制振建物に設置する座屈拘束ブレースの性能と配置箇所の合理的決定法に関する研究

<p>　In recent years, the demand for maintaining building functions after large earthquakes has been increasing especially for high-rise buildings. For this reason, the importance of vibration control systems is increasing which efficiently absorb the vibration energy of buildings during an earthquake. Among several vibration control dampers, a buckling restraint brace (BRB) is widely used in practice design of high rise building structures because of its ease of installation and maintenance. In this paper, a new design method is proposed to determine optimal placement and performance of BRBs which minimizes seismic response of building frame structure with the same amount of BRB. Different from most of other previous researches related to optimization of BRB placement, this paper uses nonlinear time-history analysis directly considering nonlinear hysteresis characteristics of BRB. Furthermore, proposed method can pursue the optimal placement continuously by increasing the total amount of BRB. </p><p>　The validity and the versatility of the of the proposed method is examined through numerical examples of 15 storied building structure. As for the difference of the structural modelling, the results of shear model and frame structure model are compared. As for the difference of input ground motion, the results using three types of seismic waves, i.e. El Centro 1940 NS, Hachinohe 1968 NS and TAFT 1952 EW, are compared. Furthermore, as for the difference of BRB grouping in the frame structure model, the results using two types of grouping, i.e. "story grouping" and "subdivided grouping", are compared. The "story grouping" gives the same cross section to BRBs in the same story. The "subdivided grouping" gives the same cross section to BRBs in symmetrical place of the same story. </p><p>　As a result, the findings are summarized as follows. </p><p>1)　An optimal algorithm proposed for the shear model is extended a method for the frame structural model. This algorithm makes candidate solutions with different installation locations of minute amounts of BRB and selects the candidate solution with the smallest maximum response estimated by nonlinear time history response analysis. The effectiveness and validity of the proposed method is demonstrated through comparison of responses of structural models with random placement and optimal placement of BRB.</p><p>2)　In some cases of numerical examples using three types of input seismic waves, the seismic responses increase in spite of additional damping effect due to BRB. It is caused by the combination of the shortening of the natural period of the building and the periodic characteristics of the response spectrum of the seismic waves.</p><p>3)　The optimal placements of BRBs and seismic responses of the frame structural model and shear model generally correspond when the total amount of BRBs is small. However, the difference between two models increases as the total amount of BRBs increases. The seismic response reduction is overestimated when the shear model is used because there are BRBs that do not work effectively depending on the location in frame structural model.</p><p>4)　It is demonstrated that the optimal BRB placement and amount of BRB can be selected in more detail by using subdivided grouping. However, in the examples in this paper, the difference between the two types of grouping is small and further examination is necessary for the models in which the overall bending deformation is remarkable.</p>