DESIGN OF PURLINS

DL, deck, metal 20 gage = 120 PA

LL, = 1000 PA

WL, = 870 PA

Spacing of purlins = 0.80 M

Spacing of trusses = 5 M

Slope of roofing = 5 / 24

Solution:

HREQD = 5000 / 30 = 166.67 SAY 175 MM

TRY LC 175 X 50 X 20 X 4.5

Properties:

WT = 9.81 KG/M T = 4.50 MM

H = 175 MM SX = 30 X 103 MM3

B = 50 MM SY = 5.5 X 103 MM3

Solution:

Dead load

Wn = 120 ( 0.80 )( cos 11.77o ) + 96.24 ( cos 11.77o )

WN = 188.20 N/M

WT = 120 ( 0.80 )( SIN 11.77o ) + 96.24 ( SIN 11.77o )

WT = 39.21 N/M

LIVE LOAD

Wn = 1000 ( 0.80 )( cos 11.77o )

WN = 783.18 N/M

WT = 1000 ( 0.80 )( SIN 11.77o )

WT = 163.19 N/M

WIND LOAD

Wn = 870 ( 0.80 ) = 696 N/M

WT = 0

LOAD COMBINATION:

I. DL + LL

Wn = 971.38 N/m

Wt = 202.40 N/m

II. DL + 0.75( LL + WL )

Wn = 1297.59 N/m

Wt = 161.60 N/m

III. DL + WL

Wn = 884.20 n/m

Wt = 188.20

By inspection, case II governs

Check for compactness,

502.0

< ? 170

√248

25 > 10.80

Therefore, non-compact

Interaction equation:

1297.59∗5∗58∗58.40∗0.60∗248

+ 161.60∗5∗5

8∗9.50∗0.60∗248

< 1.0

0.82 < 1.0

Therefore, safe!

Check for deflection

δn(dl+ll) = 5∗971.38∗50004

384∗2x 105∗58.40 x 103∗175 /2 <

5000360

7.73 < 13.89

Therefore, safe!

Therefore, use LC 175 X 50 X 20 X 4.5

Purlins spaced @ 800 mm o.c