I have few queries-
1. I understand that two different spectra can be defined in spectrum definition option, say I have HORZ and VERT as one set of spectrum which is applicable for few nodes in the system ( say which are below 5 m level) . Few more modes are above 5 m ,where I want to apply different spectra, 5HORZ & 5VERT . (Basically vertical spectra is derived from horizontal one). I define different spectra and then while applying it in dynamic case identify node numbers against each spectrum ( i.e. start node and end node) . Is this approach OK ?

2. If suppose I want to apply ISM for third set of spectrum IHORZ and IVERT. This ISM value of displacement will be only magnitude ( not + ve or -ve ). Please advice. Again I will be identifying the nodes for which this spectra is to be applied.

3. I am having a system which is on an unloading platform. Do I have to apply the ISM at all support nodes or only at anchor nodes ? There are 4 unloading tie-ins ( anchors) . Is it sufficient to apply it only at anchors ? Or I have to apply the unloading platform movement at all support nodes? When I apply at all support nodes there is very high failure in stress.

4. The unloading line then moves to tresstle portion where trestle displacements are different than unloading platform. How to handle such scenarios in modeling?

Regards,
bag_piper