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Variation of modal parameters of pile-supported structures in seismically liquefiable soils.

Lombardi, Domenico; Bhattacharya, Subhamoy

Authors

Domenico Lombardi

Subhamoy Bhattacharya



Abstract

This paper presents experimental results that aimed to investigate the effects of soil liquefaction
on the modal parameters (i.e. frequency and damping ratio) of pile-supported structures. The tests
were carried out using the shaking table facility of the Bristol Laboratory for Advanced Dynamics
Engineering (BLADE) at the University of Bristol (UK) whereby four pile-supported structures (two
single piles and two pile groups) with and without superstructure mass were tested. The experimental
investigation aimed to monitor the variation in natural frequency and damping of the four physical
models at different degrees of excess pore water pressure generation and in full-liquefaction condition.
The experimental results showed that the natural frequency of pile-supported structures may
decrease considerably owing to the loss of lateral support offered by the soil to the pile. On the other
hand, the damping ratio of structure may increase to values in excess of 20%. These findings have
important design consequences: (a) for low-period structures, substantial reduction of spectral
acceleration is expected; (b) during and after liquefaction, the response of the system may be dictated
by the interactions of multiple loadings, that is, horizontal, axial and overturning moment, which were
negligible prior to liquefaction; and (c) with the onset of liquefaction due to increased flexibility of
pile-supported structure, larger spectral displacement may be expected, which in turn may enhance Pdelta
effects and consequently amplification of overturning moment. Practical implications for pile
design are discussed.

Conference Name 2nd European Conference on Earthquake Engineering and Seismology
Start Date Aug 25, 2014
End Date Aug 29, 2014
Publication Date 2014
Deposit Date Jan 5, 2015
Peer Reviewed Peer Reviewed
Keywords soil liquefaction; pile-supported structures; shaking table facility;
Public URL http://researchrepository.napier.ac.uk/id/eprint/7427
Publisher URL http://www.eaee.org/Media/Default/2ECCES/2ecces_eaee/2208.pdf