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Since the building is going to be a 10 storey building, a suitable structural frame that is economical and functionally efficient needs to be identified. The most widely used material for structural frames include, steel, in-situ concrete, precast concrete or timber. However with this height, timber could not be used as it would not be economically, and functionally viable. So the other available options are Steel, In-situ Reinforced Concrete and Precast Concrete.
This is the most common type of frame that is been used in the construction industry. The skeleton frames are principally series of rectangular frames placed at right angles to one another; this is done so that the loads are transmitted from member to member which sends the loads to the foundation then to the subsoil. These frames could be constructed using different types of materials, the materials used for the construction of a skeleton frame is dependant on so many factors, availability of labour and material, economics, site conditions, health and safety, capital cost, time factor, maintenance cost, fire resistance, environmental preference and personal preference.
In a cantilever frame the beam span continuously over the columns so that they cantilever out beyond columns and extend the floors of the building outside the grid lines of the columns. The beams in a cantilever frame is continuous over the columns, the cantilever effect on one side of the column will balance the load that is exerted in the centre of the span between the columns. The beam will extend over its points of support at the columns. This means that the overall bending moment, the stress that the beam must accommodate will be reduced. The optimum distance that beams should be cantilevered beyond columns is 1/4 to 1/5 of the main span of the beam between columns.
A propped cantilever frame system is one which the cantilevered part of the building is supported with light weight props. Unlike the cantilever frame which is cantilevered at 1/4 or 1/5 of the main span of the beam between columns the propped cantilever frame is extended to a greater distance, which brings about the support to the cantilever. This happens where a continuous space is required in the usable area of the building.
The props transfers a percentage of the gravity loads to the foundation and would provide wind load to be transferred to the main structure. The size of the cantilevers in frames such as this may require an uneconomic use of material because the bending stress may far exceed those that might be found in a straightforward cantilever frame. The propped cantilever frame more economical where the space is of great importance.
A parallel beam frame is where the beam is changed from a simple span to a continuous span. There is no cantilevering of beams, but the primary and secondary beams are arranged so that they span continuously over the points of support. The primary beams are fixed to seating cleats on either side of the columns; the seating cleats allow the beams to span continuously over the column while being supported by it. The secondary beams sit directly on the top flanges of the primary beams and also span continuously straight over the top of the primary beams. The parallel beam frame is suitable for industrial and commercial framed buildings, especially where highly serviced open plan areas are required. An advantage of this system is that it provides an easy way of integrating services within the floor void in the frame. A disadvantage is that due to the continuous span of the structure it is important to weld both the primary and secondary beams where the total length exceed the length of the steel; this increases the construction cost because the welding will be done on site.
The frame members of an in situ reinforced concrete frame are constructed on-site and using steel reinforcement bars and wet concrete. Formwork is a major aspect of an insitu reinforced concrete frame because it aligns and holds the concrete firmly to shape to cure/dry. In the in situ reinforced concrete frame the floor system acts as an integral part of the structural frame system.
If the building is to be increased to a height of 30 storeys, the building would be considered to be a tall structure or a skyscraper. The increase in height would have a great effect on the total load of the building; the gravity load increase as the building becomes taller also the wind load imposed to the building would also increase. The shape of the building would not be affected but the internal floor plan would be affected, braced truss steel is extended vertically from the foundation this helps to resist lateral loads. This would reduce the number of rentable space in the office.