The behavior of a single pile under cyclic axial loads

Many piled foundations have been destroyed under significant cyclic loads in earthquakes. Centrifuge modelling of a single pile subjected to cyclic loads has been conducted to investigate the influence of cyclic loads on the axial performance of the single pile. Different pile installation procedures were applied to compare the axial behaviour of different piles under cyclic loads. Pile head permanent settlements accumulated due to cyclic axial loads, and these increased with the increasing load amplitude. Also the pile head axial secant stiffness decreased with the increasing number of axial load cycles, and with increasing amplitude. Furthermore, the axial pile performance is influenced significantly by different installation methods. © 2010 ASCE.

Effect of previous cyclic axial loads on pile groups

Numerous piles are often subjected to the combination of cyclic axial and cyclic lateral loads in service, such as piled foundations for offshore platforms which may suffer swaying and rocking motions owing to wind and wave actions. In this research, centrifuge tests were conducted to investigate the effect of previous cyclic axial loads on the performance of pile groups subjected to subsequent cyclic lateral loads. Different pile installation methods were also applied to study the different behaviour of bored and jacked pile groups subjected to cyclic loads. During lateral load cycling, it is seen that cyclic axial loads to which pile groups were previously subjected could reduce the pile cap permanent lateral displacement in the first lateral load cycle but do not influence the incremental rate of permanent displacement in the following lateral load cycles. Moreover, it is found that previous cyclic axial loads could improve the pile cap cyclic lateral secant stiffness, especially for the pre-jacked pile group. When rocking motions were induced by cyclic lateral loads, pile groups subjected to cyclic axial loads before have smaller permanent settlement than those without the cyclic axial loading effect. The designers of piles that are intended to resist significant lateral loads without excessive deformations in service may wish to deploy cyclic axial preloading, accordingly.

A critical analysis of loudness calculation methods

The physical meaning and methods of determining loudness were reviewed Loudness is a psychoacoustic metric which closely corresponds to the perceived intensity of a sound stimulus. It can be determined by graphical procedures, numerical methods, or by commercial software. These methods typically require the consideration of the 1/3 octave band spectrum of the sound of interest. The sounds considered in this paper are a 1 kHz tone and pink noise. The loudness of these sounds was calculated in eight ways using different combinations of input data and calculation methods. All the methods considered are based on Zwicker loudness. It was determined that, of the combinations considered, only the commercial software dBSonic and the loudness calculation procedure detailed in DIN 45631 using 1/3 octave band levels filtered using ANSI S1.11-1986 gave the correct values of loudness for a 1 kHz tone. Comparing the results between the sources also demonstrated the difference between sound pressure level and loudness. It was apparent that the calculation and filtering methods must be considered together, as a given calculation will produce different results for different 1/3 octave band input. In the literature reviewed, no reference provided a guide to the selection of the type of filtering that should be used in conjunction with the loudness computation method.