DESIGN OF BASE PLATE. Tower Leg section ( D )
=
27.3 cm dia. Tube.
=
200 kg/cm2
=
8.15 kg/cm2
Grade of Base Plate Steel ( fy )
=
2548 kg/m2
Allowable bending stress ( fb, allow = 0.66 fy )
=
1681.68 kg/m2
Grade of concrete -M-20 ( f
ck
)
Bond stress of concrete tbd ( IS -456-1978)
FOUNDATION LOADS: Ultimate Compression ( Fuc )
=
71847 kg
Ultimate Tension ( Fut )
=
69346 kg
Ultimate shear ( X-dir ), Fsx
=
4748 kg
Ultimate shear ( Z-dir ), Fsz
=
4748 kg
Resultant shear per leg ( Fs )
=
6714.69 kg
Dia. Of foundation bolt ( d )
=
3.6 cm
No. of foundation bolts ( n )
=
Length of embeddment ( L )
=
100 cm
Bolt edge distance ( ed )
=
7 cm
Bolt to bolt distance ( g )
=
9 cm
Fs = Sqrt( Fsx2 + Fsz2 ) FOUNDATION BOLT DETAILS:
8 no.s
X Foundation bolt Base plate. 52.5 38.5 Stiffener C.G.line
15 3
X 7
52.5 Base plate
BASE PLATE DETAILS: Size of Base Plate ( B )
=
52.5
x
52.5
Thickness of Base Plate ( t )
=
Size of Stiffner
=
15
Permissible bearing stress in concrete 0.25 fck ( Clause 33.4 of IS-456-1978 )
=
50 kg/cm2
Bearing area provided ( A = B x B )
=
Max. bearing pressure on plate ( p = Fuc/A )
=
cm
3 cm x
1.2 cm
CHECK FOR BEARING PRESSURE:
2756.25 cm2 26.07 kg/cm2
<
50
kg/cm2
HENCE. O.K. CHECK FOR BENDING STRESS IN PLATE ( LEG IN COMPRESSION ) Max. bending moment about X-X ax is. M x-x
=
175190.4 kg-cm.
C.G. of Base plate & stiffner- section-X-X, x
=
Xmax.
=
15.58 cm
Moment of Inertia about the axis X-X. ( I xx )
=
1764.09 cm4
Section modulus, ( Z x-x (min) = Ix-x/Xmax )
=
113.23 cm3
Bending stress fb = Mx-x/Zx-x( min )
=
2.42 cm from bottom of base plate.
1547.21 kg/cm2
<
1681.68
<
1681.68
HENCE. SAFE. CHECK FOR BENDING STRESS IN PLATE ( LEG IN TENSION ): Max. bending moment about X-X, M x-x: Force in each bolt ( F = Fut / n )
=
8668.25 kg.
Distance of outer bolts to tube
=
5.6 cm
Max. moment, M x-x
=
97084.4 kg-cm.
Section modulus, Z x-x
=
113.23 cm3
Ultimate bending stress ( f )
=
857.4088 kg/cm2
HENCE. SAFE.
CHECK FOR STRESSES IN FOUNDATION BOLTS: Dia of foundation bolt, d
=
No. of foundation bolts, n
=
Gross area ( Ag )
=
10.18 cm2
Net area ( Anet )
=
8.65 cm2
Tension on each bolt
=
8668.25 kg
Shear on each bolt ( s )
=
839.34 kg
Calculated bolt stress in tension ( fbt,cal )
=
1002.11 kg/cm2
Calculated bolt stress in shear ( fbs,cal )
=
82.45 kg/cm2
Permssible bolt stress in axial tension( fbt) Clause 8.9.4.1, Table 8.1 of IS-800-1984
=
1223 kg/cm2
Permssible bolt stress in shear
=
815 kg/cm2
=
0.92 <
( fbs)
3.6 cm 8 no.s.
Interaction for combined bolt tension and shear: fbt, cal/fbt + fbs, cal/fbs
1
Hence bolts are o.k. Foundation bolt embeddment length( L )
=
100 cm
Bond strength of each bolt
=
9212.76 kg
>
Hence, provide embeddment length is o.k.
