Precast Plank Design

7/24/2019 Precast Plank Design

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

10.0) DESIGN OF Precast Concrete Plank as BEAM supported on column

10.1) The 50 mm thick precast Plank will be inserted in the 50mm wide spout in the column.

The column will be solid rectangular till ground level. The column above ground level will have 50/60mm thick x 35 mm deep groove for the Precast plank

insert. The bottom plank will be resting on the column having bearing of 30 mm on both side of column.

Total Number of Planks will be 7 of 300 mm depth.

Bottom Plank will act as simply supported beam resting on column and other 6 planks will be resting on bottom plank.

Bottom Plank is designed as simply supported beam and same design will be applied to all planks.

2.25

Effective span of Plank 2.17 - 0.035 = 2.135 m

Design of Bottom Plank supporting other Planks above

Plank Thickness = = 50 mm

Plank Depth = = 300 mm

Plank Length = = 2160 mm

Uniform Load over Bottom Plank = 0.050 x 2.10 x 25 = 2.625 kN/m

Maximum BM @ Midspan = 2.625 x 2.135 2 / 8 = 1.496 kNm

Ultimate Moment Mu = 1.50 x 1.496 = 2.244 kNm

Maximum Shear Force @ Support = 2.63 x 2.14 / 2 = 2.802 kN

Ultimate Shear Force Vu = 1.50 x 2.802 = 4.203 kN

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Design of Individual Plank for its self weight while lifting

Also each Panel shall be designed for its self weight while lifting at both end.

Uniform Load of one Plank due to self weight 0.050 x 0.30 x 25 = 0.375 kN/m

Maximum BM @ Midspan = 0.375 x 2.16 2 / 8 = 0.219 kNm

Ultimate Moment Mu = 1.50 x 0.219 = 0.328 kNm

Maximum Shear Force @ Support = 0.38 x 2.16 / 2 = 0.405 kN

Ultimate Shear Force Vu = 1.50 x 0.405 = 0.608 kN

10.2) Prestressing detail & Check for section :

Use 3 Nos. of 3 mm of ultimate strength of 1865 Mpa

Allowable stress in Prestressing steel = 0.80 fy = 1492 Mpa

Total Prestressing steel area = 3 x / 4 x 3 ^ 2 = 21.21 mm2

Total Prestressing force = 21.210 x 1492 = 31.65 kN

10.2.1 ) Losses due to pretension :

( As per IS : 1343-1980, Cl 18.5)

Stress in cable after prestress = 1492 N/mm2

Stress in concrete at CG of cable 31650 / ( 50 x 300 ) = 2.110 N/mm2

10.2.1.1) Loss due to elastic shortening : (IS 1343:1980, Cl 18.5.2.4 b)

= 1 x modular ratio x avg. stress in concrete at c.g. of cable

2

Grade of concrete at the time of stressing = 30 N/mm2

Ec = 5700 x 30

= 31220 N/mm2

m = 210000 = 6.7

31220

Loss = 6.7 x 2.11 = 14.2 N/mm2

= 0.95 %



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10.2.1.2) Due to creep of concrete : (IS 1343:1980, Cl 18.5.2.1)

Age of loading @ 28 days Take creep coefficient = 1.6

Loss = 1.6 x 2.1 x 6.7 = 22.7 N/mm2

= 1.52 %

10.2.1.3) Due to shrinkage of concrete : (IS 1343:1980, Cl 18.5.2.2)

Shrinkage strain = 0.0002/Log(t +2) = 0.00021

Between 3 and 21 days

Loss = 0.00021 x 210000 = 44.0 N/mm2

= 2.95 %

10.2.1.4) Loss due to relaxation of H.T. steel at first stage loss : (IS 1343:1980, Cl 18.5.2.3)

@ 0.800 UTS = = 90.0 N/mm2

= 6.03 %

Total loss due to elastic shortening, creep , shrinkage & relaxation :

= 14.2 + 22.7 + 44.0 + 90.0 = 171 N/mm2

= 11.46 %

10.2.2 ) Prestress after Losses :

