The accuracy of determination of the second-order effects for concrete structures is dependent upon a reasonable estimation of the concrete long term properties. Consequently design codes can require that analysis stiffness adjustment factors are applied to concrete members, (as the appropriate properties to use in analysis are load and time dependent).

For non-concrete members it is also possible that you will want to apply an adjustment to properties for various other investigations. One suggested example is the assessment of steel structures subject to corrosion. Another classic requirement in this regard relates to torsion, it is common engineering practice to assume that if it will work without assuming any torsional strength, then torsion can be ignored.

In order to make these adjustments in Tekla Structural Designer you can apply modification factors from the Analysis Settings dialog.

Note that while modification factors affect analysis (and hence the forces considered in design), they have no effect on Tekla Structural Designer member design checks, including deflection calculations.