DYNA6.1 FAQs - PAGE 2 

 

Question: Can the foundation/pile stiffness values calculated by the software by used by popular structural engineering software such as SAP.

Answer: Definitely yes.


Question:  The vertical and horizontal stiffness are not identical, but if I just divide the group stiffness values by 12 then clearly the values for each individual pile will be the same as each other regardless of the shape of the pile group or their position within the group. It that correct?

Answer: The individual pile stiffness will differ depending on its position within the group. However, the group stiffness already accounts for the interaction between the piles, which depends on the configuration of the pile group. When we divide the group stiffness by the number of piles, we get the average stiffness per pile. This is sufficiently accurate for the purpose of getting the dynamic response of the machine-foundation system (global behaviour). 


Question:  Currently we model our turbine and generator foundations using finite element models (concrete plate elements) where the soil is represented as simple springs and the harmonic forces are placed on concentrated masses at the rotor support points. What I would like to be able to do is to compare the output from DYNA6.1 to our finite element output for the same problem.

Answer: The main advantage of DYNA6.1 is its ability to calculate the frequency dependant stiffness and damping constants of both shallow (footing) and deep (pile) foundations. These 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 these stiffness and damping constants.

To summarize, The program DYNA6.1 can be used to calculate stiffness and damping constants, as well as the response of 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).


Question: We have a power plant project and are now designing a foundation for the gas turbine and generators. I would like to know could DYNA6.1 generate more than one natural frequency of the system (consists of machines + foundation + soil). And how to do that.

Answer: DYNA6.1 will show at least 6 modes (i.e. 6 natural frequencies) associated with the rigid body movements. This means you will have a natural frequency along the vertical and 2 horizontal directions as well as torsional and 2 rocking directions. After you run DYNA6.1, you can plot the responses vs. frequency at the C.G. of the machine-foundation system. These responses will display peaks. The location of the peak identifies the natural frequency.


Question:  Our company has pump foundation design which need be dynamic analysis.

Answer:  DYNA6.1 can solve the problem you cited.  It is very widely used in the industry for similar projects.

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Updated June 24, 2013 by cquintus
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