The metropolitan cities are developing at a very high rate and the expecting rise in population is putting pressure on these cities to grow further by expanding their boundaries continuously. But in the case of cities like Mumbai, Chennai and international coastal cities, the sea is behaves like a boundary for urban settlement, resisting its further expansion. This situation has produced challenges for urban planners to deal with lack of space and demand for basic amenities. In such condition coastal metropolitans, oceans can be used to develop the floating form of satellite towns, urban pockets & structures as a coastal expansion of city boundaries due to the enormous flexibility and limitless possibilities which water offers.
The earth contains all kind of resources to sustain life and need of all human beings, plants & animals. But it is greed of humans which is exploiting these resources to fulfill their endless greed. According to the medium variant of the 2010 Revision of World Population Prospects, the world population is expected to increase from 6.9 billion in mid-2011 to 9.3 billion in 2050 and to reach 10.1 billion by 2100. . The majority of the population growth in upcoming years will occur in urban areas of developing countries. The basic and the most important resource for the survival of human being is the land. For a long term perspective for our future land will become a major issue. According to US Geological survey, presently we have land area of about 148,300,000 sq. km, as about 29% of total surface area of earth, from which almost 50% is unsuitable for habitation & agricultural purpose due to poles, deserts & hard rocks & mountains. the remaining 71% surface area of planet earth is occupied by water , & from this total quantity, 96.54% founds in oceans, seas and bays , which is about 68.54 of total surface area.
According to forecasts of the IPCC (2013), the ocean level will rise from 20 to 90 cm during the 21st century (versus 10cm in the 20th century) . According to the research, published in the Proceedings of the National Academy of Sciences, a global mean temperature elevation of 1°c will lead to rise of 2 meter in mean sea level . Increase of 1 m would bring out the world to loose of approximately 0.31% of ground & 1, 30% of GDP. Further effect of this rise of 1M in MSL is given in Table 1 and Fig. 1 shows the most impacted countries according to land area. .
Historical Development of off-Land Structures
The development of off land structures is not a new concept for the world. Early applications of floating structures take the form of floating boat bridges over rivers that date back to antiquity. In around 480 BC, King Xerxes of Persia led his army across the Hellespont, now called the Dardanelles, using two rows of floating bridges, each consisting of about 300 boats laid side by side as shown in Figure 2. 
Such kind of floating bridges were mainly built as a necessity of war, permitting the movement permitting the movement of soldiers and equipment between ground bases and marine vessels during that period. Later on many bridges were constructed on this concept of tying the boats & ships. Other than the bridges there are many examples of very old floating villages throughout history. They have appeared in different parts of the world due to various needs & reasons. Figure 3 shows in the sixteenth or seventeenth century, Ganvie’s floating city (Sometimes called the Venice of Africa) was established by the Tofinu people, as a protective measure from Dahomeys which was a slave trading tribe that dominated the region during the time.  Other than this example, Vietnam, Indonesia, Thailand, China, Peru and Bolivia also have a history of floating villages. There are many countries which have floating habitation not for permanent living but for the tourism purpose e.g. boat houses in Kerala and Kashmir in India.
In our contemporary history use of floating structures other than bridges, primarily starts after industrial revolution. Original concept of floating habitation begins by the primitive man who built small boats as a means of navigation. Later on, as man started progressing he built bigger boats, which were used to cross the sea. It took him several days, months. He had to stay on these boats and this gave rise to the concept of boat houses . With the development in construction and technology men designed huge ships (cruises) as warships and as a mode of transport that can accommodate more than thousands of people.
Scope of off-Land Structure
The scope of neighborhood sized, self-sustained independent ‘off land’ floating structures can be decided on basis of the criteria of land use systems of different categories like agriculture and industries should be promoted to be used on ground. The purpose to build the ‘off land’ structure is to provide an isolated, peaceful and efficient environment for working and living. For this kind of structure, preferably residential, office, institutional, academic, commercial or recreational buildings are needed to be developed as single or mixed use form. For example, IT parks with all basic amenities and residential features for its employees can be developed in the form of floating structures. Residential townships can be developed to cater the requirements of farm houses, beach houses, & bungalows. This kind of specific block will be self-sustained in itself. These off land structures ought to be designed as net zero energy buildings as well as with net zero carbon foot print and self-sustained in terms of energy by using renewable energy resources to make it environmentally favorable.
