Dynamic load cases

Dynamic load cases cover the following:

• response to a harmonic vibration,

• response to a seismic load.

A dynamic calculation is carried out for defined dynamic load cases simultaneously with a static calculation. Dynamic load cases can be arbitrarily combined with static load cases. As a result, SCIA Engineer provides for a direct combination and evaluation of results for static and dynamic analysis. For example, both static and dynamic wind can be included into one selective group and the program automatically determines which one is more unfavourable.

Dynamic load cases can be input only after mass groups and their combinations have been defined. A dynamic load case can be input as a standard variable load case; only its type must be set to dynamic. Impulses, usually but not exclusively point impulses in nodes, can then be defined in these load cases.

A load factor can be defined for a dynamic load case. The meaning of the factor is the same as for static load case. Other parameters of a dynamic load case depend on its type.

The meaning of the nodal impulse differs according to the type of dynamic load case. No impulses appear in eigenvalue problem (free vibration analysis) or in seismic calculation. For harmonic vibration, impulses of exciting forces must be specified.

In case of dynamic wind, impulses from static wind are defined. The impulse size is 1 kN/m2 regardless of the height (i.e. the product of node-corresponding area and shape coefficient). For orthogonal vibration, one must specify the node-corresponding length of cylindrical parts of the structure where vibration can occur.