Footing Design-conn & Lift Check

VIKRAM UDYOGPURI LIMITED, UJJAIN, MADHYA PRADESH SPML - OM METALS (JV)

9.3 Design of Footing as beam for Lifting case:

0.10

0.475 0.3 0.475

Precast footing at the time of lifting will behave as simply supported beam subjected to its self weight.Concrete grade of column = 20 MpaConsider the age of concrete at the time of lifting as = 7 DaysConsider Strength of concrete at 7 Days is 60% = 12 MpaReinforcing steel grade = 500 MpaWidth of Footing is = 925 mmDepth of footing is middle portion = = 100 mmDepth of footing at edge portion = = 400 mm

Udl (kN/m) 9.25 2.31 9.25

1.05

Reaction (kN) 4.74 4.74Maximum Bending Moment = = 0.68 kNmMaximum Shear Force = = 4.74 kNUltimate Bending Moment Mu = = 1.02 kNmUltimate Shear Force Vu = = 7.11 kNDepth at Maximum Bending Moment = = 100 mmClear cover to reinforcement = = 50 mmEffective depth = 45 mmMbal = 0.133*fck*b*d^2 = 2.99 kNmAst required = 0.5 fck / fy x (1-sqrt(1-(4.6 Mu/ fck b d2 ))) b d = 55 mm2

Provided reinforcement is Y 10 Dia @ 200 in Width of925 mm = 363 mm2

SafeShear stress due to shear force Τv = ( 7.11 x 1000) / (925 x (400 - 50 - 5) )= 0.022 N/mm2

Shear capacity of concrete (Pt = 0.114%) Τc = 0.28 N/mm2

Safe

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9.4 Precast Column to foundation Socket connection:

In socket connection, the precast columns are fixed rigidly to the foundation and loads are transmitted by skin friction in socket and by end bearing.The design of socket connection may adopt the following steps:

Figure - A

Support Reactions:Referring to figure - A, a rotation of the column in the socket under moment shifts the support reactionat the column base from centre line towards the edge. The resultant reaction R at the basemay be assumed to act at a distance a/6 from the column centre line.

From Figure - A, following forces may be derived:a. Horizontal force HB :-

Moment about Point AM + (N x a/2) + (HD x 0.9h) = (HB x 0.8h) + (μHB x a) + (R x (a/2+a/6))

Support Recation at column base is R = N - μ HB

Substitution R into the above equation and after rearranging,HB = (M - 0.17 a N + 0.9hHD) / (0.8h + 0.33aμ)

a = 0.30 m Depth of columnRecation at footing top is : (Ref Cl 8.1.2.3)

Vertical Load N = 15.294 kNHorizontal Load HD = 7.158 kN



Moment M = 11.712 kN mIf the height of socket is taken as h = 0.30 m i.e. h=1.00a and

For smooth surface, the coefficient of friction μ = 0.30 is used,

substituting the above values, equation obtained is:

HB = = 47.7 kNHA = = -40.54 kNVertical reaction on base = R = N - μ HB = 0.98 kN

As the majority of vertical reaction at base is resisted by friction betweencolumn and socket foundation. Balance reaction exerts pressure on base.Beraing strenght of concrete at base needs to be checked. However reactionR at base is too less which will be less than permissible bearing strength of concrete.

Contact Area of HB on socket footing/column = h/2 x Width of column

150 mm x 300 mmBearing stress on concrete of column/Socket footing due to HB = HB / Contact Area

=47.7x 10^3 / (150 x 300) = 1.06 N/mm2

Bearing stress on concrete of column/Socket footing due to HA = HA / Contact Area

=40.54x 10^3 / (150 x 300) = 0.9 N/mm2

Permissible Bearing strength of concrete = 0.45 fck (IS 456:2000, Cl 34.4) = 9.00 N/mm2

Safe

Strenght of filler material should also be greater than 1.06 N/mm2

Check of Column Section for Shear:Maximum Shear Force = = 47.7 kNColumn Size = 300 mm x 300 mmClear cover to steel = 25 mmTotal steel percentage provided = 0.80 %Shear capacity of concrete ignoring increase in shear capacity due

to axial compression (IS 456, T-19) Τc = 0.56 N/mm2

Shear stress due to shear force Τv = ( 47.7 x 1000) / (300 x (300 - 25) )= 0.58 N/mm2

As Τv > Τc, Shear reinforcement is requiredAsv / Sv required = (Τv - Τc) b /(0.87 fy) = 0.02 mm2/mm

Provide 2 Leg Y 8 Dia @ 150 c/c = 0.67 mm2/mm

At 2 Nos of Stirrups in embedded region Safe


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Footing Design-conn & Lift Check