Lift and waffle slab
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RIBBED SLAB AND WAFFLE SLAB
LIFT SLAB AND WAFFLE SLABBUILDING TECHNOLOGY 5WAFFLE SLAB CONSTRUCTION
WAFFLE SLABWhat 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
4WAFFLE 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-WAYTwo-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
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 supportsCONSTRUCTIONWith 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
(a) Plan of tendon layout (b) 3D view of tendonsFIGIRE 3-3 TENDON ARRANGMENT IN THE WAFFLE SLAB CONSTRUCITONDETAIL 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 materialsLong spansAttractive soffit appearance if exposedEconomical when reusable formwork pans usedVertical penetrations between ribs are easy.
Disadvantages:Depth of slab between the ribs may control the fire ratingRequires special or proprietary formworkGreater floor-to-floor heightLarge vertical penetrations are more difficult to handle.
USESRibbed 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 SLABLift-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 PLACEDLift 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 METALSECTION OF THE CONCRETE
PLAN OF THE LIFT SLAB
SECTIONSPECIFICATIONSwidth of lift-slab min. 1700mm - max. 2600mm length of lift-slab min. 1700mm - max. 5000mm bearing surface per lift-slab girder max. 2500mmSPECIFICATIONSlift-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/m play between wall and girder must be kept as low as possible
USES OF LIFT SLABLift 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