So I was doing some FE work (w/ NASTRAN) to determine the stiffness in all 6 DOF of a model bolted to another model. To characterize the bolted interfaces I attached surface nodes within the bolt frustums to rigid body elements (RBE2). Then, these RBE2s were connected with a directional stiffness element (CBUSH) to model the bolt. To determine the directional stiffnesses I used a method suggested by another person with much more experience. Using Shigley's method, I found the bolt stiffness as so Kb = E*At/L'. Where At was the tensile area and L' was the effective grip length. Then, to approximate the surrounding material stiffness, I multiplied Kb by 2. This was the longitudinal directional stiffness (2*Kb). The transverse directional stiffness was found by multiplying the longitudinal joint stiffness by G/E ~ 0.4 to get a short beam in shear vs. tension stiffness. This is a method that I had never heard of, or thought of. But because it was based on industry experience, I used with it. Does anybody have any comments or thoughtful input on this method?