Truss design

Design of Roof (Pratt) truss

Design Data:-

Plan length of the building l = 10.13mPlan depth of the building w = 5.72mHeight of the building excluding pitched roof h = 3.35mDead weight of AC sheets = 0.13KN/sqmDead weight of purlins,fixtures and false roofing system = 0.45KN/sqmSpan of the truss = 5.49mHeight of the truss = 1.00mSpacing of trusses = 3.30m

0.55KN/sqmDistance between the nodal points(purlin locations) on top rafter = 0.97mWind coefficients:-k1 (risk coefficient assuming 50 years of design life) = 1.00k2 (assuming terrain category 2) = 1.00k3 = 1.0 (topography factor) 1.00

50.00m/sec

0.20Slope of the pitched roof in degrees = 20

Load Calculations:-

Dead Load of roof = 0.58KN/sqm

Dead load/m run on rafter = 1.914KN/m

Live Load = 0.55KN/sqm

Live load/m run on rafter = 1.815KN/m

Calculation of Wind Load:-

Assuming the building is situated in Vijayawada, the basic wind speed is = 50.00m/sec

50.00m/sec

1.50KN/sqm

Wind Load on walls:-

Exposed area of the wall per frame normal to the wind direction, A = 11.06sqm

0.20

Live load on pitched roof (For pitched roof having slope 200 ) =

Basic wind speed Vb =

Internal wind pressure coefficient Cpi (Buildings with low permeability) =

Design wind speed, Vz = k1 k2 k3 Vb =

Design wind pressure, Pd = 0.6*Vz2 =

The wind load, WL acting normal to the individual surfaces is given by

WL = (Cpe – Cpi ) A*Pd

Assuming buildings with low degree of permeability,the internal pressure coefficient Cpi =

For the proposed building, h/w = 0.585664

l/w = 1.770979

From table 4 of IS 875--Part-3:1985,the external wind pressure coefficients are as given below:-

Wind angle Total wind load in KNin degrees Windward Leeward Windward Leeward Windward Leeward

00.7 -0.3 0.20 0.5 -0.5 8.295 -8.2950.7 -0.3 -0.20 0.9 -0.1 14.931 -1.659

90-0.5 -0.5 0.20 -0.7 -0.7 -11.613 -11.613-0.5 -0.5 -0.20 -0.3 -0.3 -4.977 -4.977

Wind Load on Roofs:-

Exposed area of each slope of roof, per frame is 9.64sqm


Wind angle Total wind load in KNin degrees Windward Leeward Windward Leeward Windward Leeward

0-0.7 -0.5 0.20 -0.9 -0.7 -13.014 -10.122-0.7 -0.5 -0.20 -0.5 -0.3 -7.23 -4.338

90-0.8 -0.6 0.20 -1 -0.8 -14.46 -11.568-0.8 -0.6 -0.20 -0.6 -0.4 -8.676 -5.784

Concentrated loads on nodes :-

Dead load at intermediate node points = 1.75KN(corresponding to purlin locations)

Superimposed load at intermediate node points = 1.66KN(corresponding to purlin locations)

Wind load at intermediate node points on windward side = -2.41KN

Wind load at intermediate node points on leeward side = -1.45KN

Vertical component of wind load on windward side@ = -2.26KNintermediate nodal points

Vertical component of wind load on leeward side@ = -1.36KNintermediate nodal points

Vertical component of wind load @ at ridge = -1.81KN

Horizontal component of wind load on windward side@ = -0.82KNintermediate nodal points

Horizontal component of wind load on leeward side@ = -0.50KNintermediate nodal points

Horizontal component of wind load @ at ridge = -0.66KN

Cpe Cpi (Cpe-Cpi)

Cpe Cpi (Cpe-Cpi)

Load combinations :-

i) 1.5DL + 1.5LL

Vertical load windward = 5.12KN

Vertical load leeward = 5.12KN

Vertical load at ridge = 5.12KN

ii) 1.5DL + 1.5LL+1.05WL




Horizontal load windward = -0.82KN

Horizontal load leeward = -0.50KN

Horizontal load at ridge = -0.16KN (Windward side)

The results of analysis using STADD.Pro.2007 are as given below :-


Design Data:-

Plan length of the building l =Plan depth of the building w =Height of the building excluding pitched roof h =Dead weight of AC sheets =Dead weight of purlins,fixtures and false roofing system =Span of the truss =Height of the truss =Spacing of trusses =

Distance between the nodal points(purlin locations) on top rafter =Wind coefficients:-k1 (risk coefficient assuming 50 years of design life) =k2 (assuming terrain category 2) =k3 = 1.0 (topography factor)

Slope of the pitched roof in degrees =

Load Calculations:-

Dead Load of roof =

Dead load/m run on rafter =

Live Load =

Live load/m run on rafter =


Assuming the building is situated in Vijayawada, the basic wind speed is =


Exposed area of the wall per frame normal to the wind direction, A =










l/w = 1.770979020979


Wind angle Total wind load in KNin degrees Windward Leeward Windward Leeward Windward

00.7 -0.3 0.20 0.5 -0.5 8.2950.7 -0.3 -0.20 0.9 -0.1 14.931

90-0.5 -0.5 0.20 -0.7 -0.7 -11.613-0.5 -0.5 -0.20 -0.3 -0.3 -4.977


Exposed area of each slope of roof, per frame is



0-0.7 -0.5 0.20 -0.9 -0.7 -13.014-0.7 -0.5 -0.20 -0.5 -0.3 -7.23

90-0.8 -0.6 0.20 -1 -0.8 -14.46-0.8 -0.6 -0.20 -0.6 -0.4 -8.676












Cpe Cpi (Cpe-Cpi)

