DESIGN OF DOG-LEGGED STAIR pkn
Name of work :1
Stair hall measure
2.50
2
Available verical space between floor
3.00
m
3000
mm
3
Horizontal Span of stair case
1.20
mtr
1200
mm
4
Risers
0.15
mtr
150
mm
5
Treads
0.25
mtr
250
mm
6
Conrete
M-
20
scbc
7
fy
x
5.00
wt. of concrete N/mm
2
25000
m
3
N/m
m
13.33
sst
230
N/mm
30
mm
2
7
Steel
8
Nomi Nomin nal cover ver
25
Effective cover
Reinforcement Main Bottom slab
10
mm F bars
100
Anchor bars (Bottom )
8
mm F bars
2
Strirrups
8
mm F bars
270
415
10 mm f
200 mm c/c
2050 17 5 0
120 0
1 50
1 .2 0 250
1200 10 mm f
100 mm c/c
3 .0 0
15 0 8 mm f
270 mm c/c
250
1.80 10 mm f 18 0
200 mm c/c
mm
1050
1 05 0
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2.75
120 0
mm c/c Nos. mm c/c
DESIGN OF DOG-LEGGED STAIR Name of work :pkn Stair hall measure Available verical space between floor Horizontal Span of stair case Risers Treads Concrete Steel Nominal cover
2.50 3.00 1.20 0.15 0.25 M- 20 7 cbc fy- 415 25
x m m m m
5.00 1200 150 250 wt. of concrete m
mm mm mm 2 25000 N/mm 13.33 230 N/mm st Effective cover 30 mm
N/mm mm
1 Genral arrngment:- Fig. shows plan of stair hall. Height of 1 flight. = 3.00 / 2 No. of risers required = 1.80 / 0.15 No. of treads required = 12 1 Spce occupied by treads = 11 x 0.25 Keep width of landing equal to \ Space left for passage st Height of 1 flight. = 1.20 m No. of risers required = 1.20 / 0.15 No. of treads required = 8 1 Spce occupied by treads = 7 x 0.25 Keep width of top landing st
= = = = = =
1.50 12 11 2.75 1.20 1.05
m minimum 1.8 st No. in 1 flight. No. in 1st flight. m m m
= = = =
8 No. in 2 flight. 7 No. in 2nd flight. 1.75 m m
m which is heigher
nd
2 Design Constants:- For HYSD Bars Cocrete M = 20 2 2 sst = 230 N/mm wt. of concrete = 25000 N/mm 3 scbc = N/mm 7 m = 13.33 13.33 m*c x 7 k= = = 0.289 13.33 x m*c+sst 7 + 230 j =1-k/3 R =1/2xc x j x k
= =
1
-
0.289
/
3
0.5
x
7
x
0.904
=
0.904
x 0.289 =
0.913
3 Loading Each Flight :- The landing slab is assume to span in the same direction as stair, and is considered as acting together to form a single slab. Let the bearing of landing slab in wall be = 160 mm The effective span =
2.75 +
Let the thickness of waist slab '= \Weight of slab w' on slope =
1.20 +(
0.16 /
5.00 x 0.2 x
40 1
Dead weight of horizontal area w1= w' x 1 2 Total Dead weight per meter run Weight of fiishing etc. Live load 2
Dead weight of step is w
\
=
x
2
2
)'= 4.03 m
x
1
x
=
5000
x
x
####
2
R +T T 150 1000
say
25000 150 2+ 250 250
=
4.00
m
= =
200 5000
mm N/m2
5831
N/m
1875
N/m
2
=
=
2
= 7706 N = 100 N = 2500 N Total weight = 10306 N 8431 will not come on it. However, Note. The load w on the landing portion will be 10306 - 1875 = a uniform value of w has been adopted here.
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4 Design of waist slab :- B.M.
=
Effective depth required But available = 5 Reinforcement:- Ast =
=
150
+
BM x 100 sst x j x D
=
10 mm F bars
using
Nomber of Bars
=
Spacing Hence used =
Distribution steel using
8
Hence used
= 8
= =
10306 x 8
4.00
20612000
0.913 x Rxb 2x cover = 25
1000
2
= 20612 = =
150
mm
175
mm
say =
20612000 = 659.91 mm2 230 x 0.904 x 150 2 3.14xdia 3.14 x 10 x 10 A = = 4 x100 4 x 100 660 x 1.20 = 11 No 78.50 1200 / 11 = 109 mm c/c F mm bars = 100 mm c/c 0.12
mm F bars
Spacing
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= 10
wl2 8
x
150 x 100 3.14xdia2 A = 4 x100 50 x 1000 180.31 mm F bars =
1000
= = =
180 3.14 x 4 279
270 mm c/c
mm 8 x
N-m
180 mm
=
79
mm
2
=
50
mm
2
2
x 8 100
mm c/c
DESIGN OF DOG-LEGGED STAIR
2.50
1.20
UP 5.00
2.75
1.05
1.20 11 10 8 mm F 270
9 8
7 #### mm F ####
6 250
5 150
4 3 2 1 Foor level
