Columns and Struts - Economic points - Steel Structures.

Strut design is a relatively straightforward design task involving choice of cross-sectional type, assessment of end restraint and thus effective length, calculation of slenderness, determination of compressive strength and hence checking that the trial section can withstand the design load. Certain subsidiary checks may also be required part way through this process to ensure that the chosen cross section is not slender (or make suitable allowances if it is) or to guard against local failure in compound members.Thus only limited opportunities occur for the designer to use judgement and to make choices on the grounds of economy.

Essentially  these are restricted to control of the effective length, by introducing intermediate restraints where appropriate, and the original choice of cross section.

However, certain other points relating to columns may well have a bearing on the overall economy of the steel frame or truss. Of particular concern is the need to be able to make connections simply. In a multi-storey frame, the use of heavier UC  sections thus may be advantageous, permitting beam-to-column connections to be made without the need for stiffening the  flanges or web. Similarly in order to accommodate beams framing into the column web an increase in the size of UC may eliminate the need for special detailing.

While compound angle members were a common feature of early trusses, maintenance costs due both to the surface area requiring painting and to the incidence of corrosion caused by the inherent dirt and moisture traps have caused a change to the much greater use of tubular members. If site joints are kept to the minimum tubular trusses can be transported and handled on site in long lengths and a more economic as well as a visually more pleasing structure is likely to result.

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