Lift and waffle slab

LIFT SLAB AND WAFFLE SLABBUILDING TECHNOLOGY 5

WAFFLE SLAB CONSTRUCTION

WAFFLE SLAB

What are Waffle Slabs? They are a reinforced concrete

footing and slab system constructed on ground. They consist of a perimeter footing (edge beam) and a series of narrow internal beams at one metre nominal centres running each way. The whole footing and slab system is constructed on top of the ground.

PLAN OF WAFFLE SLAB

WAFFLE SLAB

Waffle slabs tend to be deeper than the equivalent ribbed slab. Waffle slabs have a thin topping slab and narrow ribs spanning in both directions between column heads or band beams. The column heads or band beams are the same depth as the ribs.

ALSO CALLED TWO-WAY

Two-way concrete joist system ( waffle slab ) Waffle slab is used for long spans ( 6.0-14.4 m. ) heavy loads. Bays should be as square as possible.

DETAIL OF WAFFLE SLAB

CONSTRUCTION

Waffles are generally limited to the interior of a slab, leaving one or two of the forms out to create a solid fill around the supports. The solid fills provide the strength required for shear transfer to the supports

CONSTRUCTION

With larger loads and longer spans, such as is common in department stores a heavier solid SLAB BAND between the supports accommodates the overage of reinforcement from the individual waffle stems in each direction

CONSTRUCTION

(a) Plan of tendon layout (b) 3D view of tendonsFIGIRE 3-3 TENDON ARRANGMENT IN THE WAFFLE SLAB CONSTRUCITON

DETAIL OF WAFFLE SLAB

WHERE SHOULD IT BE PUT?

A Place for Waffle SlabsWaffle slabs are not recommended on highly reactive clay sites because the requirements for good drainage are almost impossible to achieve.

Advantages:

Savings on weight and materials

Long spansAttractive soffit appearance if exposed

Economical when reusable formwork pans used

Vertical penetrations between ribs are easy.

Disadvantages:

Depth of slab between the ribs may control the fire rating

Requires special or proprietary formwork

Greater floor-to-floor heightLarge vertical penetrations are more difficult to handle.

USES

Ribbed and waffle slabs provide a lighter and stiffer slab than an equivalent flat slab, reducing the extend of foundations. They provide a very good form where slab vibration is an issue, such as laboratories and hospitals.

LIFT SLAB CONSTRUCTION

DETAIL IN ATTACHING LIFT SLAB

LIFT SLAB

Lift-slabs are work floors which are pulled up per stage. Used mainly for lift cores, stairwells, etc.

This lift-slab works with a tongue system. In a previous phase a groove must be provided for each tongue of a min. 250 mm high and 150 mm wide.

HOW ARE THEY PLACED

Lift slab construction is a method of constructing concrete buildings by casting the floor or roof slab on top of the previous slab and then raising (jacking) the slab up with hydraulic jacks, so being cheaper and faster as not requiring boxing and supports for casting in site.

SECTION OF THE METAL

SECTION OF THE CONCRETE

PLAN OF THE LIFT SLAB

SECTION

SPECIFICATIONS

width of lift-slab min. 1700mm - max. 2600mm

length of lift-slab min. 1700mm - max. 5000mm

bearing surface per lift-slab girder max. 2500mm

SPECIFICATIONS

lift-slab girder can be adjusted every 25 mm

lift-slab girder can be adjusted at a max. 50 mm less than the concrete measurement. max. load 200 kg/m²

play between wall and girder must be kept as low as possible

USES OF LIFT SLAB

Lift slab can be used for heights up to about 16 stories. Economical column spacing ranges from 22 to 32 feet.

Columns may be pipe, tubes or wide flange sections; concrete columns may be used in 3- to 4-story buildings not requiring splices