Hongyan Ding

Negative pressure consolidation of silt inside bucket foundation

A series of model experiments of bucket foundations concerning suction installation and negative pressure consolidation in saturated silt were carried out in a cube steel bin at Tianjin University. The experimental results show that the silt inside the bucket has been strengthened by negative pressure, and the strengthening effect decreases with the increase of the distance from the bucket. A three-dimensional numerical model of the experiments was built by means of finite element software ABAQUS with fluid-solid coupling method. The results show that the bearing capacity of the silt inside the bucket foundation increases significantly at the former stage of negative pressure consolidation, while the increasing trend slows down over time. The rotation centers of the bucket foundation and the inner soil region tend to be closer to each other based on the consolidation. The bearing capacity of the bucket foundation is improved effectively with the increase of soil strength. The effects of negative pressure consolidation on the bearing capacity of bucket foundation were also illustrated by an actual offshore wind power project case.

Fatigue Damage Assessment for Concrete Structures Using a Frequency-Domain Method

A fatigue damage assessment for concrete was carried out according to Eurocode 2. Three frequency-domain methods, the level crossing counting (LCC) method, the range counting (RC) method, and a new proposed method, were used for the damage assessment. The applicability of these frequency-domain methods was evaluated by comparison with the rainflow counting method in the time domain. A preliminary numerical study was carried out to verify the applicability of the frequency-domain methods for stress processes with different bandwidths; thus, the applicability of the LCC method and the new method was preliminarily confirmed. The fatigue strength of concrete had a minor effect on the fatigue damage assessment. The applicability of the LCC and the new methods deteriorated for relatively low coefficients of variance of the stress process because the ultimate number of constant amplitude cycles was sensitive to the range of the cycles. The validity of the joint probability functions of the two methods was proven using a numerical simulation. The integration intervals of the two frequency-domain methods were varied to estimate the lower and upper bounds on the fatigue damage, which can serve as references to evaluate the accuracy of the time-domain method results.