CHAPTER 6 - STAIRCASE
DEFINITION
ď ą a series of steps arranged for the purpose of connecting different floors of building. ď ą
may be made from various materials e.g timber, stone, bricks, steel, plain or reinforced concrete
FUNCTION
ď ą to provide for the movement of people from one floor level to another. ď ą To provide a suitable means of escape in case of fire.
Requirements of a good staircase
ď ą A well-planned staircase should provide : o
o
Easy and quick mode of communication Safe mode of communication
Anatomy of a Staircase
Steps – the portion comprising the tread and riser Tread – horizontal upper part of the step Riser – vertical portion of a step Flight – series of step without any platform or landing Landing – a platform provided between 2 flights for the purpose of 1. Point of rest 2. Means of turn Nosing – the outer projecting edge of tread either square or round Winders – tapering steps which are provided for changing direction of stairs (Uniform Building By-Law -UBBL 109) Going – horizontal distance between steps and landings Soffit – under surface of a stair
Anatomy of a Staircase Line of nosing – imaginary line touching the nosings of each tread Pitch / slope – the angle which the line of nosing of stairs makes with the horizontal Handrails – provided to assist in negotiating a stairway Baluster – vertical member supporting a hand rail Balustrade – consist of row of balusters surmounted by a rail provided to perform the function of a fence / guard Headroom – clear vertical distance between tread and soffit of flight or ceiling of landing
Anatomy of a Staircase
Reinforced Concrete Staircase
ď ą Reinforced concrete staircase predominates stairs made from other materials. ď ą This is due to the various advantages: o Can be mould to any desired form o Fire resisting qualities o Can be designed for greater width / span o Easily cleaned o Cost of maintenance is nil
Reinforced Concrete Staircase construction Mild steel or high yield are used as reinforcement. Handrails and balustrades must be of noncombustible material, continuous and on both sides, if width exceeds 1200mm Height of handrail – between 825 – 900mm (Uniform Building By-Law -UBBL 107)
Handrails and Balustrades
Types of Structure
String Beam stairs
Cranked Slab Stairs
Cantilever Stairs
Inclined Slab stairs
Spiral Staircase
Continuous slab
String Beam Stairs
String or edge beam used to span landing to landing Results in thinner waist dimension saving in concrete volume required but more cost on extra formwork. If stairs are free standing, string beam can either be upstand or downstand
Cranked Slab Stairs  Often used as special feature since half landing has no visible support.  Need to reinforced both surfaces of landing and slab thus creating site problems regarding placing and compacting the concrete.  Also known as continuous stair or scissor stair or jack knife stair
Cantilever Slab Sometimes called spine wall stairs Consist of central vertical wall from which flights and landing are cantilevered. Wall provides fire resistance between flights , therefore used for fire escape. Plan arrangements can be a flight or two equal flights.
Inclined Slab  Landing span from well edge to load bearing wall  Stair flights span from floor to landing and from landing to floor
Continuous Slab Stairs
There are two types of stair flights, classified on the direction of span. Transverse: the steps may be supported on both sides or may be cantilevered from an adjacent wall Longitudinal: the stairs flight spans onto landings or beam at either end of the stair flight
Spiral Slab Considered to be aesthetically pleasing but are expensive to construct. Can be defined as those describing a helix around a central column whereas a helical a helical stair has an open well. Open well helical stair is usually circular or elliptical in plan.
Types of Staircase
Dogged Leg
Bifurcated Quarter turn Geometrical
Dogged Leg (open well)
Dogged Leg (close well)
Bifurcated
Bifurcated
Quarter turn 2 or 3 flights of stairs with a 90 degrees turn at landing. Primarily linear in nature with one long flight or it may have equal flights May also be extended with short flights between corner landings. When insufficient space is available for a normal quarter turn, landing may be omitted and replaced by winder stair , though are not popular as it is hazardous due to minimal foothold at the turn
Quarter turn
Geometrical The plan shape is generally based on a circle Occupies a minimum amount of space in plan and generally used in residential buildings, hotels or in low traffic areas. It is not acceptable for fire exit stairs
Geometrical
Dimensions Riser : 150-180mm & Tread: 255mm for normal staircase. DOMESTIC: 150mm (6”) for riser & 255mm (10”) for tread. Riser: 180mm max Tread: 255mm min for exit staircase (in case of fire) - (Uniform Building By-Law -UBBL 106) Max 16 nos. of riser per flight Min width of landing shall be same width of flight. DOMESTIC: 1100mm (3’ 7”) Min width of landing for straight flight staircase is 1800mm (6’ 0”)
QUIZ 2 storey bungalow has a floor to floor height of 3000 mm. Propose type of staircase & determine the following:
Number & size of risers Number & size of treads Size of landing Length of flight
ANSWER TYPE: DOGGED LEG STAIRCASE Size of RISER = 150mm(domestic) 3000 mm divided by 150 = 20 RISERS ( 2 Flights ) (1 Flight = 10 Risers) Formula – In 1 flight, the number of tread will always be 1 less than the number of riser. Nos. of TREAD = 18 (9 nos. per flight) Size of TREAD = 255mm Size of landing = width of flight = MIN. 1100mm Length of flight = 9 x 255mm = 2295mm