model a support with limited load

[hualiong]

Hi,

I have an existing foundation with 6 piles supporting the footing, but the allowable working load of one of these piles is limited to 150kips. But the applied external force is about 180kips on this perticular pile. How I can model this support in SAP2000 with the maximum reaction limit to 150kips?

Thank you in advance.

 

[par060]

...reduce the applied load

 

[hualiong]

thanks, but the load is already there and I am looking how to model the support with limited capactiy.

 

[patswfc]

Have you modelled the 6 piles as pinned supports. If so change the pile that attracts 180kN to a spring (in the vertical direction)support. Next perform a run of the model and look at the load on that pile. Update the spring stiffness accordingly and repeat the process until the reaction is 150kN. The additional 30Kips will be transferred to adjacent piles. If these exceed the max. of 150kips then you will have to do the same process on these piles, but it becomes more complicated as the original pile that exceeded 150kips is likely to start to exceed this limit again and you will have to alter the spring stiffness on more than one pile at a time which will be a pain in the backside to try and get these to reach the limit of 150kips simultaneously.

Hopefully once you sort the first pile out, none of the others will exceed 150kips, otherwise good luck.

 

[hualiong]

Thanks for your thought, I will take a try.

 

[masomenos]

Why isn't it possible that the pile may really be overloaded? That means that you will have to reconfigure your pile locations or add additional piles. If you are modeling the foundation using shell elements, make sure that you do not assign joint loads on the same joint as the pile, because in reality, the foundation will spread the load.

Modeling the piles using a pinned restraint gives you the worst case load which is typically the reaction that you would want to use in a new design. Modeling the piles as springs (calculated based on pile section, pile length and soil data) will obviously add some flexibility which may change load distribution.