Multi-bolted connections are complex structural assemblies characterised by non-linear contact interactions between joined components. To model these assemblies efficiently, a systems-based approach is proposed, in which the connection is decomposed into four interconnected subsystems: the bolt-nut sets, the joined components, and the contact layer between them. This paper presents the mathematical formulation and experimental validation of this approach applied to a preloaded asymmetrical multi-bolted connection subjected to an external operational force inducing combined normal and shear stresses. The global system equilibrium is derived via a partitioned block stiffness matrix capturing inter-subsystem elastic couplings. The preloading phase was simulated using a three-pass tightening sequence and solved via finite element analysis in ANSYS. Numerical predictions were validated against experimental measurements on a physical test rig. The results show that the model accurately captures the elastic interactions during preloading, underestimating final bolt forces by less than 1%. Under monotonic operational loading up to 40 kN, the maximum relative error between numerical and experimental working forces remained below 1%. The proposed systems-based approach significantly reduces computational complexity whilst maintaining high accuracy, demonstrating its suitability for analysing non-linear structural connections under complex loading conditions.