Pranay Kumar Todepktode@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

Installation of ConcreteInstallation of Concrete

• 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

Installation of ConcreteInstallation of Concrete

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