Miranova Condominiums Columbus, Ohio Chris Crilly Structural Option Spring ‘04
Presentation Outline Project Background Existing Conditions Problem Statement Goals Proposed Solution Floor System Lateral System Other Considerations Acoustics Construction Management Summary/Conclusions Acknowledgments Questions
Project Background Location N Columbus, Ohio Adjacent to I-70 Along Scioto River Faces North into the city I-70
Project Background Construction Dates Groundbreaking was in July of 1998 Substantial Completion was in October of 2000 Tenant fit out continued into 2002 Size Gross Building Area Garage - 123,254 SF 5 Stories Tower - 332,862 SF 22 Stories Total - 456,116 SF 27 Stories Cost $52 Million Total Cost
Project Background Building Occupancy Basement Visitor Parking Ground Floor Reception/Lobby Approximately 146 High-end Storage Luxury Condominiums Social Spaces Offices Approximately 226 Total parking Fitness Areas Spaces Levels 2-4 Resident Parking Small Storage Spaces Levels 5-28 Condominiums
Project Background Project Team Design Architect – Arquitectonica Architect of Record – HKS Inc. Structural Engineer – The Thornton–Tomasetti Group MEP Engineer – Flack & Kurtz Consulting Engineers Lighting Designer – Lighting Design Alliance Civil Engineer – E M H & T, Inc. Construction Manager – Turner Construction Company Wind Tunnel Consultant – Cermak Peterka Peterson, Inc.
Existing Conditions Architecture North Façade – Blue Tinted Glass Curtain Wall Other Façades – 6” Precast Conc. Panels Level 1 – 5 120’ x 250’ Tower 60’ x 280’ 655’ Radius
Existing Conditions Structure – Foundation Concrete Mat Foundation f’ c = 4000 psi – Normal Weight Concrete Placed on a 2” Mud Slab 5’-3” to 5’-9” thick under the tower 2’-9” to 3’-3” thick under 5 story portion
Existing Conditions Structure – Floor System 8” Post-Tensioned Flat Plate f’ c = 5000 psi – Normal Weight Conc. Post Tensioning ½” ∅ , 270 ksi Low-Relaxation Strands Banded in 6’ Width over Col. Lines in E/W Direction Uniformly Spaced in N/S Direction
Existing Conditions Structure – Lateral System Concrete Shear Walls f’ c = 5000 psi – Normal Weight Conc. Thickness Decreases up the Building 22” to 12” Thick
Goals/Criteria Problem Statement Possibility exists for owner to purchase to adjacent units and connect the two to make a larger living space Very difficult and expensive to execute future expansions: Vertically – due to post-tensioned slabs Horizontally – due to R/C shear walls
Goals/Criteria Goals Allow greater and cheaper flexibility for possible future renovations Vertically Horizontally Minimize impact on overall cost Minimize impact on architecture
Proposed Solution Floor System Steel Systems More flexible to future changes than concrete Easier to add openings for stairways and ducts Lighter Steel floor systems are typically deeper I will concentrate on Low Floor-to-Floor systems to minimize impact on architecture and cost
Proposed Solution Lateral System Steel Braced Frames More flexible to future changes than concrete shear walls Easier to add openings for doorways Lighter Braced frames allow for only discrete door locations I will concentrate on maximizing the area for door openings for greater future flexibility
Floor System Composite Slab and Beam System Slight modification to Beam-Girder connections over typical connections Reduces floor depth Reduces fabrication time and costs Connection L4x4x12x3” Erection Angle 3 – 1/2” ∅ Erection Bolts
Floor System Infill Beams (N-S Span Direction) W10 x 22 – Center Bay W10 x 17 or W10 x 19 – Outer Bays Girders (E-W Span Direction) W12 x 26 to W12 x 40 ∆ EL b/w Top Beam and Top Girder 1.625” – 1.875” Allows for 1/8” Mill Tolerance 2” Max Required - 2” – 18 gage VLI Deck
Floor System Connection Check Yield Line Analysis Initially Studied by W. S. Easterling of Va. Tech. Followed up with Master’s Thesis by Wey-Jen Lee at Va. Tech R = Nominal Strength of Girder Flange ⎡ ⎤ 2 b F y = Yield Strength of Girder + b ⎢ ⎥ t f = Thickness of Girder Flange 4 b 2 ⎢ ⎥ = g 2 b b = Width of Beam Flange R F t ⎢ ⎥ y f d b g = Length of Girder Flange (b f /2 – k 1 ) − 1 ⎢ ⎥ D = Length of Beam Bearing 2 b ⎣ ⎦ g φ = 0.9 - Assumed
