Design and Analysis of Truss Systems for a Steel Shed with Wind Loading - A Case Study

Abstract

This paper insights into a detailed case study of the structural design and static analysis of a Pratt truss system for a single-bay steel industrial shed. It looks at different load combinations such as dead load, live load, and wind load following IS: 875 standards. The team modeled a 12-meter span shed with a 4:12 roof pitch and checked it against three different wind exposure categories. To find the member forces, used both the method of joints and the method of sections, focusing on the critical load combination: 1.2 DL + 1.6 LL + 0.8 WL. The parametric study shows wind uplift plays the biggest role in sizing upper chord members, while the internal pressure coefficient matters most for web members that reverse forces. Designed the selected members to IS: 800-2007 standards using plastic section classification. The study shows Pratt trusses outperform Howe and Fink trusses when wind uplift dominates, coming in at 10-14% less weight compared to configurations optimized just for gravity loads.

Introduction

This case study presents the analysis and design of a steel industrial shed roof truss subjected to dead, live, and wind loads. Industrial steel sheds are commonly used for warehouses, workshops, and agricultural storage because they are lightweight, economical, and easy to construct. However, their open-bay configuration makes them highly susceptible to wind loads, which can cause roof uplift and significant lateral forces.

Objective of the Study

The study investigates a 12 m span Pratt roof truss located in Nagpur, India (Wind Zone III) with the following objectives:

1. Determine design loads according to IS 875 Parts 1, 2, and 3.
2. Analyze the Pratt truss under critical load combinations using the method of joints.
3. Design critical members according to IS 800:2007.
4. Evaluate the effect of different wind attack angles (0°, 45°, and 90°).

Structural Details

Shed Geometry

• Plan dimensions: 12 m × 30 m
• Truss spacing: 6 m
• Eave height: 4 m
• Roof slope: 18.43° (4:12 pitch)
• Truss type: Eight-panel symmetric Pratt truss
• Span: 12 m
• Rise: 2 m

The Pratt truss was selected because it efficiently carries roof loads through tension and compression members, making it economical for industrial structures.

Design Loads

1. Dead Load (DL)

Includes:

• Roofing sheets
• Purlins
• Truss self-weight

Total dead load:

• 0.30 kN/m²
• Equivalent nodal load: 2.7 kN per node

2. Live Load (LL)

Based on roof slope reduction as per IS 875 Part 2:

• Live load intensity: 0.58 kN/m²
• Nodal load: 5.22 kN

3. Wind Load (WL)

Wind loading was calculated according to IS 875 Part 3:

• Basic wind speed: 44 m/s
• Design wind speed: 46.1 m/s
• Design wind pressure: 1.276 kN/m²

The most critical case occurred when wind acted parallel to the ridge (90°), producing:

• Net pressure coefficient = −1.0
• Maximum uplift pressure = −1.276 kN/m²
• Nodal uplift force = −11.48 kN

Wind uplift was found to be the governing load condition.

Load Combinations

Four load combinations were evaluated:

Governing Case

LC3 (0.9 DL + 1.5 WL) was identified as the most critical combination because wind uplift reversed forces in several members.

Factored uplift load:

• −14.79 kN per node

Truss Analysis

Using the method of joints, support reactions and member forces were determined.

Support Reactions

Under gravity loading:

• Left support reaction = 41.58 kN
• Right support reaction = 41.58 kN

Critical Member Forces

A key observation was that some members changed from tension to compression under wind uplift, requiring design for force reversal.

Member Design (IS 800:2007)

Top Chord Design

• Section: Double angle 2 ISA 100×100×10
• Compression force: 131.6 kN
• Design capacity: 776.4 kN

Result:

• Capacity greatly exceeded demand.
• Utilization ratio = 0.17
• Section is safe.

Bottom Chord Design

• Section: ISA 100×100×10
• Tension force: 124.7 kN
• Design strength: 432.5 kN

Result:

• Member is safe under tension loading.

Connection Design

• M16 HSFG bolts used.
• Required bolts at critical gusset connection:
  • 4 bolts

Wind Angle Parametric Study

Three wind directions were examined:

Key Finding

Wind acting parallel to the ridge (90°) generated the largest member forces and therefore represents the critical design condition.

Conclusion

Design and Analysis of an 8-panel Pratt Roof Truss for 12m span for industrial application. Steel shed in Wind Zone III has been performed. The following conclusions are drawn: 1) Wind at 90° to the ridge with dominant opening on the windward wall (Cpi = +0.20) Generates the important design loads. The governing load combination is LC3 (0.9 DL + 1.5) For top chord & diagonal members, the WL should be used, not LC1. 2) Member force reversal due to wind uplift is essential: bottom chord tension members See up to 32% gravity tension value compression reversal. These must be Reclassified and designed to be compression members, as required, with appropriate slenderness checks. 3) The designed sections (2ISA 100×100×10 for top chord; ISA 100×100×10 for bottom the minimum sizes for purlin attachment and welding (chord) are applicable. 4) This corresponds with the findings of other similar pH studies, which did not rely on computed forces. Lightweight shed structures. 5) The Pratt truss will be determined to be the most structurally efficient for the combined loading regime of this shed. Its diagonals are kept in tension for the majority of the time. Simply gravity and wind load combinations and thus do not unnecessarily load compression members. Howe or Fink alternatives are available, but may also include penalties. 6) Extension to dynamic wind effects, in time domain, should be considered for future work. Simulations for higher wind zones, and interaction of truss flexibility. The forces that the cladding fasteners have to resist.

References

[1] Bureau of Indian Standards. IS: 875 (Part 1) — Dead Loads. BIS, New Delhi, 1987. [2] Bureau of Indian Standards. IS: 875 (Part 2) — Imposed Loads. BIS, New Delhi, 1987. [3] Bureau of Indian Standards. IS: 875 (Part 3) — Wind Loads. BIS, New Delhi, 2015 (revised). [4] Bureau of Indian Standards. IS: 800 — Code of Practice for General Construction in Steel. BIS, New Delhi, 2007. [5] Duggal, S.K. Design of Steel Structures. 4th ed., Tata McGraw-Hill, New Delhi, 2014. [6] Subramanian, N. Steel Structures: Design and Practice. Oxford University Press, New Delhi, 2010. [7] Holmes, J.D. Wind Loading of Structures. 3rd ed., CRC Press, Boca Raton, 2015. [8] Gere, J.M. & Goodno, B.J. Mechanics of Materials. 8th ed., Cengage Learning, 2012. [9] Trahair, N.S., Bradford, M.A., Nethercot, D.A. & Gardner, L. The Behaviour and Design of Steel Structures to EC3. 4th ed., Taylor & Francis, 2008. [10] Eurocode 1: EN 1991-1-4:2005 — Actions on Structures: Wind Actions. CEN, Brussels, 2005.

Copyright

Copyright © 2026 Onkar Kalwade, Manoj Wagh, Shashir Daule. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.