The Design Theory Research And Mechanical Property Analysis Of All-steel Buckling-restrained Brace

Relying on the mechanism that the core bears load with the encased steel's constraint, Buckling-Restrained Brace(BRB) is capable of yield without buckling no matter under tension or pressure, showing an outstanding hysteretic performance. When large earthquake or even rare earthquake occurs, the characteristics that making fully use of material strength and whole section yield dissipate earthquake energy enable BRB to minimize the earthquake impact on major structure just like a fuse. Based on the margin yield criterion and the core's high-order multi-wave buckling assumption, the calculating formula of ideal value gap and margin yield limit stress is derived, providing theoretical basis for the design of BRB. The major research work of this thesis is as follows:First of all, assumed that the encased steel's stiffness is infinite without any bend and core will produce multi-wave buckling under the influence of initial imperfection and pressure, defining the pressure of the moment core's margin yield is margin yield limit stress and meanwhile the maximum deflection is the ideal gap value, the universal calculation formula of linear-shape and cruciform-shape BRB's gap value and margin yield limit stress is derived. In order to figure out the change rule and characteristics of the gap and limit stress, different section types are compared. Furthermore, the parameter analysis is made towards core's initial bend, core length, core width, core thickness and half-wave number.Moreover, considering the constraint and deflection of encased steel, based on the margin yield criterion, the calculating formula of BRB's gap value and margin yield limit stress is improved, which agree more with the BRB's actual working conditions. By means of the improved calculating formula and the concept of confinement stiffness ratio, the minimum required stiffness of encased steel calculating formula is proposed. Taking advantage of the reduction of the limit stress' s increment, the number of half-wave number is computed and hence the width-to-thickness ratio's range is acquired. What's more, new type of BRB, the BRB with double steel cube is introduced.Finally, based on the assumption that encased steel's stiffness is infinite, the Finite element model of cruciform-shape BRB is established, along with the element type choosing, material and meshing. Making use of ANSYS software, different kinds of constraint is compared to choose the fittest one. Under the same condition, the difference of limit stress between ANSYS and theory is analyzed. According to the conclusion that core's width has nothing to do with the linear-shape BRB's limit stress, the calculating formula proposed by this thesis is verified. Appling progressive loading to the BRB model, the core's multi-wave buckling development from low order to high order is simulated. At last, the stress-strain curve and hysteresis curve under different gap value is compared.