Finite Element Model Updating of the UCF Grid Benchmark Connections Using Experimental Modal Data

Structural connections are a crucial component of any structural system. The connection stiffness can impact the static and especially the dynamic behavior of a structure. Therefore, reliable finite element modeling of the structural systems involves accurate estimation of their connections stiffness parameters. Accurate representation of connection stiffness parameter is one of the most challenging steps in model verification as connections are physically small parts of a structure and some parameter estimation procedures may lack the sensitivity to change in connection behavior to capture the stiffness parameter of connection elements. One of the most well-known experimental structures which has been extensively used in the model updating research field in recent years is a structural frame set up in the University of Central Florida which is known as the UCF Grid. This experimental structure is an instrumented planar grid comprised of several steel members interconnected by gusset plates. The grid is instrumented by eight uniaxial accelerometers to capture the accelerations of the specific nodes of the structure when the grid vibrates due to an excitation. In this paper, the modal data of the grid obtained experimentally by an impact test are used for estimation of the stiffness parameters of the grid joints. A modal based error function method is employed to update the finite element model of the grid built in SAP2000 (R) environment. For the model updating computations, an optimization MATLAB (R) code is linked to the SAP2000 (R) Open Application Programming Interface to facilitate the parameter estimation procedure. The updated finite element model of the grid based on new estimations for its joints' stiffness parameters could represent the structural behavior of the grid in a more reliable scheme.