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Roof Truss Design for Bhopal

The document details the design of roof truss members AB, AL, and BL for an industrial building in Bhopal, India. Given the truss geometry, loading conditions from dead load, live load and wind load, and material properties, it calculates the forces in each member and selects appropriate ISMB cross sections based on the required areas.

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139 views3 pages

Roof Truss Design for Bhopal

The document details the design of roof truss members AB, AL, and BL for an industrial building in Bhopal, India. Given the truss geometry, loading conditions from dead load, live load and wind load, and material properties, it calculates the forces in each member and selects appropriate ISMB cross sections based on the required areas.

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Design of Roof Truss Members AB, AL, and

BL
Your Name
May 28, 2024

1 Introduction
This document details the design of members AB, AL, and BL for a roof truss
in an industrial area of Bhopal. Given the truss geometry, loading conditions,
and wind speed, we perform the calculations and select appropriate ISMB
sections.

2 Given Data
• Span of truss: 12 meters

• Half-span: 6 meters

• Truss spacing: 5 meters

• Angle at joint A: 20◦

• Weight of GI sheets: 180 N/m2

• Self-weight of purlin: 200 N/m

• Basic wind speed: Vb = 39 m/s

• Coefficients: K1 = 1.0, K2 = 0.98, K3 = 1.0, (Cpe − Cpi ) = −0.3

1
3 Load Calculations
3.1 Dead Load (DL)

Weight of GI sheets = 180 N/m2 × 3 m = 540 N/m


Self-weight of Purlin = 200 N/m
Total DL per meter length = 540 N/m + 200 N/m = 740 N/m
DL per panel point = 740 N/m × 1.5 m = 1110 N = 1.11 kN

3.2 Live Load (LL)

Live Load = 0.75 kN/m2 × 3 m = 2.25 kN/m


LL per panel point = 2.25 kN/m × 1.5 m = 3.375 kN

3.3 Wind Load (WL)

Vz = Vb × K1 × K2 × K3 = 39 × 1.0 × 0.98 × 1.0 = 38.22 m/s


Pz = 0.6 × Vz2 = 0.6 × (38.22)2 = 876.98 N/m2 = 0.877 kN/m2
WL = Pz × (Cpe − Cpi ) = 0.877 kN/m2 × (−0.3) = −0.2631 kN/m2
Wind Load = −0.2631 kN/m2 × 3 m = −0.7893 kN/m
Total WL per panel point = −0.7893 kN/m × 1.5 m = −1.184 kN

3.4 Combined Load

Total Load per panel point = DL + LL + WL


= 1.11 kN + 3.375 kN − 1.184 kN = 3.301 kN

4 Geometry of Truss Members

Height at joint L (h) = AB × tan(20◦ )


= 6 × tan(20◦ ) ≈ 2.18 meters
p
Length of the diagonal member AL = (AB)2 + (h)2
√
= 62 + 2.182 ≈ 6.38 meters

2
5 Forces in Truss Members
5.1 Force in member AL

Total Load
FAL =
sin(20◦ )
3.301 kN
= ≈ 9.64 kN
sin(20◦ )

5.2 Force in member BL

FBL = Total Load = 3.301 kN

6 Section Check
Using permissible stress for steel:
fy 250 MPa
σpermissible = = ≈ 227.27 MPa
γm0 1.1
Required cross-sectional area for member AL:

FAL × 103
Arequired =
σpermissible
9.64 × 103 N 2
= 2 ≈ 42.4 mm
227.27 N/mm

7 Conclusion
Based on the calculations, the appropriate ISMB section should have a cross-
sectional area greater than 42.4 mm2 to ensure safety and compliance. A
similar check can be performed for member BL. Detailed design should be
verified using structural analysis software and adhering to IS 800:2007 stan-
dards.

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