2.75
1.20
1.05
2050 1750
1200
150
1.20 250 1200
10 mm f
100 mm c/c
8 mm f
270 mm c/c
3.00
0 0 180
mm 1.80
1050 1050
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2.75
1200
2050 1750
1200
150
1.20 250 1200
10 mm f
100 mm c/c
8 mm f
270 mm c/c
3.00
0 0 180
mm 1.80
1050 1050
1200
2.75
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VALUES OF DESIGN CONSTANTS Grade of concrete Modular Ratio
M-15 18.67
M-20 13.33
M-25 10.98
M-30 9.33
M-35 8.11
M-40 7.18
scbc N/mm2 m scbc
5
7
8.5
10
11.5
13
93.33
93.33
93.33
93.33
93.33
93.33
kc
0.4
0.4
0.4
0.4
0.4
0.4
jc
0.867
0.867
0.867
0.867
0.867
0.867
Rc
0.867
1.214
1.474
1.734
1.994
2.254
Pc (%)
0.714
1
1.214
1.429
1.643
1.857
kc
0.329
0.329
0.329
0.329
0.329
0.329
jc
0.89
0.89
0.89
0.89
0.89
Rc
0.89 0.732
1.025
1.244
1.464
1.684
1.903
Pc (%)
0.433
0.606
0.736
0.866
0.997
1.127
kc
0.289
0.289
0.289
0.289
0.289
0.289
j
0 904
0 904
0 904
0 904
0 904
0 904
(a) sst = 140 N/mm2 (Fe 250) (b) sst = 190 N/mm2 (c ) sst =
VALUES OF DESIGN CONSTANTS Grade of concrete Modular Ratio
M-15 18.67
M-20 13.33
M-25 10.98
M-30 9.33
M-35 8.11
M-40 7.18
scbc N/mm2 m scbc
5
7
8.5
10
11.5
13
93.33
93.33
93.33
93.33
93.33
93.33
kc
0.4
0.4
0.4
0.4
0.4
0.4
jc
0.867
0.867
0.867
0.867
0.867
0.867
Rc
0.867
1.214
1.474
1.734
1.994
2.254
Pc (%)
0.714
1
1.214
1.429
1.643
1.857
kc
0.329
0.329
0.329
0.329
0.329
0.329
jc
0.89
0.89
0.89
0.89
0.89
Rc
0.89 0.732
1.025
1.244
1.464
1.684
1.903
Pc (%)
0.433
0.606
0.736
0.866
0.997
1.127
kc
0.289
0.289
0.289
0.289
0.289
0.289
jc
0.904
0.904
0.904
0.904
0.904
0.904
Rc
0.653
0.914
1.11
1.306
1.502
1.698
Pc (%)
0.314
0.44
0.534
0.628
0.722
0.816
kc
0.253
0.253
0.253
0.253
0.253
0.253
jc
0.916
0.916
0.916
0.914
0.916
0.916
Rc
0.579
0.811
0.985
1.159
1.332
1.506
Pc (%)
0.23
0.322
0.391
0.46
0.53
0.599
(a) sst = 140 N/mm2 (Fe 250) (b) sst = 190 N/mm2 (c ) sst = 230 N/mm2 (Fe 415) (d) sst = 275 N/mm2 (Fe 500)
Permissible shear stress Table 100A s bd < 0.15 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 and above
v
in concrete (IS : 456-2000)
Permissible shear stress in concrete tv N/mm M-15 M-20 M-25 M-30 M-35 0.18 0.22 0.29 0.34 0.37 0.40 0.42 0.44 0.44 0.44 0.44 0.44 0.44
0.18 0.22 0.30 0.35 0.39 0.42 0.45 0.47 0.49 0.51 0.51 0.51 0.51
0.19 0.23 0.31 0.36 0.40 0.44 0.46 0.49 0.51 0.53 0.55 0.56 0.57
0.2 0.23 0.31 0.37 0.41 0.45 0.48 0.50 0.53 0.55 0.57 0.58 0.6
0.2 0.23 0.31 0.37 0.42 0.45 0.49 0.52 0.54 0.56 0.58 0.60 0.62
2
M-40 0.2 0.23 0.32 0.38 0.42 0.46 0.49 0.52 0.55 0.57 0.60 0.62 0.63
Maximum shear stress tc.max in concrete (IS : 456-2000) Grade of concrete
tc.max
M-15 1.6
M-20 1.8
M-25 1.9
M-30 2.2
M-35 2.3
M-40 2.5
Permissible Bond stress Table rade of concret tbd (N / mm2)
M-10 --
M-15 0.6
M-20 0.8
M-25 0.9
bd
in concrete (IS : 456-2000) M-30 1
M-35 1.1
M-40 1.2
M-45 1.3
Development Length in tension Plain M.S. Bars
H.Y.S.D. Bars
Grade of concrete
tbd (N / mm2)
kd = Ld F
tbd (N / mm2)
kd = Ld F
M 15
0.6
58
0.96
60
M 20
0.8
44
1.28
45
M 25
0.9
39
1.44
40
M 30
1
35
1.6
36
M 35
1.1
32
1.76
33
M 40
1.2
29
1.92
30
M 45
1.3
27
2.08
28
M 50
1.4
25
2.24
26
Permissible stress in concrete (IS : 456-2000) Grade of concrete M M M M M M M M M
10 15 20 25 30 35 40 45 50
2 Permission stress in compression (N/mm ) Permissible stress in bond (Average) for 2 Bending acbc plain bars in tention (N/mm ) Direct (acc)
(N/mm2) 3.0 5.0 7.0 8.5 10.0 11.5 13.0 14.5 16.0
2
Kg/m 300 500 700 850 1000 1150 1300 1450 1600
(N/mm2) 2.5 4.0 5.0 6.0 8.0 9.0 10.0 11.0 12.0
2
Kg/m 250 400 500 600 800 900 1000 1100 1200
(N/mm2) -0.6 0.8 0.9 1.0 1.1 1.2 1.3 1.4
in kg/m -60 80 90 100 110 120 130 140
2
M-50 1.4
