Foundation Design

[MohammadZaman]

Hi

I want to design a grid foundation. After I have designed the super structure , for modeling the foundation , I deleted the constrains of the base nodes then drew beams on the base elevation and assign elastic properties to them . But when I run the analysis I receive the error. I don't want to consider uplift force  I want to eliminate uplift from the elastic properties.

What should I do now?

Could you please help me?

Could you correct the model ? 

thank you very much.

[Artur.Kosakowski · Accepted solution]

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@MohammadZaman wrote:

Hi

I want to design a grid foundation. After I have designed the super structure , for modeling the foundation , I deleted the constrains of the base nodes then drew beams on the base elevation and assign elastic properties to them . But when I run the analysis I receive the error. I don't want to consider uplift force  I want to eliminate uplift from the elastic properties.

What should I do now?

Could you please help me?

Could you correct the model ? 

thank you very much.

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[MohammadZaman]

Hello.

I have already install SP4 for robot 2013 and I modeled a simple building with foundation(bar on elastic ground),but I think there is a problem!!!. There is instability on seismic lateral force. The structure goes as rigid body in x and y directions. I restrained support in x and y directions. But....!!!

I attached model.

Could you please help me to solve these issue?

Thank you.

[Artur.Kosakowski]

but .... you just ignored the information about lack of the convergence of the non linear analysis for cases 4 and 5 and then checked the results .....

My assumptions is that you 'overturned' the structure applying horizontal load without having any vertical ones to counteract.

Try to check the results for combinations where you have both vertical and seismic loads acting together and just ignore the ones that are calculated for seismic cases alone.

[MohammadZaman]

HELLO

Thank you. I deleted seismic loads Accordance with ASCE7 and define manual seismic load 0.5 kg/m2 in each floor (it's very low seismic load) but there is still a problem about convergence. More over I increased unreasonably kz for soil. I attached file.

[Artur.Kosakowski · Accepted solution]

I'll try to explain again. Please look at the picture below:

As you can see there is the uplift in the left support. If you declare it as UZ+ then it stops working and the structure collapses (or there is no convergence of non linear analysis). You need to add some vertical load to prevent this situation and this is what you have in 7:COMB2. In  other words treat case 4 as the auxiliary and check the results for the combination only (it converges). 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.