12-11-2009, 07:24 PM
If you are student you dont need to read the following, but if you have to perform calculation for real project let me give you the "cold shower".
For such type of dam (concrete gravity type) you HAVE TO pass through the following steps:
1. Foundation prior to the dam construction shall be modeled for proper stress estimation, especially in layered foundation (the foundation is usually the weaker part of all). That is because you will need the stresses to assess the safety factor, and weightless foundation makes the stresses there completely unreal (but the displacements are fine).
2. Stresses in the foundation should be kept, but the displacements set to zero.
3. Next stage is the dam construction (single stage or several stages, depending on what you want to obtain). After that displacements should be set to zero again in most cases.
4a. Seepage analysis through the foundation should be made, this giving the water pressure on the upstream face and the uplift pressure on the dam foundation; or
4b.If you can't do seepage analysis you must directly put the uplift pressure acting on both directions (perpendicular) to a thin contact layer between the rock and the dam body. This is not correct in respect to the foundation, so you should then limit your results only in the dam-body part, and forget any results in the rock - that means you can't do the following steps.
5. If you did 4a you can use effective stress plastic criteria (Coulomb-Mohr, Hoek-Brown) to check the foundation.
6. You can integrate normal and shear stresses on the dam-foundation contact, or several sliding planes passing through the foundation, or lift-joints in the dam body (for lift-joits you don't need foundation seepage) to obtain the sliding factor of safety.
7. Perform pseudo-static, response spectrum, or transient analysis for earthquake (MCE and OBE) and check the stresses and stability again.
I suspect that SAP2000 is not completely suited for staged construction with plastic material behavior.
For such type of dam (concrete gravity type) you HAVE TO pass through the following steps:
1. Foundation prior to the dam construction shall be modeled for proper stress estimation, especially in layered foundation (the foundation is usually the weaker part of all). That is because you will need the stresses to assess the safety factor, and weightless foundation makes the stresses there completely unreal (but the displacements are fine).
2. Stresses in the foundation should be kept, but the displacements set to zero.
3. Next stage is the dam construction (single stage or several stages, depending on what you want to obtain). After that displacements should be set to zero again in most cases.
4a. Seepage analysis through the foundation should be made, this giving the water pressure on the upstream face and the uplift pressure on the dam foundation; or
4b.If you can't do seepage analysis you must directly put the uplift pressure acting on both directions (perpendicular) to a thin contact layer between the rock and the dam body. This is not correct in respect to the foundation, so you should then limit your results only in the dam-body part, and forget any results in the rock - that means you can't do the following steps.
5. If you did 4a you can use effective stress plastic criteria (Coulomb-Mohr, Hoek-Brown) to check the foundation.
6. You can integrate normal and shear stresses on the dam-foundation contact, or several sliding planes passing through the foundation, or lift-joints in the dam body (for lift-joits you don't need foundation seepage) to obtain the sliding factor of safety.
7. Perform pseudo-static, response spectrum, or transient analysis for earthquake (MCE and OBE) and check the stresses and stability again.
I suspect that SAP2000 is not completely suited for staged construction with plastic material behavior.