Response Analysis of Berthing Structures for Wave and Earthquake Induced Forces Including Soil - Structure Interaction

Abstract

Countries surrounded by ocean can easily achieve tremendous progress in trade and industry provided proper planning of ports and harbours is made for transportation of goods and materials through sea transport. 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. Berthing structures are classified as vertical face structures such as diaphragm walls and open piled structures such as jetties. These berthing structures are to be designed for berthing force, mooring force, wave force, current force, seismic force, active earth pressure and differential water pressure, in addition to self-weight of the structure and live load. The deck of berthing structure is generally supported by vertical piles Waves contribute to major loads on marine structures. Therefore it is important to quantify wave-induced load effects to ensure a reasonable, safe and robust design of berthing structures. <br> The piled structures are the most commonly adopted structures in shallow water and deep water. Safe operations on such structures have pressed the necessity to design them to resist the disturbing wave environment, since wave forces are random and vary with time. In the present work, an attempt is made to study the response of vertical member and a simplified piled berthing structure with and without soil structure interaction. Miniature model of such structures are tested for finding natural frequency and response to forced vibrations. All of the experimental observations are reproduced quite accurately by the simulation. It was found that inclusion of water and the soil tend to increase the natural frequency of the structure.<br> In this research conceptual layout of jetty for berthing 200000 DWT ship is carried out based on the available environmental data and the ship dimensions at New Mangalore Port Trust, Mangalore. Static and dynamic wave response analysis is carried out using StruCAD 3D software, considering various load combinations. Responses are estimated for various pile diameters and the results are compared. Responses are also found for 45º, 90º and 135º wave directions and it is seen that the structural response is maximum for wave direction perpendicular to the structural alignment. The detailed analysis of berthing structure, for the design significant wave height of 3. 2m and maximum wave height of 5.5 m is carried out for a full cycle of wave and responses are found out.<br> In order to carryout analysis of a structure under earthquake conditions a representation of the earthquake loading is essential. In such situation dynamic analysis of the structure will be required in which case accelerograms will be used given that they offer detailed representation of the ground motions during earthquakes. At the same time they provide the nature of the earthquake ground shaking. In this thesis three types of recorded accelerograms were used for the time history analysis of berthing structure with and without soil structure interaction. From the time history analysis optimum width was found for the deflection criteria. It was found that soil – structure interaction causes increase in displacements of the structure, which can cause large increase in natural period, leading to much larger relative displacements.