R.C.C. STAIRS
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Reinforced concrete is well-suited for constructing stairs due to its fire resistance, durability, strength, and pleasing appearance. R.C.C. stairs can be designed in various forms including straight flights, inclined slabs with half landings, string beams, cranked slabs, cantilevers, and spirals. The type of stair adopted depends on the space and loading conditions. Common stair arrangements include single straight flights, inclined slabs spanning longitudinally, string beams with horizontal slab spanning, cranked slabs inducing bending and torsion stresses, cantilever stairs with central supporting walls, and spiral or helical stairs used in prestige buildings.
R.C.C. STAIRS
- 1. 3. R.C.C. STAIRS • Reinforced concrete is perhaps the most suitable of all the said materials for the construction of stairs. • The various advantages of reinforced concrete stairs are given below - They have requisite fire resisting qualities to a great extent - They are durable strong pleasing in appearance and can beThey are durable, strong, pleasing in appearance and can be easily rendered non-slippery. - They can be designed for greater widths, longer spans and any heightheight. - They can be moulded in any desired form to suit the requirements of the architect. Th b il l d- They can be easily cleaned. - The cost of maintenance is almost nil. - They can be pre-cast or cast-in-situ.y p - To change their appearance, R.C.C. stairs can be covered/finished with thin slabs of stone, marble tiles or terrazzo finish.
- 2. DESIGN PRINCIPLE AND SUPPORT SYSTEM:DESIGN PRINCIPLE AND SUPPORT SYSTEM: • The choice of the type of stair to be adopted depends very much upon the size of the staircase hall and the loading conditionthe size of the staircase hall and the loading condition. • DIFFERENT STAIR ARRANGEMENT IN CASE OF R.C.C. • Single Straight Flight Stairs • Inclined Slab Stairs With Half Space Landings • String Beam Stairs • Crancked Slab Stairs• Crancked Slab Stairs • Cantilever Stairs • Spiral Stairsp
- 3. SINGLE STRAIGHT FLIGHT STAIRS: • Although simple in design and construction is notconstruction, is not popular because of the plan space it occupiesoccupies • The flight behaves as simply supported slab, spanning from landing to landing. • The effective span/total horizontal going is usually taken as landing d d b idi d d d b h l diedge to edge by providing a down stand edge beam to each landing. • If these edge beams are not provided, the effective span would betaken as overall of the landings, resulting in a considerably increased bending moment and hence more reinforcement.
- 4. INCLINED SLAB STAIRS WITH HALF SPACE LANDINGS:S C N NGS: (STAIR WITH SLAB SPANNING LONGITUDINALLY) • This type of stairs gives more compact plan layout and better i l i h h i l i hcirculation than the single straight flight stairs. • The half space or 180o turn landingp g is introduced at the midpoint of the total rise, giving equal flight spans, thus reducing the effective span andthus reducing the effective span and hence reducing bending moment considerably. I t d i th l di• In most designs, the landings span crosswise on to a load bearing wall or beam and the flights span from landing to landing.
- 5. • The point of intersection of the soffits to the flights with the landing soffits can be detailed in any of two ways:y y 1) INTERSECTION OF SOFFITS IN LINE, BUT NOSINGS OUTIN LINE, BUT NOSINGS OUT OF LINE IN THE PLAN: 2) INTERSECTION OF FLIGHTS2) INTERSECTION OF FLIGHTS AND LANDING SOFFITS ARE OUT OF LINE ON THE UNDERSIDE BUT THEUNDERSIDE, BUT THE NOSINGS IN LINE ON PLAN • i.e. first and last riser in i fli h i liconsecutive flights in line on
- 6. 1) INTERSECTION OF SOFFITS IN LINE, BUT NOSINGS OUT OF LINE IN THE PLAN: i.e. first and last riser in the consecutive flights are not in line
- 7. 2) INTERSECTION OF FLIGHTS AND LANDING SOFFITS ARE OUT OF LINE ON THE UNDERSIDE BUT THEARE OUT OF LINE ON THE UNDERSIDE, BUT THE NOSINGS IN LINE ON PLAN i.e. first and last riser in consecutive flights are in line
- 8. STRING BEAM STAIRS: (STAIR WITH SLAB SPANNING HORIZONTALLY) • In this category, the slab is supported on one side by side wall or stringer beam and on the otheror stringer beam and on the other side by a stringer beam • I.e. a string or edge beam is used to span from landing to landing toto span from landing to landing to resist bending moment with the steps spanning horizontally. I thi th i t l b i• In this case, the waist slab is thinner and an overall saving in the concrete volume required can be achieved but this saving inbe achieved, but this saving in material is usually offset by the extra formwork cost required for string beamstring beam. • The string beam can be either up stand or down stand in format and can be on both sides if stairs arecan be on both sides if stairs are free standing.
- 9. • Each step is designed as spanning horizontally with thespanning horizontally with the bending moment equal to wll/8, where w is the uniformly distributed load per unit area ondistributed load per unit area on the step, inclusive of the self weight. • Sometimes, for wider steps, a central string beam spanning between the end walls or column is provided on which the stairs slab is supported. • The waist slab is designed as• The waist slab is designed as slab cantilevering from both the sides of the string beam
- 10. CRANCKED SLAB STAIRS: • These stairs are very often used as avery often used as a special feature since the half space l di hlanding has no visible support being designed as a cantilever slab. • Bending, Buckling and torsion stresses are induced with this form of design creating the need for the reinforcement to both faces of the landing and the waist slablanding and the waist slab. • Hence the amount of reinforcement required is high which can sometimes create site problem with regards to placing and compacting th tthe concrete.
- 11. CANTILEVER STAIRS: • They are also called spine wall stairs.p • They consist of a central vertical wall from which the flights and halfthe flights and half space landings are cantilevered. Th ll id d f fi i t b t th fli ht d i• The wall provides a degree of fire resistance between the flights and is therefore used mainly for the escape stairs. • Since both flights and landings are cantilevered the reinforcement is placed in the top of the flight slab and in the upper surface of the landing to counteract the induced negative moment. • The plan arrangement can be a single straight flight or two flights with half• The plan arrangement can be a single straight flight or two flights with half space landings.
- 12. R.C.C.SPIRAL AND HELICAL STAIRS • Mainly used as accommodation stairs in the foyers of prestige buildings such as theatres, banks,buildings such as theatres, banks, commercial complexes etc. • Can be expensive to construct- normally at least seven times thenormally at least seven times the cost of conventional stairs. • The plan shape is generally based on a circle; it is also possible to designa circle; it is also possible to design an open spiral stair with an elliptical core, which is known as helical stairsstairs. • The spiral an be designed around a central large diameter circular column where the steps arecolumn, where the steps are cantilevered from that, or in case of helical stairs, can be designed as open circular well.open circular well.
- 13. • A large amount of steel reinforcement is used to resist the bending moment, shear force and torsional moment. • The continuous slab varies in thickness from top to bottom- less at top and increasing at the bottomat top and increasing at the bottom. • There are two or three sets of reinforcement with top and bottom layer in each: – Continuous bars running the length of the spirale gt o t e sp a – Cross or radial bars – Diagonal bars laid tangential in two directions to the inner curve.
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