Prestressing force after losses = 31.65 x 88.54 % = 28.02 kN

Stress due to prestressing force = 28.02 x 1000 / ( 50 x 300 ) = 1.87 MPa

Permissible Compressive stresses = 0.34 fck = 10.2 N/mm2

(Refer IS 1343, Cl. 22.7.1(b) & Fig 7)

Permissible Tensile stresses = = 0.0 N/mm2

(Refer IS 1343, Cl. 22.7.1 Type - 2)

10.2.3 ) Check of Section

A. Section Check for Stress

Section oment b D Moment Cg of NA Cg of NA Sect ModulusSect Modulus Bending stress M/Z Stress due to Resultant stress Rem-

(kN-m) of Inertia from Top from Bottom ZTOP ZBOTTOM @ Top @ Bottom Initial Prestress @ Top @ Bottom ark

(mm) (mm) (mm4) m m (m

3) (m

3) N/mm

2N/mm

2N/mm

2N/mm

2N/mm

2

Compressiv Tensile Compressive Compressive Compressive

(i) (ii) (iii) (i) + (iii) (ii) + (iii)

Bottom Plank 1.50 50 300 0.000113 0.15 0.15 0.00075 0.00075 1.99 -1.99 1.87 3.86 -0.13 Unsa

Midspan

Individual Plan 0.22 300 50 0.000003 0.025 0.025 0.00013 0.00013 1.75 -1.75 1.87 3.62 0.12 Safe

Midspan



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B. Section Check for Limit State of Collapse

The ultimate strenght of cross section is calculated according to the recommendattions of IS 1343, Appendix B

Section Bottom Plank Individual Plank

Mult. = 2.244 kN-m 0.328 kN-m

fck Concrete grade = 30 N/mm2

30 N/mm2

D Depth of Section = 0.300 m 0.050 m

B Width of Section = 0.050 m 0.300 m

c.g.st Depth of cg of prestressing steel from top of section = 0.150 m 0.025 m

db = D-cgst or cgst Effective depth to cg of steel from top = 0.150 m 0.025 m

Ac Area of compression zone = 0.0014 0.0014

cg1 Depth of compression zone = 0.0143 0.0024

Mult. conc. Ult imate Moment capacity under concrete failure = 2.33 kN-m 0.39 kN-m

As Area of Prestressing steel = 21.21 mm2 21.21 mm

2

fp Ultimate tensile strength of prestressing steel = 1865 N/mm2 1865 N/mm2

(Ap fp) / (b d fck) (Ref IS 1343, T-11) = 0.088 0.088

fpu/(0.87fpu (Ref IS 1343, T-11) = 1.000 1.000

Xu/d (Ref IS 1343, T-11) = 0.191 0.191

fpu = 1623 1623

Xu = 0.029 m 0.005 m

Ast Non Prestressing steel = 0 mm2 0 mm

2

Mult. Due to yielding of steel = 4.748 kN-m 0.791 kN-m

Mult. Capacity of section = 2.332 kN-m 0.389 kN-m

Remark safe safe

C. Check for Limit State of Shear



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Section Shear b D clear d Shear Ast prov. Pt % Shear Remark.

Force cover stress dia provided

capacity

of(kN) (mm) (mm) (mm) (mm) v(N/mm ) (mm) c(N/mm )

IS1343, T-6

Bottom Plank4.20 50 300 25 274 0.307 3 mm 3 Nos. 0.155 0.370

Shear Reinf

Not Required

Midspan

Individual Plan0.61 300 50 25 25 0.081 3 mm 3 Nos. 0.283 0.370

Shear Reinf

Not Required

Midspan

10.3) Check for Bearing strength on concrete column bearing area due to reaction from planks:

Reaction at one end of column 1.5 x 2.625 x 2.16 / 2 = 4.25 kN

Bearing Area = 30 x 50 = 1500 mm2

Bearing Stress on column 4250 / 1500 = 2.83 N/mm2

Permissible bearing strength on concrete 0.45 fck = 13.5 Mpa (Ref IS 456:2000, Cl 34.4)

Safe


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Precast Plank Design