Bolted joints are important elements of all mechanical systems, including gas turbine engines produced by Pratt & Whitney. The assembly consists of a bolt, a nut, a washer, and stack members (such as a flange). At assembly, the bolt is tightened, putting the bolt in tension and the stack in compression. Consequently, the bolt tries to return to its original length but the stack prevents it from doing so. The clamping force that keeps this system together is referred to as bolt preload. Bolts are tightened to certain preloads to ensure that assemblies remain tight during the flight cycle. This project considers what happens to the bolt preload force when compressive yielding occurs in the stack under the bolt head. The first objective of the project is to investigate the effect that compressive yielding in the stack has on bolt preload. This is done through a series of hand calculations and elastic/plastic finite element analysis (FEA) using Ansys. The second objective is to design and fabricate a test rig that will validate the effect of compressive yielding on bolt preload as found through the prior analysis.