5 Design Examples

7/17/2019 5 Design Examples

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8.5 Design Examples

8.5.1 Design example (slab base)

A built-up steel column comprising two ISWB 400 RSJ sections with their

webs spaced at 32mm and connected b! "0 mm thic# battens transmits an

a$ial load o% 2000 #&' SB( o% boil at site)300#&*m2' +he sa%e permissible stress

on the concrete bed) 4&*mm2' ,esign a suitable %oundation %or the column

adopting a slab base and s#etch the details o% the %oundation'

1. Data

A$ial load on column ) 2000#&

.ermissible compressi/e stress on concrete ) 4&*mm2

(olumn built up o% two ISWB 400 RSJ sections connected b! "0 mm thic#

battens'

2. Column base

Area o% base plate ) 2000 * 40001 ) 0' m2

using a suare base plate

Side length o% base plate ) ) 0'0 m

Adopt a base plate o% si5e 0mm $ 0mm'

Re%erring to %igure 6'"0 the pro7ection o% the base plate %rom the edge o% the

column is obtained as

a ) greater pro7ection

) 0'0 - 4201 ) " mm

b ) smaller pro7ection

) 0'0 - 21 ) ""2' mm



Intensit! o% pressure on base plate

) 3' &*mm2

.ermissible bearing stress in base plate sbs ) "6&*mm2

+he thic#ness o% the base plate is obtained %rom the relation

22

bs

3w bt a

4

= − ÷ ÷σ

Aiming the thic#ness o% base plate

( )2 2 m0s f

yt 2.5w a 0.3b t

f γ = − >

Figure 8.10 Column base plate

223 x 3.56 112.5

165 37mm185 4

− = ÷ ÷



Adopt a base plate o% si5e 0mm $ 0mm $ 40mm'

3. Cleat angle

8or connecting the column section to the base plate adopt ISA "00 $ "00

$ "0 mm angles with %our 22mm diameter ri/ets on %lange side and ISA $ $

6 mm with three 22mm diameter ri/ets in the webs'

8.5.2 Design example (gusseted base)

8or the built-up column o% design e$ample 6''" design a suitable

%oundation adopting a gusseted base'

1. Sie o! base plate

Area o% base plate ) 2000 * 40001 ) 0' m2

Adopt ISA "0 $ "00 $ "2 mm gusset angles on the %lange side with

"00mm leg hori5ontal gusset plate "2mm thic# "0 mm batten and co/er plates'

9inimum length reuired allowing 30mm pro7ection on either side in the direction

parallel to the webs

) 400 : 20 : 24 : 200 : 01 ) 04mm

;ength o% base plate parallel to the %langes ) 0mm'

Adopt a base plate o% si5e 0mm $ 0mm as shown in 8ig '2a

2. "#i$%ness o! base plate

Intensit! o% pressure below the plate



w ) 2000 $ "03 * 0 $ 01 ) 3' &mm2

Re%erring to 8ig '2b cantile/er pro7ection o% plate %rom the %ace o% the

gusset angle ) "4" mm'

Bending moment22 3.55 x 141wL

M 35288 N / mm2 2

= = = ÷ ÷ ÷ ÷

I% t ) thic#ness o% plate reuired

2 bs

bs

btM

6

6 x 352886Mt 33.8mm

b 185 x 1

σ= ÷ ÷

= = =σ

In ;S, &o allowable being stress

In WS, σb allow )0' % !

