IsolatedFdn-1_BS8110

http://www.civildesignhelp.info Design Code BS 8110

Foundation for Pipe Support

MATERIAL DATA:Grade of Concrete Fck = 30 N/mm2

Yield Strength of reinforcement = 460 N/mm2

Dia of Reinforcement in direction of L = 12 mmDia of Reinforcement in direction of B = 12 mmClear Cover to Reinforcement = 75 mmUnit Weight of Concrete 24 KN/m3

Unit Weght of Soil = 18 KN/m3

Unit Weight of Backfill = 18 KN/m3

Net allowable bearing pressure = 200 KN/m2

Internal angle of friction of soil = 34 O

Angle of friction between conc and soil = 23 O

Factor of safety against overturning = 1,75 (1.4 for Test/ Erection case)Factor of safety against sliding = 1,75Depth of Water table from Ground = 10 m

GEOMETRICAL DATA :

(Water Table)

Width of Footing B = 1,80 m Width of Pedestal CB = 0,50 mLength of Footing L = 1,80 m Length of Pedestal CL = 0,50 m

Total height of Pedestal = 1,30 m Depth of Footing, D = 0,40 mProjection of pedestal above ground = 0,3 m

X

Y

Z

CL

CB B

L

FY

FX

FZ

H

D

L

Isolated FootingPrepd. by: Shanti Srinivasanemail:[email protected]

Page 1 of 8 Output Date :05/02/2016


LOAD DATA (a) Load for Stability (f = 1.0 )

LOAD COMBINATION

JOINT FY FX FZ MX MZ

MAX 159,2 25,1 3,88 0 0

(b) Ultimate load combination for concrete design. LOAD COMBINATION


MAX 191,03 30,13 4,67 0 0

(c) Load combination for bearing pressure check:. LOAD COMBINATION


MAX 1 159,2 25,1 3,88 0 0

1. CHECK FOR STABILITY AGAINST SLIDING AND OVERTURNING(a) Sliding in X direction:

Sliding force in X direction = FX = 25,1 KNResisting frictional force = Ptan = 106,94 KNP= FY+Footing weight + Pedestal weight +Soil weight- BF = 251,92 kNF.O.S. against sliding in X dir = 4,26

O.K. as value greater than permissible value(b) Sliding in Z direction:

Sliding force in Z direction = FZ = 3,88 KNResisting frictional force = Ptan = 106,94 KNP= FY+Footing weight + Pedestal weight+Soil weight -BF= 251,92 KNF.O.S. against sliding in Z dir = 27,56

O.K. as value greater than permissible value(c) Overturning about Z

Forces acting at bottom of footing about ZFY = 159,20 KNMZtot = (MZ +FX*(D+H)) = 42,67 KN-mSelf Weight of Foundation = 31,104 KNWeight of Pedestal = 7,80 KNWeight of Backfill = 53,82 KNBuoyancy force = 0,00 KN

0,3 Taking moment about POverturning moment due to Tension =

1,00 0,00 KN-mOverturning moment = MZtot =

42,67 KN-m

0,9

P




Total overturning moment 42,67 KN-mRestoring Moment 226,73 KN-m

Factor of safity against overturning = restoring mom/overturning mom = 5,31O.K. , As value is greater than 1.75

(d) Overturning about XForces acting at bottom of footing about XFY = 159,20 KNMXtot = (MX +FZ*(D+H)) = 6,60 KN-mSelf Weight of Foundation = 31,104 KNWeight of Pedestal = 7,80 KNWeight of Backfill = 53,82 KNBuoyancy force = 0,00 KN

0,31,00 Taking moment about P

Overturning moment due to Tension =

0 Kn-m

Overturning Moment = MXtot

0,9 6,60 KN-m

Total overturning moment = 6,60 KN-mRestoring Moment = 226,73 KN-m

Factor of safety against Overturning = Restoring Moment/Over turning Moment =34,37 HENCE O.K. , As value is greater than 1.75

P




2. CHECK FOR NET BEARING PRESSURE

Gross vertical load PY = FY+ Weight of Footing including pedestal+ Weight of B/F 251,92 KN

Total Moment about X = MXtot =MX+ FZ(H+D) 6,60 KN-m

Total Moment about Z = MZtot =MZ+ FX(H+D) 42,67 KN-m

ex = MZtot/PY = 0,17 M e<L/6, No Tension in footing.

ez = MXtot/PY = 0,03 M e<L/6, No Tension in Footing.

Gross pressure distribution underfooting is given by:

q =

= 128,44 40,64 114,87 27,07 Kn/m2 p3p1 p2 p3 p4 +Mx

Mx(If there is negative gross pressure then it will be corrected using Teng's Chart) p2 Mz p1ex/L = 0,09 ez/B = 0,01

Sign ConventionFrom Teng's chart value of k = 1,652 x = - y = -

Maximum Gross Pressure = K*P/BL = 128,44 KN/m2

Net pressure intensities under the footing is given by:p1net = 103,24 KN/m2

p3net = 89,67 KN/m2

p2net = 15,44 KN/m2p4net = 1,87 KN/m2

Maximum net pressure intensity = 103,24 KN/m2 O.K. Less than allowable bearing pressure

p4

)B

e6

L

e6 1(

LB

PZxY




3. CHECK FOR MOMENT AND SHEAR

Net pressure generated below footing due to design load.

Gross vertical load PY = FY+ Weight of Footing including pedestal+ Weight of B/F 283,75 KN


Total Moment about Z = MZtot =MZ+ FX(H+D) 51,22 KN-m

ex = MZtot/PY = 0,18 M e<L/6, No Tension in footing.

ez = MXtot/PY = 0,03 M e<B/6, No Tension in Footing.

