Week 2 Challenge
1. a)
b = 260mm
d = 20mm
d0 = 20 - 2 = 18mm
t = 20mm
No. of bolts = ((b - 2xe)/p )+1
P = 2.5d = 2.5 x 20 = 50
e = 1.5d = 1.5 x 20 = 30
No. of bolts = ((260 - 2 x 30)/50)+1
No. of bolts = 6
Net section area = ( b - ndo )t
Net section area = ( 260 - 6 x 18) 20
Net section area = 3000 mm^2
b)
b = 260mm
d = 20mm
d0 = 20 - 2 = 18mm
t = 20mm
No. of bolts = ((b - 2xe)/p )+1
P = 2.5d = 2.5 x 20 = 50
e = 1.5d = 1.5 x 20 = 30
No. of bolts = ((260 - 2 x 30)/50)+1
No. of bolts = 6
Net section area = ( b - ndo )t
Net section area = ( 260 - 6 x 18) 20
Net section area = 3000 mm^2
c)
b = 200mm
d = 20mm
d0 = 20 - 2 = 18mm
t = 12mm
No. of bolts = ((b - 2xe)/p )+1
P = 2.5d = 2.5 x 20 = 50
e = 1.5d = 1.5 x 20 = 30
No. of bolts = ((200 - 2 x 30)/50)+1
No. of bolts = 6
Net section area = ( b - ndo )t
Net section area = ( 200 - 6 x 18) 20
Net section area = 1840 mm^2
2.
Assume centre to centre distance of Rafter spaced at 8 m , spacing of purlin = 1.2 m, Self weight of roofing (including thermal insulation)= 60 kg/m2 ,
Wind pressure intensity = 150 kg/m2,Slope of rafter = 15 degrees, Live Load =75 kg/m2. Assume self weight of purlin as 100 kg/m.
F = 5/8 x w x sinO x s x 4
F = 5/8 x 100 x 9.81 x sin15 x 8 x 4
F = 5061.96 N
Areq = F / 0.6fy
pixd^2/4 = 5061.96 / 0.6 x 250
d = 6.5 mm
3.
Assume 4mm weld size , fy = 250MPa, fu = 410 Mpa
approximate gross area = 1.1Tdg/fy = 1.1 x 250 x 1000/250 = 1100 mm^2
from steel table, select ISA 100x75x8mm connected to gusset plate by longer length Cxx = 31mm
area of connected leg = ( 100 - 8/2) x 8 = 768mm^2
area of outstanding leg = ( 75 - 8/2) x 8 = 568mm^2
Ag = 768+568 = 1336mm^2>1100mm^2 ,hence ok
design strength due to yielding of gross section ,
Tdg = Agfy/rmo = 0.91 x 1336 x 250 /1000 = 303.94kn
design strength due to rupture at net section,
Tdn = a An fu/rm1
fu = 0.8x1336x410/1000
fu = 438.21 Kn
design strength due to block shear,
for calculation of block shear, length of weld is required
P1 x 100 = 250 x (100 -31)= 172.50Kn
P2 = 250 - 172.50 = 77.5 Kn
strength of 4mm weld = 0.7 x 4 x 0.462 x 410 = 530.37 kn/mm
effective length of weld on head side = 172.5 x 1000/530.37 = 325mm
effective length of weld on toe side = 77.5 x 1000/530.37 = 146mm
Total welded length = 325 + 146 = 471mm
Avg = Avn = 471 x 8 = 3768 mm^2
Atg = Atn = 100 x 8 = 800mm^2
Tdb1 = 0.525Avg x fy + 0.72 x Atn x fy
= 0.525 x 3768 x 250/1000 + 0.72 x 800 x 410/1000 = 730.31kn
Tdb2 = 0.416 Avn x fu + 0.91Atg fy
= 0.416 x 3768 x 410/1000 + 0.91 x 800 x250/1000 = 824.67Kn
tensile strength provided = 438.21kn, 303.94KN and 730.71KN > 250KN
hence safe.