Hysteretic Model of Frictional Steel Truss Coupling Beams

The coupling beams couple two or more RC walls in series, and transfer vertical forces between adjacent walls to resist a portion of total overturning moments. However, the RC beams may suffer brittle shear failure in earthquakes, which poses a risk to the life safety. In addition, the damaged RC coupling beams are difficult to repair and may render the whole building irreparable. To mitigate these problems, the frictional steel truss coupling beams (FTCBs) was proposed. The FTCBs concentrate inelastic deformation into the replaceable friction dampers while the main body remains elastic. Compared to metallic dampers, the friction dampers are anticipated to be low-damage and can be rapidly repaired by retightening or replacing the bolts after a major earthquake. The limiting shear strength of FTCBs relies merely on the stable sliding strength of friction dampers while the initial stiffness is determined by the truss members. The strength and stiffness can thus be separately designed for FTCBs, which offers great design flexibility. To support the seismic design of coupled wall or dual systems incorporating FTCBs, the hysteretic model of FTCBs was proposed. The model consists of a trilinear backbone curve and the unloading and reverse loading rules. The model has eight control parameters. The initial stiffness and limiting shear strength are defined by theoretical formulae and the others are derived through regression analysis on test results. The hysteretic model fitted well with both test and FE results, indicating its applicability to FTCBs with varying core design parameters.