Floor and slabs

Pranay Kumar Tode
pktode@yahoo.co.in

 List wood floor systems
 Explain the advantages and disadvantages
of specifying precast over site-cast
concrete.
 Explain why precast concrete structural
elements are usually cured with steam.
 Explain the difference between a one-way
and two-way concrete floor system.
 List and explain the different types of one-
way concrete floor systems.
 List and explain the different types of two-
way concrete floor systems.

 1”x12” T&G sheet floor decking
 Laminated 2”x4”’s or 2”x6”’s on edge at right angles to
the floor beams
 Spiked together side by side

 Can be wood beam or steel beam with wood
nailer on top
 Heavy planks, tongue and groove, spiked to
the beams

 Slabs on grade
› Durability depends on concrete strength
and finish
› Strength of slab depends on reinforcing and
supporting subgrade
 Structural slabs
› Span between columns and beams
› Strength depends on concrete strength and
the amount of reinforcing steel

 Able to control the quality of materials and workmanship
better than onsite (able to build in the rain, sleet, or snow).
 Able to vibrate the concrete mechanically to achieve
maximum density and highest surface quality.
 Able to reuse formwork more than onsite, thus reducing
formwork cost per unit.
 Able to steam cure, thus accelerating curing with the
steam’s heat and adding moisture for full hydration.
 Steam curing, coupled with the use of Type III cement
enables the plant to produce a fully cured structural element
in 24 hours.

 Although light compared to other building
elements, precast structural elements are
heavy to transport over the roads and hoist
into place.
 This also restricts the size and proportions of
most precast elements (they can be long,
but they can only be as wide as the
maximum legal vehicle width of 12 to 14
feet.

 One-Way
 Beams run in one direction, parallel to
one another, between perpendicular
girders that transfer the load to columns.
 Two-Way
 Beams run in two directions, parallel and
perpendicular to one another.

 The One-Way Solid Slab System
 Beams and girders are poured the same
time as the slab.
 Economical when the slab does not
span very far between beams.
 Slab depths are usually 4-10 inches.
 Uneconomical on spans of more than
20’

 The One-Way Concrete Joist System
 Longer one-way spans than solid slab systems.
 Joists are formed with metal pans supported on
longitudinal strips of wood or on a plywood deck.
 Distribution ribs are placed at mid-span to distribute
concentrated loads to more than one joist.
 When fire-resistance requirements of the building
code dictate a slab thickness of 4.5 inches or more,
the slab is capable of spanning a much greater
distance. This enables wide-module pans that
separate the joists by 4-6 feet.

 Beams run in two directions, parallel and
perpendicular to one another.
 “Generally, two way floor systems are
more economical than one-way systems
in buildings where columns can be
spaced in bays that are square or nearly
square in proportion”.

 The Two-Way Solid Flat Slab System
 A system in which the slab is supported by a grid of beams
running in both directions over the columns.
 Used for very heavily loaded industrial floors.
 Slab depth = 4 to 12 inches
 Maximum span = 34 feet
 Most two-way floor systems are made without beams.
Instead, “the slab is reinforced in such a way that the varying
stresses in the different zones of the slab are accommodated
within a uniform thickness of concrete”.

 The Two-Way Solid Flat Slab System (cont.)
 Formwork is completely flat except for a thickening of the
concrete to resist the high shear forces around the top of
each column (drop panel). Historically the columns under
the drop panels also had mushroom capitals.
 “Reinforcing is laid in both directions in half-bay-wide strips of
two fundamental types: column strips are designed to carry
the higher bending forces encountered in the zones of the
slab that cross the columns, and the middle strips have a
lighter reinforcing pattern”.

 The Two-Way Flat Plate System
 “In more lightly loaded buildings, such as
hotels, hospitals, dormitories, and
apartment buildings, the slab need not be
thickened at all over the columns.”
 “This allows some columns to be moved off
of the grid to facilitate a more efficient floor
plan (Allen, p. 483).
 Slab depth = 5-10 inches.
 Maximum span = 32 feet

 The Two-Way Waffle Slab System
 A.k.a. The two-way concrete joist system
 Metal or plastic pans called domes are used to
eliminate the nonworking concrete from the slab,
allowing a greater economy in longer spans.
Domes now have a special fitting that allows one
to shoot compressed air between it and the
concrete to remove the dome.
 Standard Domes form joists 6” wide on 36” centers
or 5” wide on 24” centers.
 Solid concrete heads are created around the tops
of the columns by leaving the domes out of the
formwork. These serve the same function as the
drop panels in the two-way flat slab system.

