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How to correctly define a free load?

Definition

A free load differs from a ‘regular load’ by the fact that it is NOT attributed as an additional data to a specific 2D member. A free load can be created at an arbitrary position in space, and afterwards the user can specify to which element(s) the projection of this load is attributed to.

Attention: The geometry of a free load always has to be inputted in the XY plane of the current UCS. It is thus necessary to adapt the UCS in advance, and to assign the XY plane as the Active working plane.

A free load can load all elements which are cut by the projection of the free load. Which elements will be actually loaded by the free load, depends on the parameters Select: Auto(matically), Select; and Validity: All, -Z, Z=0, +Z, From-to.
Validity = -Z means: Only the elements situated under the free load (situated in the half-space defined by the negative Z direction of the UCS at input), can be loaded.
Validity = +Z means: Only the elements situated above the free load (situated in the half-space defined by the positive Z direction of the UCS at input), can be loaded.

 

Example

An apartment building, where it is likely that the same load configuration acts on more than one storey floor.

 

Let’s suppose: Four plates situated right above each other, and a free surface load inputted exactly IN the plane of the 3rd plate.

Main menu > Calculation, Mesh > Calculation; choose ‘Test of input data’
Main menu > Calculation, Mesh > 2D data viewer > Surface loads

1) Select = Auto, Validity = All

2) Select = Auto, Validity = +Z / Validity = –Z
(Attention: The free surface load is placed exactly IN the plane of the 3rd plate.)

3) Select = Auto, Validity = Z=0
(Attention: The free surface load is placed exactly IN the plane of the 3rd plate.)

4) Select = Select, Validity = All
Actions > Update 2D members selection > Select the 1st and 3rd plate
Result: The load only acts on the manually selected plates.

Attention when Select is put to Select, and Validity to e.g. +Z or -Z !