Cpe Cpi (Cpe-Cpi)


i) 1.5DL + 1.5LL




ii) 1.5DL + 1.5LL+1.05WL






Horizontal load at ridge = -0.25KN


Member Location Nature of force

1--9 Top chord 26.40 Tension9--7 Top chord 18.00 Tension7--10 Top chord 17.70 Tension10--5 Top chord 27.90 Tension1--2 Bottom chord 1.09 Tension2--3 Bottom chord 1.11 Tension3--4 Bottom chord 1.08 Compression

Force(Case-II)in KN

1 2 3 4 5

9

7

10

1.40

[4'-7"]

1.40

[4'-7 1/4"]

1.40

[4'-7"]

1.40

[4'-7"]

1.49

[4'-10 1/2"]

1.49

[4'-10 1/2"]

1.00

[3'-3 1/4"]

SECTION OF THE TRUSS

4--5 Bottom chord 1.12 Compression9--2 Verticals 0.52 Compression7--3 Verticals 6.49 Compression10--4 Verticals 0.50 Compression9--3 Diagonals 7.09 Tension10--3 Diagonals 9.41 Tension


10.13m5.72m3.35m

0.13KN/sqm0.45KN/sqm

5.49m1.00m3.30m

0.55KN/sqm 25.6266 61.91875 1586.7671.46m

1.001.00 212.43061.00

50.00m/sec

0.2020

24.5 58.25 158.56948.75 58.3 56.68056

215.25

0.58KN/sqm33.25 58.25 215.2014

1.914KN/m

0.55KN/sqm1258.63

1.815KN/m 147.222941.868136.7836

50.00m/sec

50.00m/sec

1.50KN/sqm

11.06sqm

0.20

Total wind load in KNLeeward-8.295-1.659

-11.613-4.977

9.64sqm

Total wind load in KNLeeward-10.122-4.338

-11.568-5.784

(Windward side)

1 2 3 4 5

9

7

10

1.40

[4'-7"]

1.40

[4'-7 1/4"]

1.40

[4'-7"]

1.40

[4'-7"]

1.49

[4'-10 1/2"]

1.49

[4'-10 1/2"]

1.00

[3'-3 1/4"]

SECTION OF THE TRUSS

Design of Roof truss

Design Data:-

Plan length of the building l =Plan depth of the building w =Height of the building excluding pitched roof h =Dead weight of AC sheets =Dead weight of purlins,fixtures and false roofing system =Span of the truss =Height of the truss =Spacing of trusses =

Distance between the nodal points(purlin locations) on top rafter =Wind coefficients:-k1 (risk coefficient assuming 50 years of design life) =k2 (assuming terrain category 2) =k3 = 1.0 (topography factor)

Slope of the pitched roof in degrees =

Load Calculations:-

Dead Load of roof =

Dead load/m run on rafter =

Live Load =

Live load/m run on rafter =


Assuming the building is situated in Vijayawada, the basic wind speed is =


Exposed area of the wall per frame normal to the wind direction, A =










l/w = 1.8769106999195



00.7 -0.25 0.20 0.5 -0.45 9.0541710.7 -0.25 -0.20 0.9 -0.05 16.29751

90-0.5 -0.5 0.20 -0.7 -0.7 -12.67584-0.5 -0.5 -0.20 -0.3 -0.3 -5.432503


Exposed area of each slope of roof, per frame is



0-0.88 -0.4 0.20 -1.08 -0.6 -32.28385-0.88 -0.4 -0.20 -0.68 -0.2 -20.32687

90-0.75 -0.6 0.20 -0.95 -0.8 -28.39783-0.75 -0.6 -0.20 -0.55 -0.4 -16.44085












Cpe Cpi (Cpe-Cpi)

Cpe Cpi (Cpe-Cpi)


i) 1.5DL + 1.5LL




ii) 1.5DL + 1.5LL+1.05WL






Horizontal load at ridge = -0.20KN


Member Location Nature of force

1--9 Top chord 26.40 Tension9--7 Top chord 18.00 Tension7--10 Top chord 17.70 Tension10--5 Top chord 27.90 Tension1--2 Bottom chord 1.09 Tension2--3 Bottom chord 1.11 Tension3--4 Bottom chord 1.08 Compression4--5 Bottom chord 1.12 Compression9--2 Verticals 0.52 Compression7--3 Verticals 6.49 Compression10--4 Verticals 0.50 Compression9--3 Diagonals 7.09 Tension10--3 Diagonals 9.41 Tension

Force(Case-II)in KN

Design of Roof truss

23.33m12.43m

3.81m0.13KN/sqm0.45KN/sqm

12.20m1.52m3.30m

0.67KN/sqm 25.6266 61.91875 1586.7671.26m

1.000.98 212.43061.00

50.00m/sec

0.2014

24.5 58.25 158.56948.75 58.3 56.68056

215.25

0.58KN/sqm33.25 58.25 215.2014

1.914KN/m

0.67KN/sqm1258.63

2.211KN/m 147.222941.868136.7836

50.00m/sec

49.00m/sec

1.44KN/sqm

12.57sqm

0.20

Total wind load in KNLeeward

-8.1487539-0.9054171

-12.6758394-5.4325026

20.75sqm

Total wind load in KNLeeward

-17.93547-5.97849

-23.91396-11.95698

3.78

(Windward side)

Truss design

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