Designing the springs for Seismic Loading

Hi All,

I have one question about the seismic analysis. Should springs be designed for operating condition or for seismic case? In one of our project, the spring (constant) is goverend by the siesmic loading and comes out to be much bigger than the one designed for operating conditions. The space does not allow the bigger spring can.

Thanks for your help

MW

Basically, a constant support is just a force acting in your piping system. I understand that the seismic calculation says that a bigger force is needed in that place in order to save your system. I would understand that without that bigger force, your system will not survive in case of a seismic event. The conclusion is yours.

However, you need to understand that introducing a bigger force in system will not disturb the operating case.

My first option would be to re-think the system. But this may be applicable or not, it depends on a lot of things.

to add: second option would be seismic snubbers.

First you should review the system to find out as to why seismic cases are governing the spring design, too many springs? excessive flexibility? poorly supported heavy masses? etc. and if possible reroute/ add rigid supports near the heavy masses to stabilize the system for the dynamic loads. As pointed out by mariog, you may consider use of seismic snubbers at appropriate locations.

Now about the query, generally selection of spring support is done considering operating condition, but one should always ensure that selected spring can accommodate extreme movements/ travel and that spring support does not bottom/ top out. So, IMHO you should consider the displacements in seismic case while deciding travel for constant spring supports. There are different configurations for the spring support and attachment types with pipe and structure to chose from. Have look at Type VBM from Bergen Pipe supports catalogue for reference.