Floor System Connection Check Connection Check These Capacities are CONSERVATIVE. Why? Proven by experimental tests Bearing point is assumed to be at Center of Bearing Area Connection similar to un-stiffened seated connection Bearing point determined by beam web limits states simultaneously with bending limit state Beam Web Limit states were also checked and found to be OK
Floor System Other Design Considerations Sound & Impact Transmission through floor system Investigated under Acoustic Breadth Floor Vibrations Typical beams checked Interior Bays Fell in upper half of barely perceptible range of the modified R-M scale Max. acceleration – 0.339% < 0.5% OK Exterior Bays Fell in lower half of slightly perceptible range of the modified R-M scale Max acceleration – 0.495% < 0.5% OK
Floor System Typical Composite System A typical composite floor system was also designed Typical connections No depth restrictions Partially composite beams Same beam and girder layout was used Infill Beams – W12x19 Girders – W16x26 to W16x30 Beam to Girder Connections – Shear Tab (3) – ¾” ∅ A325 Bolts PL – 3/8” x 4 ½” x 9” A36 5/16” fillet weld φ R n = 27.8 k
Floor System Cost & Time Advantages Cost & Time Advantages Shallow System This was done to compare: Heavier Members Material costs Slightly more shear studs Fabrication costs Less Connection Material & Less Beam Fabrication (Copes) Fabrication time
Lateral System Combination of R/C shear walls and steel braced frames Shear Walls Keep existing walls around 2 building cores Walls added around building core • Better protection in emergencies • Stiffens building Steel Braced Frames Replace large shear walls in N-S Direction 3 options studied to: • Determine most efficient system • Determine most economical system • Maximize available space for future doors
Lateral System Option #2: Outer Braces Option #1: All Braces Center Brace – Same as option #1
Lateral System Option #3: Eccentrically Braced Frames Design Summary 4 ft link in larger bay Ext. Columns – W14x426 to W14x48 Int. Columns – 2 to 3 sizes smaller Beams – W16x45 to W18x60 Braces – W12x40 to W12x45 Pros 4X area for doors in center frame 2X area for doors in outer frames Smaller Columns Acceptable building and story drifts Cons Slightly larger beams Approx. 2X # bracing connections Approx. 2X # braces
Lateral System Final Design Outer Braces Center Brace
Lateral System Comparison b/w Existing and Proposed System
Lateral System
Level 5 Diaphragm Existing Building used Wind Loads from wind tunnel test I used Code stipulated loads which were larger Change in lateral system at level 5 caused large shears in diaphragm Check proved existing diaphragm to be adequate
Impacts on Arch. 15 ft Building height increase over 20 stories Locations of existing doors in shear walls had to be slightly moved to accommodate the braces, did not greatly impact space layouts 3 additional columns – easily hidden 8” increase in party wall thickness – 4” loss of living space on each side
Acoustics Floor System Building Code Design Criteria: STC � 50 IIC � 50 Fire Rating – 2 HR Recommended Design Criteria for Luxury Residences: STC � 60 IIC � 60
Acoustics Properties STC ≅ 62 IIC ≅ 74 – with carpet IIC ≅ 60 – with hard flooring on foam rubber underlay Fire Rating – UL No. D916 – 2 HR rating with 3 ½” slab • Actual slab is 4 ¼”
Acoustics Brace Infill Wall Building Code Design Criteria: STC � 50 Fire Rating – 1 HR Recommended Design Criteria for Luxury Residences: STC � 60 Properties: STC � 60 Fire Rating – UL No. U411 • 2 HR
Constr. Management Cost Estimate Existing Structure Cost Material Labor Equipment Total Floor Slab 1406825 1195081 194338 2796244 Columns 164808 147230 8420 320458 209181 290109 10497 509787 Shear Walls Totals $1,780,814 $1,632,420 $213,255 $3,626,489 Steel Structure Cost Material Fabricaction Erection/Labor Total Beams Gravity 328309 131203 114878 574390 Lateral 19723 1291 5253 26267 Braces 23495 2336 6458 32288 Columns Gravity 122870 1538 31102 155510 Lateral 62540 985 15881 79406 Connections 33276 108003 35320 176599 Shear Walls 201814 0 459507 661321 Floor Slab 926751 0 252953 1179703 42251 0 28743 70994 Fire Protection Totals $1,761,028 $245,357 $950,095 $2,956,480 Square Ft. Cost = 8.88 $/SF
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