Analysis of effect of vertical ground shaking in bridges isolated with spherical sliding bearings

Abstract

Studies have shown that in structures isolated with spherical sliding bearings, the seismic base shear increases when the vertical component of ground shaking is explicitly considered, since the dynamic variation of bearing axial force is passed on to the base shear due to the friction mechanism. In this paper, the effect of vertical shaking is systematically investigated in multi‐span concrete box‐girder highway bridges isolated with triple pendulum bearings. Grounded in the theory of bearing mechanics, a simplified method to predict the amplification of base shear with vertical ground shaking intensity in such bridges is developed and evaluated. The simplified approach is potentially applicable for bridge design based on equivalent static analysis. At low to moderate vertical intensities, the simplified method can capture the observed variation in the base‐shear coefficient with isolation system parameters. The differences in base‐shear amplification for bridge superstructure parameter variations are insignificant, and thus the method is widely applicable. At high intensity vertical ground shaking, the base shear coefficient can be affected by an uplift and impact phenomenon. Thus, application of the simplified method should be limited to motions with peak vertical acceleration up to 1 g; simulation with 3D motions is recommended for intensities beyond 1 g.

Ground-Motion Intensity Measures for the Seismic Response of the Roof-Isolated Large-Span Structure

“…Despite the fact that extensive research has been carried out on the efficiency of intensity measures across various structural types, only a limited number of studies have specifically examined isolated structures. According to Ryan [35], the PGV measure is a generally reliable IM when it comes to forecasting the behavior of base-isolated structures. Narasimhan et al [36] examine the efficiency of velocity-based IMs in predicting the nonlinear behavior of structures with base-isolation elements and find that the PGV measure can reduce the variability of maximum base displacement.…”

Carrying Capacity of Spherical Hydrostatic Bearings including Elastic Deformation

“…Hydrostatic bearings possess desirable characteristics such as low running friction, minimal viscous dissipation, high load-carrying capacity, and high stiffness, making them essential for heavy-duty industrial applications in modern machinery such as machine tools, precision instruments, hydraulic pumps, motors, telescopes, gyroscopes, dynamometers, radar units, and marine engines. Spherical bearings, in particular, offer advantages over other configurations due to their self-aligning nature and ability to withstand radial and thrust loads without being affected by angular misalignments [4][5][6][7].…”