soil structure interaction

[neforun]

can someone help me with understanding this statement please.
a structure should be designed to be flexible as possible and as stiff as necessary in relation to the design of structures and foundations?

 

[Qshake]

As I read it and given my leve of understanding for structures.....

The more flexible the structure the less lateral load that will need to be resisted by the foundation. The more stiff a structure the more lateral demand on the foudnation.

For example a pinned portal frame that resist lateral load primarily through the column connections with the beam will not transmit lateral load to the foundation. A fixed based frame will thus requiring special consideration of the soil-structure interaction. Of course there are many different foudnation methods that can readily handle the fixed base foundation but the point is, I think, is that deep foundations are expensive and not always necessary.

I hope this helps.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[TDAA]

What was the context of the quote?

You could also just be talking flexibility to handle differential settlements, but stiff enough not to cause damage to the structure, foundations, and the finish work attached to them.

 

[oneintheeye]

I see it as flexible enough against settlements, stiffness will relate to how the whole system interacts for the foundation design. i.e. found/superstructure and soil mass.

Qshake, not sure i understand what you are getting at. All the load is ultimately transferred to the foundation no matter what the structure. How it is transfers varies but it still has to go there.

 

[letrab]

I think it is meant that the structure should be able to deform significantly without fracture ie ductile and stiff enough to transmit the loads to the foundation and resist the loads it is subjected to without breaking the finishes and partitions. I agree with Qshake that the foundation stifness required to transmit fixed end moments to the soil is much larger than the stiffness required to only transmit lateral and vertical forces and is a possin=ble example of what is meant by the statement.

 

[letrab]

I think it is meant that the structure should be able to deform significantly without fracture ie ductile and stiff enough to transmit the loads to the foundation and resist the loads it is subjected to without breaking the finishes and partitions. I agree with Qshake that the foundation stifness required to transmit fixed end moments to the soil is much larger than the stiffness required to only transmit lateral and vertical forces and is a possible example of what is meant by the statement.

 

[vandede427]

agree with herewegothen, pin-based portal frames do transfer lateral loads, just shear not moment.

 

[BAretired]

The statement may be in reference to seismic behavior where excessive stiffness can cause brittle failure.

BA

 

[Qshake]

herewegothen - My comment is based on moment resistance and not vertical or shear.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[neforun]

thanks to everyone who got back to me
S