Portal Frame Construction: Technique Of Designing And Constructing (Other (Not Listed) Sample)
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PORTAL FRAME CONSTRUCTION
PORTAL FRAME CONSTRUCTION
Portal frame construction refers to the technique of designing and constructing structures, whereby two-dimensional rigid frames with basic characteristics of the rigid joint are between the beam and the column are utilized (Hiriyur,2010). The main aim of using this method of designing and construction is to reduce the bending moments in the beam in order to allow the frame to act as one structural unit. With that, the size of the structural element can be reduced or at the same time, and the span can be increased for the same size of the structural elements. Due to that, the portal frames are considered being very efficient and reliable construction method to be used for the buildings with long span.
Portal frames are generally, used in the low-rise structures, which are comprised of beams, columns or pitched rafters connected by the moment resisting connections. A suitable haunch offers the resistance to vertical and lateral actions, or the deepening of the rafter sections .This type of continuous frame structure is usually stable in its plane, and it offers clear span, which is not obstructed by the bracing. In most cases, the portal frame construction is used in the construction of single-level structures, and it is usually seen in the construction of factories, warehouses, barns and other areas where large open spaces are needed at low cost and a pitched roof is also accepted.
A portal frame structure usually comprises a series of transverse frames which are braced longitudinally. The primary steelwork is made up of rafters and columns, which makes the form portal frames and bracing. The gable frame can be either a portal frame or a braced arrangement of columns and rafters.
The light gauge secondary steelwork is made up of the side rails which are used for the walls and the purlins that are used for the roof. The secondary steelwork offers support to the building envelope, but it also plays a very significant role in restraining the primary steelwork. The wall cladding and the roof separates the building envelope from the external environment as well as offering acoustic and thermal insulation. The function of cladding is to transfer the loads to the secondary steelwork and at the same time to restrain the flange of rails or purlins to which it is attached (Paolacci and Giannini 2012). The figure below shows the anatomy of a typical portal frame.
Fig 1: A cross-section showing portal frame and its restraints
Fig 2: Principal Components of a portal framed structure.
The key focus of this paper provides a discussion of the technical aspects of the portal frame construction. The area which is analyzed in this paper include; structural system, footing system, wall system, floor system, roof system, and services. The information which is contained in this paper is based on the deep investigation of Industrial unit 6D,1-3 Endeavour road. The photographs are included in the discussion part to over clarification. The areas which were mentioned in the assignment brief have been covered for simplicity.
The industrial unit is located within the center of the Sutherland Shire's Industrial Precinct. It has a total area of approximately 850 m2. The ground floor is typically a warehouse of approximately 600m2 while the upper floor of 150m2 is for office. The warehouse has a parking capacity of 10 vehicles. The main structure is a fixed structure of steel portal frame with a clear span of 18m and a ceiling height of 7.0 m. The figures below are illustrations of the Industrial unit 6D,1-3 Endeavour road.
Fig 3: Industrial unit 6D,1-3 Endeavour road.
Fig 4: 6D,1-3 Endeavour road interior
3.0 Footing system
Footing refers to the components of the building which transfers the load from the build to the foundation. The primary purpose of designing the footing is to ensure that the loads from the structure are safely transmitted to the subsoil, economically and at the same time ensuring that there is no unaccepted movement during the construction process and throughout the anticipated lifespan of the structure.
The factors which are usually put into consideration during the design of the footing system are; type of the structure, the soil conditions, economic factors, structural loadings, construction problems and the proposed construction period. Of all these factors structural loading and the soil condition are the most essential during the design process of the footings. The footing system which is properly designed can significantly help to eliminate or minimize the differential settlement which occurs when the weight of the structure stresses the soil. In the cases where no settlement occurs, it must occur equally under the building.
According to the geotechnical report of the industrial unit above the site, foundation materials are made up of sandy over the shale, having a high bearing capacity at a depth of about three meters. According to this data, it is reasonable to assume that there is some soil movement on the upper stratum of the foundation. Hence it is much safer to rest the footing at the shale level which offers sound bearing pressure with very minimal movement. The engineer used two types of footing during design. A 150mm thick structural raft shaft having stiffened edge and integral beams over the piers were driven to the shale foundation. The main function of the raft is to distribute the load both the live and dead load evenly over a large base in order to reduce the load which is acting per unit area. The piers were used to bypass the reactive soil and at the same time transfer the superstructure load at the edge beam to the lower level of subsoil where suitable ABP exist. The figure below shows the arrangement of this structural members.
Another appropriate kind of footing possibly is pad footing. This is the most common footing style for the portal frame. A concrete pad footing is the easiest and cheapest type of footing used in vertical support and transmitting of structure loads to the subsoil. A pad footing of adequate size to stop uplift will be sufficient as long as it does not surpass an Acceptable Bearing Pressure of 100kPa. Occasionally deep pad footing has to be used to reach the soil lay providing sufficient APB, or a pedestal may be required to support the column base plate. The figure below shows how the pad footing is connected to the frame.
Fig 5: pad footing connection
The images below which were obtained from the site shows a holding down bolt, a pad footing having HD bolt that are cast in situ and a universal...
- Portal Frame Construction: Technique Of Designing And ConstructingDescription: Portal frame construction refers to the technique of designing and constructing structures, whereby two-dimensional rigid frames with basic characteristics of the rigid joint are between the beam and the column are utilized....17 pages/≈4675 words| No Sources | Other | Engineering | Other (Not Listed) |