3. R.C.C. STAIRS

• Reinforced concrete is perhaps the most suitable of all the saidmaterials 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 terrazzofinish.

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

SINGLE STRAIGHT FLIGHT STAIRS:

• Although simple indesign andconstruction is notconstruction, is notpopular because ofthe plan space itoccupiesoccupies

• The flight behavesas simply supportedslab, spanning fromlanding to landing.

• The effective span/total horizontal going is usually taken as landingd 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 betakenas overall of the landings, resulting in a considerably increasedbending moment and hence more reinforcement.

INCLINED SLAB STAIRS WITH HALF SPACE LANDINGS:S C N NGS:

(STAIR WITH SLAB SPANNING LONGITUDINALLY)

• This type of stairs gives morecompact plan layout and betteri 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 thetotal rise, giving equal flight spans,thus reducing the effective span andthus reducing the effective span andhence reducing bending momentconsiderably.I t d i th l di• In most designs, the landings spancrosswise on to a load bearing wallor beam and the flights span fromlanding to landing.

• The point of intersection of thesoffits to the flights with thelanding soffits can be detailedin any of two ways:y y

1) INTERSECTION OF SOFFITSIN LINE, BUT NOSINGS OUTIN LINE, BUT NOSINGS OUTOF LINE IN THE PLAN:

2) INTERSECTION OF FLIGHTS2) INTERSECTION OF FLIGHTSAND LANDING SOFFITS AREOUT OF LINE ON THEUNDERSIDE BUT THEUNDERSIDE, BUT THENOSINGS IN LINE ON PLAN

• i.e. first and last riser ini fli h i liconsecutive flights in line on

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

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

STRING BEAM STAIRS:(STAIR WITH SLAB SPANNING HORIZONTALLY)

• In this category, the slab issupported on one side by side wallor stringer beam and on the otheror stringer beam and on the otherside by a stringer beam

• I.e. a string or edge beam is usedto span from landing to landing toto span from landing to landing toresist bending moment with thesteps spanning horizontally.I thi th i t l b i• In this case, the waist slab isthinner and an overall saving inthe concrete volume required canbe achieved but this saving inbe achieved, but this saving inmaterial is usually offset by theextra formwork cost required forstring beamstring beam.

• The string beam can be either upstand or down stand in format andcan be on both sides if stairs arecan be on both sides if stairs arefree standing.

• Each step is designed asspanning horizontally with thespanning horizontally with thebending moment equal to wll/8,where w is the uniformlydistributed load per unit area ondistributed load per unit area onthe step, inclusive of the selfweight.

• Sometimes, for wider steps, acentral string beam spanningbetween the end walls orcolumn is provided on whichthe stairs slab is supported.

• The waist slab is designed as• The waist slab is designed asslab cantilevering from both thesides of the string beam

CRANCKED SLAB STAIRS:

• These stairs arevery often used as avery often used as aspecial feature sincethe half spacel di hlanding has novisible supportbeing designed as acantilever slab.

• Bending, Buckling and torsion stresses are induced with this form ofdesign creating the need for the reinforcement to both faces of thelanding and the waist slablanding and the waist slab.

• Hence the amount of reinforcement required is high which cansometimes create site problem with regards to placing and compactingth tthe concrete.

CANTILEVER STAIRS:

• They are also calledspine wall stairs.p

• They consist of a centralvertical wall from whichthe flights and halfthe flights and halfspace landings arecantilevered.

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 istherefore used mainly for the escape stairs.

• Since both flights and landings are cantilevered the reinforcement is placedin the top of the flight slab and in the upper surface of the landing tocounteract 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 halfspace landings.

R.C.C.SPIRAL AND HELICAL STAIRS

• Mainly used as accommodationstairs in the foyers of prestigebuildings 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 thecost of conventional stairs.

• The plan shape is generally based ona circle; it is also possible to designa circle; it is also possible to designan open spiral stair with an ellipticalcore, which is known as helicalstairsstairs.

• The spiral an be designed around acentral large diameter circularcolumn where the steps arecolumn, where the steps arecantilevered from that, or in case ofhelical stairs, can be designed asopen circular well.open circular well.

• A large amount of steelreinforcement is used to resist thebending moment, shear force andtorsional moment.

• The continuous slab varies inthickness from top to bottom- lessat top and increasing at the bottomat top and increasing at the bottom.

• There are two or three sets ofreinforcement with top and bottomlayer 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 innercurve.

Th k YThank You