IsolatedFdn-1_BS8110

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

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

of 8 Output Date :04/08/2023

ISOLATED FOOTING DESIGN

MATERIAL DATA:

30

Yield Strength of reinforcement = 460Dia of Reinforcement in direction of L = 12 mmDia of Reinforcement in direction of B = 12 mmClear Cover to Reinforcement = 81 mmUnit Weight of Concrete 24Unit Weght of Soil = 18Unit Weight of Backfill = 18Net allowable bearing pressure = 100

22Angle of friction between conc and soil = 23

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 :

Width of Footing B = 1.80 m Width of Pedestal CB = 0.28 mLength of Footing L = 1.80 m Length of Pedestal CL = 0.28 m

Total height of Pedestal = 1.30 m Depth of Footing, D = 0.40 mProjection of pedestal above ground = 0.3 m

Grade of Concrete Fck = N/mm2

N/mm2

KN/m3

KN/m3

KN/m3

KN/m2

Internal angle of friction f of soil = O

O

X

Y

Z

CL

CB B

L

FY

FX

FZ

H

D

L




LOAD DATA

JOINT FY FX FZ MX MZ

MAX 10 0.5 -0.01 0.01 -0.04

(b) Ultimate load combination for concrete design.


MAX 15 0.6 0 0.012 -0.048(c) Load combination for bearing pressure check:.


MAX 1 10 0.5 0 0.01 -0.04

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

0.5 KN

42.63 KN

100.42 kNF.O.S. against sliding in X dir = 85.25

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

-0.01 KN

42.63 KN

100.42 KNF.O.S. against sliding in Z dir = -4262.67

NOT O.K.(c) Overturning about Z

Forces acting at bottom of footing about ZFY = 10.00 KN

0.81 KN-mSelf Weight of Foundation = 31.104 KNWeight of Pedestal = 2.36 KNWeight of Backfill = 56.96 KNBuoyancy force = 0.00 KN

0.3 Taking moment about POverturning moment due to Tension =

1.00 0.00 KN-m

0.81 KN-m

0.9

(a) Load for Stability (gf = 1.0 )LOAD COMBINATION

LOAD COMBINATION

LOAD COMBINATION

Sliding force in X direction = FX = Resisting frictional force = Ptand =

P= FY+Footing weight + Pedestal weight +Soil weight- BF =

Sliding force in Z direction = FZ = Resisting frictional force = Ptand =

P= FY+Footing weight + Pedestal weight+Soil weight -BF=

MZtot = (MZ +FX*(D+H)) =

Overturning moment = MZtot =

P




Total overturning moment 0.81 KN-mRestoring Moment 90.38 KN-m

Factor of safity against overturning = restoring mom/overturning mom 111.58 O.K. , As value is greater than 1.75

(d) Overturning about XForces acting at bottom of footing about XFY = 10.00 KN

-0.01 KN-mSelf Weight of Foundation = 31.104 KNWeight of Pedestal = 2.36 KNWeight of Backfill = 56.96 KNBuoyancy force = 0.00 KN

0.31.00 Taking moment about P

Overturning moment due to Tension =

0 Kn-m

0.9 -0.01 KN-m

Total overturning moment = -0.01 KN-mRestoring Moment = 90.38 KN-m

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

MXtot = (MX +FZ*(D+H)) =

Overturning Moment = MXtot P




1. CHECK FOR NET BEARING PRESSURE

100.42 KN

0.01 KN-m

0.81 KN-m

0.01 M e<L/6, No Tension in footing.

ez = 0.00 M e<L/6, No Tension in Footing.

Gross pressure distribution underfooting is given by:

q =

= 31.84 30.17 31.82 30.15 p3p1 p2 p3 p4 +Mx

Mx(If there is negative gross pressure then it will be corrected using Teng's Chart) p2 Mz p1

0.00 0.00Sign Convention

From Teng's chart value of k = 1.027 x = - y = -

Maximum Gross Pressure = K*P/BL = 31.84Net pressure intensities under the footing is given by:

6.64 6.62

4.97 4.95

Maximum net pressure intensity = 6.64 O.K. Less than allowable bearing pressure

Gross vertical load PY = FY+ Weight of Footing including pedestal+ Weight of B/F

Total Moment about X = MXtot =MX+ FZ(H+D)

Total Moment about Z = MZtot =MZ+ FX(H+D)

ex = MZtot/PY =

MXtot/PY =

Kn/m2

ex/L = ez/B =

KN/m2

p1net = KN/m2 p3net = KN/m2


KN/m2

p4

∑ P Y

LB(1±

6 exL

±6eZB

)




2. CHECK FOR MOMENT AND SHEAR

Net pressure generated below footing due to design load.

