Presentation Slides

12/17/2014
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“Voided Slabs – New Trends”
Mike Mota, PhD, PE, SECB, F.ASCE, F.SEI, F.ACI
Vice-President of Engineering
Concrete Reinforcing Steel Institute
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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About the Speaker
• Mike Mota
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Member of ACI 318, 318B and 318R (2019)
Chair of ACI 314 “Simplified Design of Concrete Structures”
Member of ASCE-7 (2016)
Board of Directors CIB/NYC-ACI Chapter
Fellow of ACI, ASCE and SEI
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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Design Guide for Voided Concrete Slabs
• Overview of different types of
voided slab systems
• Detailed design example
• Case studies of recently
completed US projects
• Published by CRSI (2014)
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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Overview
• Overview of traditional systems
• New trends
– Flat plate voided slab
– Basic design principles
• Case Studies in North America
• CRSI Concept
• Q&A
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Overview of Traditional Systems
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Overview of Traditional Systems
Slag Block
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Overview of Traditional Systems
Wide-Module Joists
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Overview of Traditional Systems
Waffle Slabs
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Overview of Traditional Systems
Hollow Core Plank
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Overview of Traditional Systems
Filigree Systems
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CI Article
(May 1983)
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• 688,000 sq. ft. “Low-rise”
”
• 40 ft Unobstructed Spans
• Heavy LL (125 PSF)
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Structural Steel
Voided Flat Plate
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Anchoring The Voids
Courtesy: Engineered Devices Corporation
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Anchoring The Voids
Courtesy: Engineered Devices Corporation
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New Trends
Crate type voids
Tubes
Plastic spheres
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New Trends
Cast in place
Pre-cast
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Cast
New
in Trends
Place
Courtesy: Cobiax USA
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Voided-Slab Cross Section
1st concreting stage:
Anchorage layer to prevent
buoyancy
2nd concreting stage: Remaining
concrete after initial setting of 1st
layer
Courtesy: Cobiax USA
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Implementation
Installation video
POSITIONING CAGES USED AS WIRE CHAIRS
Courtesy: Cobiax USA
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Overview of Benefits
• LARGE SPANS – NO BEAMS
• REDUCED DEAD LOAD
• LOWER EARTHQUAKE
FORCES
• IMPROVED VIBRATION
PROPERTIES
Conventional
system
Voided-slab
Courtesy: Cobiax USA
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Major Advantages
Courtesy: BubbleDeck
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Bundled for Transport
Courtesy: Cobiax
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Cage Placement
Courtesy: Cobiax
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Two-way Shear
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Placing Concrete
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Initial Concrete Stage
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Site Adaptability
Slab fixtures
Post tensioning
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Research example: Bending
m e a su r e d b e n d i n g m o m e n t
[k Nm ]
Bending tests each for solid and voided
slab samples voided slab response
does not differ from a solid slab
expected bending moment
250
200
150
100
50
0
with ball
B1-34
(mK)
B2-34
(oK)
B3-34
(mK)
B4-34
(oK)
B5-34
(mK)
B1-34
(oK)
massive
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Research example: Shear
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Solid specimens compared to voided ones
with spheres
Experimental shear resistance factor of
55% found for voided slabs (for specimens
without wire cages) compared to solid
ones
For voided slab specimens fitted with wire
cages the resistance factor found is
around 100%
Factor of 55% on the safe side
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Research Example: Fire protection
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Pressure first absorbed in voids
Thus, spalling retarded
Same design criteria as solid slab
Homologation for up to F180
German Homologation
MFPA P-SAC 02/IV-065
Swiss Homologation
N° Z-12599
French Test Certificate
CSTB RS06-148
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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Calculation of Equivalent Thickness
• Determine fire rating using equivalent thickness
– Sample Calculation per IBC 703.2
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Design Principles
• The voided slab is designed like a solid flat plate slab
• The presence of void formers results in the following
numeric modification factors:
– Dead load
– Deflection (smaller absolute deflection)
– Shear (necessity for solid areas)
• Common FE-Tools can be used for design
• Designers can easily adopt procedure
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Design Principles
• Flexural behavior is similar to a solid slab.
