how to model Soil Structure Interaction on Etabs,Sap2000 8

[Captains210]

Hi...
I'm trying to model soil structure interaction on sap2000
I'm using George Gazetas rules to replace the (soil and foundation) with a Springs to represent the dynamic stiffness and damping with six DOF
I want to use link element to model the spring but i wonder how i will do that??!
1- at the base of column(one point ?)
2- plain stress strain element OR solid element OR Area spring
what's the correct Approach ?
thanks a lot

Saad

 

[niyi123]

I am a new user. Please I am currently in graduate school of structural Engineering and will like to do my thesis on impact of soil structure interaction on drift simulations of tall buildings. Though, I have a basic knowledge of ETABS and SAFE and SAP2000. Please, Any idea and ETABS study material will be appreciated. Thank you.

 

[yazan1990]

Mr. stressed
Where can assign these links to area springs or to the base of coloumn

 

[yazan1990]

I mean that i already have a mat foundation with an area spring

 

[stressed]

yazan, when you assign an area spring, you have options to use compression-only or selected link properties to the area. If raft foundation supported by soil (no piles), then assign to the area assuming you modeled the foundation with shell or solid finite elements.

 

[kwstis19]

Hello, i am a new user of Sap2000 and in order to complete me thesis i have to work on that program. Does anyone know if its possible to pass into the program the P-Y, T-Z and the bearing curves? Because i have them in a excel sheet from the previous part of my thesis and i am trying to find a insert thoses curves into the program in order to form their springs.

Thank you..

 

[SteeliestFire55]

@kwstis19

P-Y data can be modeled as NL link elements. See Define > Section Properties > Link/Supports.
Changing the link type to 'Multilinear Elastic' will allow you to define the curves. Note that the U1, U2, U3 are in the link local axis such that U1 will always be axial. You need the non-linear box to be checked in order to enter the P-Y data.

I recommend drawing these links as 2- joint links with one end connected to the frame element and the other to a support.

If you define non-symmetric links, you have to be careful which orientation the links are drawn on.

Lastly, the defined P-Y links require all relevant load cases to be run non-linear.

These links can also be assigned as area springs (eg: for bearing)

 

[frameingineering2014]

Hello fellow engineers,
I think there is no one way in modelling soil stiffness as links or area Springs. Most handbooks I have read about soil structure interactions with raft foundations always uses area Springs. Let me share my method even though I have not concluded it's the best way.
I modeled the raft in ETABS as shell thick. Then I manually meshed the raft slab say 1x1m. Then I assign area Springs to these meshed Slabs. I define modulus of subgrade reaction in the 3 direction. There is an option to choose whether it's linear, compression or tension. I choose linear. I also restrain the springs in the X and Y direction. Does using 4DOF.What also define nonlinear load cases to my linear load cases. What do u make of my method.

 

[paultom91]

Im very sorry to butt myself in this conversation. But im a Masters scholar doing my thesis on Soil Structure Interaction. I am modelling a 2d model of soil in sap2000 to get the natural frequency. My topic is on the resonance effect due to SSI on rcc framed structures.
So i have created a rcc structure modedl whose natural frequency i have obtained. I am varying the soil layer thickness and setting the system in resonance by adjusting the shear wave velocity (by using SHAKE or PROSHAKE) and finally conducting a time history analysis to study the response.

My problem is for modelling the soil I had no clue how to assign transmitting boundaries for which i have brief idea now after reading the dialogue here. I am considering the bottom to be bed rock so the bottom will be fixed. The sides however have to be truncated and a viscous transmitting boundary has to assigned. I have read various journals which give similar views to the conversation here. But can someone help me by telling me how to go about with the modelling as to which elements to use for the meshing and how to calculate stiffness and damping values based on the mesh used. Im sorry for asking so much. I really dont have a knowledge level as intense as you people here. Thanks in advance..hope somebody helps.

 

[Captains210]

frameingineering2014

my method is replacing the (soil and foundation) with a Springs to represent the dynamic stiffness and damping by using link element
maybe you didn't consider the dynamic effects and soil properties in your method..