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by

R.Goentoro

Senior Civil & Marine Engineer

Jakarta, 11 June 2011

MODUL-3.2

STEEL STRUCTURE FOUNDATION

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G E N E R A L

The training purpose is to give general guideline in how to designFoundation for Structure.

As a basis: Structure is designed separately and the support reactionsfrom Structure design are used as input data.

Support reactions shall include both temporary and permanentcondition and both factored and un-factored load.

Un-Factored load stability check

Factored loadMember stress design

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Input Data

All data is given by Structure Group:

1. Structure Column Layout and Orientation

2. Structure Support reactions, with Factored and Un-factoredLoad and Loading Combination

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On Soil

Check Stability:

1. Soil Bearing

2. Overturning (with SF)

3. Sliding (with SF)

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On Soil

Soil Bearing

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On Soil

Soil Bearing:

M = P.e, e = M/P

e < b/6,

SB = P/A +/- (M * y / I)

P = total vertical load

A = footing area = ab

M = total moment load

y = distance on the respective axis = a or b

I = total moment inertia of footing on the respective axis = 1/12 ba3 or 1/12 ab3

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On Soil

Soil Bearing:

e > b/6,

SB = 2P / (3a (b/2 e))

SB = 2P / (3A ( e/b))

SB < SB Allowable (ton/m2) ..

For both permanent and temporary condition

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On Soil

Overturning

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On Soil

Overturning:

moment resistance = P * Wf / 2

P = total vertical load (incl. weight or fdn and soil)

Wf / 2 = distance to the analyzed point

Overturning moment = Mx or Mz

= total moment load from structure

SF = (moment resistance) / (Mx or Mz)

SF >= 1.5 temporary condition

SF >= 2.0 permanent condition

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On Soil

Sliding

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On Soil

Sliding:

Sliding resistance = P * mP = total vertical load (incl. weight or fdn and soil)

m = drag coefficient (= 0.3)

Sliding force = H

= total hor. load from structure = (FX2 + FZ2)^0.5

SF = sliding resistance / H

SF >= 1.5 temporary condition

SF >= 2.0 permanent condition

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On Pile

Sliding is assumed to be received by Pile horizontal capacity

Horizontal Pile reaction = horizontal load/pile nos = H/n

Overturning and Soil bearing will be treated as moment+vertical

loads that is received by Pile vertical reaction

Pile reaction =

P / n +/- M * y / I

Pile reaction < Pile allowable stress (as recommended by Project)

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On Pile

Where:

P = Total vertical load

n = number of piles

M = Overturning moment at base of footing

I = Pile group moment of inertia (= S I)

(treat the pile as a node, Ip = 0, A = 1 I = S y2)

y = distance between pile group c.g to pile in question

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Member Design

1. To find Stress on Footing from Soil pressure

2. Check Punching Shear and Beam Shear to find footing thickness

3. Find footing re-bar designed as cantilever beam

4. Do pedestal design

designed as column (receive shear Vu dan moment Mu)

5. Find Anchor Bolt arrangement

similar to pile design (shear and tension)

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The End