In a time-dependent Dynamics analysis, the dynamic load is defined through a combination of a dynamic load value and a time-history function, with the latter being a collection of load multiplier values over time (see Figure 1).
When a dynamic load is activated in a given dynamic phase, the value of each of its components (e.g., along y-direction) at each instant of dynamic time, t, is given by:
qy(t) = qy,start,ref x multipliery(t)
See also How to activate a dynamic load.
Figure 1. Definition of Load Multiplier
Of the various options for load distribution, the Perpendicular distribution is relevant for application of load acting normal to the plane. In conjunction with a circular plane, selection of this Perpendicular distribution results in a uniform load acting radially against the circular plane.
This can be useful when applying perpendicular distributed loads on circular tunnels (PLAXIS 2D and PLAXIS 3D), or circular volume piles or shafts in PLAXIS 3D.
The calculation will scale the dynamic component’s load values with the load multiplier in the Cartesian directions. To keep the load perpendicular, the dynamic load multipliers should apply the same factor for these cartesian directions. In this case, for a perpendicular load in the XY-plane (e.g. PLAXIS 2D or the horizontal plane in PLAXIS 3D) the input field of Multiplierx and Multipliery, should use the same Load Multiplier (Figure 2): internally the program resolves the multiplier values in the x-direction and y-direction along the circular plane, accordingly.
Figure 2. Definition of Dynamic Load Acting Radially against Circular Plane
How to activate a dynamic load [Tips and Tricks]
Time step used in dynamics calculation [Tips and Tricks]
How to prescribe a dynamics displacement [Tips and Tricks]
On the use of dynamic boundary conditions [Tips and Tricks]