| Buckling restrained brace(BRB)has been widely used as an energy dissipating member in energy dissipation technology with both function of common brace and metal damper.After decades of development,more and more new types of BRBs have emerged aiming at new materials,new structural types and easy fabrication,which have better function of energy dissipation and re-centering capacity.Magnesium alloy has been widely used in the fields of military,aviation,automotive with lighter weight,stronger strength deformability compared with steel.In civil engineering,the application of magnesium alloy materials needs to be expanded based on previously feasibility study on magnesium alloys applying to BRB,the main work and conclusions in the paper are as follows.(1)Firstly,constitute elements,working principle and the combine hardening constitutive model of BRB are respectively introduced.Then,two steel-core-material BRBs with different sections presented in previous study were simulated by using Abaqus.Finally,the force-displacement curves and skeleton curves were compared and analyzed.Results show that the refined finite element analysis(FEA)are in good agreement with the experimental results,which verifies the correctness of the proposed modeling method.It is also shown that the BRB can be better simulated by adopting combine hardening constitutive model for steel core material.(2)The experimental stress-strain constitutive relationship for GW83 Mg alloy was used to calibrate the combine hardening constitutive parameters.The accuracy of calibration results was verified by FEA using the calibration parameters.Then the related indexes and calculation methods for evaluating the performance of BRB were introduced.When magnesium alloy BRB and magnesium alloy-steel composite section BRB are designed,parametric analysis of the length and area of the magnesium alloy core material is conducted for magnesium alloy-steel composite section BRB.Results show that magnesium alloy materials have larger plastic deformation capacity and plastic hardening characteristics than steel materials.The damping ratio and energy dissipation capacity of magnesium alloy BRB under each loading grade is smaller than that of steel BRB,but magnesium alloy BRB has more stable stiffness characteristics than steel BRB with slower stiffness degradation under each stage loading grade.Considering the energy dissipation and self-centering capacity of magnesium alloy-steel composite section BRB,it's suggested the length ratio should be less than 0.3 and the area ratio should be greater than 0.5.(3)Based on existing principles of equal stiffness and strength for pure steel-core-material BRB to be simplified in Abaqus,a method of constitutive parameter correction is used to simplify tandem magnesium alloy-steel composite section BRB.Parallel magnesium alloy-steel composite section BRB are simplified by adding spring element at both sides.Then,the BRB is simplified as truss elements or triple-segment beam elements and the comparison between them and refined FEA models are performed.The result shows that both methods are in good agreement with refined FEA result and suitable for engineering application.When using truss element method to simplify BRB constitutive parameters based on the results of the BRB test or refined FEA are required.For triple-segment method the modification of constitutive parameters is not necessary however the modeling process is more complicated than the former.Considering the precision and convenience in engineering application,it's suggested to use the truss element to simplify BRB.(4)Using a coal machine building structure in high-intensity areas as an example,the steel BRB,Tandem BRB(length ratio 0.3)and parallel BRB(area ratio 1.0)are respectively arranged in the positions of the first and fifth corner columns along two main axes in the structure by using the principle of equal stiffness.Through the elastic-plastic time history analysis,the properties and influence on the seismic performance of three type of BRB were compared and analyzed.Result shows that the parallel BRB is better than tandem BRB and steel BRB in reducing the structural displacement response,residual deformation and protecting the main structure.Thus it verifies that the parallel BRB has both function of energy dissipation and re-centering capacity.The innovations points of the paper are as follows.(1)The combine hardening constitutive parameters of magnesium alloy materials were determined,providing reference for using magnesium alloys in BRB and other engineering structures.(2)Based on the refined FEA,the length ratio and the area ratio of the inner core materials for magnesium alloy-steel composite section BRB are proposed which provide theoretical guidance for the subsequent experimental studies.(3)Taking engineering precision and convenience using into account,a simplified modeling method magnesium alloy-steel composite section BRB is proposed.(4)Taking a coal machine building structure used in high-intensity areas as an example,it's verified that the BRB adding magnesium alloy has better self-centering capacity than ordinary steel BRB. |
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