Pullout Capacity Of Plate Anchors Research Articles

Numerical investigation of inclined plate anchors in clay with linearly increasing undrained shear strength

Plate anchors have been increasingly used to provide a mooring system for offshore floating facilities due to their relatively high efficiency and low costs. The analysis of anchor behaviour can be usually divided into two categories “immediate breakaway” and “no breakaway”, which correspond to the “vented anchors” and “attached anchors”. Most of the previous literatures focus on these two extreme cases: vented anchors in clays without weight and attached anchors. However, the vented anchors in clays with weight, as a most common state, are in the intermediate state of the two extreme cases. At the cases, the change law of the pullout capacity of plate anchors with embedment depth, inclination angles and overburden pressure is relatively complex and needs further study. This paper investigates the pullout behaviour of inclined strip plate anchors in clays with linearly increasing shear strength by performing a series of finite element analysis, and clarify the change law of the pullout capacity and the failure mechanism of plate anchor in the intermediate state. Two new formulas are proposed to predict the pullout factor for inclined vented and attached anchors. Related research results can provide a reference for the engineering design of inclined plate anchors in undrained clay.

Experimental study of pullout capacity of plate anchors shallowly embedded in hydrate bearing sediments

Plate anchors are commonly used in mooring systems of offshore facilities for gas and oil production in deep and ultra-deep water. They may encounter hydrate-bearing sediments widespread in marine continental margins. The pullout capacity of square anchors embedded shallowly in a hydrate-bearing sand is investigated with small-scale model tests using tetrahydrofuran (THF) hydrate as the substitute of gas hydrate. The results show that the pullout capacity of the anchors increases with the increase of the anchor width and the burial depth. The pullout capacity of the anchors can be estimated by a dimensionless breakout factor. This factor increases with the increase of the burial depth ratio (defined as the ratio of the burial depth to the width of a plate anchor), exhibiting a trend similar to that obtained numerically and experimentally from plate anchors shallowly-embedded in undrained clays. Hydrate dissociation brings detrimental effects on the pullout capacity of the anchors. The pullout capacity of the anchors drops to 0.3% of the initial value after the hydrates dissociate. This pronounced reduction highlights the need for further investigation on the effect of oceanic hydrate dissociation on engineering performance of offshore facilities as a result of natural or anthropologic perturbation.

Generalized Design Approach for Inclined Strip Anchors in Clay

Abstract The estimation of the undrained pullout capacity of plate anchors is vital for the design of offshore floating facilities and has been an active topic of research for several years. Most of the previous studies have proposed empirical relationships to predict the undrained pullout capacities of inclined anchors. Generally, the buoyancy effect is added to the shearing resistance to obtain the total capacity, which is less than or equal to the maximum capacity. In this paper, an alternative mechanism-based simple design methodology is proposed to estimate the undrained pullout capacity of inclined anchors. A series of finite-element analyses are performed for a range of anchor inclinations in soils with uniform and heterogeneous shear strength. The effects of anchor embedment, soil unit weight, and anchor–soil interface tensile capacity are studied in a systematic manner. A relationship has been developed to estimate the depth at which the anchor undergoes a transition in the failure mechanism from...

Kinematic limit analysis of pullout capacity for plate anchors in sandy slopes

The pullout capacity of plate anchors has been studied extensively over the past 40 years. However, very few studies have attempted to calculate the pullout capacity of anchors in sandy slopes. In this paper, three upper bound approaches are used to study the effect of a sloping ground surface and friction angle on pullout capacity and failure of plate anchors. This includes the use of; simple upper bound mechanisms; the block set mechanism approach; and finite element upper bound limit analysis. The aim of this research is to better understand the various failure mechanisms and to develop a simple methodology for estimating the pullout capacity of anchors in sandy slopes.

The Criterion for Determining the Ultimate Pullout Capacity of Plate Anchors in Clay by Numerical Analysis

The Ultimate Pullout Capacity (UPC) is an important index in designing and analyzing plate anchors. However, there are still uncertainties in determining the UPC through the load-displacement curves calculated from numerical analysis. The review on the existing criteria for determining the UPC also demonstrates that there has not been a generally accepted criterion and most existing criteria are not only uncertain but also irrational. Considering that there are still divergences and confusions in determining the UPC and specific studies are rare, further investigations are needed to clarify this basic but important topic before analyzing the UPC and the performance of plate anchors. The present work just emphasizes on the criterion for determining the UPC of plate anchors in clay. After a review of current studies on this topic, the maximum resistance criterion based on large deformation finite element analysis is recommended to determine the UPC of plate anchors, which accords with two rules. The first, a deterministic value of UPC can be obtained by using the criterion. The second, the criterion must be rational which means that it implies clear and right physical meaning and can be generally applied. This criterion is validated firstly by three model tests and then applied to rectangular and circular plate anchors at different embedment depths in both uniform and linear clays to calculate the bearing capacity factors.

Numerical study on plate anchor stability in clay

Although the pullout capacity of plate anchors in clay has been studied extensively, the results considering the coupling effects of anchor inclination, clay non-homogeneity and self-weight are relatively rare. In the present paper, finite-element analyses are carried out to investigate the coupling effects of these factors on the pullout capacity of strip plate anchors in clay. The numerical solutions are presented in the familiar form of pullout capacity factors based on various anchor embedment depth, clay strength profile and clay self weight, and are also compared with existing numerical and empirical solutions. A design procedure based on the data-fitting equations of the present finite-element solutions is also presented for the convenience of design engineers.

UPPER BOUND SOLUTION FOR PULLOUT CAPACITY OF ANCHORS ON SANDY SLOPES

By making use of limit analysis, an upper bound solution in a closed form for determining the ultimate pullout capacity of plate anchors buried in sandy slopes has been established. The anchor plate orientation has been considered either horizontal or parallel to the slope, with the pullout force applied perpendicular to the plate. It has been found that the pullout capacity for horizontal anchors, even on slopes, remains the same as that on horizontal ground surface as long as the average embedment ratio is kept constant. Whereas for anchors which are aligned parallel to the slope the collapse load decreases continuously with the increase in the inclination of slope. © 1997 John Wiley & Sons, Ltd.