Seismic control for elevated roads

Past earthquakes have demonstrated the vulnerability of deck bridges, which are the most common type in elevated roads. Especially over-loading of piers and drop-off of sections are a continuing concern. Seismic Control concepts, when correctly understood and applied, can provide the necessary physical force limits and reduced displacements even under loading beyond the design limit. The concept of choice here is the Hysteretic Device System since deck bridges usually provide a natural seismic link between piers and deck. To study the performance and robustness of this concept, shaking table tests were performed at IZIIS, Skopje during the NATO-SfP project ISUbridge on a model deck bridge using controllable friction devices UHYDE-fbr to simulate the behavior of different passive devices including device failure. The tests showed that a stiff-ductile device in the link not only protects the piers from over-load, but also provides superior performance compared to viscous or soft base-isolation devices. Failure of such a device further reduced the demand on the piers but did not lead to excessive deck displacements or damage, thus confirming considerable seismic robustness for the HDS concept. This corroborates observations on the Bolu viaduct during the Kocaeli event. Unfortunately, HDS is often confused with Base- Isolation, which leads to the application of BI-devices, like LRBs and thus a reduction in performance and robustness. This is even more true for viscous devices, which are favored today.