ls eccentric reversible (symmetric)

23
INPUT DATA Size of the column (mm*mm) Load on the column (kN) Grade of concrete for footing Grade of steel DESIGN CONSTANTS DESIGN OF THE FOUNDATION Assume weight of footing + backfill Weight of footing + backfill (kN) Total load (kN) Reversible Uniaxial moment, Mux (kN-m) SBC of soil (kN/m 2 ) x u, max /d Ru, lim DESIGN OF ISO ECCENT By Lim (Reversible mom

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Page 1: LS Eccentric Reversible (Symmetric)

INPUT DATA

Size of the column (mm*mm)

Load on the column (kN)

Grade of concrete for footingGrade of steel

DESIGN CONSTANTS

DESIGN OF THE FOUNDATION

Assume weight of footing + backfill

Weight of footing + backfill (kN)

Total load (kN)

Reversible Uniaxial moment, Mux (kN-m)SBC of soil (kN/m2)

xu, max/d

Ru, lim

DESIGN OF ISOLATED FOOTINGS WITHECCENTRIC LOADING

By Limit State Method(Reversible moment acting on column)

Page 2: LS Eccentric Reversible (Symmetric)

The dimensions of the footing can be obtained by the expression

Proposed size of footing (m*m)

Provide Custom size of footing?

Custom size of footing (m*m)

DEPTH FROM BENDING MOMENT CONSIDERATION

Effective Depth (mm) proposed from Bending Moment consideration

Clear Cover Provided (mm)

Diameter (mm) of Rebar to be used in long directionDiameter (mm) of Rebar to be used in short direction

Effective Cover to the lower layer of steel (mm)Effective Cover to the upper layer of steel (mm)

Overall Depth proposed (mm)

Provide Custom Overall Depth

Custom Overall Depth (mm)

Maximum Soil Pressure, p01 (kN/m2)

Minimum Soil Pressure, p02 (kN/m2)

Pressure Intensity under the column axis, p0 (kN/m2)

Intensity of net soil pressure below the column face, p0' (kN/m2)

Maximum Bending Moment, Mx (kN/m2)

Factored Bending Moment, Mux (kN/m2)

Effective Depth for long span, dx (mm)Effective Depth for short span, dy (mm)

Page 3: LS Eccentric Reversible (Symmetric)

CHECK FOR ONE WAY SHEAR

Assume thickness (mm) at the edges of the footing

Cantilever Length to the right of the critical section (mm)

Width of footing at the top of the critical section (mm)

Assume pt % =

Tv < ks*Tc

CHECK FOR TWO WAY SHEAR

Critical Section for one way shear lies at a distance d from the column face.

Intensity of pressure p0" at the critical section (kN/m2)

Effective Depth, d' (mm)

For a balanced section, xu, max/d is equal to

For an under-reinforced section, adopt xu/d' =

xu (mm)

Width of the section at N.A., bn (mm)

Shear force Vu (kN) at the critical section

Nominal Shear Stress, Tv (N/mm2)

Tc (N/mm2)

Page 4: LS Eccentric Reversible (Symmetric)

Tv < ks*Tc

DESIGN FOR REINFORCEMENT

Design for reinforcement in the long direction

No. of bars required

Spacing (mm)

Development Length Check

Development Length required (mm)

Critical Section for Two way shear is at a distance davg/2 from the column periphery.

davg (mm)

Punching Shear, Fu (kN)

Effective Depth of the footing at the critical section, d0 (mm)

Nominal Shear Stress, Tv (N/mm2)

Permissible Shear Stress, Tc (N/mm2)

ks*Tc (N/mm2)

Mux/b1dx2 (N-mm2)

pt required

Ast1 (mm2) required

Ast1 (mm2) provided

Ld/φ for given grade of concrete and steel

Page 5: LS Eccentric Reversible (Symmetric)

Development Length available (mm)

Design for reinforcement in the short direction

No. of bars required

No. of bars required for the central band width reinforcement

Spacing (mm)

No. of bars required in each band strip

No. of bars provided in each of the outer band strips of length

Development Length Check

Development Length required (mm)Development Length available (mm)

Muy/b2dy2 (N-mm2)

pt required

Ast2 (mm2) required

Ast2 (mm2) provided

Ast2(B) (mm2) provided in central band width equal to

Remaining Area in each band strip (mm2)

Ld/φ for given grade of concrete and steel

Page 6: LS Eccentric Reversible (Symmetric)

CHECK FOR TRANSFER OF LOAD AT THE BASE

A2 (mm2)

At a rate of spread of 2:1, A1(mm2)

√(A1/A2)

Value of √(A1/A2) to be adopted

Permissible bearing stress (N/mm2)

Actual bearing stress (N/mm2)

Page 7: LS Eccentric Reversible (Symmetric)

Short Dimension Long Dimension300 500

666.66666666666780

200M20

Fe 415

0.479

2.76

10% of column load

66.67

733.34

DESIGN OF ISOLATED FOOTINGS WITHECCENTRIC LOADING

By Limit State Method(Reversible moment acting on column)

Page 8: LS Eccentric Reversible (Symmetric)

Length Breadth2.3 2.1

NO

Length Breadth2.7 2.5 Hence, OK

181.23

94.82

138.03

DEPTH FROM BENDING MOMENT CONSIDERATION

147.42

144.55

216.825

512

60

1616

6884

580

NO

450

512496

Pu/BL + Mu/BL2 ≤ qu

Page 9: LS Eccentric Reversible (Symmetric)

200

388

166.65

1324

301

0.479

0.4

120.4

1905

212.59

0.371

0.35

0.414

Hence, OK

Critical Section for one way shear lies at a distance d from the column face.

