Axial restraint performance of small span-to-depth ratio coupling beams reinforced with diagonal and rhombic bars

Abstract

High ductility is necessary for coupling beams because they are the key energy dissipating components in shear wall structures. However, the axial restraint by the coupled wall piers with high stiffness at both ends negatively affects ductility. Moreover, effectively obtaining the variation laws of the seismic performance of coupling beams under variable axial force using the existing methods is difficult. This study established a statically indeterminate strut and tie model of axial restraint hybrid reinforced coupling beams with a span-to-depth ratio less than 1.5, and the analysis program was compiled. The model was validated by the comparative results of four test examples with span-to-depth ratios ranging from 0.8 to 1.5. Key responses of deformation, bearing capacity, relationship between the axial force and axial deformation, and ductility characteristics subjected to different axial restraints were investigated through combination analysis of the shear-compression, span-to-depth, longitudinal to diagonal bar, and diamond to diagonal bar ratios. The results demonstrated that the axial and lateral forces of the coupling beams with axial restraint were greater than those of the unrestraint, and their amplitude first increased and then decreased with the axial deformation. The stronger is the axial restraint, the greater the yield deformation. Moreover, the smaller is the failure deformation, the more prominent the shear deformation in the total deformation and the worse the ductility. The results also showed that the ductility of the coupling beam in the coupled wall structure designed according to the current specification was insufficient when the wall stiffness was large, requiring more strict measures to be taken under rare earthquakes.