Numerous proposals have been made for very large floating structures like floating airport, military bases, wave power generators and deep ocean mining platforms. Till now, most of the off land buildings and structures have been developed for oil exploration and tourism only but due to future scenario these all are going to become a need with mix of technological advancement. Advancement in term of technologies can be of construction, development of new materials, energy generation system, security and control system. Economically-the development cost will be very high so it will target a specific category higher income group.
Academic buildings like colleges, universities with hostels, specific research labs can also be developed in form of off land structure. This category required bigger area in peaceful environment so these kinds of structures can be accommodated in such urban pockets. Jails and prisons can be design in such structures in isolated forms from main town. In such case it will be very easy to handle safety and security based issues. Ashrams, Yoga centers, Meditation centers and Spiritual centers also needed isolated and peaceful environment, so these structures can be designed here in form of floating structures.
Entertainment facilities & utility plants are also one of the important categories of buildings which can be designed in floating form. Emergency rescue bases in floating form can be developed in earthquake prone areas like Japan, (sea sided earthquake prone countries) and in flood prone areas.
The off land structures or mega-floats have advantages over the traditional land reclamation solution for space creation in many ways like they will be cost effective in case of large water depth. It should be noted that the cost of imported sand for land reclamation in some countries has risen significantly and it may come a time that sand may not be even available from neighboring countries), environmental friendly as they will not damage the marine eco-system, or silt-up deep harbors or disrupt the tidal/ocean currents, they will be easy and fast to construct (components may be made at different shipyards and then brought to the site for assembling) and therefore sea-space can be speedily exploited, they will be easy to removed (if the sea space is needed in future) or expanded(since they are of a modular form).
Case Study 1: Green Star, Maldives
There are various off land structures have been constructed and few are under construction in the form of floating structure. Water studio from Netherlands has designed a Floating Hotel and Conference Center named as Greenstar (Fig. 4a and fig 4(b), in Maldives (a nation widely considered to be on the front lines of global warming because of its sea level). The Greenstar, contains 800 rooms and a Conference Center for up to 2000 participants. The Greenstar will blend-in naturally with the existing surrounding islands. The green covered star-shape building symbolizes Maldivians innovative route to conquer climate change. This will become the next location for conferences about climate change, water management and sustainability. A unique Floating Restaurant Island will be built next to it .
Case Study 2: Floating Golf Course, Maldives
Another important floating structure which is going to be developed in Maldives is the world’s first floating golf course. Threatened with rising sea levels from climate change, the island nation may be doomed to a watery grave unless it transitions to floating developments. Developed by Dutch Docklands and designed through a collaboration between golf course developer Troon Golf and Waterstudio. NL, the zero-footprint solar-powered golf course will be one of the first floating developments and is expected to bring in a wave of new tourists. It is also designed to minimize its impact on the surrounding ecosystem. The artificial floating islands will incorporate technologies such as water cooling, water desalination, and the use of floating solar blanket fields. Underwater tunnels will connect the holes and facilities together, while allowing golfers to experience the reef .
Case Study 3: Lily Pad – The Floating Ecopolis
In 2008 a conceptual model of The Floating Ecopolis (Fig. 5a and Fig. 5b), otherwise known as the Lilypad, was designed by Belgian architect Vincent Callebaut for climatic refugees. “It is” he says, “a true amphibian, half aquatic and half terrestrial city, able to accommodate 50,000 inhabitants and inviting biodiversity”. Callebaut imagines his structure at 250 times the scale of a lilypad, with a skin made of polyester fibres coated in titanium dioxide which would react with ultraviolet light and absorb atmospheric pollution.
The Lilypad comprises of three marinas and three mountain regions with streets and structures strewn with foliage. “The goal is to create a harmonious coexistence of humans and nature,” said Callebaut. With a central fresh water lagoon acting as ballast, the whole construction would be carbon neutral utilizing solar, thermal, wind, hydraulic, tidal and osmotic energies. With high density populations living in low-lying areas – The Netherlands, Polynesia, Bangladesh – the ecopolis, its creator believes, could be the answer to mass human displacement that global warming is predicted to cause .
