Research And Experimental Study On Mechanical Behaviors Of An Ultra-lightweight BRB Restrained By Composite Materials

As a type of efficient energy dissipation element, buckling restrained braces(BRBs), in recent years, have been applied to more and more engineering structures forseismic design. The disadvantages such as high cost, easy to rust, or heavy weight arecommonly seen in traditional BRBs. Meanwhile it is also difficult to implementtransformation or strengthening of existing braces in situ using steel or motor materials.FRP (Fiber Reinforced Polymer) and timber are anisotropic materials which havesimilar mechanical properties as well as the advantage of lightweight. In this paper, theauthor designed a new type of BRB using steel as the core component, GFRP andsquare timber as the constraints to achieve high efficiency in energy dissipation as wellas ultra-lightweight. This research also practiced the manufacturing of productionprocess, and conducted cyclic quasi-static tests to full-scale BRB specimens.A total of14specimens are sub-batches and classified by the material used for thecomponents of BRBs. The core steel having in-line section and the core steel havingcrisscross section are used for energy consumption component, while GFRP pultrudedprofiles with and without grout and Douglas fir are used for restraint component. Thefollowing variables are studied in the tests: the combinations of the components, thethickness of wrapping layer, the wrapping angle and the formation at the ends. The testresults include specimen failure modes, load-displacement hysteretic curves, skeletoncurves, seismic performance evaluation indicators such as energy cyclic dissipation, thecumulative plastic deformation ration and additional damping ratio.According to the test results, major conclusions are made as follows:(1) Well designed braces have satisfactory mechanical properties and energydissipation capacity.(2) Increasing the thickness of the wrapping layers is helpful to improve theseismic performances of the braces while wrapping angle of the GFRP layer does nothave much effects on the performance of the braces.(3) Strengthening the ends of the brace could improve the seismic capacity andfailure modes of the brace.(4) Compared to the core steel having in-line section, the core steel havingcrisscross section exhibits better performances due less compression from the core steel on the outside GFRP restraint units.(5) The GFRP profiles filled with grout showed satisfactory performance due toenhancement on the local bearing capacity and stiffness of the outer constraint.(6) Steel-timber BRBs could easily achieve superior energy dissipation capacitywith less self-weight, thus it is an ideal formation of ultra-lightweight BRB.(7) The inadequate local bearing capacity of the outer constraints always leads toinefficiency in seismic performance and local buckling failure mode of the brace.Thereby appropriate measurements should be taken.