Study On Stability Of FRP-wrapped Concrete Filled Steel Tubular Buckling Restrained Brace

The buckling restrained brace is a bifunctional member that can serve as a support member to provide lateral stiffness to the structure and is a good energy damper.The bending rigidity are provided by the constraints of the outsourcing constraining members,and the plastic deformation of the inner core consumes energy.In this paper,FRP wrapped buckling restraint brace is mainly because the test piece is easy to recover after the earthquake,and the inner core can be replaced by directly cutting the fiber cloth;in addition,the fiber composite material has good corrosion resistance and can be applied to special scenes.In addition,basalt and fiberglass cloth are inexpensive,so this paper mainly studies the stability of buck-constrained brace of FRP-wrapped circular steel tube concrete.In this paper,three sets of six buckling restraint brace tests were designed and carried out.Through the reasonable design of the test loading system and measurement scheme,the buckling restraint brace hysteresis curve and strain data were obtained.Carbon fiber,glass fiber,basalt fiber and three kinds of fibers were also designed.Basic mechanical properties of composites,including longitudinal stretching,transverse stretching,longitudinal compression,transverse compression,and longitudinal and transverse shear tests.The analysis of the FRP wrapped buckling restraint brace test results is completed.The energy consumption performance of the six test pieces is better,and the cumulative plastic ductility is more than 400.The lateral force generated by the multi-wave buckling of the inner core causes the fiber cloth to be pulled and further The gap between the core and the constraining member increases,and the inner core produces multi-wave buckling,which causes the displacement to increase the bearing capacity sharply,which is manifested as "jumping" on the hysteresis curve.The multi-wave buckling of the inner core is more pronounced,and the tensile stiffness degradation is more obvious.From the hysteresis curve,the multi-wave buckling state of the inner core can be seen.From the analysis of finite element parameters,it is known that the gap between the inner core and the constraining member is the key parameter affecting the buckling constraint support performance.The increase of the gap value will cause the hysteresis curve to be more and more unsatisfactory,and the curve jump is more obvious;too small The gap value is easy to cause the Poisson phenomenon,so the actual component design and processing focus on the gap value.As the friction coefficient increases,the difference between the tensile and compressive bearing capacity becomes larger and larger,and when the friction coefficient is larger,the stress at the end of the inner core loading end is larger,and it is also a place that is easily damaged during the test.The inner core buckling wavelength obtained by finite element analysis is consistent with the experimental buckling wavelength,and the lateral force is in good agreement with the theoretical analysis.Through the finite element analysis of the non-stress cloud map,the force state of each part of the component can be visually reflected,and the damage position of the test piece can be judged accordingly.From the FRP basic mechanical properties test results,FRP can be seen.It is a typical anisotropic material,so when performing finite element simulation,FRP uses a two-dimensional hashin progressive failure criterion.It can be seen from the experimental data that the strength and elastic modulus of the basalt fiber are low,and only the basalt fiber cloth is broken during the test.The thickness of FRP composites obtained by the equivalent uniform load calculation model is close to the simulation,and the practical application effect is better;the damage of FRP is concentrated at the end of the loading end.In practical applications,the thickness of FRP can be increased at both ends of the support,the middle part A small amount of woven fabricBy analyzing the equilibrium relationship between the inner core and the restraining member,considering the influence of the inner core reinforcing section and the restraining member stiffness,the maximum lateral force of the inner core and the maximum bending moment of the restraining member are obtained;the maximum lateral force of the inner core is checked by simulation analysis,based on the specification Checking the flexural capacity of the restraint members meets the requirements.The buckling constraint support local stability is a dynamic process.When the inner core transitions from a low-order mode to a high-order mode,the intermediate horizontal segment with a bending moment of zero satisfies kli=2?.This critical state is an important boundary condition for local stability problems.Through the research on the overall stability,local stability and FRP thickness check of buckling constraint support,combined with the previous experimental results and theoretical model research,the design proposal of FRP wrapped buckling restraint brace is proposed.The results show that the thicker FRP package can enhance the restraining effect of FRP,and reduce the gap and friction between the inner core and the restraining member,which will greatly improve the overall performance of FRP wrapped buckling restraint brace,and help to further improve the energy consumption of buckling restraint brace.performance.