Specifics of Using Tension Members 2

Tips & Tricks

The previous post on this topic describes instabilities that may occur when using tension members. The example shown refers primarily to wall stiffening. Now, instability error messages can also refer to nodes within the range of supports. Especially truss girders and support trusses are susceptible to this. So what causes the instability here?

A major part of tension members fails due to shortening of the upper chord in the case of solely vertical loads. This leads to a significant increase in the effective length about the minor axis (see Figure). In the case of truss girders, lateral restraint of hinged posts or diagonals leads again to a significant increase in the effective length.

An initial prestress of roof bracing is not always helpful, since there are big compressive strains of truss girders due to the relatively small chord and high compression forces. Therefore, the “Failing members to be removed individually during successive iteration” option under the “Global Calculation Parameters” tab seems to be the best option for trusses as well.

By the way: RF‑STABILITY and RSBUCK allow for determination and graphical representation of buckling loads and buckling shapes. With this, instability causes can be recognized easily.

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