Long beams can benefit from ultra-thin webs to maximise material usage based on yield strength. However, these thin webs are susceptible to buckling before they reach their full capacity. To prevent this and utilise the post-buckling strength, traditional designs incorporate intermediate stiffeners within the web. Unfortunately, these stiffeners add significant fabrication costs, outweighing the initial economic advantage of a thin web.

Corrugated steel webs emerged as an innovative solution to this challenge. This design allows for efficient use of the web material without requiring the expensive fabrication techniques associated with traditional stiffeners. Beyond cost-effectiveness and improved efficiency, corrugated steel webs can also provide an aesthetic benefit to joists.

Sinusoidal corrugations are the preferred choice among various profiles (including rectangular and trapezoidal) due to their superior resistance to buckling. Unlike trapezoidal profiles with flat sections susceptible to buckling at sharp corners, the smooth, curved form of the sine wave eliminates local buckling entirely. This translates to a significant advantage for structural stability and overall beam performance.

This paper delves into the advantages of sinusoidal corrugated webs, explores their applications in design, and showcases real-world examples that demonstrate their effectiveness.

Advantages of Corrugated Webs
Corrugated webs offer several key advantages over flat webs:

– Increased strength and efficiency: The corrugated pattern improves out-of-plane stiffness and shear resistance. This eliminates the need for additional stiffeners, leading to significant reductions in material and fabrication costs.
– Lighter Weight, Longer Spans: Structures with corrugated webs can be 30-60 per cent lighter than those with flat webs while maintaining load capacity. This allows for designing beams with longer spans without exceeding weight restrictions.
– Improved Aesthetics: The corrugated pattern adds a unique visual element, enhancing the overall aesthetics of the structure.
– Cost-Effectiveness: For beams exceeding 50 m in span, corrugated steel webs in box girders offer a competitive and economical option.

Applications
The following examples demonstrate how corrugated webs can be utilised effectively in bridge design:
– Curved Portal Frames in Exhibition Halls: The lightweight nature of corrugated webs allows for expansive, unobstructed spaces ideal for exhibition halls.
– Horizontally Curved Pedestrian Bridges: The aesthetic appeal and structural efficiency of corrugated webs make them suitable for curved pedestrian bridges.
– Long Gantry Girders in Material Movement: The high strength and reduced weight of corrugated webs are beneficial for long gantry girders used in material handling applications.

Industrial Crane Application
This case study describes the redesign of a crane girder in an industrial building located in Coimbatore, India. The original design consisted of a 12 m span girder supported by columns spaced at 6 m on both ends. Production changes required a column-free space at one end, necessitating a new 30 m span gantry girder.

– Problem: Increased Span and Weight
The increased span significantly increased the bending load on the girder, with its own weight becoming the primary concern. To address this challenge and maintain deflection within limits, a deep girder with a 1.2 m depth was initially considered.

– Solution: Corrugated Web for Weight Reduction
A conventional deep box girder design typically requires stiffeners to improve stability. However, these stiffeners add weight to the already heavy structure. To overcome this limitation, the design was optimised using a corrugated web. This innovative approach allowed for a thinner web without compromising strength, eliminating the need for stiffeners and reducing the overall weight of the girder.

– Successful Implementation and Benefits
After convincing the relevant authorities, the redesigned girder with a corrugated web was fabricated and erected. This solution achieved the desired column-free space while maintaining the girder’s both in-plane and locally. The use of a corrugated web resulted in significant weight savings compared to a conventional design with stiffeners.

Codissia Exhibition Hall (Hall D) – Coimbatore, India
Codissia Industrial Complex, known for housing some of India’s largest exhibition halls, constructed a remarkable 50m x 200m hall back in 1999. In the second phase of development, they built Hall D, featuring a 50m span and 100m length. The architects envisioned a unique curved portal design for this hall, with a maximum cross-section depth of 1.2 metres.

– Challenge: Achieving Strength and Economy
However, standard I-girders with flat webs and numerous stiffeners were deemed too expensive by the client. The challenge was to create a strong and economical design that adhered to the architect’s vision and depth restriction.

– Solution: The Power of Corrugated Webs
The answer came in the form of a 1.2m deep box girder with a corrugated web. This innovative design utilised 3mm thick web plates, press-braked into a sinusoidal shape and then shop-welded into a closed box section. The entire frame was then erected as a single unit, followed by the addition of purlins.

– Hall D: A Standing Example of Efficiency
Hall D stands as a testament to the structural capabilities of corrugated webs. It effectively handles both direct shear and the torsional shear induced by lateral instability in the 50-metre-long rafters. This project demonstrates how corrugated webs can provide a strong and cost-effective solution for large-scale structures.

– Passage rafter and columns
Both the right-hand end frame’s rafters and posts, and the left-side frame’s curved arch, utilised corrugated web elements for construction. The flanges of the rafters and posts were specifically designed to resist bending (flexure), while the corrugated webs in both elements were optimised to handle shear forces. In the left-side frame’s arch, the continuously curved flanges took on both axial and bending stresses, while the strategically designed web provided shear resistance.

PSG College’s Footbridge: From Curved Walkway to Corrugated Solution
The Coimbatore campus of PSG College of Technology (PSGCT) was previously connected by a footbridge (FOB) that served as a city landmark for many years. Built in 2005, it spanned a busy national highway but was recently dismantled due to highway flyover construction. Plans are underway for a new low-level FOB to be erected soon.

– The Challenge: Designing a Functional Access Ramp
A unique aspect of both the past and the new FOB design is one of the approaches. A horizontal ramp connects the bridge to the second floor of the adjacent main building, which also has elevators. The existing bridge featured a 15-metre long, horizontally curved walkway with a width of 2.4 metres. This walkway was designed as a deep metal deck (750mm) with multiple webs to manage torsional stress.

– The Innovation: Corrugated Webs for Strength and Efficiency
To achieve a deep section without the need for additional stiffeners, the design incorporated corrugated sheet metal web panels. This innovative approach using corrugated webs provided the necessary strength and rigidity for the walkway while maintaining a lightweight and cost-effective solution.

Conclusion
Corrugated web technology offers a compelling alternative for bridge girder design. By combining superior strength, lighter weight, and improved aesthetics with cost-effectiveness, corrugated webs are poised to play a significant role in the future of structural frame construction.

Contributed by
Dr LS Jayagopal, Managing Director, Mithran Structures Pvt Ltd

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