FLAT SLABIn reinforced-concrete buildings, slabs are used to provide flat, useful surfaces. A reinforced-concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so. By definition, a flat slab structure consists of a slab built monolithically with columns and supported directly by these columns without the aid of beams and girders.Flat slabsare appropriate for most floor situations andalsofor irregular column layouts, curved floor shapes, ramps etc. The benefits of choosing flat slabs include a minimum depth solution, speed of construction, flexibility in the plan layout (both in terms of the shape and column layout), a flat soffit (clean finishes and freedom of layout of services) and scope and space for the use of flying forms.These slabs are classically used in foundations, although they can also be used in the construction of roadways, paths, and other structures. Depending on the size and complexity of a flat slab, it may need to be designed by an engineer who is familiar with the limitations and needs of slabs, or it may be possible for a handy do it yourselfer to make one in an afternoon for a simple project.Typically, a flat slab is made withreinforced concrete, in which rebar is crisscrossed in the forms to provide support and reinforcement once the concrete is poured and hardened. The slab design is designed to be reinforced in several directions so that it can withstand stresses such as shifting ground, earthquakes, frost, and so forth. Failure to fully reinforce a flat slab can cause it to crack or give along weak lines in the concrete, which will in turn cause instability.

The flexibility of flat slab construction can lead to high economy and yet allow the architect great freedom of form.

ILLUSTRATIONExamples are; solid flat slab, solid flat slab with drop panel, solid flat slab with column head, coffered flat slab, coffered flat slab with solid panels, banded coffered flat slab.

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FLAT PLATEA concrete slab reinforced in two directions, and supported directly on the columns witnout column capitals or beams.A flat plate floor system is a two-way concrete slab supported directly on columns or loadbearing walls with reinforcement in two orthogonal directions. Primarily used in hotels, multi-family residential buildings, and hospitals, this system has the advantages of simple construction and formwork and a flat ceiling, the latter of which reduces ceiling finishing costs, since the architectural finish can be applied directly to the underside of the slab. Even more significant are the cost savings associated with the low-story heights made possible by the shallow floor system. Smaller vertical runs of cladding, partition walls, mechanical systems, plumbing, and a large number of other items of construction translate to large cost savings, especially for medium and high-rise buildings.It is one of the most common forms of construction of floors in buildings. The principal feature of the flat plate floor is a uniform or near-uniform thickness with a flat soffit which requires only simple formwork and is easy to construct. The floor allows great flexibility for locating horizontal services above a suspended ceiling or in a bulkhead. The economical span of a flat plate for low to medium loads is usually limited by the need to control long-term deflection and may need to be sensibly pre-cambered (not overdone) or prestressed.An economical span for a reinforced flat plate is of the order of 6 to 8 m and for prestressed flat plates is in the range of 8 to 12 m. The span L of a reinforced concrete flat-plate is approximately D x 28 for simply supported, D x 30 for an end span of a continuous system, to D x 32 for internal continuous spans. The economical span of a flat plate can be extended by prestressing to approximately D x 30, D x 37 and D x 40 respectively, where D is the depth of slab.

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RIBBED FLOOR SLABRibbed floors consisting of equally spaced ribs are usually supported directly by columns. It is a one-way spanning system.

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WAFFLE SLABWaffle slab is a reinforced concrete roof or floor containing square grids with deep sides. This type of slabis used in construction projects needing intense strength to weight ratios. Waffle slab is a popular option for commercial construction work such as industrial building projects, bridges and others needing extra stability.

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LIFT SLAB