Abstract: In order to solve the problem that the equivalent stiffness of BRB is difficult to match the serial stiffness of its system, a calculation method of BRB yield force is proposed by introducing the ratio of member length to axis length (length ratio). Based on the deficiency of the simplified algorithm of equivalent bracing, the key factors affecting the stiffness matching are analyzed; According to the modified parallel force method, the relationship between the length ratio and the support angle, axis length, yield force and other parameters is analyzed, and then the calculation formula is fitted and the reference range in practical engineering is given; The method of BRB yield force based on length ratio is deduced, and the influence of different yield force values on stiffness error is analyzed. The results show that the modified parallel force method is simple and reasonable; The length ratio, yield force and system stiffness are interrelated. If the yield force is too small, the stiffness error increases with the reduction of the yield force. If the value is too large, the stiffness error increases with the increase of the yield force. The BRB yield force value taking method based on the length ratio can effectively match the equivalent stiffness and achieve the unified coordination between product design and engineering application. It is suggested that the BRB project design should be referred to.

Key words: equivalent stiffness, BRB, modified parallel force method, yield force, length ratio