Conventional (code-based) seismic bridge design provides the necessary strength and ductility to the structure to withstand seismic forces. However, a severe earthquake might be accompanied by irreversible structural deformation and therefore damage after the end of the excitation. Rocking, as a means of seismic isolation, allows the bridge piers to uplift and pivot (rocking behavior) relieving the structure from deformation, stresses and hence damage. As a consequence, rocking behavior leads to structures of lower cost which are simpler to construct and is currently resurging.

Due to the increasing demand to predict the response of more realistic rocking structures, the present study investigates, analytically and numerically, the seismic response of a rocking bridge bent (fram...[ Read more ]

Conventional (code-based) seismic bridge design provides the necessary strength and ductility to the structure to withstand seismic forces. However, a severe earthquake might be accompanied by irreversible structural deformation and therefore damage after the end of the excitation. Rocking, as a means of seismic isolation, allows the bridge piers to uplift and pivot (rocking behavior) relieving the structure from deformation, stresses and hence damage. As a consequence, rocking behavior leads to structures of lower cost which are simpler to construct and is currently resurging.

Due to the increasing demand to predict the response of more realistic rocking structures, the present study investigates, analytically and numerically, the seismic response of a rocking bridge bent (frame) which is either free-standing, or hybrid; i.e. enhanced with supplemental damping and re-centering capacity. The study examines its seismic stability under various ground excitations. Further, the case of the symmetric rocking frame is extended, by examining a more general bridge frame configuration, the asymmetric frame (with columns unequal in height). For both structural configurations, the equations of motion are derived from the principles of analytical dynamics, while the deformation of the structural members is ignored. The analysis considers both pulse-type and non-pulse-type ground motions, to examine how the additional damping and stiffness affect the seismic response, and to assess the stability of both (symmetric and asymmetric) hybrid rocking bridge frames against overturning.

Further, this study revisits analytically the impact phenomenon during rocking. To this end, it adopts a non-smooth dynamics approach assuming impacts in rocking structures behave as unilateral contacts. To validate the proposed methodology, it examines the simplest rocking structure, the archetypal rigid rocking block. More specifically, the present work studies the impact and the uplifting (detachment) events during rocking. It treats impact and uplifting through a system of inequalities, which is known as the linear complementarity problem (LCP). Throughout the study, the impact is considered to be instantaneous and to be described by contact laws (Newton’s and Poisson’s). These set-valued laws capture the behavior in the normal direction of the (unilateral) contacts. Further, it is assumed that in the tangential direction sliding is prevented by designing the contact points to act as shear keys. The study demonstrates the ability of the proposed methodology to capture the impact behavior during rocking.

The results of the present analysis demonstrate the marginal effect of the asymmetry on the seismic stability of the asymmetric rocking frame compared to the pertinent of the symmetric, despite the very different kinematics. Further, it becomes clear that for both structural configurations (symmetric and asymmetric) the seismic performance of the hybrid rocking frame is very sensitive to the fracture elongation of the supplemental re-centering (tendons) and damping devices. The results also confirm the high seismic performance of the planar rocking frame, thus illustrating its potential as an alternative seismic bridge design paradigm. Finally, the proposed linear complementarity problems (LCPs) verify the corresponding results of other studies/methodologies, while offering a more concise description of the impact problem in rocking structures.

Author keywords: rocking structures, analytical dynamics, prefabricated bridges, overturning, linear complementarity problem, non-smooth, impact, uplifting