Gross pressure distribution underfooting is given by:

q =

= 148,44 43,05 132,11 26,71 Kn/m2 p3p1 p2 p3 p4 +Mx

Mx(If there is negative gross pressure then it will be corrected using Teng's Chart) p2 Mz p1ex/L = 0,10 ez/B = 0,02

Sign ConventionFrom Teng's chart value of k = 1,695 x = - y = -

Maximum Gross Pressure = K*P/BL = 148,44 KN/m2

Net pressure intensities under the footing is given by:p1net = 123,24 KN/m2

p3net = 106,91 KN/m2

p2net = 17,85 KN/m2p4net = 1,51 KN/m2

Maximum net pressure intensity = 123,24 KN/m2

p4

)B

e6

L

e6 1(

LB

PZxY




(a) Check for Moment and One way Shear in X direction

p2 =17,85 122,5 p1 =

85,18 103,86 123,24 ( d= D-75-6 319 mm )

Moment at the Critical section 1: 23,36 KN-m/m Width of Footing.Shear at critical section 1: 121,93 KNShear at critical section 2: 67,66 KNShear at critical section 3: 2,65 KN

Tensile Reinforcement:K= M/fcubd2 = 0,00765 < 0.156z= d[0.5+(0.25-k/0.9)] = 316,26 mm0.95*d = 303,05 mmHence z = 303,05 mmAst = M/0.95fyz = 176,36 mm2/m

Minmum Reinforcement 0.13% = 520,00 mm2/mReqd. Spacing of 12 mm dia bar = 218 mmProvided Spacing = 200 mm Ast,provided 565 mm2/m

Design Concrete shear stress c = 0,399 N/mm2

Section 1 Ultimate shear stress v1 = 0,212 N/mm2

Maximum allowed 0.8fcu = 4,382 N/mm2 O.K. (Clause 3.7.7.2)


Maximum allowed 1.5c = 0,599 N/mm2 O.K. (Clause 3.7.7.4)


Maximum allowed c = 0,399 N/mm2 O.K.

d d

1 2 3

1 2 3

CRITICAL SECTIONS FOR MOMENT AND SHEAR.

FACTORED PRESSURE DISTRIBUTION AT SALIENT POINTS




(b) Check for Moment and One way Shear in Z direction

p3 = 123,14

106,91 p1 = ( d= D-75-12-6 307 mm )117,34 120,13 123,24

Moment at the Critical section 1: 25,62 KN-m/m Width of Footing.Shear at critical section 1: 140,74 KNShear at critical section 2: 75,13 KNShear at critical section 3: 7,98 KN

Tensile Reinforcement:K= M/fcubd2 = 0,009061 <0.156z= d[0.5+(0.25-k/0.9)] = 303,88 mm0.95*d = 291,65 mmHence z = 291,65 mmAst = M/0.95fyz = 201,02 mm2/m

Minmum Reinforcement 0.13% = 520,00 mm2/mReqd. Spacing of 12 mm dia bar = 218 mmProvided Spacing = 200 mm Ast,provided 565 mm2/m

Design Concrete shear stress c = 0,384 N/mm2

Section 1 Ultimate shear stress v 1 = 0,255 N/mm2

Maximum allowed 0.8fcu = 4,382 N/mm2 O.K. (Clause 3.7.7.2)


Maximum allowed 1.5c = 0,576 N/mm2 O.K. (Clause 3.7.7.4)


Maximum allowed c = 0,384 N/mm2 Hence O.K.

d

d

1

2

3

1 2 3

FACTORED PRESSURE DISTRIBUTION AT SALIENT POINTS CRITICAL SECTIONS FOR MOMENT AND SHEAR.

d

d

1

2

3

1 2 3

FACTORED PRESSURE DISTRIBUTION AT SALIENT POINTS CRITICAL SECTIONS FOR MOMENT AND SHEAR.




(c) Check for Punching Shear

d = average of effective depth in two directions = 313 mm

U0 = 2(CB+CL) = 2000 mm

U1 =U0 +12d = 5756 mm

Maximum ultimate Vertical load on column FY = 191,03 KN

Ultimate shear stress for U0 = 0,3052 N/mm2

Maximum allowed 0.8fcu = 4,382 N/mm2 O.K.

Ultimate shear stress for U1 = 0,106 N/mm2

Maximum allowed c = 0,384 N/mm2 O.K.

(d) Design for PedestalPU = 191,03 KN


Total Moment about Z = MZtot =MZ+ FX(H+D) 51,22 KN-mHeight of Pedestal = 1,30 mWidth of Pedestal in X direction (CL)= 0,5 mWidth of Pedestal in Z direction (CB)= 0,5 m

Effective length of pedestal = 1.5* Height = 1,95 mHef/CL = 3,9 <10, Hence Short Column

Hef/CB = 3,9 <10, Hence Short Column

Ultimate Axial Load if no reinforcement is privided 3000 KNHence Nominal steel reinforcement as required by code to be provided.

Minimum reinforcement percentage 0,4Area of main reinforcement 1000 mm2

Option Main Bar Dia

Nos Area Provided

Link dia Spacing

(mm) (mm2) mm mm1 8 20 1005 6 962 10 13 1021 6 1203 12 9 1018 6 1444 16 5 1005 6 1925 20 4 1257 6 240

UO

U1

1.5d

1.5d



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IsolatedFdn-1_BS8110