sybie99
Structural
- Sep 18, 2009
- 150
Hi
I often have to model a basement or other ground bearing structure where I have to assign a spring stiffness to model the ground support realistically. If the ground is say a type of sand or clay with say a safe bearing capacity based on likely settlement, I usually calculate the spring stiffness (which in all the software programmes I use is expressed as kN/m, ie deflection for given force) as follows: If SBC is say 150kPa or kN/m2, I can usually find out from the soils report what settlement would occur for this loading. Say 20mm. Therefore my spring stiffness would be 150/0.02 = 7500kN/m. In other words if I applied 7500kN force on a square meter of this material it would settle/deflect by a meter. I then place a spring every square meter. If I wanted to model supports at every 500mm, I would have to reduce the spring stiffness by a factor of 4 as I would have 4 supports per square meter.
What I would like to know is how to calculate the spring stiffness (in kN/m) for rock where I do not know what deflection would occur under load. I was thinking that maybe the elasticity modulus of the material could be used, but cannot figure out how I would do this.
What have you guys done when modelling a rock support? And is there a way that E, the elasticity modulus, can be used to get a spring stiffness? I was hoping to find some information on the net giving spring stiffnesses for various soils and rock but have been unsuccesful.
Looking forward to your replies and opinions
Thanks
Seb
I often have to model a basement or other ground bearing structure where I have to assign a spring stiffness to model the ground support realistically. If the ground is say a type of sand or clay with say a safe bearing capacity based on likely settlement, I usually calculate the spring stiffness (which in all the software programmes I use is expressed as kN/m, ie deflection for given force) as follows: If SBC is say 150kPa or kN/m2, I can usually find out from the soils report what settlement would occur for this loading. Say 20mm. Therefore my spring stiffness would be 150/0.02 = 7500kN/m. In other words if I applied 7500kN force on a square meter of this material it would settle/deflect by a meter. I then place a spring every square meter. If I wanted to model supports at every 500mm, I would have to reduce the spring stiffness by a factor of 4 as I would have 4 supports per square meter.
What I would like to know is how to calculate the spring stiffness (in kN/m) for rock where I do not know what deflection would occur under load. I was thinking that maybe the elasticity modulus of the material could be used, but cannot figure out how I would do this.
What have you guys done when modelling a rock support? And is there a way that E, the elasticity modulus, can be used to get a spring stiffness? I was hoping to find some information on the net giving spring stiffnesses for various soils and rock but have been unsuccesful.
Looking forward to your replies and opinions
Thanks
Seb
