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PLAZA AT PPL CENTERAllentown, PA
Economical
Design
Considerations
for Steel
Construction
Amy S. Graver - Structural Option Spring 2003 Senior Thesis
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
INTRODUCTION
Plaza at PPL Center Amy S. Graver - Structural
Owner: Liberty Property Trust
Primary Tenant: PPL EnergyPlus
Architect and Landscape: Robert A. M. Stern Architects
Structural Engineers: Thornton-Tomasetti
MEP, Fire Protection: PPL Energy Services Mid-Atlantic, LCC
Construction Manager: L.F. Driscoll
Architect of Record: Kendall/Heaton Associates, Inc.
Civil Engineers: Pennoni Associates
Lighting Consultant: Quentin Thomas Associates, Inc.
INTRODUCTION
PROJECT TEAM
Plaza at PPL Center Amy S. Graver - Structural
INTRODUCTION
LOCATION
LINDEN STREET LINDEN STREET
HAMILTON STREETHAMILTON STREET
PLAZA AT PPL CENTERTOWER AT
PPL CENTER
NORTH
BUILDINGPROPOSED
PARKING GARAGE
N.
EIG
HT
H S
TR
EE
T
N.
NIN
TH
ST
RE
ET
N.
TE
NT
H S
TR
EE
T
Plaza at PPL Center Amy S. Graver - Structural
INTRODUCTION
BUILDING FACTS
Size
$29 million base building cost, $19 million tenant specific costs
256,000 sq. ft.
200,000 sq. ft. to be leased by PPL Corporation
Uses
8-story Multi-use Building
First Floor: Retail Space
Floors 2-6: Office Space for PPL EnergyPlus
Floors 7-8: Energy Securities Trading Floors
Plaza at PPL Center Amy S. Graver - Structural
INTRODUCTION
BUILDING FACTS
Architecture
LEED Gold Certification
Central Atrium
Winter Gardens
and Roof Top Garden
Glass Façade with Strips of
Pre-cast Concrete Panels
Plaza at PPL Center Amy S. Graver - Structural
FoundationPartial Basement w/ Poured Concrete Walls
Continuous Concrete Spread Footings
Gravity SystemComposite Steel Beams
Composite Deck
14’-20’ Stories
30’x42’ Bays
Typical Sizes
Beams: W18
Columns: W14
INTRODUCTION
STRUCTURE
Plaza at PPL Center Amy S. Graver - Structural
INTRODUCTION
STRUCTURE
Lateral System
Moment Frame A
Moment Frames B/C
Moment Frame D
East-West: Moment FramesNorth-South: Braced FramesA
D
B
C
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
ECONOMY
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Implications
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
40 40
3533 33 33 33
30 29 30
25 26 25 27
22
20 19
15
10
5
01983 1988 1993 1998 1983 1988 1993 1998 1983 1988 1993 1998
Material Erection Labor Shop Labor
40 40
3533 33 33 33
30 29 30
25 26 25 27
22
20 19
15
10
5
01983 1988 1993 1998 1983 1988 1993 1998 1983 1988 1993 1998
Material Erection Labor Shop Labor
CONSIDERATIONS
ECONOMY
Low Seismic Design
Braced Frames
Partial Composite Construction
% o
f C
onst
ruct
ion C
ost
s
% o
f C
on
stru
ctio
n C
ost
s
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
MOMENT FRAME COMPARISONS
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
SEISMIC DESIGN
Allentown, PA
Not Considered a High Seismic Area
Seismic Design Category B
Under More Recent Codes
Seismic Can Control
Subject to Seismic Provisions when R>3
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
SEISMIC DESIGN
Ductility
Lower Base Shear with Increased Ductility
Response Modification Factor
To account for ductility of a system
Cs is indirectly proportional to R
Since V= CsW, a lower R-Factor corresponds to a higher base
shear
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
SEISMIC DESIGN
Applied Code: IBC 2000
References AISC Seismic Provisions & Supplement 1
Connections must be designed by Seismic Provisions if R>3
AISC Seismic Provisions for Structural Steel Buildings
Connections must be stronger than connected members
Classifies moment frames based on a rotation criteria
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
Connection Moment Capacity per AISC
Mp
Mp
1.1RyMp
Mu
Connection Moment Capacity per FEMA 350
1.1RyMp
1.1RyMp
1.1RyMp
Mu
Response Modification Factor
R=8
R=6
R=4
