Design Guide For Steel Trusses (part 1) 4o5ld

DesignToEurocodes.com - Design guide for steel trusses (part 1).

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Design guide for steel trusses (part 1).

Design guide for steel trusses (part 1).

Trusses are structures comprising one or more triangular units constructed with straight whose ends are connected at ts referred to as nodes.They are the most cost effective solution to a large amount of weight and span great distances. This is the first out of two articles that will present some basic tips for the preliminary design of steel trusses.

8/24/2013 2:04 PM

DesignToEurocodes.com - Design guide for steel trusses (part 1).

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http://www.designtoeurocodes.com/forums/content.php/168-Design-guide-for-steel-trusses-(part-1)

Fink (triangular) trusses are more commonly used for the roof of houses and can span a distance 8-20m. Trusses with N shaped diagonals can span a distance 15-30m. Trusses with N shaped diagonals and secondary can span a distance 30-50m. We use secondary in order to create loading points and reduce the buckling length of the diagonals under compression. There are trusses where their top and bottom chords are parallel to each other. In this case, the distance, H, between the chords should be L/15-L/10.

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The purlins (and all point loads) should only be applied at nodes in order the to be subjected only to axial forces and not to bending moments. The distance between the top chord nodes (and the purlins) should be 1.80-2.40m. Every half-span should be divided into an even number of intervals. By doing this, x bracings of equal length will be placed every three purlins. The minimum height, h, of an N shaped truss is h=0.40-0.50m for L=20m and

8/24/2013 2:04 PM

DesignToEurocodes.com - Design guide for steel trusses (part 1).

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http://www.designtoeurocodes.com/forums/content.php/168-Design-guide-for-steel-trusses-(part-1)

h=1.00-1.20m for L=45m. The maximum height, H, of an N shaped truss is H=4.50m so that it can be easily transported to the construction site. The inclination of the top chord should be 3-25% in order not have water accumulation on the roof. In general it is better the inclination to be more than 20% in order to avoid such problems. The angle between the vertical and the diagonals should be greater than 30o so that the node will be better formed. If this can’t be done, secondary should be used. The diagonal should be always in tension for the predominant loads that are subjected to the truss otherwise the longest should be subjected in tension and the shorter in compression.

A truss can either be simply ed or can be arranged as a portal frame. In the first case the truss doesn’t contribute to the lateral stability of the structure whereas in the second case it does. For simply ed trusses the upper chord is in compression for gravity loading and the bottom chord is in compression for uplift loading. Uplift loads are predominant in open buildings (sheds). For portal trusses each chord is partly in compression and partly in tension.

8/24/2013 2:04 PM

DesignToEurocodes.com - Design guide for steel trusses (part 1).

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http://www.designtoeurocodes.com/forums/content.php/168-Design-guide-for-steel-trusses-(part-1)

Trusses can give economic solutions for spans over 20-25m. The span to depth ratio should be chosen in the range of 15-10. Long span trusses should be divided into two or more parts with maximum length 14-15m in order to be easily transported to the construction site. Please like us on facebook or follow us on twitter to stay informed of all the latest news and articles. Categories: Steel Design Tags: span to depth ratios, truss design

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8/24/2013 2:04 PM