Load Calculation and Design of Purlin

LOAD COMPUTATION: Case-1 (101.6M purlin pipe) Note: this sheet only contains load computation and design of purlin. For desing of truss refer another attachment

Grade of steel tubular pipe used

Yst25

As per IS 1106-1963

Purlin size 101.60mm (M) Height of Truss Length of Top Chord Equal spacing of purlins on chord

2.5 m 7.844 m 1.310 m

Unit wt of material CGI sheet

2 0.142 KN/m

CGI sheet

0.199 KN/m

1. DEAD LOAD Truss Spacing Equal spacing of purlins on chord Bottom Chord Length Half of bottom chord due to symmetical Length of Top Chord Roof slope Self weight of Purlin/m (Out dia 101.6x4.5 M)

2

5.080 1.310 14.870 7.435 9.005 0.322 0.0975

= 0.142+0.142*40/100=0.1988KN/m2 (40% additional for lapping of CGI sheet )

m m m m m rad KN/m

Weight of CGI Sheet Self wt. of purlin Total dead load

1.324 KN 0.495 KN 2.002 KN

10% increased due to cleat plates, nuts, bolts

Total dead load on purlin (Wd) Total dead load on truss

0.394 KN/m 2.002 KN

(Total dead load /spacing of purling) (dead load on purlin*length of purlin pipe)

2. LIVE LOAD 2 0.75 KN/m

Live load

2

Minimum imposed load roof where access not provided IS 875

Live load as per IS 875 for roof slope >10º

0.581 KN/m

= 0.75-0.02*(18.44º-10) refer IS 875

Live load on purlin Live load on truss structure

0.722 KN/m 2.446 KN

= 0.581*cosθ*spacing of purlin (1.306m) = 2/3*0.581*cosθ*spacing of purlin*spacing of truss (reference IS 875 & LS Negi book)

3. WIND LOAD Pz = Where, Vb = k1 = k2 = k3 =

Slope less than 3° Slope greater than 3° Where, Z L s F= Where, Cpe = Cpi =

0.6 Vz2

basic wind speed in m/s at 10m height. Probability factor (or risk coefficient) Terrain, height and structure size factor Topography factor = 1 for upwind slope θ>3º = k3=1 k3=1+C.s 1 to 1.36 for upwind slope θ>º C=Z/L Height of crest or hill Projected length of upwind zone from avg. ground level to crest in wind direction. factor, it is dermined from cliff and escarpment fig. (Cpe - Cpi)*Apz external pressure coeffient internal pressure coefficent

Basic wind speed (Vb) k1 k2 k3 VZ

47 m/s 1.07 1 1.054 53.006 m/s 2

1685.760 N/m

Pz

2

1.686 KN/m

Pz Width of building Length of building Height of building h/w

Probability factor of risk (refer table) Terrain, height, structure size factor (refer table)

w l h

15.1 31.8 12.5 0.8278146

m m m m

0.5 < h/w < 1.5

θ=18.447º Wind ward 0 0 EF GH -0.7621 -0.515

Wind angle Face Cpe

Lee ward 90 90 EG FH -0.8 -0.6

Assuming the building to be of medium permeability Cpi = Cpe+Cpi = Cpe-Cpi

0.5

-0.5

-0.2621 -1.2621

-0.015 -1.015

-0.442 upward -2.128 upward

Wind pressure -0.025 -0.506 upward upward -1.711 -2.191 upward upward

-0.3 -1.3

-0.1 -1.1

-0.169 upward -1.854 upward

KN/m2 KN/m2

2

2.1915 KN/m 2.871 KN/m 14.584 KN

Design wind load intensity Wind load on purlin Wind load on truss (nodal load)

upward upward

Design of purlin Permissible bending stress in extreme fibres in Tension and Compression as per IS:806-1968 Grade Fb Yst21 Yst25 Yst32

kgf/cm2 1400 1655 2050

N/mm2 137 162 201

Selected material for design of Purlin and Truss

Case-1 (DL+WL) Select 101.6mm dia. medium pipe Modulus of section Dead load

3 29100 mm 0.394 KN/m

vertical W2= 0.393/1.33 (if wind is load considered combination of dead load W1=2.576/1.33 and wind load is 33% less effective)

Total vertical load Wind load

W2 W1

0.296 KN/m -2.159 KN/m

Mx = (w1+w2*cosθ)*L*L/10 My= (w2*sinθ)*L*L/10

Mx My

4845172.4 Nmm 241911.14 Nmm

Maximum fibre stress= Mx/Zx+My/Zy

σbc or σbt σbc or σbt

174.814

2

174.814 N/mm

Case-2 (DL+LL) Select 101.6mm dia. medium pipe Modulus of section

2

N/mm

3 29100 mm

>162 N/mm2 Not OK 2

>150 N/mm Not OK

As per IS 806-1968 As per IS 806-1984

Dead load Live load Total vertical load

W2

0.394 KN/m 0.722 KN/m 1.116 KN/m

Wind load

W1

0 KN/m

Mx = (w1+w2*cosθ)*L*L/10 My= (w2*sinθ)*L*L/10

Mx My

2732645.5 Nmm 911520.49 Nmm

Maximum fibre stress= Mx/Zx+My/Zy

vertical vertical

Perpendicular to CGI sheet 2.73264545 0.91152049 2

125.22907 N/mm

<162 N/mm2 OK