R=3
Four Types of Moment Frames
Special Moment Frames (SMF)
Intermediate Moment Frames (IMF )
Ordinary Moment Frames (OMF)
Steel Systems not Detailed for Seismic Resistance
Required Rotation
θ=0.4 radians
θ=0.2 radians
None
None
DESIGN STATEMENT
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
Comparison
SMF
IMF
OMF
R=3
DESIGN STATEMENT
MOMENT FRAME COMPARISONS
Dec
reas
ing
R-F
acto
r
Incr
easi
ng B
ase
She
ar
Less
Str
inge
nt D
etai
ling
Larg
er M
embe
rs
Sm
alle
r C
onne
ctio
ns
Mor
e E
cono
mic
al
Fas
ter
Con
stru
ctio
n
Differences Results
Plaza at PPL Center Amy S. Graver - Structural
Connection Design
FEMA 350: rotation criteria
SMF & IMF
LRFD Manual: strength design
OMF & R=3
Web-Bolted, Flange-Bolted Connections
Approved for Seismic Use
Tested by Federal Emergency
Management Agency (FEMA)
Meets Rotation Requirements
for SMF and IMF
CONNECTIONS
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
Included Costs
Material Costs
Fabrication Labor
Erection Labor
Excluded Costs
Quality Inspection
Special Fabrication Procedures
COST COMPARISON
MOMENT FRAME COMPARISONS
Plaza at PPL Center Amy S. Graver - Structural
R=3SMF
Actual LoadsDesign Capacity of Members
Strong Column, Weak Beam
Smaller Members
CONNECTION COMPARISON
MOMENT FRAME COMPARISONS
Moment Frame A
W18x60 W24x62
W14
x74
W14
x99
Deeper Beams
Heavier Columns
Plaza at PPL Center Amy S. Graver - Structural
Costs Time
System R-Factor Materials Labor Fabrication Erection
Existing: SMF 8 $189,392 $85,224 1208 hrs. 467 hrs.
Most Economical 3 $237,117 $14,918 117 hrs. 484 hrs.
Savings -$47,724 $70,306 1091hrs. -17hrs
COMPARISON
MOMENT FRAME COMPARISONS
$22,500 1070hrs.
Plaza at PPL Center Amy S. Graver - Structural
1000 hrs. of Fabrication TimeCost of Stiffeners
Saves 3 weeks
Critical Path
Added Float
Start Later
ErectionRemains on Critical Path
Dependent on Sitework
and Foundation
SCHEDULE EFFECTS
MOMENT FRAME COMPARISONS
3 weeks
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
BRACED FRAME ANALYSIS
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
Results of the Moment Frame Comparison
Low Seismic is More Economical
Connections Drive Cost
Try Braced Frames in East-West Direction
Eliminates 410 Moment Connections
Works Within the Proposed Floor Plan
DESIGN STATEMENT
BRACED FRAME DESIGN
Plaza at PPL Center Amy S. Graver - Structural
Chevron Braced
Adequate for Proposed Openings
14’ Minimum Floor-to-floor Height
Accommodates a Double Door
Tenant Fitout
Rooms along
column grids
30-year lease
Try Braced Frames
ARCHITECTURE
BRACED FRAME DESIGN
Plaza at PPL Center Amy S. Graver - Structural
FLOOR PLANS
BRACED FRAME DESIGN
Existing Moment Frames
Proposed Braced Frames
Plaza at PPL Center Amy S. Graver - Structural
DESIGN
BRACED FRAME DESIGN
Seismic is the Governing Lateral Force for Members
Concentric Braced Frame
R=3
V=1182K
Typical Sizes
W14 Columns and Braces to Match North-South Direction
W24x68 Beams
Plaza at PPL Center Amy S. Graver - Structural
COST COMPARISON
BRACED FRAME DESIGN
Included Costs
Moment frame members now sized for gravity only
Additional cost of connections above a typical shear connection
System Total Costs
Moment Frames (R=3) $300,861
Braced Frames $226,636
Savings $74,225
Plaza at PPL Center Amy S. Graver - Structural
Additional Time Savings
Fabrication
Not on the critical path
Adds 3 weeks of float
Erection
On the critical path
Project Completion: 3 weeks earlier
SCHEDULE
BRACED FRAME DESIGN
Project Complete: April 30, 2003
Project Complete: April 12, 2003
Time Savings
Fabrication Erection
3 weeks 3 weeks
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
COMPOSITE FLOOR EVALUATION
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
Cost of 1 Shear Stud = 10lbs. of Steel
$0.50 Material Cost
$1.50 Labor Cost
Try Partial Composite
Is a heavier beam with fewer shear studs more economical?
