STUDY ON THE SEISMIC RETROFIT OF ANGLE BRACE JOINT USING KNEE MEMBERS

Abstract

 The brace joint fracture was observed in several severe earthquakes which occurred in the past. That's because fracture prevention of a brace joint wasn't considered by old seismic design code. The important problem to promote seismic retrofit works of a brace joint in the future is fire-less and compact seismic retrofit method which doesn't use a welding and gas-cutting.

 

 In this paper, the seismic retrofit method with the knee members for preventing the joint fracture of the angle brace was proposed. This method joins a brace, a column and a girder using the knee members and high tension bolt. Therefore it became possible to build this method without using fire at a site of retrofit works. And an obstacle in retrofit works could be avoided by adjusting the location and holding angle of the knee members. This method aims at fracture prevention of a brace joint by adding a load transfer routes of the knee members.

 

 A series of loading test and a series of analysis have been carried out to investigate strength improvement effect of this method. The strength and stiffness evaluation model of each part in this method were proposed. And a relation between story drift angle of the frame which occurred by the seismic force and the load sharing ratio of the knee members was investigated analytically.

 

 As a result, the following knowledge was obtained.

 [1] The joint fracture prevention before a brace yielding was confirmed by installing the knee members in both sides of the brace. However, story drift angle of the frame which occurred by the seismic force wasn't considered by this result.

 [2] The load sharing ratio could be expressed by an evaluation model proposed by this paper. However, story drift angle of the frame which occurred by the seismic force wasn't considered by this result.

 [3] Consideration is needed by the load sharing ratio changed by holding angle of the knee members, the installed height of the knee members, stiffness of the knee members and holding angle of a brace to make this method reach the reinforcement target. And it's necessary to consider story drift angle of the frame which occurred by the seismic force.