DESIGN OF  STAIR CASE

Vertical distance between two floors= 3.2 m
Assuming two flights
Height  Of each  flights= 3.2/2 = 1.6m
Clear Width Of each Step=1500mm
Rise  Of  each Step =150mm
No  of  rise/flight=12
Going of each flight=12×230 = 2760mm
Width of Support=230mm

SPAN OF STAIR CASE:
Clear Span=6m
Effective Span=6000+230 =6230mm

DESIGN OF FLIGHT:
Bearing of the flight  = 150mm
Effective horizontal Span=6.075m

THICKNESS OF SLAB:
Considering 50mm Per m of Span
1.6×50=300mm
3.Finish=50×24=1200 N/m2 = 6950N/m2
( R2+T2)/T)×L
Waist slab&ceiling finish =8.300N/M

MOMENT AND REACTION:
RA=50.19KN & RB=50.30KN
Moment @3.0M
50.3×3.0-(8.5×0.5×0.32)+(12.52×1×1.10)+(30.26×0.720)
M  =95.68KNM
Mu=Mu  limit
95.68 6  =0.138×20×1000×d2
d  =186.18mm<200mm

TO GET AST:
Ast         = 50×(1-1√1-(4.6/20)×(95.68×106/1000×2002))/(415/20))
=1.12%
Ast         =1.12/100×1000×200 = 2240mm
No .of 16mm dia bars = 2240/(3.14(16)2/4) = 11 bars
DISTRIBUTION BARS
(0.12/100)×1000×200 =240mm2
Spacing of 6mm dia bars =(3.14(6)2/4)240×1000=120mmc/c
Provide 6 mm dia @ 120mmc/c as distribution steel

DESIGN OF LANDING:
Reaction from flight = Rb×1.5-(8,5×0.5)×0.5+(12.52×1) ×0.5
=68KNM
Mu  =  Mu limit
68×106 = 0.138×20×1000×d2
d  =  157 < 200mm
Ast  =  50×(1-1√1-(4.6/20)×(68×106/1000×2002))/(415/20))
=0.8%
Ast =0.8/100×1000×200=1600mm2
Spacing of 12 mm dia bars =(3.14(12)2/4)1600×1000= 70mm
Provide 12 mm dia @ 70mmc/c   on  landing  