Localized Differential Settlement Research Articles

Three-dimensional Deformation Behavior for Buried Pipe Joints Subjected to Local Differential Settlement Using Three-direction Strain Measurement

Three-dimensional Deformation Behavior for Buried Pipe Joints Subjected to Local Differential Settlement Using Three-direction Strain Measurement

Buckling behavior of floating-roof steel tanks under measured differential settlement

Large vertical cylindrical steel tanks constructed on soft foundations may bring forth various types of settlement, which is well known as the uniform settlement, the planar tilt and the differential settlement. Measured settlements of steel tanks in several practical projects are first summarized according to the in-site surveying data, and two kinds of settlement patterns are clearly defined, which are referred to as the global differential settlement and the localized differential settlement. Two practical floating-roof steel tanks are taken as the illustrative examples of large steel tanks, which are marked TK-2020 with the height-to-radius ratio of 0.35 as the representatives of large volume tanks and TK-2090 with the height-to-radius ratio of 0.7 as representatives of smaller volume tanks in this paper. Buckling behaviors of the two illustrative tanks under the global and localized differential settlement are investigated using the general-purpose finite element computer package ABAQUS by means of the geometrical nonlinearity algorithm. It is shown that for tanks under global differential settlement, local buckling occurs first at the eave wind girder, followed by a stable post-buckling behavior, so that the local buckling of the wind girder can be taken as the serviceability limit state and the post-buckling strength can be utilized in structural design of tanks. Moreover, the behavior of tanks under localized differential settlement is related to the degree of localization. The buckling behavior in the case of a large circumferential central angle for localized settlement is similar to that under global differential settlement, while the effect of the localized settlement with a relatively small central angle is more obvious than that of the global differential settlement, and the snap-through buckling induced by localized settlement would govern the design.

Stability Analysis of Floating-Roof Tanks under Differential Settlement

Vertical cylindrical steel tanks are sensitive to differential settlement beneath the tank wall. Most previous studies were based on idealized harmonic settlement, however, for thin shell structures of high nonlinear behavior, it is obviously inappropriate to obtain the results under real settlement by simple summation of harmonic solutions. Real settlement of steel tanks can be grouped into two types - global differential settlement and local differential settlement. This paper examines the nonlinear response and stability behavior of floating-roof steel tanks under both types of settlement. It is shown that, for tanks under global differential settlement, local buckling occurs at the eave ring, followed by a stable post-buckling behavior, and final failure is by overall buckling of the tank shell; while for tanks under local differential settlement, the structural response is related to the degree of localization. At highly localized settlement, local snap-through buckling occurs at the tank wall, but it does not lead to a serious consequence, and the post-buckling behavior can also be utilized in design.

Axially compressed cylindrical shells with local settlement

The design of cylindrical metal silos and tanks is often controlled by considerations of buckling under axial compression. Whilst the effects of geometric imperfections on the buckling strength have been extensively explored, few studies have explored the effects of defects in the boundary conditions and the effects of residual stresses have received even less attention. This paper investigates the initiation and development of imperfections caused by local differential settlement at the supported base and their effect on the elastic buckling of a thin cylindrical shell under axial compression. The shells were treated as initially perfect with perfect support, but developing geometric imperfections and residual stresses as a consequence of local displacement at the supported edge and with residual stresses consistent with the induced geometric imperfections. The results raise interesting questions concerning the criteria of failure and appropriate tolerance measurements for constructed cylindrical shells.

Displacements in Oil Storage Tanks Caused by Localized Differential Settlement

This paper presents design charts for predicting the maximum radial distortion of open-topped storage tanks caused by localized differential settlement of the tank foundations. It is well known that differential settlement can produce radial deflection of the tank shell sufficient to cause jamming of the floating roof. Predictions of shell deflections have often assumed the shell to be inextensional, an assumption which may not always be valid, particularly where the settlement is localized. Consequently, the authors have recently completed a more refined analysis of the deflections and stresses in the shell and the primary wind girder [1] in which the shell is considered to act as a membrane. They concluded that this membrane analysis is valid for all practical applications and proposed a procedure for predicting shell displacements caused by any general differential settlement profile using Fourier analysis. This paper firstly reviews the new membrane analysis and then illustrates its application to two specific localized settlement profiles commonly found in practice to produce easy-to-use design charts. Finally, the paper refers to experimental testing of a model tank, carried out to verify the validity of these design charts [2].