R. Sundaravadivelu

DEGRADATION MODEL FOR ONE-WAY CYCLIC LATERAL LOAD ON PILES IN SOFT CLAY

Abstract 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.

THE HYDRODYNAMIC BEHAVIOUR OF LONG FLOATING STRUCTURES IN DIRECTIONAL SEAS

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.

Interaction curves for stiffened panel with circular opening under axial and lateral loads

Stiffened panels in ships and offshore oil platforms are provided with circular openings for repair, access and maintenance. This paper presents the numerical study carried out on the ultimate strength of stiffened panel with central circular opening subjected to axial load, lateral load and a combination of axial and lateral loads. Ultimate strength of the panel was evaluated considering both geometric and material non-linearities using FEA software ANSYS. Plates of varied widths and open section unequal angle stiffeners covering plate and column slenderness ratios in the practical range of 1.0–4.5 and 0.32–1.00, respectively, keeping the opening ratio equal to 1.0 are the parameters considered in this study. On the basis of the study, interaction curves were developed for normalised axial load and normalised lateral load. The developed interaction curves for stiffened panels with angle stiffeners and circular opening were found to be non-linear for lower plate slenderness ratio up to 2.0 and for the range of column slenderness ratio covered in the present study. Interaction equations were also proposed based on non-linear regression analysis for determining the ultimate strength of stiffened panel under axial, lateral and also under combined axial and lateral loads.

Stability of initially stressed square plates with square openings

Abstract 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.

Ultimate strength of stiffened panels with cutouts under uniaxial compression

Abstract 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.

A knowledge based expert system for design of berthing structures

Abstract Rapid growth in the water transport system demands the construction of more port and harbour structures. Berthing structures are constructed in ports and harbours to provide facilities such as berthing and mooring of vessels, loading and unloading of cargo and embarking and disembarking of passengers. Quays, wharfs, piers, jetties and dolphins are the most widely used berthing structures. The construction and maintenance of these structures are very expensive and, therefore, the most economical design should be adopted. These structures will be checked against limit state of crack, which is important in respect to preventing corrosion. A knowledge based expert system, KNOWBESTD, has been developed using LEVEL5 OBJECT for the design of berthing structures. This paper describes the development of KNOWBESTD and illustrates the design of a typical berthing structure.

Experimental study on collapse load of stiffened panels with cutouts

Abstract Experimental investigations are carried out up to collapse on eighteen stiffened steel plates having initial imperfections under uniaxial compression with simply supported boundary conditions on both loading and unloading edges. The thickness of the flange plates is varied as 4 mm and 5 mm respectively. Three types of commercially available open section rectangular flats are used as stiffeners. Six panels without cutout, six panels with square cutout which extends the full width in between stiffeners (d/b=1.0), four panels with rectangular cutout (d/b=1.5) and two panels with reinforced rectangular cutout are fabricated. The initial geometric imperfections such as plate imperfection Δx, overall imperfection of the whole panel Δsx and torsional imperfection in stiffener Δsy are measured for all panels fabricated. The axial deformation of the whole panel, out-of-plane deflections and strains along the midsection of the panels measured during the tests is discussed. The reduction in strength of the panels due to the presence of square cutout, rectangular cutout and increase in strength due to reinforcement around rectangular cutout are calculated based on the experimental observations.

Review of the research on emerged and submerged semicircular breakwaters

Scientists and researchers are currently focusing considerable attention on the hydrodynamic characteristics of semicircular breakwaters worldwide, particularly in Japan and the People’s Republic of China. A semicircular breakwater is a composite breakwater made of prestressed concrete and has several merits over a conventional rubble mound breakwater, e.g. it is technically advanced, economically viable and aesthetically pleasing. At low water levels, it serves as a rubble mound breakwater and, at high water levels, it acts as a composite breakwater in the emerged condition. It reduces the considerable magnitude of dynamic forces if constructed in front of a vertical wall (the main structure) under the submerged condition and also reduces coastal erosion along the shoreline. Many research studies are being carried out all over the world to evaluate the performance of a semicircular breakwater in the laboratory and in the field. The authors of this review paper have also conducted a large number of experiments to study the hydrodynamic characteristics of a semicircular breakwater and to optimize the parameters such as the rubble mound height, the water depth and the size of perforations. The experiments were conducted for both the emerged condition and the submerged condition subjected to regular and random waves with various wave heights and periods to find the suitability of a semicircular breakwater in the field, and the optimum parameters were recommended in their previous publications. Hence, a sincere attempt has been made in this review paper to present the ongoing research on semicircular breakwaters, which has been carried out all over the world to facilitate the studies of researchers and to provide related information to people working in the area of semicircular breakwaters.

Experimental investigation on a single point buoy mooring system

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.

Hydrodynamic characteristics of moored floating pipe breakwaters in random waves

The hydrodynamic performance characteristics of a floating pipe breakwater (FPBW) model (row of pipes separated by a distance equivalent to the pipe diameter) moored to the flume floor with slack moorings has been investigated in random waves through an experimental programme. The tests have been conducted on three models each with pipes of different diameter. The average reflection and transmission coefficients are evaluated from measurements and reported as a function of relative breakwater width. The motion responses, as well as the variations in the forces on the seaside and lee side mooring lines, are also presented. In addition, statistical analysis has been carried out to prove that the heave and surge motions, as well as the peak mooring forces, follow the Raleigh distribution. The details of the models, set-up, experimental procedure and analysis of results are presented and discussed.