Figure 1 Strip Foundation (Cuddle and Greene 2005, p. 3, figure 2. 2. 1) A strip foundation is a continuous, longitudinal strip of concrete, which is designed to spread the load of the building through the walls to the subsoil below. As shown in the figure above, the projection beyond the face of the wall should be at least the thickness of the foundation, to comply with the building regulations. The spread of the strip foundation Is dependent on the bearing pressure and shear strength of the subsoil, as well as the loads Imposed by the building.
The depth of the strip foundation Is dependent on the strength of the foundation materials (Emmett and Gorse 2010). Generally a strip foundation Is constructed using a relatively wide trench of mm to mm wide, with a layer of concrete poured into the trench in depth of mm. This provides a relatively level base from which to construct the walls off building. Figure 2 Trench Fill Foundation (Cuddle and Greene 2005, p. 107) A trench fill foundation is essentially a deep strip foundation; a narrow trench is dug, with the width only slightly wider than the walls.
The trench is filled with concrete to almost ground level. The advantage of a trench fill foundation Is that because the trench Is elatedly narrow It reduces the level of earthworks and excavation time compared to strip foundations. This construction method Is relatively safe, since the trench Is excavated using a narrow bucket mechanical excavator and there Is no need for workers to be in the trench. Unlike strip foundations, trench fill foundations do not fail through bending or punching shear (Fleming 2009).
Strip foundations have the advantage of being relatively shallow and are an effective method of transferring loads to the subsoil where the subsoil is sufficiently strong to transmit the loads. However, a strip foundation is relatively thin and the load of the wall acts as a point load, with the resultant ground pressure inducing tension on the underside of the strip. This means that the strip foundation should be constructed using tensile reinforcement in the lower face of the foundation, which It could be argued adds to the cost of the strip foundation (Cuddle and Greene 2005).
Both types of foundation provide a level base from which to start construction. The advantage of a strip foundation over for example a pad foundation Is that reduces the likelihood of talent and can span over small areas of soft ground or ground, which has variable bearing pressures. The fact that the trench fill foundation is constructed to which can be difficult with limited working room. It also removes the necessity for having temporary trench supports and therefore speeds up this element of the construction process.
Although this type of foundation uses a great volume of concrete, the costs of this additional material are offset by the reduction in working below submerged level. One potential disadvantage is that it does lead to the excavation of a higher volume of earthworks compared to a strip foundation and this means that the material must be used on site or potentially incur a disposal cost off- site (Emmett and Gorse 2010, Cuddle and Greene 2005). Question 2 Design and construction of buildings is governed by the building regulations.
The building regulations are in pace to ensure that all buildings are suitable for purpose ad provide a structurally safe and stable structure using the appropriate materials. There is a range of different building types; however all have common structural elements, including a foundation, external and internal walls, floors, and a roof. These elements work together to create a stable structure and the strength of this structure is a function of the elements used, the manner in which these elements are arranged and the materials used.
For health and safety reasons, all buildings must be stable and strong enough to withstand both the dead load of the building itself and any loads which are imposed on the structure. Imposed loads include wind loading, snow loading and the loads imposed by the occupants and users of a building. The design of strength and stability starts at foundation level, when the inundation is designed to create a strong and level base on which to construct the building.
A designer will ensure that a foundation is suitable for the particular site by assessing the bearing capacity of the in-situ soil, calculating the loads that will be imposed by the building (including dead loads of the weight of the building and the likely loads imposed on that structure). The designer will then chose a suitable foundation type, such as strip, pad, raft, or pile, depending on the capability of the soil.
The purpose of the foundation is to transmit these loads to the soil, if the inundation is not strong enough to carry out this function then it is likely that the foundations will settle, creating cracking and in the worse-case scenario structural failure off building (Emmett and Gorse 2010). The walls of the building provide shelter, noise, and thermal insulation, a framework for windows and doors as well as structural stability for the building.
The walls of a building provide lateral stability to the structure (Reid 1984). The type of walls depends on the building, for example, a two-storey house will generally have brick/block walls, where a multi-storey building ay have a structural steel skeleton frame with infill wall or cladding panels. A building may also have a structural frame, which is generally timber for low-rise construction and structural steel or reinforced concrete for multi-storey construction (Emmett and Gorse 2010).
In either case, the purpose of the walls is to act as a structural frame for the building. The stability of the walls is ensured by limiting the height of between floors and tying the floors into the wall at intervals to give the building envelope structural stability(Chew 2009). Although there are many different hypes of walls that can be used in building construction, fundamentally the materials chosen must be capable of supporting the floors and roof of that building.
The strength of a brick/block wall is achieved by using a specific bond and the fact that of a steel frame is achieved by either welding or bolting the Joints together so that the beams and columns, which make up the frame, transmit the loads of the building into the supporting foundations. In a reinforced concrete frame, the columns and beams are caste in-situ so that the Joints are rigid giving the frame strength and ensuring stability. It should be added that in each type of structural frame with individual structural members, for example the beams and columns are designed to carry the loads imposed by the building (Emmett and Gorse 2013).
The floors off building are supported by the walls, and are in place to divide the building space into compartments and are designed to carry the dead load of the floor materials plus the imposed load due to people, furniture, and any other imposed load. The floor Joists, panels, or slabs transmit these loads to the walls for transmission to the foundations of the building (Reid 1984). The roof of a building has a dual purpose, it peps the inside of the building dry and sheds water from the building, and it also acts as a tie at the top of the structure.
The roof consists of a series of trusses, which support the roof coverings such as roofing felt and tiles. A roof will be subjected to and therefore must resist a number of imposed loads, including snow, rain and wind. A roof is often designed as a pitched element of the building so that these elements are shed off the roof away from the building, to minimize the additional load on the building structure. As with most elements in building construction, a roof consists of number of structural elements called trusses, which form the basis for the roof construction.
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