DESIGN STATEMENT
COMPOSITE CONSTRUCTION
Plaza at PPL Center Amy S. Graver - Structural
FLOOR PLANS
COMPOSITE CONSTRUCTION
Floors 2-6
Existing: 100% Composite Re-design: 90% Composite
W18x35 [48]
W18x35 [44]
Plaza at PPL Center Amy S. Graver - Structural
FLOOR PLANS
COMPOSITE CONSTRUCTION
Floors 1, 7-8
Existing: 100% Composite Re-design: 40% Composite
W18x40 [48]
W21x44 [24]
Plaza at PPL Center Amy S. Graver - Structural
Floors 100% Cost Partial Cost Savings
2-6 W18x35 [48] $94,800 W18x35 [44] $92,640
1, 7-8 W18x40[48] $55,100 W21x44 [24] $51,970$5,290
COMPARISON
COMPOSITE CONSTRUCTION
Total Building Savings $5,290
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
MECHANICAL RE-DESIGN
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
Composite Beam Comparison
W18 to W21
3” decrease in usable ceiling plenum
Original Design
28”x12” SA duct below beams
Air Flow Rate = 2500CFM
Air Velocity = 1150FPM
Static Pressure Drop = 0.1in.w.g.
DESIGN STATEMENT
MECHANICAL EFFECTS
Plaza at PPL Center Amy S. Graver - Structural
Initial Size Problems
9” duct height is required to maintain existing plenum
To supply 2500CFM at 0.1in.w.g.,
42”x9” required
Does not meet the 4-to-1 width-to-height ratio
RE-DESIGN
MECHANICAL EFFECTS
Plaza at PPL Center Amy S. Graver - Structural
SOLUTION
MECHANICAL EFFECTS
Design
2500CFM First 16’
1900CFM Past Branch
Results
Turning Vanes in Elbow
4-to-1 Ratio past
Branch
Maintains Design
Criteria
34”x9” 42”x9”
600CFM VAV Box
Plaza at PPL Center Amy S. Graver - Structural
PRESENTATION OUTLINE
MECHANICAL RE-DESIGN
Introduction
Economical Design Considerations
Moment Frame Comparisons
Braced Frame Design
Composite Floor Evaluation
Mechanical Re-Design
Conclusions
Plaza at PPL Center Amy S. Graver - Structural
Cost SavingsMoment Frames with R=3 . . . $22,000
Braced Frames . . . . . . . . . . . $100,000
Composite Construction . . . . . $5,300
Time SavingsMoment Frames with R=3 . . . Fabrication: 3 weeks
Braced Frames . . . . . . . . . . . Fabrication: 6 weeks
. . . . . . . . . . . Erection: 3 weeks
ECONOMY
CONCLUSIONS
Plaza at PPL Center Amy S. Graver - Structural
Braced Frames are Most Economical Lateral System
Feasible with architectural layout
$100,000 cost savings
Project Completion: 3 weeks earlier
Deeper, Heavier Beams with Less Composite Action
Increases floor depth
Ceiling plenum height retained with shallower duct
RECOMMENDATIONS
CONCLUSIONS
Plaza at PPL Center Amy S. Graver - Structural
ACKNOWLEDGMENTS
CONCLUSIONS
Pennoni Associates: Civil Engineer
Frank Adams, P.E., AIA
Jeff Ott, P.E.
Ed Sander, P.E.
The Adams Division
Thornton-Tomasetti: Structural Engineer
Hi Sun Choi, P.E.
L.F. Driscoll: Construction Manager
Ed Jackowski
Stewart-Amos Steel
Curt Zeigler
A huge thank you to everyone one who answered questions, provided information and offered support… your time and efforts are greatly appreciated.
AE Faculty
Dr. Hanagan, P.E.
Walt Schneider, P.E.
Professor Parfitt, P.E.
Jonathan Dougherty
AE Class of 2003
Rebecca Mittel
Melissa Rosol
My Family and Friends
Last but certainly not least…
Plaza at PPL Center Amy S. Graver - Structural
QUESTIONS
CONCLUSIONS
?
Plaza at PPL Center Amy S. Graver - Structural
QUESTIONS
CONCLUSIONS
?
Plaza at PPL Center Amy S. Graver - Structural
Section d Composite S/A Duct Air Volume Friction Velocity
(in.) (%) (in.) (CFM) (per 100') (FPM)
W18x40 17.9 100 28x12 2500 0.10 1250
W21x44 20.7 40 36x9 2500 0.13 1300
RESULTS
MECHANICAL EFFECTS
Higher Air Velocity to Maintain Air Flow Rate
Increased noise through diffusers
Not a large enough increase to impact occupants
Duct meets industry standard for 4-to-1 ratio