Connection of which the beam web is connected to gusset plate of column through high strength bolts is considered as a pin connection in structural design of Japan. In the pin connection, a number of bolts are used to resist axial and/or shear forces due to the external force such a seismic excitation. Moreover, at a pin beam-end connection in braced frame, the connection is required to resist not only axial force but also sufficient rotation. However, design procedures in order to achieve sufficient rotation capacity of the pin connection under compression have not yet been established. In other words, effects of the number of bolts and their arrangement on the rotation capacity is unclear. A purpose of the present study is to evaluate rotation capacity of the pin connection under compression and to establish requirements to achieve a sufficient rotation capacity.
At first of the present paper, cyclic loading tests of pin connection under compression were carried out to investigate the effects of different connection details on rotation capacity. The test specimen is a full-scale cantilever beam consisting of a beam, a gusset plate, and their bolted connection. The main test parameter is the differences in connection detail, such as beam-web thickness, depth of beam, bolt pitch, diameter of bolt, and the number of bolts. In addition, compressive axial force and the loading protocol (constant or perfectly rigid-plastic slip) are also important parameters to confirm rotation capacity. The pin connection without compressive force has sufficient rotation capacity until reaching 0.08rad rotation although the wider pitch causes bolt fracture. On the other hand, compressive force caused local buckling at the beam web near the connection and reduced rotation capacity of the pin connection down to less than 0.006rad. It indicates that local buckling has very important effect on the rotation capacity of the pin connection under compression. Local buckling might occur at the effective cross section, because force transfer from beam to gusset plate might cause stress concentration around the bolts depend on the bolt arrangement. It is clarified because the rotation capacity limited by local buckling is affected by beam-web thickness, bolt pitch, and the number of bolts. Therefore, in this paper, the effective cross section related with local buckling occurrence is proposed by an assumption of force transfer based on the test results. The axial stress at the effective cross section has negative correlation to rotation capacity of pin connection under compression. It enables to achieve sufficient rotation capacity if the effective stress is less than 155 N/mm
2. Here, the required rotation capacity is assumed as ±0.03rad rotation at the beam-end connection in braced frame subjected to a strong earthquake excitation.
Finally, cyclic loading tests of a full-scale braced frame were carried out to verify the applicability of the proposed requirements in the frame. The test specimen is a 2 story-1 bay braced frame with various connection details. The test parameters are beam-web thickness, bolt pitch, and yield strength of the braces. The braced frames with the thick beam-web plate showed the predictable lateral strength based on yielding of brace, and a sufficient plastic deformation of over 0.02rad. On the other hand, because the local buckling occurred at the beam web near the connection before reaching 0.02rad beam rotation, the braced frames with the thin beam-web plate, of which the effective stress is over 155 N/mm
2, showed a poor seismic performance. Therefore, the proposed requirements for achieving sufficient rotation capacity have been proved to be applicable in the frame.
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