Research and Development of Thin Buckling Restrained Braces for Seismic Buildings
Date Issued
2010
Date
2010
Author(s)
Lin, Pao-Chun
Abstract
The Buckling Restrained Braces (BRBs) have been widely used in seismic buildings around the world. However, in order to save more space in the buildings, the development of “Thin BRB” may be warranted. Because the flexural buckling and or the local buckling are prone to occur while the thickness of the restraining units are reduced, the research on the precise restraining mechanism and capability of a thinned BRB is required before the thin BRBs can be reliably used. The seismic resisting behavior and the design methods of thin BRB are the research priority of this thesis.
This thesis includes: (a) research and develop the design of an all-steel thin BRB, verify the BRB design by conducting cyclic load tests; (b) develop three different types of thin BRBs using the hollow structural section and infill concrete as restraining unit, apply one type in a full-scale three-story BRB frame tests; (c) before and after the BRB frame tests using the pseudo dynamic procedures, predict and simulate the responses using both PISA3D and OpenSEES programs; (d) the high buckle mode of the BRBs were investigated using bi-linear solid elements and ABAQUS models, the failure modes of restraining members were investigated for BRBs in the frame and component tests. The design methods for the restraining units to prevent the local buckling are proposed.
The proposed designs of the all steel thin BRB reduce the brace thickness and economize the use of the steel material. Based on the cyclic load tests of four all-steel BRBs, the proposed all-steel cross section, but not the end connection details, worked well during the component tests. In the pseudo dynamic frame tests using the 10/50 earthquake, except the thin BRBs, all of the standard concrete-infill type BRBs performed well. The braces in each story resist more than 70% of the story shear and dissipated most of the seismic input energy. During the pseudo dynamic test, one of the two thin BRB in the 1st story failed due to the cyclic local buckling and the subsequent fracture. It is found that the the wave length of the high mode buckleing of steel core observed in the tests could be simulated by finite element analysis and hand calculation using double modulus theory for the steel core. Gain the relationship between contact forces induced by high mode buckle and the sizes of restraining members to prevent failure due to local buckling of BRB core. Research results suggest that under severe compressive strains, the BRB steel core high mode buckle wave length is about 20 times the core plate thickness. The local buckling design load for the steel casing can be determined. It depends on the peak brace compressive load, the thickness of the unbonding layer, the thickness of the concrete between the steel core and the steel casing, and the buckle wave length.
Subjects
buckling restrained brace (BRB)
all steel buckling restrained brace
local buckling
pseudo dynamic test
Type
thesis
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