S-Shaped Web Members for Metal Roof Truss Buckling
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Solution Overview
Problem
Metal roof trusses with C-shaped web members are prone to flexural torsional buckling and require thicker metal or additional bracing, increasing costs, while tubular web members are expensive to manufacture and require welding, which adds cost and complexity.
Innovation Solution
The use of S-shaped web members with a central web and parallel flanges and returns, where the center of gravity and shear coincide, reducing the need for heavier gauge metal and eliminating the need for welding, thus lowering production costs and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If C-shaped web members are used, then manufacturing is simpler, but the members are prone to flexural torsional buckling requiring thicker metal or additional bracing
Solution Approach 1:
The patent applies asymmetry by transitioning from a symmetric C-shaped cross-section to an asymmetric S-shaped cross-section. The S-shape creates a more favorable distribution of material relative to the shear center and centroid, improving resistance to flexural torsional buckling while maintaining cold-formed manufacturing simplicity. The asymmetric geometry allows the shear center to coincide with the centroid, eliminating the torsional instability inherent in C-shaped members.
2Strength
If tubular web members are used, then strength is improved, but manufacturing cost increases due to welding requirements
Solution Approach 1:
The patent extracts the welding operation from the manufacturing process by using a cold-formed S-shaped cross-section that can be assembled without welding. This eliminates the costly and time-consuming welding step required for tubular members while maintaining adequate strength through the optimized cold-formed geometry and mechanical fastening methods.
Solution Approach 2:
The patent adopts cold-formed S-shaped members that can be manufactured and assembled more economically than welded tubulars. While individual cold-formed members may have lower inherent strength than thick-walled tubulars, the overall system achieves comparable performance through optimized geometry and connection details at lower cost.
3Ease of manufacture
If C-shaped web members are used, then manufacturing is simpler, but lateral bracing is required increasing production cost
Solution Approach 1:
The S-shaped asymmetric cross-section inherently provides torsional stability by aligning the shear center with the centroid, eliminating the need for additional lateral bracing that would be required for symmetric C-shaped members. This geometric asymmetry built into the cross-section prevents flexural torsional buckling modes.
Data Source
AI summary
The metal truss assembly disclosed herein is made from generally U-shaped metal chords and multiple generally S-shaped web members extending between the chords. A typical truss assembly has a pair of elongated, opposed, diverging metal upper chords and a lower chord, with the chords each forming generally U-shaped channels defining an interior chord space. A plurality of elongated metal web members extend between the upper and lower chords, with each of the web members extending into the interior space of an upper chord and the lower chord and attached to the chords. The web members, as taught herein, have a generally S-shaped cross-section. The shape of the web members is an advancement of prior art web members.