Experimental and numerical study on seismic response of inclined tower legs of cable-stayed bridges during earthquakes

Abstract

More than half of cable-stayed bridges adopt the tower with inclined legs, which can be loaded with a combination of bending, torsion, shear and axial force under earthquakes. To study the seismic response of inclined tower legs, shake table tests were conducted on a 1/20 scaled cable-stayed bridge model with an inverted Y-shaped tower. A description of the model design was introduced and observed damages including horizontal and diagonal cracks at inclined tower legs were presented. A numerical model, considering reduction of torsional stiffness of inclined tower legs after diagonal cracking, was established. The feasibility of the numerical model was validated by a comparison of numerical and test results, which showed good correlation in displacement response at tower top and deck end, and cable force. Based on numerical results, the crack torsional moment of the inclined tower could be easily reached at small peak ground acceleration (PGA), leading to a substantial reduction of torsional stiffness of the section. This reduction helped alleviate the torsional moment demand at larger PGAs and delay the torsional failure of the tower legs. Numerical results also revealed that the bending moment is the primary factor to cause concrete cracks at the lower regions of inclined tower legs whereas complex interaction of large bending moment and torsion results in flexural and torsional damage near the intersection. Conventional ways, which adopt an elastic behavior of torsion, either using stiffness prior to or after diagonal cracking, will lead to intensive overestimation or underestimation of torsional response of the inclined tower legs.