There has been a wide range
of study, investigation and review of the seismic design
suggested by the codes in recent years; one of these hot
topics was the concept of “Rocking isolation design”.
The main goal of this new design
approach is to investigate the possibility of allowing
below ground supports systems to respond to strong
seismic shaking by going beyond number of thresholds
that would be conventionally imply failure and are today
forbidden by design codes such as sliding at
soil-foundation interface, separation and uplifting of
shallow foundations, mobilization of bearing capacity
failure mechanism for foundations, structural yielding
of pile foundations & combination of some of the
previous.
Of course some of the disadvantages
are the residual angle of rotation and settlement may
exceed the serviceability limits mentioned by the codes.
Here the question came in case of the
seismic performance of highway bridges the new design
concept proved to be safer in terms of protecting the
structure from failure. But what if the superstructure
in this case the deck of the bridge is huge thus it has
influential rotational inertia that may affect the
overall stability in that case and threatening the whole
concept and takes away the advantage of preventing
failure.
This study focuses mainly on
the effect of the rotational inertia of the
superstructure on the seismic performance of highway
bridges. The effect generally was in fact ignored in
most studies and experiments for simplicity in both
numerical analysis and modeling. Whether this effect
would diminish the advantages of the Rocking isolation
design concept or it would confirm them and should it
always be accounted for in analysis or modelling. This
will be the scope of this study.
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