.92”
Structural Redesign – SolutionAlleviate interstory drift problemsLimit overall building drift to 12”Started with exterior frames
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural Redesign – North/South DirectionAnalyzed several bracing configurations using iterative procedure.Eliminated interstory drift problems, limited total drift to 12”
Structural Redesign – North/South DirectionUsed same procedure for interior lateral frames along column lines 4 & 7
Could not limit drift to 12”
2 7 9 10
E
F
NELEVATORS STAIR TOWERS
LATERAL FRAMES
LATERAL FRAME
1 3 4 5 6 8
D
C
B
A
Structural Redesign – North/South Direction
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
Results
Structural Redesign – Cost AnalysisUsed R.S. Means to estimate total cost of original structure 20% total building cost = $ 40 million
Performed take-off to calculate cost of lateral system redesignCompared additional cost to overall structural cost
Cost Increase = 0.6% Structure CostCost Increase = 0.1% Structure Cost
Mechanical Redesign
Mechanical System Redesign
Fan powered VAV systemSupply Air: 80% return, 20% outdoor airExhaust: based on 150 cfm/toilet, 20 cfm/sinkTypical Air Handler Size: 23,500
System Description
ProcedureUse ASHRAE Bin data to analyze a full year cycleBased on 2 design condition: on peak – business hours, off peak – evenings and weekends
Calculated total building load with/without use of enthalpy wheelCompared loads and calculate savings
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
Mechanical System Redesign - Results
Using Peco Energy Rates:
Total Energy Savings:
671,236 kwh
Total Cost Savings:
$28,506/year
CONCLUSION
Conclusion
Based on lateral load assumptions used for this analysis, the lateral frames in the North/South direction should be designed with increased stiffness based on occupancy comfort criteria.
Redesign of lateral force resisting system is an economic solution compared to overall cost of structure
Enthalpy wheels should be utilized by the mechanical system to increase overall efficiency and save $$$.
Acknowledgments
AE Faculty and Staff
Dr. Memari and Dr. Geschwindner
Dr. Hanangan and Prof. Parfitt
Jeff Weinstein and Andy Bush, Brandywine Realty Trust
Dr. Banavalker, Ingenium Inc.
Peter Jennings, Jaros, Baum, and Bolles
My Family and Friends
My wife Nicole