Page 10: LS Eccentric Reversible (Symmetric)

504

832.87

407

0.566

1.118

1.118

Hence, OK

2.757

0.95

1460

8

1610

281

Hence, OK

47752

davg/2 from the column periphery.

Page 11: LS Eccentric Reversible (Symmetric)

840

Hence, OK

1.931

0.61

1513

8

1609

2100 mm = 1536

8

298

Hence, OK

73

1

0.1 m = 2

47752840

Hence, OK

Page 12: LS Eccentric Reversible (Symmetric)

250000

7952400

5.64

2

18

4

Hence, OK

Page 13: LS Eccentric Reversible (Symmetric)

2.34.83

YESNO

Hence, OK

Resize the footing

Page 14: LS Eccentric Reversible (Symmetric)

20 M20 20 Fe 250 250

415 M25 25 Fe 415 415

M30 30 Fe 500 500

M35 35M40 40

201.062201.062

2.1

difference B L (L-a)/2

733.34 0 4 1.358 429200 0 3.95 1.371 435.5

0 3.9 1.385 442.50 3.85 1.398 449

0 3.8 1.412 456

0 3.75 1.426 463

Resize the footing 0 3.7 1.441 470.50 3.65 1.456 4780 3.6 1.472 4860 3.55 1.487 493.50 3.5 1.504 5020 3.45 1.52 5100 3.4 1.538 5190 3.35 1.555 527.5

0.149fckbd2

0.138fckbd2

0.133fckbd2

Area of one bar (mm2) long directionArea of one bar (mm2) short direction

Page 15: LS Eccentric Reversible (Symmetric)

0 3.3 1.573 536.50 3.25 1.592 5460 3.2 1.611 555.50 3.15 1.631 565.50 3.1 1.652 5760 3.05 1.673 586.50 3 1.694 5970 2.95 1.717 608.50 2.9 1.74 6200 2.85 1.764 632

50 6 0 2.8 1.789 644.560 8 0 2.75 1.814 657

75 10 0 2.7 1.841 670.512 0 2.65 1.868 684

16 0 2.6 1.897 698.520 0 2.55 1.926 71322 0 2.5 1.957 728.525 0 2.45 1.989 744.5

28 0 2.4 2.022 76132 0 2.35 2.057 778.5

0 2.3 2.093 796.50 2.25 2.13 815

0 2.2 2.17 835YES 580 0 2.15 2.21 855

NO 0 2.1 2.253 876.524 2.05 2.298 899

72.5 2 2.345 922.5122 1.95 2.394 947173 1.9 2.446 973

225.5 1.85 2.501 1000.5279 1.8 2.558 1029

334.5 1.75 2.619 1059.5391.5 1.7 2.683 1091.5450.5 1.65 2.751 1125.5511.5 1.6 2.823 1161.5

575 1.55 2.9 1200640.5 1.5 2.981 1240.5

709 1.45 3.068 1284780.5 1.4 3.161 1330.5855.5 1.35 3.261 1380.5934.5 1.3 3.369 1434.51017 1.25 3.484 14921105 1.2 3.61 15551198 1.15 3.746 16231297 1.1 3.894 1697

Page 16: LS Eccentric Reversible (Symmetric)

140 1403 1.05 4.056 17781517 1 4.234 1867

161

6.6348745594 Column1 Column2150 1.3175 1.25

Tv < ks*Tc Hence, OK 200 1.2

Tv > ks*Tc NOT SAFE 225 1.15250 1.1275 1.05300 1

1

1004 804

1

Page 17: LS Eccentric Reversible (Symmetric)

0.63411

Hence, OKProvide bars of less diameter

M20 2 2 Fe 250 2 3

M25 3 Fe 415 3 Fe250

M30 4 Fe 500 4 Fe415

M35 5 Fe500

M40 6

237.4766

0.44413

Hence, OK

N/A (as the footing is square). Separate dowel bars are required to transfer the load

Page 18: LS Eccentric Reversible (Symmetric)

2.98 0.2 0.531 10% of col 0.1

2.76 0.479 15% of col 0.15

2.66 0.456

(B-b)/2 min B L (L-a)/2 (B-b)/2

1850 24 2.05 2.298 728.5 110018251800 900 9001775

1750

1725

17001675165016251600157515501525

Page 19: LS Eccentric Reversible (Symmetric)

1500147514501425140013751350132513001275

12501225

12001175

1150112511001075

10501025

1000975

950925

900875850825800775750725700675650625600575550525500475450425400

Page 20: LS Eccentric Reversible (Symmetric)

375350

Page 21: LS Eccentric Reversible (Symmetric)

M20 M25 M30 M35 M40 and above

45 39 36 32 29

47 40 38 33 3057 49 45 40 36

Separate dowel bars are required to transfer the load