8668.25
DESIGN OF BASE PLATE. Tower Leg section ( D ) Grade of concrete -M-20 ( f
=
27.3 cm dia. Tube.
) ck
=
200 kg/cm2
Bond stress of concrete tbd ( IS -456-1978) Grade of Base Plate Steel ( fy )
=
8.15 kg/cm2
=
2548 kg/m2
Allowable bending stress ( fb, allow = 0.66 fy )
=
1681.68 kg/m2
FOUNDATION LOADS: Ultimate Compression ( Fuc ) Ultimate Tension ( Fut ) Ultimate shear ( X-dir ), Fsx Ultimate shear ( Z-dir ), Fsz Resultant shear per leg ( Fs ) Fs = Sqrt( F
2 sx
+F
2 sz
= = = = =
41339 44344 1271 1271
kg kg kg kg
1797.47 kg
)
FOUNDATION BOLT DETAILS: Dia. Of foundation bolt ( d ) No. of foundation bolts ( n ) Length of embeddment ( L ) Bolt edge distance ( ed ) Bolt to bolt distance ( g )
= = = = =
3 8 90 7 9
cm no.s cm cm cm
X Foundation bolt Base plate. 40 26 Stiffener C.G.line
15 2
X 7
40
BASE PLATE DETAILS: Size of Base Plate ( B ) Thickness of Base Plate ( t ) Size of Stiffner
= = =
40 x 40 cm 2 cm 15 x 1.2 cm
=
50 kg/cm2
CHECK FOR BEARING PRESSURE: Permissible bearing stress in concrete 0.25 fck ( Clause 33.4 of IS-456-1978 ) Bearing area provided ( A = B x B ) Max. bearing pressure on plate ( p = Fuc/A )
=
1600 cm2
=
25.84 kg/cm2
<
50
kg/cm2
HENCE. O.K. CHECK FOR BENDING STRESS IN PLATE ( LEG IN COMPRESSION ) Max. bending moment about X-X ax is. M x-x C.G. of Base plate & stiffner- section-X-X, x Xmax. Moment of Inertia about the axis X-X. ( I xx ) Section modulus, ( Z x-x (min) = Ix-x/Xmax ) Bending stress fb = Mx-x/Zx-x( min )
= = = = = =
132300.8 2.56 14.44 1425.8 98.74 1339.89
kg-cm. cm from bottom of base plate. cm cm4 cm3 kg/cm2 < 1681.68
HENCE. SAFE. CHECK FOR BENDING STRESS IN PLATE ( LEG IN TENSION ): Max. bending moment about X-X, M x-x: Force in each bolt ( F = Fut / n ) Distance of outer bolts to tube Max. moment, M x-x Section modulus, Z x-x Ultimate bending stress ( f )
= = = = =
5543 -0.65 -7205.9 98.74 -72.97853
kg. cm kg-cm. cm3 kg/cm2
<
1681.68
HENCE. SAFE. CHECK FOR STRESSES IN FOUNDATION BOLTS: Dia of foundation bolt, d No. of foundation bolts, n Gross area ( Ag ) Net area ( Anet ) Tension on each bolt Shear on each bolt ( s ) Calculated bolt stress in tension ( fbt,cal ) Calculated bolt stress in shear ( fbs,cal ) Permssible bolt stress in axial tension( fbt) Clause 8.9.4.1, Table 8.1 of IS-800-1984 Permssible bolt stress in shear ( fbs) Interaction for combined bolt tension and shear: fbt, cal/fbt + fbs, cal/fbs
= = = = = = = = =
3 cm 8 no.s. 7.07 cm2 6.01 5543 224.68 922.3 31.78 1223
cm2 kg kg kg/cm2 kg/cm2 kg/cm2
=
815 kg/cm2
=
0.79 <
1
Hence bolts are o.k. Foundation bolt embeddment length( L ) Bond strength of each bolt
= =
90 cm 6909.57 kg >
Hence, provided embeddment length is o.k.
5543
