What is the meaning of 'substructure' and 'superstructure' of a building. State the functions and elements of these two structures.
Answer:
The 'substructure' is that part of the building situated below the ground or damp - proof coarse. The purpose of the substructure is to transfer the load from the superstructure to the surrounding ground. An essential part of the substructure is the foundation. The 'superstructure' is normally taken to be that part of the building above the ground on the damp-proof course. Its purpose is to carry the loads imposed on the building though deal and imposed and winds loads and transfer them to the substructure.
The substructure which is usually applied to construction below the ground such as basement and the essential foundation. Thus the substructure though the foundation which is that part of a building which rests directly on or in the ground. It enables the loads of the building to be transferred to the ground below the foundation with exception of solid rock, foundations are built on soils which are capable of being compressed by the imposed load. Thus the functions of the sub-structure though the foundation are:
1. Safely transmit the dead and imposed loads from a building to the soil such that settlement is limited and the ground is not overstressed.
2. Safely distribute the weight of the building over large area so as to avoid over loading of the soil beneath.
3. Load the sub-stratum evenly and thus prevent uneven settlement.
4. Provide a level surface for building ??persctions
5. Take the structure deep into the ground and thus increase its stability and prevents overturning.
6. Avoid damage from smelling shrinkage or freezing of the subsoil.
7. Resist attack by sulphates or other harmful ??watten in the subsoil.
The stability of a foundation assuming of has been designed satisfactorily will depend upon, how the subsoil on which it rests, behaves under load. This information can be deduced from the report after a soil investigation has been carried out.
The application of a load through the foundation of a building can result in deformation of the ground and some building movement known as settlement. This settlement may not be serious if its uniformly distributed when settlement varies, this produces a condition known as differential settlement which can be lead to the building distorting and in more serious instances, collapse of the structure.
The superstructure of a building may be defined as all elements of the structure situated above and including the damp-proof course. The elements include:
1. Damp-proof courses and membrane.
2. Walls
3. Frame structures
4. Floors
5. Roofs
6. Stains
7. Windows / doors
The conventional superstructure is a framed construction using beams and column to support roof, floor and cladding. Competition between steel and concrete frames is fierce and the popularity of each depends on the ??resiation in piece. the client and architect usually want as much uninterrupted floor space as possible. This is because buildings are priced on floor area and must be flexible enough to accommodate ??vesying internal partition ??anangements as the use may change many times throughout then designed life. Framed structure are good at providing open space floors but they do have the disadvantages of internal columns which reduce internal space and dictate the layout of working areas. One step towards overcoming these disadvantages in medium rise structures is to use composite construction of steel and concrete to achieve long spans. Another popular solution is to use a central core, particularly in mufti-storey structures. The floors are cantilevered from the central core which is used to house lights, stains and service access. There are, of course limits to the spam of such cantilevered floors which limit the size of the building. Props at the end of the cantilevers provided by perimeter columns can greatly increase span but these can affect external appearance.
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