合成梁の接合部係数の算定方法

Abstract

In the seismic design, beam-to-column connections should prevent early fracture in order to keep enough energy absorption capacity of members after beam yielding. Especially, beam-to-column connection is very important to retain seismic performance of buildings, therefore, the maximum strength of connection is designed by connection coefficient α as following; jMu ≧ α·bMp This formula is defined dealing with bare steel members because all members of building are postulated as bare steel on the calculation of general strength in the present design. That is, composite effect by concrete slab on steel beam is neglected in the calculation. In previous studies of composite beam, it has been already pointed out that strength is greater than bare steel beam by moving the neutral axis to near concrete slab, and plastic deformation is less than bare steel beam. However, it is not clear that growths of strength of composite beam, and difference of plastic deformation of composite beam between composite beam and bare steel beam. Therefore, according to the connection coefficient of bare steel members, it is hard to judge that composite beam-to-column connection can keep enough energy absorption capacity. In order to judge whether composite beam-to-column connection have enough energy absorption capacity or not, connection coefficient of composite beam are needed. Connection coefficient of composite beam is defined the ratio of the maximum strength to the plastic strength of composite beam. The plastic strength that means strength when plastic hinge created. It also means the changing point from elastic area to plastic area in relationship between moment and deformation such as full-plastic moment in bare steel beam should be clarify its verification. The maximum strength of composite beam is obtained by rectifying the calculation of connection strength based on the study of Tanaka et al. In this study, a series of cyclic loading test of connection of RHS column and composite beam is conducted. The parameters are two; thickness of column skin plate to consider relation between moment transmission efficiency and hysteresis, and beam width to clear effect of cross-section area between concrete slab and steel beam. The database of composite beam under cyclic loading is constructed not only above tests but also previous studies of experiments in RHS column and composite beam. Moreover, fundamental study of connection coefficient of composite beam regarding strength of material and width-to-thickness ratio of column is also conducted. Through the considerations, following knowledge are obtained; (1)The plastic strength of composite beam is verified as creating plastic hinge at beam-end and to be appropriate as base of connection coefficient of composite beam. (2)Connection coefficient of composite beam is obtained as the ratio of the modified maximum strength to the plastic strength of composite beam. The value of connection coefficient of composite beam is less than connection coefficient of bare steel beam, especially it is remarkable in case that moment transmission efficiency of bare steel is low. (3)In parametric study, connection coefficient of composite beam is affected by the material strength of steel and width-to-thickness ratio of column. To quantitatively evaluate composite beam-to-column connection have enough energy absorption capacity, it is necessary not only connection coefficient of composite beam but also the plastic deformation capacity of composite beam corresponded to bare steel beam. The details of connection coefficient and the plastic deformation capacity of composite beam will be clear based on analytical parametric studies in the next paper.