+hic#ness o% base plate ) t - thic#ness o% angle leg1 ) 33'6 - "21 ) 2"'6mm

Adopt 0 $ 0 $ 22 mm base plate'

3. Conne$tions

<utstand on each side ) 0 - 4001*2 ) " mm

;oad on each connection ) " $ 0 $ 3'1*"000 ) 4 #&

=sing 22mm diameter ri/ets

Ri/et /alue in single shear )

2x 23.5 x 10043.4kN

4 x 1000

π= ÷ ÷

Ri/et /alue in bearing )23.5x12x300

84.6kN1000

= ÷



+here%ore least /alue o% ri/et ) 43'4#&

&umber o% ri/ets ) 4*43'41 ) ""

Adopt " ri/ets connecting gusset angles with plate and the same number o%

ri/ets to connect the gusset plate with the column' +he arrangement o% ri/ets and

the details o% the gusseted base are shown in 8ig 6'"2

8.12 (a) Details o! base plate



(b) Cantille&er pro'e$tion

Fig 8.12 usset and base plate details

8.5.3 Design example (grillage !oundation)

,esign a suitable grillage %oundation %or the gusseted column o% design

e$ample 6''2 which supports an a$ial load o% 2000#&' Assuming SB( o% soil at

site ) 300 #&*m2 draw the ele/ation and plan o% the grillage %oundation'

1. rea o! grillage

=sing gusseted base %or the column

+otal load on %oundation

) 2000#& : "0> %or sel% weight o% %oundation1

) 2200 #&



+wo tiers o% girders will be used'

Bottom-tier area ) 2200*3001 ) '33 m2

=sing a suare grillage side length ) 7.33 ) 2'2 m

Adopt a grillage o% si5e 2'm $ 2'm'

Allowing "2mm concrete co/er on all the sides the o/erall si5e o% the grillage

bloc# ) 3'0m $ 3'0m1



Fig 8.13 rrangement o! ri&ets and details o! gusseted base

2. Design o! top*tier girders

+he bending moment is obtained as 9 ) W*6 ; - ;"1

Where W ) a$ial load on column ) 2000#&

; ) length o% grillage ) 2'm

;" ) length o% base plate ) 0'm

9 ) 2000*6 2' - 0'1 ) 00#&m

Allowable stress can be increased b! 33'33> since the beams are encasedin concrete'

+here%ore σbt ) " $ "'331 ) 220 &*mm2

64 3

bt

500x10MZ 227 x10 mm

220

= = = ÷ ÷ ÷σ

Section modulus



=sing three beams in top tier

? %or each beam ) 22 $ "04 * 31 ) 00mm3

=se ISB9 30 ha/ing the section properties

?$$ ) 6@00 mm3

t% ) "4'2 mm

tw ) 6'" mm

+he ma$imum shear %orce is gi/en b! ( )1

WV L L

2L

= − ÷

) 2000 * 2 $ 2'1 2' - 0'1 ) 30 #&

Shear %orce per beam ) 30 * 31 ) 243'33 #&

A/erage shear stress τ/ ) 243'33 $ "03 * 6'" $ 301

) 6 &*mm2 "00 &*mm2

minimum gap between two beams ) mm

3. Design o! bottom*tier girders



B9 is obtained as

( )

( )

2

64 3

bt

WM L L

8

2000

2.75 0.758

500x10MZ 227 x10 mm

165x1.33

= −

= − ÷

= = = ÷ ÷ ÷σ

=sing eight beams in the bottom tier

? %or each beam ) 23@ $ "04 * 61 ) 2@6 $ "03

=se IS;B 20 ?$$ ) 2@ $ "03mm3

Spacing o% beams ) " * 2' - 0'"21 ) 0'3 m

=se eight beams o% IS;B 20 spaced at 3 mm c*c'

9a$imum shear %orce is gi/en b!

( ) ( )2

W 2000V L L 2.75 0.75 730kN

2L 2 x 2.75

= − = − = ÷

Shear %orce per beam ) 30 * 61 ) @"'2 #&

Shear stress ) τ/ ) @"'2 $ "03 * '" $ 20 1 ) 0 &*mm2 "00&*mm2

Adopt separators made up o% angles ISA 0 $ 0 $ mm and 2' m long

welded or bolted with "2mm diameter bolts to the %langes o% the lower-tier girders

at two ends to pre/ent displacement o% girders'

+he plan and ele/ation o% the grillage %oundation is shown in %igure 6'"4'



Fig 8.1+ ,lan and ele&ation o! grillage !oundation

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5 Design Examples