Design Methods for off Land Structures
Now next condition is related to transportation and connectivity. In case of transportation, huge energy is consumed. So, design of such mega floating structure should be in such a manner to minimize the horizontal travelling distance. A clustered form of planning in the form of vertical towers can be good for decreasing the transportation distances. This condition will be defined by concentrated load bearing condition of these structures. There should be proper means to have access to boat, ship, submarine & helicopter.
At site level condition, a breakwater (usually needed if the significant wave height is greater than 4 m as a thumb rule) is needed for reducing wave forces impacting the floating structure (Fig. 6). This breakwater will be formed by a ring of columns around the structure with the option to bear the turbines to generate the electricity due to movement of waves.
The mooring system must be well designed so that it can ensure the stability of very large floating structure to keep it in position so that the facilities installed on the floating structure can be reliably operated and to prevent the structure from drifting away under critical sea conditions and storms.
A freely drifting very large floating structure may lead to damage not only the surrounding facilities but also the loss of human life if it collides with ships. Note that there are a number of mooring systems such as the dolphin-guide frame system, mooring by cable and chain, tension leg method and pier/quay wall method (Fig. 7). Another feature could be the design of the edges of the structure. By proper choice of edge layout, the propagation of the incident waves into the main part of the structure can be reduced by efficient scattering or reflection of the incident waves on the weather side.
The materials to be used for the floating body may be steel, or concrete or steel-concrete composite and the relevant specifications have to be followed for the main structure. This concrete will be in category of special water tight, light weight concrete to increase water tightness of structure and to decrease overall density by reducing its dead load. In case of the buildings of the structures we will use recyclable material having lesser energy consumption according to their life cycle assessment, to make such structure environment friendly.
Almost 40% of the total produced energy is used by the buildings. Heating, cooling and lighting are big contributors in this. So optimized positioning of window and light shelves can save this energy. Again windows can become the cause for great heat loss and heat gain so it must be optimized as per requirement of different climatic conditions to reduce heat gain and heat loss through windows and ventilators but without compromising with the view and natural light. Light shelves and fibre optic cables can be used to provide more light inside the interiors. Climatic conditions should be one of the major factor to decide the material and design related parameters.
Considerations for off Land Structures
Adequate performance of offshore structures has to be ensured by designing them to comply with serviceability and safety requirements for a service life of 100 years or more. Serviceability criteria are introduced to ensure that the structure should fulfill the function required to perform as, and are specified by the standards, owner and user. Major serviceability requirements are related to performance during movement of waves.
An important design issue regarding safety of personnel is evacuation and rescue. An effective safety measure related to this can be to provide a safe place where people can survive or board after an accident. In principle the global failure modes of floating structures include capsizing, sinking, structural failure and drift-off.
For such condition we have to design the installed blocks on main floating surface as they should also be floating type independently in itself. This will be a safety measure if there is any disaster due to any reason if main structure tends to submerge in water then these structures will start flowing independently. Planning wise it can be designed in form of radial planning form with a control center & main building as a nucleus. Other buildings can be planned in a concentric ring from to be placed as per decreasing priority form center to periphery.
Technically there will be some other considerable load based factor in design of floating structures such as abnormal loads like impact loads due to collision of ships with the floating structure, effects of earthquakes including dynamic water pressure, effects of temperature change, effects of water current, effects of tidal change, effects of seabed movement, snow load, effects of tsunamis, effects of storm surges, ship waves, seaquake, brake load, erection load, effects of drift ice and ice pressure, effects of drifting bodies, effects of marine growths etc.
There is a strong need to form a special authority for such type of structures to define rules and regulations related to design, construction, security, control and environmental aspects etc. As these urban pockets will be very high in cost so they will have higher surface coverage and Floor Area Ration (FAR) as per load bearing capacity & available resources around the pockets.
There is a need to find out proper solutions for upcoming problems due to population explosion, increase in sea level and limited amount of available land. For agricultural and industrial purpose we have very limited usable land area (approximate 12% of earth) so development of off land structure is the option where we can look forward for solution of our problems related to housing, employment and infrastructure and investment. This development of ‘off land’ structure in sea will definitely reduce the load on the shoulders of our mother earth.
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