Design and drawing of RC Structures

CV61

Dr. G.S.Suresh

Civil Engineering Department

The National Institute of Engineering

Mysore-570 008

Mob: 9342188467 Email: gss_nie@yahoo.com

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Portal frames

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Learning out Come Review of Design of Portal Frames Design example Continued

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INTRODUCTION

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For Shed

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For Rectangular Buildings

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For Bridges

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For Viaduct

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INTRODUCTION Step1: Design of slabs Step2: Preliminary design of beams and

columns Step3: Analysis Step4: Design of beams Step5: Design of Columns Step6: Design of footings

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PROBLEM 1

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11

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Step3:Analysis(Contd) Moment Distribution Table

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Step3:Analysis(Contd) Bending Moment diagram

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Step3:Analysis(Contd) Design moments: Service load end moments: MB=102 kN-m,

MA=51 kN-m Design end moments MuB=1.5 x 102 = 153 kN-m,

MuA=1.5 x 51=76.5 kN-m Service load mid span moment in beam

= 27x82/8 102 =114 kN-m Design mid span moment Mu+

=1.5 x 114 =171 kN-m Maximum Working shear force (at B or C) in beam

= 0.5 x 27 x 8 = 108kN Design shear force Vu = 1.5 x 108 = 162 kN15

Step4:Design of beams: The beam of an intermediate portal frame is

designed. The mid span section of this beam is designed as a T-beam and the beam section at the ends are designed as rectangular section.

Design of T-section for Mid Span : Design moment Mu=171 kN-m Flange width bf= Here Lo=0.7 x L = 0.7 x 8 =5.6m bf= 5.6/6+0.4+6x0.12=2m

fwo D6b

6L

++

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Step4:Design of T-beam:bf/bw=5 and Df /d =0.2 Referring to table 58 of SP16, the moment resistance factor is given by KT=0.459, Mulim=KT bwd2 fck = 0.459 x 400 x 6002 x 20/1x106 = 1321.92 kN-m > Mu SafeThe reinforcement is computed using table 2 of SP16

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Step4:Design of T- beam:Mu/bd2 = 171 x 106/(400x6002)1.2 for this pt=0.359Ast=0.359 x 400x600/100 = 861.6 mm2No of 20 mm dia bar = 861.6/(x202/4) =2.74Hence 3 Nos. of #20 at bottom in the mid span

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Step4:Design of Rectangular beam:Design moment MuB=153 kN-mMuB/bd2= 153x106/400x6002 1.1 From table 2 of SP16 pt=0.327Ast=0.327 x 400 x 600 / 100 = 784.8 No of 20 mm dia bar = 784.8/(x202/4) =2.5Hence 3 Nos. of #20 at the top near the ends for a distance of o.25 L = 2m from face of the column as shown in Fig 6.6

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Step4:Design of beams Long. Section:

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Step4:Design of beams Cross-Section:

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Check for Shear:Nominal shear stress =

pt=100x 942/(400x600)=0.390.4Permissible stress for pt=0.4 from table 19 c=0.432 < v Hence shear reinforcement is required to be designedStrength of concrete Vuc=0.432 x 400 x 600/1000 = 103 kNShear to be carried by steel Vus=162-103 = 59 kN

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Check for Shear:Nominal shear stress =

pt=100x 942/(400x600)=0.390.4Permissible stress for pt=0.4 from table 19 c=0.432 < v Hence shear reinforcement is required to be designedStrength of concrete Vuc=0.432 x 400 x 600/1000 = 103 kNShear to be carried by steel Vus=162-103 = 59 kN

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Check for Shear:Spacing 2 legged 8 mm dia stirrup sv=

Two legged #8 stirrups are provided at 300mm c/c (equal to maximum spacing)

31 05 9

6 05 024 1 58 7.0V

dAf8 7.03

u s

s vy =

=

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Step5:Design of Columns: Cross-section of column = 400 mm x 600

mm Ultimate axial load Pu=1.5 x 108 = 162 kN

(Axial load = shear force in beam) Ultimate moment Mu= 1.5 x 102 = 153 kN-m (

Maximum) Assuming effective cover d = 50 mm

d/D 0.1

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0.06 0 04 0 02 0

1 01 5 3b Df

M2

6

2c k

u =

=

0.06 0 04 0 02 0

1 01 6 2b Df

P 3

c k

u =

=

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Step5:Design of Columns: Referring to chart 32 of SP16, p/fck=0.03;

p=20 x 0.03 = 0.6 Minimum steel in column should be 0.8 %,

Hence min steel percentage shall be adopted

Ast=0.8x400x600/100 = 1920 mm2 No. of bars required = 1920/314 = 6.1 Provide 8 bars of #20

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Step5:Design of Columns:8mm diameter tie shall have pitch least of

the following Least lateral dimension = 400 mm 16 times diameter of main bar = 320 mm 48 times diameter of tie bar = 384 300mmProvide 8 mm tie @ 300 mm c/c

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600

Tie #8 @300 c/c8-#20

400

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Step6:Design of Footings: Load: Axial Working load on column = 108 kN Self weight of footing @10% = 11 kN Total load= 119120 kN Working load moment at base = 51 kN-

m

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Step6:Design of Footings: Approximate area footing required =

Load on column/SBC= 108/150 =0.72 m2

However the area provided shall be more than required to take care of effect of moment.

The footing size shall be assumed to be 2mx3m (Area=6 m2)

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Step6:Design of Footings: Maximum pressure qmax=P/A+M/Z =

108/6+6x51/2x32 = 35 kN/m2

Minimum pressure qmin=P/A-M/Z = 108/6-6x51/2x32 = 1 kN/m2

Average pressure q = (35+1) = 18 kN/m2

Bending moment at X-X = 18 x 2 x 1.22/2 = 25.92 kN-m

Factored moment Mu39 kN-m

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Step6:Design of Footings: Over all depth shall be assumed as 300

mm and effective depth as 250 mm,

Corresponding percentage of steelfrom Table 2 of SP16 is pt= 0.1%,Minimum pt=0.12%

3.02 5 02 0 0 0

1 03 9b dM

2

6

2u =

=

34

Step6:Design of Footings: Area of steel per meter width of footing

is Ast=0.12x1000x250/100=300 mm2 Spacing of 12 mm diameter bar =

113x1000/300 = 376 mm c/c Provide #12 @ 300 c/c both ways

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Step6:Design of Footings: Check for Punching Shear Length of punching influence plane = ao= 600+250 =

850 mm Width of punching influence plane = bo= 400+250 =

650 mm Punching shear Force = Vpunch

=108-18x(0.85x0.65)=98 kN Punching shear stress punch= Vpunch/ (2x(ao+bo)d

=98x103/(2x(850+650)250) = 0.13 MPa Permissible shear stress = 0.25fck=1.18 MPa > punch

Safe

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Step6:Design of Footings: Check for One Way Shear Shear force at a distance d from face of

column V= 18x2x0.95 = 34.2 kN Shear stress v=34.2x103/(2000x250)=0.064

MPa Referring to table 19 of IS456 this stress is

very small and hence safe Details of reinforcement provided in footing

is shown in Fig.37

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Dr. G.S.Suresh

Civil Engineering Department

The National Institute of Engineering

Mysore-570 008

Mob: 9342188467 Email: gss_nie@yahoo.com

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Design and drawing of RC StructuresCV61Portal frames Learning out ComeSlide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40