Week 2 Challenge

Effective net area along section (1-2-3-4)

n=4, dn=20+2=22mm, t=20mm

An=(b-ndn)t

An=(260-4x22)20º

An=3440mm2

Along section (1,2,7,11,12)

n=5, n'=2, p=60,g=60

An= [(b-ndn)+n'xp2/4g]t

An=[(260-5x22)+2x60x60/4x60]x20

An=3600mm2

Along section (5,6,10,11,12)

n=5,n'=1,p=60,g=60,t=20mm

An=[(b-ndn)+n'xp2/4g]t

An=[(260-5x22)+1x60x60/4x60]x20

An=1100mm2

minimum net area=1100mm2

For zig zag bolting

Effective net area along section (1,2,3,4)

n=2,dn=20+2=22mm,t=20mm

An=(b-ndn)t

An=(260-2x22)x20

An=4320mm2

Along section (4,3,6,10,9)

n=3, n'=2, p2=60x50, g=60

An=[(b-ndn)+n'xp2/4g]t

An=[(260-3x22)+2x60x50/4x60]x20

An=4380mm2

Along section (8,7,6,5,10,9)

n=4, n'=1, p=50, g=60,t=20mm,dn=22mm

An=[(b-ndn)+n'xp2/4g]t

An=[(260-4x22)+1x50x50/4x60]x20

An=3648.33mm2

minimum net area of plate section=3648.00mm2

Angle ISA200x100x12

Bolt=M20=20mm, dn=20+2=22mm

Plate width b=200+100-12=288mm

g'=70+60-12=118mm

Critical section ABCD

An=(288-2x22)x12

An=2928mm2

Critical section AEF

An=(288-2x22+50x50/4x90)x12

An=3011.33mm2

Critical section AEGH

An=(288-3x22+50x50/4x90+50X50/4X118)x12

An=2810.88mm2

minimum net area of plate section=2810.88mm2

2) Sag rod design problem

Rafter spacing=8m

purlin spacing=1.2m

slope of rafter=15º

Self weight of roofing=60kg/m2

=(60x9.81)=588.6N/m2

Selfb weight of purlin=100kg/m=981N/m

Live load=75kg/m2=735.75N/m2

Total dead load=588.6x1.2x8+981x8=5650.56+7848=13498.56N

Total live load=7063.2N

Total (dead+live)load=20561.76N

Load on each sag rod=(20561.76/3)xSin15º=1775.17N

Tdn=0.9xAnxFy/γm1

1775.17=0.9xAnx250/1.25

An=9.86mm2

π/4xd2=9.86

d2=9.86x4/π=12.56

d=3.54mm

3)Tdg=AgxFy/γm0

Ag=Tyxγm0/Fy=500x10³x1.1/350=1571.43mm2

Provide gross section area

a) Ag=1571.43+200=1771.43mm2

b)Ag=1.15x1571.43=1807.14mm2

Choose angle section from steel table

ISA 125X75X10

Ag=1902mm2

Cxx=42.4mm

γmin=16.1mm

design strength due to yield

Tdg=AgxFy/γm0=1902x350/1.1x1000=605.182KN

It is greater than Ty hence safe.

design strength due to rupture of critical section-

Tdn=αxAnxFy/γm1=0.8x1902x490/1.25x1000=596.46kn

Tdn>500KN hence safe.