DESIGN OF STAIRCASE

Diagram showing support condition

Data and calculations• Height between floor=2.79 m

• Tread=250 mm

• Riser=155 mm

• Width of staircase=1000 mm =1 m

• Number of riser =2790/155 =18 nos.

Continued…

• So givingFirst flight: 8 tread and 9 riserSecond flight: 8 tread and 9 riser

• Height of landing = 9155 =1395 mm =1.395m

Continued…

• Then effective span will be provided as =going span +x+y;

l=2+x+y

l=2+0.45+0.3675

l=2.82 m (since: x<1m and y<1m.)

Based upon IS 456:2000 code specification

• Minimum reinforcement for HYSD bar =0.12%

• For pt =0.12%.

• Modification factor for tension reinforcement =1.25

• Taking (span/depth) ratio 32.

• l/d =32.

• d=2820/32 =88.125 mm

• Clear cover = 15 mm;

• Steel diameter =10 mm.

Continued..

• Total depth of waist =88.125+15+10/2 =108.125 mm

• Provide total depth = 110 mm.

• B=

= 0.294m

LOAD CALCULATION: Load on landing:

Live load =3 KN/m2.Finishing load=1 KN/m2.

Dead load =250.11=2.75 KN/m2

Total load on landing = 6.75 KN/m2.(not factored)

Load on going:Live load =3 KN/m2.

Finishing load=1 KN/m2

Dead load = (WB+ 0.5RT)25/T ; (refer diag.) =(0.1100.294+0.50.1550.25)25/0.25;

=5.1715 KN/m2;Total load on going =9.1715 KN/m2 (not factored)

Loading diagram

MB=0 RA2.82 - 10.1250.37(0.370.5+2.45) - 13.75721.45 - 10.1250.50.452=0

RA=18.0112 KN

RA+RB = 35.8165 KN RB=17.805 KN

MX=17.805X – 10.1250.37(X-0.370.5) -13.757(X-0.37)2 0.5dM/dx =0

x=1.39166 mhence MX=13.073 KNm/m

Mu/bd2 =(13.07106)/(1000852)=1.809

Using SP 16 From table 1; for M20 and fy=415 N/mm2

Pt =0.565 %Pt = Ast =(0.565100085)/100 =480.25 mm2/m

Spacing = 160 mmASt min= 0.121000110/100=132 mm2/m

Take distribution bar: 8mm dia.

Spacing =(100064)/(4132) =380 mm

Primary bar spacing check:Smax =3d (or) 300 mm

=255 mmWe have , spacing = 160 mm< 255 mm -ok

Secondary bar spacing check:Smax =5d (or) 450 mm

=425 mmSo provide spacing = 380 mm

Detailing of staircase: