Abstract
SummaryRocking motion, established in either the superstructure in the form of a 2‐point stepping mechanism (structural rocking) or resulting from rotational motion of the foundation on the soil (foundation rocking), is considered an effective, low‐cost base isolation technique. This paper unifies for the first time the 2 types of rocking motion under a common experimental campaign, so that on the one hand, structural rocking can be examined under the influence of soil and on the other, foundation rocking can be examined under the influence of a linear elastic superstructure. Two building models, designed to rock above or below their foundation level so that they can reproduce structural and foundation rocking respectively, were tested side by side in a centrifuge. The models were placed on a dry sandbed and subjected to a sequence of earthquake motions. The range of rocking amplitude that is required for base isolation was quantified. Overall, it is shown that the relative density of sand does not influence structural rocking, while for foundation rocking, the change from dense to loose sand can affect the time‐frequency response significantly and lead to a more predictable behaviour.
Highlights
Following the aftermath of the New Zealand earthquakes (2011), it has become clear that buildings should be designed to be repaired after a seismic event, so that disruption is minimised
Because the sand density can govern the type of response for foundation rocking, while having very little effect on the building performance for structural rocking, visualisation of the change in frequency content with time can provide further insights on the dynamics of the response
This paper compares the seismic behaviour of 2 building models resting on dry sand and allowed to uplift and subsequently indulge in 2 different types of rocking action
Summary
Following the aftermath of the New Zealand earthquakes (2011), it has become clear that buildings should be designed to be repaired after a seismic event, so that disruption is minimised. The rigid block can be reduced to a single rocking footing,[24] or visualised as a reinforced concrete wall as part of a building,[25] or a bridge pier.[26] when all of the individual block foundations are allowed to rock on soil, an admissible kinematic mechanism must be formed, and this is achieved by allowing yielding and damping to develop at the ends of the beams/ columns, where plastic hinges would form.[27,28,29,30] While the major advantages of limiting the earthquake‐induced force because of local uplift and increased damping from soil hysteresis are maintained (and at the same time, no impacts occur that excite the superstructure), soil settlements can be a barrier to practical implementation This is true for framed structures with plastic hinges at beam members, which may be more prone to differential settlements. The main objective is to assess the acceleration and force demand that rocking systems experience during their motion as a result of strong ground shaking and of the impacts developing at the interface of the superstructure with the foundation or the interface of the foundation with the soil because of rocking
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