Yes, it can handle any number of machines on the same foundation, including the case of some being idle. Simply, the load from an operating machine represents its contribution to the response. If the machine is idle, motor/compressor combinations. Also, it can model a rectangular hole in the footing.
Yes, it can be used to evaluate the stiffness of foundations resting on homogeneous soil (half-space), two-layer system, and one-layer underlain by bedrock. For soil profile with multi-layers of different stiffnesses, a weighted average of Vs can be calculated and the half-space solution can then be used to calculate the stiffness of the foundation system.
DYNA6.1 does vertical, lateral, rocking and torsional loads.
DYNA6.1 program returns the response of rigid foundations to all types of dynamic loads. The rotation of centrifugal or reciprocating machines, shock-producing machines, earthquakes, traffic and other sources of dynamic forces can produce these loads. The foundation can be supporting single or multiple machines. The response to harmonic loading for a flexible, rectangular mat on elastic half-space or on a group of piles can also be calculated. The stiffness and damping constants of the foundation (needed for the analysis) are evaluated within the program for surface foundations, embedded foundations and piles, pile interaction in a group and other features. For rigid footings, all six degrees of freedom are considered as coupled.
DYNA6.1 is the right software for the job you describe. It can calculate the frequency-dependent stiffness and damping constants of both shallow and pile foundations to different types of dynamic loads.
The main advantage of DYNA6.1 is its ability to calculate the frequency dependent stiffness and damping constants of both shallow (footing) and deep (pile) foundations. This stiffness and damping constants can then be used to represent the foundation flexibility in your finite-element modeling to obtain the response. For the case where the foundation can be considered to behave as a rigid body, the program can also calculate the dynamic response to different types of dynamic loads (harmonic, transient, impact or random). The program DYNA6.1 complements the FE design tool you have. As a matter of fact, it offers an essential component of the design. As you probably know, the stiffness and damping constant of a foundation system subjected to dynamic loading (which is the case for foundations supporting turbines and generators) are a function of the frequency of the loading, which is in turn a function of the operating speed of the equipment. This is particularly crucial for deep foundations, and for shallow foundations resting on layered soil or homogeneous soil with Poisson's ratio approaching 0.5. In any of these cases, successful design requires the evaluation of the stiffness and damping constants representing the soil (what you describe as simple springs) must be calculated with due consideration of the loading frequency. Only DYNA6.1, not the FE model, can calculate this stiffness and damping constants. To summarize, the program DYNA6.1 can be used to calculate stiffness and damping constants, as well as the response in all types of foundations (assuming rigid body models) to different types of dynamic loads. It can also calculate stiffness and damping constants that can be later in an FE model to represent the soil (soil or pile springs).
Yes, it can handle all the tasks you describe.