| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Area: | |
| Date Logged & Current Version | Nov 2022 12.08.03.015 |
Problem:
How to model springs that are mounted in series? as shown below
Solution:
This support detail may be used in situations where a single spring does not have the movement requirements and / or a constant spring is too expensive compared to multiple individual variable springs.
Modeling approach:
As of Dec 2022, AutoPIPE’s hanger analysis will not correctly select multiple individual springs in series as pictured above. In fact, modeling this correctly in AutoPIPE is not easy. One cannot not just connect one spring to another using a short beam / segment as the model fails on E801-1 Fatal error due impart to the unsecured segment / beam in the middle. Next, if a flexible anchors was added to this arrangement, yes the model will analyze, however the results are wrong, the hanger analysis actually changed the 2nd spring to a rigid because the program thought the first spring was handling the entire load without assistance from the 2nd spring.
Avoidance:
Option #1:
Run AutoPIPE’s hanger analysis to size a single spring.
Outside of AutoPIPE, hand calculate a set of spring in series that have the same characteristics.
Option #2:
When considering 2 springs in series, one could enter in the combined cold load and spring rate into spring support dialog screen.
From Mechanical Engineering lab experiments, recall that 2 springs in series has a much softer overall stiffness
Since 1/Ktotal = 1/ K1 + 1/K2 + …+1/Kn
Option #3:
Like option #1, run AutoPIPE’s hanger analysis, this time, select a spring manufacture which has a product that contains multiple springs in series as a single component. Anvil international has multiple springs in series inside a single casing ( ex. Fig 98, Triple, or Quadruple):
- A single Fig-98 spring are built with 2 springs end to end in the same unit\
- A Triple is built with 3 springs end to end
- A Quadruple is built with 4 springs end to end.
Again, on the hanger analysis dialog, set Manufacture = (set to manufacture that has products with springs in series, example Anvil). Next, configure AutoPIPE to choose a fig 98, triples, or quadruple by setting the spring variation to a low value (ex. 1%). This should select a multiple spring product.
Option #4:
Some manufacturers do not have very soft springs like Anvil. Regardless, suggest to set the spring variation very low e.g. 1% as this should select these soft springs Instead of a constant hanger
If a specific spring manufacture does not have a single component containing multiple spring in series, suggest using Option #3, then contact a specific manufacture asking for an equivalent product with said characteristics from Anvil. Once the company provides details about a particular product, input those number into the model and run the analysis to see how it affects the model's results.
See Also
AutoPIPE help - Hanger modeling approaches
Spring - Support Type in AutoPIPE - FAQ's