Introduction to Composite ConstructionIntroduction to Composite Construction
• Composite construction refers to two load-carrying structural members that
are integrally connected and deflect as a single unit
• An example of this is composite metal deck with concrete fill, steel filler
beams, and girders made composite by using headed stud connectors
Composite
Steel Deck
Shear
Connectors
Welded Wire
Fabric
Concrete

• A steel beam which is made composite by using shear connectors,
composite metal decking and concrete is much stronger and stiffer than the
base beam alone
• Composite floor systems are considered by many to be the highest quality
type of construction
• This has become a standard type of construction selected by many
architects, engineers, and developers
Introduction to Composite ConstructionIntroduction to Composite Construction

Advantages of Composite ConstructionAdvantages of Composite Construction
In a composite floor system the concrete acts together with the steel to create
a stiffer, lighter, less expensive structure

Advantages of Composite ConstructionAdvantages of Composite Construction
Connecting the concrete to the steel beams can have several advantages:
• It is typical to have a reduced
structural steel frame cost
• Weight of the structural steel
frame may be decreased which
may reduce foundation costs
• Reduced live load deflections
• Shallower beams may be used
which might reduce building height
• Increased span lengths are
possible
• Stiffer floors

• Puddle welds (above right) are commonly used to attach the decking to
the structural steel below
• Daily output for a four person decking crew ranges from 2700 S.F. to
3860 S.F. per day depending on the depth and gauge of the decking.
Installation of DeckingInstallation of Decking

• As an alternative to welding, powder actuated tools
may be used to attach metal decking to structural steel
• Powder actuated tools use the expanding gases from
a powder load, or booster, to drive a fastener
• A nail-like fastener is driven through the metal deck
into the steel beam
• The powder actuated tool, powder load, and fastener
must be matched to the thickness of the structural
steel beam flanges
Installation of DeckingInstallation of Decking

• Shear connectors are commonly referred to as
“studs” or “shear studs” in the trade
• They are available in a range of sizes, materials,
and grades
• Headed studs (as shown) are most commonly
used
• Other, less common options for shear connectors
include hooked studs or pieces of C-channel
Shear ConnectorsShear Connectors

• Depending on the welding process used, the tip of
the shear connector may be placed in a ceramic
ferrule (arc shield) during welding to retain the weld
• Shear connectors create a strong bond between the
steel beam and the concrete floor slab which is
poured on top of the metal decking
• This bond allows the concrete slab to work with the
steel beams to reduce live load deflection
Shear ConnectorsShear Connectors

• Shear connectors are installed after the decking is in place
• Shear connectors may be installed by the steel erection contractor or a
specialty shear connector installer
• The welding equipment required for installation is provided by the shear
connector installer
• Daily output for shear connector installation averages about 1000 per day
depending on the size of the connectors.
Installation of Shear ConnectorsInstallation of Shear Connectors

• Concrete is installed by a concrete contractor on top of the composite metal
decking, shear connectors, and welded wire fabric or rebar grid (crack control
reinforcing)
• Pumping is a typical installation method for concrete being placed on metal
decking
• 10,000 to 15,000 sq. ft. of concrete slab may be installed per day depending
on slab thickness and crew size.
Installation of ConcreteInstallation of Concrete

• There is an art to the placement of concrete on metal deck and structural steel
• The work, unless shoring is used, must be executed on a deflecting surface
• An experienced concrete contractor should be employed for this work
 Concrete should be deposited over supporting members first, then spread
toward the deck midspans
 The accumulation of a deep pile of concrete must be avoided

• The contractor must be aware of camber in the beams and the expected
deflections
• Consultation with the structural engineer may be necessary
• As the concrete cures it forms a connection with the composite metal
decking and shear studs
• The composite floor system is now complete

 1” Metallic Aggregate Mix
 Terra-Cotta Tile (Ceramic)
 Mastic Finish (Epoxy)
 Resilient Tile (VCT)
 Terrazzo

Floor and slabs

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Floor and slabs