I have a simple test problem which consists of two pieces of plate joined together at their edges with a spring connector. One piece is fixed, the other free to move. Both have been meshed using shell elements. If the spring constant is 10000 N/m and the load is 10 N then Simulation reports a displacement of 1 mm - All as expected.
However if I apply a preload of 10 N within the spring element, then I would expect a displacement of 0 mm, however it Simulation still reports 1mm displacement, as it does for any other preload I care to use.