105.42 KN

0.01 KN-m

0.97 KN-m

0.01 M e<L/6, No Tension in footing.

ez = 0.00 M e<B/6, No Tension in Footing.

Gross pressure distribution underfooting is given by:

q =

= 33.55 31.55 33.53 31.53 p3p1 p2 p3 p4 +Mx

Mx(If there is negative gross pressure then it will be corrected using Teng's Chart) p2 Mz p1

0.01 0.00Sign Convention

From Teng's chart value of k = 1.031 x = - y = -

Maximum Gross Pressure = K*P/BL = 33.55Net pressure intensities under the footing is given by:

8.35 8.33

6.35 6.33

Maximum net pressure intensity = 8.35

Gross vertical load PY = FY+ Weight of Footing including pedestal+ Weight of B/F



ex = MZtot/PY =

MXtot/PY =

Kn/m2

ex/L = ez/B =

KN/m2



KN/m2

p4

∑ P Y

LB(1±

6 exL

±6eZB

)




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

p2 =

6.35 8.2 p1 =

7.50 7.85 8.35 ( d= D-81-6 313 mm )

Moment at the Critical section 1: 2.35 KN-m/m Width of Footing.Shear at critical section 1: 10.88 KNShear at critical section 2: 6.55 KNShear at critical section 3: 2.03 KN

Tensile Reinforcement:

0.000798 < 0.156

312.72 mm0.95*d = 297.35 mmHence z = 297.35 mm

18.05

Minmum Reinforcement 0.13% = 520.00Reqd. Spacing of 12 mm dia bar = 218 mmProvided Spacing = 200 mm 565

0.404

Section 1 0.019

4.382 O.K. (Clause 3.7.7.2)

Section 2 0.012

0.606 O.K. (Clause 3.7.7.4)

Section 3 0.004

0.404 O.K.

K= M/fcubd2 =z= d[0.5+Ö(0.25-k/0.9)] =

Ast = M/0.95fyz = mm2/m

mm2/m

Ast,provided mm2/m

Design Concrete shear stress uc = N/mm2

Ultimate shear stress v1 = N/mm2

Maximum allowed 0.8Öfcu = N/mm2


Maximum allowed 1.5uc = N/mm2


Maximum allowed uc = N/mm2

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 = 8.358.33 p1 = ( d= D-81-12-6 301 mm )

8.34 8.34 8.35

Moment at the Critical section 1: 2.43 KN-m/m Width of Footing.Shear at critical section 1: 11.45 KNShear at critical section 2: 6.93 KNShear at critical section 3: 2.41 KN

Tensile Reinforcement:

0.000893 <0.156

300.70 mm0.95*d = 285.95 mmHence z = 285.95 mm

19.42

Minmum Reinforcement 0.13% = 520.00Reqd. Spacing of 12 mm dia bar = 218 mmProvided Spacing = 200 mm 565

0.389

Section 1 0.021

4.382 O.K. (Clause 3.7.7.2)

Section 2 0.013

0.583 O.K. (Clause 3.7.7.4)

Section 3 0.004

0.389 Hence O.K.

K= M/fcubd2 =z= d[0.5+Ö(0.25-k/0.9)] =

Ast = M/0.95fyz = mm2/m

mm2/m

Ast,provided mm2/m

Design Concrete shear stress uc = N/mm2




Maximum allowed 1.5uc = N/mm2



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 = 307 mm

1100 mm

4784 mm

15 KN

0.0444

4.382 O.K.

0.010

0.389 O.K.

(d) Design for Pedestal

15 KN

0.01 KN-m

0.97 KN-mHeight of Pedestal = 1.30 mWidth of Pedestal in X direction (CL)= 0.275 mWidth of Pedestal in Z direction (CB)= 0.275 m

Effective length of pedestal = 1.5* Height = 1.95 m

7.090909 <10, Hence Short Column

7.090909 <10, Hence Short Column

Ultimate Axial Load if no reinforcement is privided 907.5 KNHence Nominal steel reinforcement as required by code to be provided.

Minimum reinforcement percentage 0.4Area of main reinforcement 302.5

Option Nos Link dia Spacing

(mm) mm mm1 8 7 352 6 962 10 4 314 6 1203 12 3 339 6 1444 16 2 402 6 1925 20 1 314 6 240

U0 = 2(CB+CL) =

U1 =U0 +12d =

Maximum ultimate Vertical load on column FY =

Ultimate shear stress for U0 = N/mm2


Ultimate shear stress for U1 = N/mm2


PU =



Hef/CL =

Hef/CB =

mm2

Main Bar Dia

Area Provided

(mm2)

UO

U1

1.5d

1.5d

IsolatedFdn-1_BS8110

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