IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The analysis of laterally loaded piles in soft clay is carried out idealising the pile as beam elements and the soil by nonlinear inelastic spring elements modeled with elasto-plastic sub-elements. The nonlinear hyperbolic model for static load condition is developed based on the undrained shear strength and modulus of subgrade reaction. An iterative procedure is adopted to perform a nonlinear finite element analysis and the effect of static lateral load on deflection is studied. Based on the lateral deflection at the end of first cycle (static load), the degradation factor is assumed and the p-y curve is modified. The cyclic load analysis is carried out using the static analysis program idealising the soil by modified p-y curve, which considers the effect of number of cycles and magnitude of cyclic lateral load. The results of the proposed analytical model compare well with the published experimental results, on piles subjected to one-way cyclic loading for different magnitude of cyclic lateral load and number of cycles. Copyright © 1996 Elsevier Science Ltd.

Department of Ocean Engineering

Computers and Geotechnics

Degradation Model for One-way Cyclic Lateral Load on Piles in Soft Clay

An approximate method based on strut approach to predict the ultimate strength of simply-supported stiffened panels with initial imperfections and square cutouts, subjected to uniaxial compression is presented. The reduction in stiffness of the plate between stiffeners is considered by using an 'effective width concept'. Tests are reported on welded stiffened steel panels with varying plate slenderness ratio and column slenderness ratio. Based on the experimental investigations and the proposed method, the influence of square openings, extending the full width between stiffeners, on the ultimate strength of stiffened panels is evaluated. © 1995.

Department Of Civil Engineering

Marine Structures

Ultimate strength of stiffened panels with cutouts under uniaxial compression

The diffraction/radiation boundary value problem arising from the interaction of oblique waves with freely floating long structures is studied using finite-element techniques. Further, the hydrodynamic behaviour of two-dimensional horizontal floating structures under the action of multi-directional waves has been studied. The linear transfer function approach is used to determine the wave exciting forces and motion responses of a structure of finite length in short-crested seas. The directional spectrum is obtained from a unidirectional spectrum with an associated frequency-dependent or frequency-independent cosine power-type energy spreading function. Based on the numerical predictions, the motions and forces on a rectangular floating structure experiencing unidirectional and multi-directional wave fields are computed. © 1996.

Applied Ocean Research

The hydrodynamic behaviour of long floating structures in directional seas

The stability of a simply supported square plate with openings under in-plane loading is analysed using a Finite Element program BUCSAP (BUCkling Structural Analysis Program). The openings are considered as square and central for the main study but rectangular and central for comparison with other work. Different magnitudes of tension and compression are assumed as initial pre-stress in the transverse direction before the longitudinal stress is applied. Two load cases have been considered. The longitudinal stress is assumed as uniform compression for Case 1 and is assumed as trapezoidal compression representing hydrostatic loading for Case 2. The results have been used to plot design charts. © 1992.

GENERAL

Stability of initially stressed square plates with square openings

Experimental studies on a single point taut moored buoy cable system is carried out in a 2 m-wide regular wave flume for different wave heights and wave periods. Surge and heave accelerations of the buoy are measured using accelerometers kept inside the buoy in the respective directions. Two ring gauges, one at the top and another at the bottom, are used to determine the top and bottom tensions in the cable. The results are processed to plot the variation of acceleration and tension for various wave steepnesses and relative water depths which find applications in the study of the behaviour of mooring systems. © 1991.

Ocean Engineering

Experimental investigation on a single point buoy mooring system

A finite element geometric nonlinear analysis program has been developed for the analysis of single point sub-surface deep sea moorings. The effect of diameter of the cable (D), drag coefficient (Cd), rope length (L), current velocity (V), current profile and buoyancy (T) on the mooring configuration have been studied. A design chart has been prepared based on the results of the parametric study on 12 sizes of commercially available torque-balanced jacketed wire ropes. The design of buoy system using the developed design chart is illustrated. © 1991.

Design of single point sub-surface deep sea moorings

The third general cargo berth at Paradeep Port situated on the east coast of India consists of a diaphragm wall anchored to a deaoman diaphragm wall by tie-rods. In addition, the diaphragm wall is connected to two rows of largediameter vertical piles by a rigid deck system. The deck system being rigid and tie-rods flexible, the lateral loads are shared between the piles and the deadman diaphragm wall. To assess the load sharing, forces in the tie-rods were measured before and after dredging. The results obtained were compared with those of a finite element analysis of the structural system using beam elements for the diaphragm walls, piles, and beams, and boundary elements for the soil medium. The measured tie-rod forces compared very well with the analytical result and confirmed that a substantial portion of the lateral load was transferred to the piles. Based on the studies, the design of another berth in the vicinity was modified to retain the vertical piles and eliminate the deadman diaphragm wall and tie-rods, resulting in substantial savings in cost and time. © ASCE.

