One of the computer models used for structural health monitoring and other studies of the Memorial Bridge is a 3D model constructed in SAP2000. This is a model of the south tower and south fixed truss span, which is the portion of the bridge on which the structural health monitoring sensors are installed. The model includes each structural member, the concrete deck, and masses that represent the control house, counterweight, and other nontrivial components. The truss node connections are represented by partial fixity springs at the ends of each member. The stiffness of each of these springs serves to represent the behavior of the knuckle connection used in the actual bridge. The use of the spring representation allows the model to be much less complex than if the knuckles were modeled individually. That makes this model appropriate for investigating the overall behavior of the bridge, such as its vibration under high winds or from the crossing of a heavy truck.