Question about SPRI (springs): connection to nodes

Hello everyone,

I am examining the use of the spring connecting the pedestrian and the bridge in the ASE example “step_intelligent_load.dat”. This example consists of a simple bridge of QUAD elements, onto which a pedestrian is walking, modeled as a truss element and connected to the bridge with a spring. A time-dependent load is exerted on the top side of the truss element.

The spring is modelled as follows in Teddy:

grp 99
SPRI NO 3 NA 10001 DZ 1 CP 1E3 $ contact moving spring

And in ASE:
MOVS 99003 TYPE QGRP from 1 L0 #dz[m] $ #dz see SOFIMSHA

If I understand it right, the spring is first modeled in node 10001 (which is the bottom side of the truss element), and in ASE it is connected to the QUAD elements with the MOVS command by using “from 1”, because group 1 contains the QUAD elements.

What I don’t quite understand is why the spring cannot just be modeled by defining an end node (NE) on the bridge too, instead of just the node in which the spring acts (NA), because the manual says the following: “Springs can be defined as support conditions or as coupling springs between two nodes. The second node number must not be input in the first case”. This seems to imply that if you don’t define the second node, the spring works as a support, although that’s not what the pedestrian should be.

Any help would be greatly appreciated!

Kind regards