• Common design applications; NA remains above
voids.
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Design Principles
Slab
dead-load
reduction
(approx. 30%)
Slab
stiffness
(approx. 90%)
Voided
shear
resistance
(50%)
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Seismic Considerations
• Design voided slab as a diaphragm
– Chords and collectors
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Potential Cost Savings
Direct Cost Savings
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Additional Cost Savings
Steel
– Static reinforcement
– PT cables and ducts
– Chairs & Stirrups
Concrete (LFRS)
Vertical elements
– Walls & Columns
– Stairs & Elevators
– Façades
– Finishes
Formwork
– Beams
– Coffers / Troughs
Foundation volume
MEP materials
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Construction time gain
– Cycle times (formwork & PT)
– MEP installation
Volume gain
– height reduction, and /or less
heating & AC
– addition of floors, or more
gross surface
– internal space increase, higher
value of surfaces
Surface use flexibility
– retrofitting cost reduced
– no PT cables limiting vertical
expansion
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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Voided Slab Projects in North America
Women’s
Health
Center
Watertown
RMC
York U. – Life
Science Building
Ecole
Polytechnique
LaBahn
Arena
CUMC
U of Iowa
Harvey
Mudd
College
Wright
State
University
MAM
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Jorge M. Pérez Art Museum, Miami
• 4 levels
• 280,000 sf
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Architectural Challenges
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Why Voided Slab for MAM?
• Large spans (50’)
• No down-turned beams
• 2” cover for slab reinforcing
• Reduction of weight on pile foundation
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U of W Hockey Arena
Courtesy: BubbleDeck
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Stay in Place Voided Slab Panels
Courtesy: BubbleDeck
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Stay in Place Voided Slab Panels
Courtesy: BubbleDeck
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Joint Reinforcement
Courtesy: BubbleDeck
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Minimizing Floor Thickness
Courtesy: BubbleDeck
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Why Voided Slab for UW LaBahn?
• Saved $2/SF
• Saved 174 CY of concrete
• Saved 3 days off of schedule
• Saved on shoring cost
• Saved structural depth
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Harvey Mudd College, Claremont, CA
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4 –Story Education Building
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80,000 square feet of Voided slab
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9, 11, 13.5, 17.5 and 20 inch slab
thicknesses used
(courtesy of KPFF)
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Located in high seismic zone
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Harvey Mudd College, Claremont, CA
Courtesy: BubbleDeck
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Harvey Mudd College, Claremont, CA
Courtesy: BubbleDeck
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Watertown Regional Medical Center
East Addition
Watertown, WI
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Watertown Regional Medical Center
• Emergency Dept & Women’s Health Addition
• 2-Story & 30,000 square feet
• Existing construction systems:
– Concrete waffle slabs
– Concrete pan joist
– Precast concrete and steel beams
• System selection for healthcare facilities
– Grid layout
– Story height
STEEL REINFORCED CONCRETE: It Enables. Adapts. Endures.
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Watertown Regional Medical Center
Courtesy: BubbleDeck
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Watertown Regional Medical Center
Courtesy: BubbleDeck
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Columbia U. Medical Center, NY
• Under Construction
• New Medical and Graduate
Education Center
• 14 stories
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Wright State University
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Dayton, OH
Under Construction
Academic Research
Biomedical Eng.
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U. of Iowa
• Art Building Replacement
• Under Construction
• 400,000 sf of voided slabs
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www.crsi.org
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CRSI Concept
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CRSI Concept
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Summary
• www.crsi.org
• Voided slabs are a time tested concept
• Technological advancements improve
efficiency
– Sustainable development
– Economical for commercial type structures
– Design-Build Advantages
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Made from Recycled Plastic
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References
• CRSI Voided Slab Design Guide (2014)
• Seismic Design of Cast-in-Place Concrete
Diaphragms, Chords, and Collectors - A Guide
for Practicing Engineers- NEHRP Seismic
Design Technical Brief No. 3
• Concrete Slab Collectors – SEAOC Blue Book –
Seismic Design Considerations (2008)
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Questions?
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