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3.0DESIGN CONSIDERATION OF SUBMERGED BUILT FORMS
3.0DESIGN CONSIDERATION OF SUBMERGED BUILT FORMS
3.1 Site Selection
A medium of water will be required as a site for submerged built forms. These submerged structures are usually located on special sea beds which display an abundance of aquatic life such as coral reefs and various sea creatures. The view of these underwater settings can be framed as a unique scene. Therefore, studies should be carried out through the region where project site is proposed. The water visibility, abundance aquatic creatures, local climate conditions, underwater terrain, soil conditions and even the local seismic condition have to be considered. Staying underwater is still considered to be a new experience. Currently the challenges of achieving underwater structures are more significant than the quality of site. From this perspective, initially underwater structures can be constructed as a part of existing buildings without respect to characteristic of sea bed, for example a hotel complex on island or near the sea.
3.2 Land-Water Relationship
At the beginning phases of design process, the intention of the client on the land-water relationship has to be clearly stated in order to conclude what type of project intended. The project can be whether the submerged built forms are totally independent from the land or to be linked with other terrestrial building. Not only will affect the physical appearance and also the entrance location, the decision on the type of project intended will also determine the choice of solutions on the required operational systems. There are mainly two alternatives:
• The underwater structure can be a part of complex which is located on land.
• The underwater structure itself can be independent from land.
In this case, there may be also two alternatives, which are either a full submerged structure that houses all functions or part of the structure are over water level that houses the other functions. The two parts of the structure (over water and submerged), are then can be link with staircase or elevators.
3.3 Accessibility to Submerged Built Forms
The entrance location of submerged built forms should be considered as early as the conceptual design phase. During early development of submerged structures, the only way to directly reach the entrance was by scuba diving or with the aid of submersibles. However, due to the fact that it is not preferable by visitors, various alternatives of access can be achieved by providing access on land or over water.
First, entrance space can be designed on land connecting the submerged structure. It will be a building constructed on land consists with the access to the underwater structure through horizontal, vertical or inclined tunnels according to the level and locations of the structures. Steps, escalators, ramps or travelators can be provided in tunnels. A second entrance lobby can be provided under water.
Figure 10: Entrance space was provided on land.
Secondly, entrance space can be designed over the water level right above the submerged structure. This entrance space can be either connected to land or off-shore. Visitors can reach by motorboats or via a land bridge. The access to the underwater structure can be through vertical tunnels. Elevators or staircase will be provided in tunnels.
Figure 11: Entrance space was provided over water.
These tunnels can also be used to transport air, power and water from land to the submerged structure. As suggested by Sezen the tunnels can be divided into two parts. Technical equipments and pipes can be located one section while people move in the other part.
3.4 Land Dependency of Submerged Built Forms
The living condition within the submerged built forms should be created to be similar to those on land. In order to achieved human comfort within these structures, a set of specially designed system need to be applied. The following systems should be considered and designed with engineers:
• Air supply system functions to achieve a breathable atmosphere should be achieved. Oxygen supplement and removal of carbon dioxide are essential.
• Water supply is needed for occupancy, climate control, and fire protection. For human consumption and sanitation a potable water supply is essential.
• System for waste management is another issue that should be provided for collection and removal of waste water and organic waste. The disposal of perishable and nonperishable hard waste from kitchens and rooms should also be taken into consideration.
• Electrical system is vital to survive underwater since all other systems depend on it such as lighting, heating, operation of electrical equipments and appliances. Therefore, uninterrupted electric power should be provided to underwater structures.
• Mechanical systems are required to provide comfort-zone conditions for occupants. These systems include the heating, cooling, ventilating, and air-conditioning equipments used to control the comfort factors such as air temperature, relative humidity of the air and air motion. These systems may show differences in underwater structures because of the special requirements of an enclosed atmosphere.
Submerged structure can be either land-depended or self-sufficient (autonomous). Decisions relating to this issue should be made in the beginning of design phase.
A land-dependant structure usually has its air supplied from the surface through a pressure resistant pipe. Power, water and air can be transported via tunnel to be distributed in the structure. In a partially submerged structure, the utilities for the structure can be shared by both the above water and underwater parts. According to Sezen, electric power can be transported by “submarine power cables” from land. However, to cater for emergency conditions, power generators should be available. Telephone, internet and TV connections can be made possible via fiber optic wires. In addition, wastes can also be transported to the land via tunnels or submerged pipes.
As an alternative, the structure can be fully self-dependant or autonomous by having its own power generators, water makers, satellite communication, sewage treatment plant and other equipment to create a complete, self-contained system anchored off-shore.
