The Analysis Of The Unbonded Brace Applicated In Frams Structures

The lateral resistance system adoption plays an important role in the design of high-rise building structures. The strength of the lateral stiffness is not enough if the designer chooses a pure frame structure, which only constructed in a low height because of the large lateral displacement effected by earthquake and wind loads. The use of frame-brace structure system gives a way to the degradation of stiffness in a lateral force-resistance system, however, the brace is vunerable to buckling by a axial compress force in a severe earthquake which also cause the damage of braces or the invalid of the joint connection, at the same time, seismic-resistance performance of the structure is ceased because of the reduced energy dissipation capacity of buckled braces.After the Northridge-Earthquake in 1994 and the earthquake in Osaka and Kobe in 1995, the research manifested that the premature buckling of large number of braces is an important reason to destroy the structure. Japanese engineers put forward the theory of un-bonded brace (UBB), a new brace in order to improve the anti-seismic performance. Research on UBB is advantaged in a wide range of relevant countries by means of its better buckling-restrained capacity and the advantage in energy dissipation effectively.UBB, by its stiffness and hysteretic energy dissipation caused by the buckling earlier than the main structure, can minimize or even avoid the damage of main structure in earthquake. The capacity to resist earthquakes of UBB mechanism includes vibration mode,floor shift,floor displacement angle,top time history curves of acceleration, of which the differences is not obvious compared with common brace structure. However, UBB's capacity of energy dissipation is more effective than common brace due to the performance of the hysteretic energy dissipation. However, the design theory and experiment of UBB should be improved in the construction nowdays to achieve integration of theory and practice effectively with the technology of UBB using and popularizing simultaneously.