CE 415 Design of steel structures

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CE 318

STRUCTURE ANALYSIS AND DESIGN II LAB

LECTURE 6

RCC COLUMN DESIGN

SEMESTER: SPRING 2021

COURSE TEACHER: SAURAV BARUA CONTACT NO: +8801715334075

EMAIL: [email protected]

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LECTURE PLAN

2 copyright @Saurav Barua

Column load calculation

Contributory area

Bending factor

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COLUMN LAYOUT

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COLUMN CONTRIBUTORY AREA

copyright @Saurav Barua 4

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CONTRIBUTORY AREA

• Take ½ span from each side to calculate contributory area

• Then designate columns of similar column contributory into same name, i.e. C1, C2, C3 and C4

• Contributory area of corner column C1 = (½ x 15’) x (1/2 x 16’)

= 7’-6” x 8’ = 60 sft

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CONTRIBUTORY AREA

• Contributory area of edge column C2 = (½ x (15’+18’)) x (1/2 x 16’)

= 16’-6” x 8’ = 132 sft

• Contributory area of edge column C3 = (½ x 15’)x (1/2 x (16’+16’))

= 7’-6” x 16’ = 120 sft

• Contributory area of central column C4 = (½ x (15’+18’)) x (1/2 x (16’+16’))

= 16’-6” x 16’ = 264 sft

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DEAD LOAD CALCULATION

• Slab weight = 6/12 x 0.15 = 0.075 ksf

• Wall load (WL) = 80psf = 0.08ksf

• Floor finish (FF) = 25psf = 0.025ksf

• Beam weight = [(15’ + 18’+ 15’) x 3 + (16’+ 16’) x 4] x (12 x 18)/144 x 0.15

= [48 x 3 + 32 x 4] x (12 x 18)/144 x 0.15

= 61.2 kip/ (48 x 32) = 0.04ksf [Explained in class!!]

Column weight = 12 x 20 /144 x 10 x 12x 0.15 [ 12 nos. column of 12”x 20” assumed]

= 30kip/ (48 x 32) = 0.02ksf

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• DL = 0.075 + 0.08 + 0.025 + 0.04 + 0.02

= 0.24ksf

LL = 40 psf = 0.04 ksf

Since, we will design column considering axially loaded column formula For central column C4 factor for bending moment = 1.0

For edge columns C2, C3 factor for bending moment = 1.1 For corner column C1 factor for bending moment = 1.3 This will reduce original effect of biaxial bending

Consider 10% of DL for Earthquake load and 15% of DL for Wind load.

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Column

Contributory

area (sft) Story Total contributory area (sft)

C1 60 6 360

C2 132 6 792

C3 120 6 720

C4 264 6 1584

Total contributory area = contributory area x story

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• Consider wind and earthquake combined 25% of DL and apply this load as part of DL. So, multiply DL by 1.25.

DL (ksf)

Factor for WL and

EQ

Calculated DL

C1 0.24 1.25 0.3

C2,C3 0.24 1.25 0.3

C4 0.24 1.25 0.3

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DL (ksf) LL (ksf)

Factored 1.4 DL+

1.7 LL (ksf)

bending factor

factored load

considering bending,

ksf

C1 0.3 0.04 0.49 1.3 0.63

C2,C3 0.3 0.04 0.49 1.1 0.54

C4 0.3 0.04 0.49 1 0.49

C1 corner column; C2, C3 edge column and C4 middle column