| The beam-to-column connections are usually be assumed as fully rigid or ideally pinned for convennient calculantion at present in China during the analysis and design of frames. In fact, the performance of the connections in practical engineering is something between these two positions, which is a category of semi-rigid connections. A large number of studies have shown that semi-rigid connections have a significant effect on not only to the basic mechanical properties, but also to the dynamic properties of structure, which cannot be ignored. Researches also suggest that if taking a space frame as planar frame, the varying laws of structural natural frequencies and modal shapes are shown inconsistent when analyzing the dynamic characteristics.In this paper, a dynamic characteristic analysis of semi-rigid space steel frames has been established based on spline QR method and considered the influence of shear deformation and the second-order effect. The major research content is as follows:1. Based on the cubic B-spline function, the spline QR method static analysis and dynamic analysis model of rigid connected planar and space frames have been established considering the effect of shear deformation and the second-order effect, and a correlation program has been programmed with MATLAB. The correctness and reliability of the model in this paper is verified by numerical examples. And similarities and differences of the structure dynamic characteristics analysise btween the space and planar steel frames are analyzed. Solutions show that the natural frequencies solved by space model includ ones solved by simplified planar model, and that the low order natural frequencies in the main plane of space frame can be obtained through the simplified planar model, and the results solved by the two models are close. But for the high order frequencies in the main plane, the results obtained by planar and space models may have a major error. In addition, natural vibration frequencies corresponding to the diagonal, twist and coupled modes are not been obtained by planar model.2. The dynamic characteristic experiment of semi-rigidly connected steel frame has been carried out. The structural dynamic characteristic influence of semi-rigid connections setting in different floor, and of second-order effect have been studied. The results show that structural natural frequencies are reduced because of semi-rigid connections, that the structural dynamic characteristic influence of semi-rigid connections setting in different floor is various, that it is a trend to increase the natural frequencies of semi-rigidly connected frame when the number of floors is increased.3. The dynamic characteristic model of semi-rigidly connected space steel frames considering the inffluence of shear deformation and second-order effect are researched. The dynamic characteristic experiment result of semi-rigidly connected steel frame is numerical simulated and extensive researched by the computer program in this peper, which results are identical. Parameter analysises have been performed, and the impacts of the semi-rigid connections, the number of floors, shear deformation and second-order effect on the dynamic characteristics have been explored. The results show that the value of the initial stiffness of semi-rigid nodes influenced the low order natural vibration periods greatly, that the more significant influence of semi-rigid frame structural natural vibration period will have when the more storey is, that shear deformation have greater influence on the higher natural vibration periods on the frame eventhough less effect on the low order ones, and that the second-order effect lower the structural natural frequencies.The research method and related test and numerical analysis results in this paper may provides certain reference basis for carrying out research of the space frame structural dynamics and vibration control problems. |
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