دانلود رایگان مقاله انگلیسی دیدگاه پاسخ جانبی پی های سطحی دور از ساحل - الزویر 2017

ABSTRACT

Suction caissons are often subjected to cyclic lateral loads caused by the action of wind or waves. As a result of these cyclic loads, excessive lateral deformations may be induced during a caisson's service life. Although soilfoundation response analysis requires information about stiffness and damping at the site, the methods for obtaining this information are still in question. The present study reports non-dimensional frameworks for determining the impedance functions for soil-foundation system at the load reference point along with the results of performance measure parameters that track the response of suction caissons harmonically oscillating on homogeneous soil. The equations are expressed in terms of logarithmic and polynomial models based on a statistical analysis of existing cyclic test results for small-scale Aalborg University Instrumented Suction Caissons, 300 mm in diameter and 300 mm in skirt length. The variables used in the equations for normalized secant stiffness are load characteristics (ξb and ξc) and number of load cycles. The present study also identifies critical new findings regarding the local densification and the plastic shake-down at the caisson-soil interface, which are all important factors to consider in a performance based-framework for designing offshore structures.

4. Conclusions

Summarized in this paper is a procedure for estimating the variation of k ∼ and D with horizontal displacement and time for sandy soils. The procedure is based on a review of previously published general procedures and a statistical analysis of existing laboratory test data from multiple cyclic loading experiments performed on suction caissons founded on dense silica sand. Main conclusions follow:

1. This study bridges the gap between suction caisson-soil interaction at nearly small displacements and at large deformations (plastic response) upon cyclic loading that are usually neglected in offshore foundations analyses.

2. Accordingly, appropriately defined performance measure parameters are introduced to evaluate the caisson response to distinguish between contribution of soil densification and plastic shakedown mechanism.

3. Interaction diagrams exhibits how the cyclic loading parameters, N, ξb and ξc affect cyclic response. The plots and simplified design procedures captured key aspects of the tests performed.

4. High-level cycling under one-way and two-way conditions invoked roughly different responses. The latter gave scope for higher normalized cyclic loading levels that promoted more cyclic stiffness increase rates, while the former led to less symmetric and stiffness increase.