Journal of Waterway, Port, Coastal and Ocean Engineering

Tie-rod force measurements in cargo berth

Parametric studies have been carried out on Tubular K joint using the finite element method to estimate the Stress Concentration Factor along the intersection of the branch and chord tubes. Three load cases, viz., axial symmetric, axial asymmetric and inplane bending are considered for the analysis. Multiple correlation and regression analyses have been used to develop formulae for the maximum SCF and for the variation of SCF along the intersection. Comparison of the results from author's formulae for maximum SCF and Kuang formulae has been made. Analysis of regression for the newly developed formulae is shown to demonstrate the confidence of the equations.

World University root node

International Journal of Structures

Stress Concentration in Tubular 'K' joints

Subsurface buoys are used along with deep lines for systematic long term measurements of meteorological and oceanographic parameters. The behavior of deep water mooring lines subjected to current force is a complex phenomenon. The determination of equilibrium configuration and the maximum tension developed are important in the design of subsurface buoy systems. The results of the geometrically non-linear analysis carried out for determining the above mentioned parameters using non-linear structural analysis program (NONSAP) are presented in this paper. The effects of important parameters like current velocity, net buoyancy, etc. on the behavior of mooring line are studied.

Journal of the Institution of Engineers (India), Part MR: Marine Engineering Division

Analysis of subsurface buoy systems

Many of the offshore structures used for oil exploration and exploitation are built of tubular members. The repeated damages in tubular joints have clearly shown that the safety of these structures depends on the safe fatigue design of the joints. The fatigue life of the joint depends very much on the Stress Concentration Factor, SCF. The current practice is to use semi-empirical formulas proposed by various investigators to determine SCF. While some of the formulas give the maximum SCF, others give the SCFs at both the crown and saddle points. The design of fatigue life using the value of maximum SCF is conservative, while using SCFs at crown and saddle is unsafe. The main aim of this paper is to propose a set of formulas for T and Y-joints, which gives not only the magnitude of maximum SCF as in the presently available formulas, but also the variation of SCF around intersection. © 1988 by ASME.

Journal of Energy Resources Technology, Transactions of the ASME

Formulas for variation of stress concentration around intersection in tubular joints

This paper presents studies carried out on grouted and ungrouted space tubular joints, with K in one plane and T in the orthogonal plane. Three models have been tested for different load cases adopting T, K, and both T and K (STK) configurations. The tubular joints used in offshore structures, especially in jacket platforms, are multiplanar and some are grouted and hence their study is essential. The stress concentration factor, SCF, as determined using the semi-empirical formulae which are applicable for planar joints are not appropriate for space, grouted joints. The results of the present study indicates that the SCF as determined by formulae for simple joints is unsafe in the plane of K and conservative in the plane of T for the space joint. The effect of the grout is to reduce the stress concentration. © 1987, Institution of Mechanical Engineers. All rights reserved.

The Journal of Strain Analysis for Engineering Design

Experimental studies to determine strain concentration factors for space tubular joints

The analysis of moorings for a subsurface buoy system is complex because of large changes in configuration, load dependence on the position, shape and orientation of the system, nonlinear load behavior of cable, mooring boundary, etc. A parametric study carried out on moorings, using an indigenously developed finite-element program MOOR, is reported. An incremental method and Newton-Raphson iterative schemes were used to develop the program. The effect of various parameters such as current velocity, water depth, net buoyance (pre-tension) of the buoy and specific weight of fluid on the horizontal deflection are studied. Dimensional analysis using Buckingham Pi method gives nondimensional variables. Using the nondimensional terms, design charts have been prepared. The above charts can be used for the analysis and design of moorings for a subsurface buoy system. The influence of different parameters on the design is discussed.

Oceans Conference Record (IEEE)

ANALYSIS OF MOORINGS FOR SUBSURFACE BUOY SYSTEM.

Stress concentration factors for tubular "K" joints were studied experimentally and the results compared with those of finite element analysis. The effect of a "T" in an orthogonal plane to the "K" was also considered. The experimental results were in good agreement with the finite element analysis.