Effects of Single-Surface Sliding in Double Pendulum Bearings on the Behavior of Isolated Bridges

Börekçi M., Alvarado R. G., Ryan K. L.

The 18th World Conference on Earthquake Engineering (WCEE2024) , Milan, İtalya, 30 Haziran - 05 Temmuz 2024, ss.1-12

  • Yayın Türü: Bildiri / Tam Metin Bildiri
  • Basıldığı Şehir: Milan
  • Basıldığı Ülke: İtalya
  • Sayfa Sayıları: ss.1-12
  • Yıldız Teknik Üniversitesi Adresli: Evet

Özet

In double pendulum bearings, uneven sliding on the two surfaces and even single surface sliding (i.e. sliding limited to one surface) was observed throughout an experimental program conducted at the Earthquake Engineering Laboratory at the University of Nevada, Reno. Several bearings were tested using a specialized experimental assembly, wherein a bidirectional shake table was used as an actuator to impose a displacement history on the bearing, while the top of the bearing was constrained with a reactionary frame over the top. The occurrence of the uneven or single surface sliding phenomenon was attributed to various potential factors such as water, ice, or other contaminants, rusted surfaces in the aged bearings, and caked-on soil. Also, the single surface sliding was observed occasionally even in a clean, dry bearing. This was theoretically caused by the rotation of the bearing top plate, which induces a dynamic variation in effective friction and thus unequal friction on the two surfaces.

The single surface sliding considerably alters the behaviour of an individual bearing. To estimate the effect of the single-surface sliding on the bridge response, two different bridge models were developed in OpenSees. The model variations were provided in terms of the span length, pier configuration, and deck section properties. The bridge models were subjected to a suite of motions that were scaled to the target design spectrum for the bridge based on seismicity. Single surface sliding was modelled generally as an increase in the bearing stiffness Kd (reflecting the decreased pendulum length) using a standard bearing model. Analyses were conducted for the bridges assuming conventional sliding and single surface sliding to assess comparative responses. The results of this study indicate that single surface sliding increases both the isolator and pier shear coefficients, especially in the transverse direction, with no significant effect on isolator displacement. Variations in bridge properties, such as lateral pier stiffness, have relatively insignificant effects on the response sensitivity to single surface sliding.