Well, In the SIM environment in the Bolt Pre-Load dialog box, you can use the Force on 1D elements option to define a pre-load on a bolt that is modeled with CBAR or CBEAM type beam elements. The software applies the Force that you specified in the Bolt Pre-Load dialog box to the ends of the bolts in the axial direction. The software then performs a linear statics analysis to obtain the relative displacements (U2 and U1) for each pair of nodes, and then repeat the analysis to account for the service loads. In Advanced Simulation, you can define bolt pre-loads in NX Nastran SOL 101, SOL 103– Response Simulation, and SOL 601 (106 and 129) analyses.
As a best practice, when you select the 1D elements to which to apply the bolt pre-load, you should select all the beam elements that define the shank of the bolt. In SOL 101, the software applies the pre-load to the first element you select and ignores any additional elements you select.
Of course, is mandatory to define NO PENETRATION Surface-to-Surface CONTACT between the bolting parts.