hello Is somebody knows how to sim 2

Yes, but you'll need to be more specific than that.
The short general answer--
Model all deformable parts, model the contact, and figure out a way to prescribe the pre-tension loads (there are many tricks for doing this last step, depending on the software you're using and the parameters of your analysis).

Specifically, what are you trying to do and what software is available to you?

Brad

brad
I want to simulate the behavior of two plates connected by several bolts with the stiffness of the bolts but without representing the bolts precisely
I use ansys 5.7

thanks

breizhou

I haven't used ANSYS in a long time, so I can't speak to specifics about the code.
In general terms, I would go about it this way:

1)Model the shaft of the bolt with beam elements.
2)Model the nut and bolt head with solid or plate elements, connecting the beams to the centerpoints using something which distributes the moments from the beams into the solid/shell elements.
3) Model contact between the bolt head and plate structure, and between the nut and plate structure. You may need to also model contact between the connected plate structures, depending on the physics of the problem.
4) Figure out a way to apply the tensile forces to the bolt beams. Some codes have tools to do this automatically. If yours does not, the poor man's way to do this is to assign an initial temperature to the beams, prescribe a coefficient of thermal expansion to the beam material, and then "cool" the beams, thereby invoking tension through thermal contraction. Of course, this only works if you don't some time later in your analysis need to actually evaluate temperature effects on other things.
Brad

thank you bradh

Try converting the bolt circle into an equivalent thin shell tube, with its area equal to the total area of all the bolts. You can then compute the section modulus as if it were a thin shell circle and include that as part of your model.
The Polecat

I invite people to visit my website if you wish to discuss these issues further.

breizhou
As you wish not to model the bolts in a detailed way,
maybe you can try like this.
1. Calculate the worst case loading on the bolt, tension/shear by hand and ensure it doesn't fail with good margin
2. Simply connect the nodes of both plates with rigid elements.
This assumes that the bolt does not fail and you are interested in finding failure of the plate.