Specifics of Using Tension Members 2

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. Truss girders and support trusses are especially susceptible to this. What causes the instability here?

The majority of tension members fail due to shortening of the upper chord in the case of solely vertical loads. This leads to a significant increase in the effective length around the minor axis (see the image). In the case of truss girders, the lateral restraint of hinged posts or diagonals leads again to a significant increase in the effective length.

An initial prestress of the roof bracing is not always helpful, since there are major 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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