Experimental study on seismic behaviour of eccentrically braced composite frame with vertical LYP steel shear link

Abstract

An experimental investigation is conducted to study the seismic behaviour of eccentrically braced composite frame (EBCF) with vertical shear links, which has a better repairability and replaceability compared with traditional EBCFs with horizontal shear links. Particularly, the low-yield-point (LYP) steel is applied in the shear links to verified its influence on the seismic performance of the EBCFs. Cyclic loads are applied to two composite frames respectively with a bare moment resisting frame system and with a dual system composed of the moment resisting frame and the eccentric bracing system, the comparison of results indicates that the eccentric bracing system can effectively increase the stiffness, strength and energy dissipation capacity of the composite frame, but has few effects on the force conditions on the ends of the primary beams and columns, both two specimens failed by the fracture and buckling of the bottom flanges of the primary beams at a story drift ratio of 1/38. Due to the low-yield-point property and high ductility of the LYP steel, the shear link starts to efficiently dissipate energy when the story drift ratio is only 1/300, and the shear link has reached an inelastic rotation capacity of 0.16 before failure. However, due to the strain hardening of the LYP steel, the shear link achieved an over-strength factor up to 2.78, and the over-strength property of the shear link has resulted an unignorable bending moment of the middle segment of the primary beam, the concrete slab in this area is severely damaged with a maximum crack width of 0.16 mm. Finally, the analysis of working mechanism and test data indicates that, the added stiffness, added strength, and added energy dissipation capacity by the eccentric bracing system are directly in proportional to the contribution of the vertical shear link, and formulas to evaluate the added damage of concrete slab are also given.