Dynamic Model Modification Of Infilled Frame

With the development of the nondestructive diagnosis, the vibration modes and natural frequencies are often used as diagnosis factor. The mechanics of performance of infilled frame differs greatly with the bare frame. And it is useful and meaningful to develop an analytical model to reflect exactly the dynamic behavior of the infilled frame for structural design and damage diagnosis. The common used model was applied in this paper to calculate the frame's dynamic characteristic, but the results were dissatisfactory. Thus, based on the famous equivalent strut model theory, the modified model that matched well with the tests' results was proposed, in which the width of the equivalent strut was regarded as a variable. The main contents in this paper are summarized as follows:(1) The contribution of the infills to the stiffness and capability to resist drift of the infilled frame is often ignored in seismic design, and with the structural period discounted, the bare frame was supposed to bear all the seismic action. The safety of the frames designed with this supposition was estimated by a simple derivation, and it was concluded that with the premises of favorable construction measure, the means of ignoring the stiffness and capability to resist drift of the infills can make the bare frame safer, though it can not guarantee the infills' safety.(2) It is considered that the general proportion structural damp model is applicable only when the damp is small. And based on the assumption that the noise is only related with the circuitry, and using the mutual exchange theory of dynamic response under linear state, a new estimation method of frequency response function was derived, which can eliminate the testing noise.(3) A 1/3 proportional concrete frame model was tested in the laboratory. Using the way of picking up viberation at one point and bestirring at different points, the dynamic tests of the bare frame and infilled frame were carried out in longitudinal and transverse direction. And the reliability of the tests results was validated by various checking ways .The effects to the tests results of the picking position and sampling frequency were considered. Moreover, the natural frequencies and modes information of the bare frame and the infilled frame were obtained by the analysis of the Dasp software.(4) The applicability of the pure shear floor model was discussed in details, and it was found that the floor model considering the rotation of the joints could simulatewell the dynamic characteristic of the bare frame. Based on this model, a program was compiled, and the flexible stiffness of each floor's columns and beams were identified by the sensitivity analysis.The results applied, the hinge connection diagonal strut model was modified. And a dynamic model was established in Ansys, of which the equivalent width of the diagonal strut when the infilled walls and frame were all in good condition was obtained.