Safety is one of the important elements in a submerged structure as the external environment itself can be a hazard and means of escape during emergencies are limited, hence the safety features of a submerged structure must be carefully designed and planned. For example, emergency exits and entrance for divers to access from outside should be designed. Safety places, such as shelter in terrestrial buildings, can be proposed in underwater structures. Small submarines may be placed in critical areas to transfer the people inside the structure to land. Pressure and water resistant doors have to be provided to prevent water from entering in the event of a leak.
3.6 Form and Geometry
Onouye noted that: “to structure also means to build –to make use of materials in a way as to assemble an interconnected whole that creates space suitable to a particular function or functions and besides, to protect the internal space from undesirable external elements.” (Onouye, 2002).
Structures on land have to deal with various kind of dead and live loads such as wind force, effects of gravity and earthquake. On the other hand, the primary force acted on an underwater structure is hydrostatic pressure depending on the depth of the water.
In art and design, form denotes the formal structure of a work, the manner of arranging and coordinating the elements and parts of a composition so as to produce a coherent image (Ching, 1996).
3.6.1 Fluid Mechanics
Fluid mechanics is the sub discipline of continuum mechanics that is the study of the physics of continuous materials. It is defined as the study of the physics of continuous materials which deform when subjected to a force. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion. Fluid statics is also called hydrostatics. It deals with the conditions under which fluids are at rest in stable equilibrium. Fluid pressure is the pressure at some point within a fluid. Fluid pressure can occur in 2 conditions:
220.127.116.11 Open Condition
Pressure in open conditions usually can be approximated as the pressure in static or non-moving conditions even in the ocean, because the waves and currents motions created have negligible changes in the pressure (Munson, Young, & Okiishi, 2002). Examples of open condition pressure are the ocean, a swimming pool, or the atmosphere.
18.104.22.168 Closed Condition
The pressure is due to the weight of fluid which increases linearly with depth pressing down only in the vertical direction. Due to an ability to resist deformation, fluids exert pressure normal to any contacting surface. Examples of closed condition pressure are a water line or gas line.
The pressure under water increases with depth, a fact well known to scuba divers. At a depth of 10 m under water, pressure is twice the atmospheric pressure at sea level, and increases by about 100 kPa for each increase of 10 m depth. One pascal (symbol: Pa) is equivalent to one newton per square meter (1 pascal (Pa) = 1 N.m−2).
3.6.2 Curvilinear Forms
The main concern for submerged built forms is to withstand hydrostatic pressure. Curvilinear forms such as sphere, cylinder and cone have been tested to be the most appropriate basic forms that are able to handle underwater pressure. Underwater creatures resist pressure by means of their form and geometry. The forms of manmade structures mimic the forms of the natural structures of underwater creatures. For example a sea urchin has a protective shell which allows it to survive in great depths. On the other hand, non-curvilinear forms do not only withstand less hydrostatic pressure, but also having view restriction to the exterior.
Figure 12: A sea urchin. (source: http://www.sritweets.com/sea-urchin-factssea-urchins-feed-algae/)
For underwater structure design, basic shell or surface structures are used. With the manipulation or combination of basic forms of sphere, cylinder, cone and dome, one can create new spaces according to the spatial and functional requirements. The structural capacity and behavior of these new geometrical configurations should be analyzed with considering other properties in further studies.
3.6.3 Shell Structures
Shell structures are structures consisting of thin, wide surfaces which are able to transfer load through membrane stresses. Compression surfaces and tension surfaces are two types of surface structures. Compression surfaces tend to be more rigid than tension surfaces because it has a higher tendency of buckling. The shell structure is a compression resistive surface structure with curved forms and shells are suitable for both simple and complex geometries. (Ambrose, 1967)
Shells are structurally continuous in the sense that forces can be transmitted in a number of different directions in the surface. The strength and stiffness of a shell structure are related with curvature surfaces originated from their resistance to deformations which tend to flatten them (Salvadori, 1963).
Thin shell structures are applicable to various fields and disciplines such as dome and curved roofs. Examples like pressure vessels and pipe, water cooling towers for power stations, arch dams, submarines, tunnels, grain silos, armour, and so forth applied shell structures.
Thin shells under compressive membrane forces are prone to buckling. The rapid and drastic change in geometry after buckling and consequent decrease of load capacity will eventually result in the failure and collapse of a structure. In practice construction of dams, underwater storages and submarine can be listed as examples for this structure. (Go, 2004)
Thin shell structure can transmits and resists all loads applied to it. The most efficient structure to achieve this is a thin shell structure supported by longitudinal stiffeners and transverse frames, known as asemi-monocoquestructure. Figure 2.4 illustrates a typical semi-monocoque structural component of an air craft structure.
Figure 13: Typical semi-monocoque thin shell structure. (source: http://www.aeromech.usyd.edu.au/structures/as/acs1-p7.htm)