Bolted connection - member stiffness 1

Well, hei!


A design engineer have asked me to check a flange (please see pic 1). He wants to know what is going to break first eventually: the flange or the bolts.

Lets say under a bending moment, statically.

So... I was wondering how to estimate the stiffness of the connected parts: 1, 2, 3, flange. The memebers 2,3,flange are connected in parallel: 1/k=1/k2 + 1/k3 + 1/kflange is valid. But what about the member 1?

I am so confused and curious at the same time.

Would it be right to use Ansys to estimate the stiffness of the multilayer member?

What I do is to apply a compression force simulating the bolt pretension (please see pic 2). Get deflection and then calculate the stiffness.

I get reasonable magnitudes and all seems fine.

But would like to hear if my reasoning is right.

Thanks.