Keywords: bolted joint, bending stiffness, model updating, modal analysis, experimental test, finite element model.

The stiffness of bolted joints has a strong influence on dynamic response of structures. The stiffness of the joints is difficult to determine. Nowadays, there are methods to determine the stiffness which use detailed finite element models of bolted joints. Other methods use static or dynamic test data to determine such rigidity [1,2].

In the present work the bending stiffness of bolted joints of framed structural systems has been identified by a model updating technique. The methodology with dynamic information as a tool of joint stiffness identification has been used. The problem of finding stiffness parameters can be solved as an inverse problem. From a mathematical point of view, this is an optimization problem, which means searching for the minimum value of a cost function. This cost function has residues which are the difference between the results of a numerical model and a real structure. The process is based on the determination of a sensitivity matrix, which relates the responses to the model parameters. The response used in the process of adjustment was the natural frequencies for the flexural modes in the loading plane of the joint. The stiffness of the spring element that connects joint components was used as the adjustment parameter for the finite element model of the joint.

The accuracy of the results depends on the accuracy of the finite element model used and the quality of the experimental data. So firstly, an adjustment of the joint finite element model is required. With this adjusted model, the joint stiffness can be determined more accurately. The incorporation of the stiffness of the joints in the simplified beam model of the structure has permitted similar results to be obtained to those determined experimentally. With the aim of decreasing the difference between experimental and numerical results, it is necessary to determine the values of joint stiffness in the rest of the degrees-of-freedom. So this analysis must employ more modes of vibration to adjust the values of joint stiffness through all degrees-of-freedom.

1

J.L. Zapico, M.P. González, M.I. Friswell, C.A. Taylor, "Finite element model updating of a small scale bridge", Journal of Sound and Vibration, 268, 993-1012, 2003. doi:10.1016/S0022-460X(03)00409-7

2

J.L. Zapico, A. González-Buelga, M.P. González, R. Alonso, "Finite element model updating of a small steel frame using neural networks", Smart Materials and Structures, 17, 1-11, 2008. doi:10.1088/0964-1726/17/4/045016

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