Marine Structures | Year: 2013
The objective of this paper is to examine non-linear bending of a flexible elastic bar near fixed termination and to develop analytical solutions that can be used in the design of bend stiffeners. The non-linear bending of prismatic bars of finite and se-infinite lengths is solved analytically, and results are employed to re-visit the problem of the " ideal" bend stiffener, which provides a constant curvature over its entire length. A complete solution is derived for all properties of the ideal bend stiffener, which is not limited by any assumptions on the system geometry and provides an improvement over known formulations. Other features of the non-linear bending of elastic bars are examined and examples are given to demonstrate application of the present theory to sizing bend stiffeners for flexible risers. © 2012 Elsevier Ltd.
Earthquake and Structures | Year: 2012
The capacity of pipelines to resist collapse under external pressure and bending moment is a major aspect of deepwater pipeline design. Existing design codes present interaction equations that quantify pipeline capacities under such loadings, although reasonably accurate, are based on empirical data fitting of the bending strain, and assumed simplistic interaction with external pressure collapse. The rational model for collapse of deepwater pipelines, which are relatively thick with a diameter-to-thickness ratio less than 40, provides a unique theoretical basis since it is derived from first principles such as force equilibrium and compatibility equations. This paper presents the rational model methodology and compares predicted results and recently published full scale experimental data on the subject. Predictive capabilities of the rational model are shown to be excellent. The methodology is extended for the problem of pipeline collapse under point load, longitudinal bending and external pressure. Due to its rational derivation and excellent prediction capabilities, it is recommended that design codes adopt the rational model methodology.
Kaliyaperumal G.,Intecsea |
Sengupta A.K.,Indian Institute of Technology Madras
Proceedings of the Institution of Civil Engineers: Structures and Buildings | Year: 2014
An existing reinforced concrete building with moment-resisting frames can be vulnerable during an earthquake owing to its deficient columns. The present paper reports a study on the enhancement of flexural strength and behaviour of columns, by concrete jacketing. First, the performance of the interface of additional concrete cast against the prepared surface of existing concrete was studied. Tests were then conducted on reference (without strengthening) and jacketed column specimens, to study the enhancement of strength of a retrofitted column section under the interaction of axial load and bending moment. Subsequently, interior beam–column–slab sub-assemblage specimens were tested under simultaneous vertical and lateral loading. It was observed that the selected jacketing scheme was effective in enhancing the flexural strength, as well as in retaining the ductility and energy dissipation in the behaviour. The moment–curvature behaviour of a retrofitted column section was predicted based on the layered analysis. The information was fed in the lateral load against drift analysis of a computational model of a retrofitted sub-assemblage specimen, using an incremental non-linear technique. The paper presents the method of analysis and guidelines for retrofitting of columns for seismic forces. © 2014, Thomas Telford Services Ltd. All rights reserved.
Proceedings of the Annual Offshore Technology Conference | Year: 2014
Oil and gas operators are developing subsea production systems at greater and greater distances from thenrespective hosts in deepwater basins worldwide. Many of these subsea systems have the potential to include subsea boosting systems (pumping and/or compression) in these installations, which presents the need for significant amounts of AC power to be delivered over these increasing distances. Recent experience and subsequent investigation has shown that the required AC power can be delivered efficiently and cost effectively to these installations via an innovative system approach involving a split of the major components of a typical Variable Frequency Drive (VFD) system, locating the AC/DC conversion equipment at the host facility where power is generated, locating the DC/AC conversion equipment on the seabed, in proximity to the subsea boosting equipment, and connecting the two via a DC transmission cable. Through utilization of DC power transmission, we expect to eliminate the reactive power issues and line harmonics issues associated with AC transmission. Innovational approaches such as this one will make these installations more practical and cost effective, and open the door to even further capability. Copyright 2014, Offshore Technology Conference. Copyright 2014, Offshore Technology Conference.
Numerical Methods in Geotechnical Engineering - Proceedings of the 8th European Conference on Numerical Methods in Geotechnical Engineering, NUMGE 2014 | Year: 2014
In the offshore industry small subsea structures are generally supported by mudmat foundations and these are often loaded with forces and moments acting in three directions. In deep water applications very soft clays are frequently encountered and, depending on the design, finite element analyses may be employed to verify that the capacity of the selected mudmat is sufficient to carry the expected load combinations safely. Most of these analyses are conducted based on available undrained shear strength data collected in-situ. The use of effective strength soil parameters and evaluation of stresses and deformations that may arise under longterm drained conditions has received less attention. The subsea structures supported by mudmats are generally connected to numerous pipelines and umbilical lines via elements called jumpers.Although there is some inherent flexibility in their design, foundation movements arising from settlement and operational loads can influence the integrity of the connectors at the joint locations. In this paper a mudmat resting on clay is analyzed for deflections and rotations. In particular, the influence of using effective soil strength parameters (instead of the typical undrained shear strength profile) and the influence of including a consolidation stage in the analysis is investigated. Different soil constitutive models, namely the Mohr Coulomb and the Hardening Soil models that are available in Plaxis 3D are used. Undrained and drained loading sequences are applied which reflect expected conditions that mudmats typically encounter over their service life. The results are evaluated with respect to the sensitivity of the calculated deformations to the modeling approach employed. © 2014 Taylor & Francis Group, London.