Use of Slip Form in Construction of Tall Buildings - Coursework Example

Use of Slip form in Construction of Tall Buildings Student’s Name Institutional Affiliation Introduction Slip form technique has found its application from the use of structural systems. This has subsequently offered significance engineered solutions with prosperity of engineering and contracting practice attained through the successful completion of numerous structures. Slip forming is a cost-effective, fast and precise technique of constructing reinforced concrete, or post-tensioned concrete structures. As an elementally, slip forming is a style of transferable formwork which is gently raised to allow for the continuous extrusion of concrete. The structures that uses slip forming system ranges in height from eight meters to more than 200 meters and from a simple design shape to the most complex. It has also found application in tapering structures such as chimneys, bridge pillars and telecommunication towers (Parker & Wood 2013). Slip forming process has pronounced flexibility in its application as it is used to form straight walls and curve walls with constricted radius hence they can lodge tapering structures and changeable wall thickness. It has also a safe method of constructing a tall structure. It uses scaffolds and handrails and guards that provide a safe environment for work. In advanced systems, jack climbing with an adequate diameter offers a greater stability since they increase the platform area. The system offers protection whereby the upper platform acts as a storage and distribution areaas well as acting as templates for guide in the vertical reinforcement bars. This provides protection against adverse weather and adds to the rigidity in the whole assembly. This consequently influences accuracy which can actually be achieved (Chew 2009). In general, items such as doors frames, reinforcement, and mechanical equipment to be cast on the walls are stored in this surface hence reducing congestion on the middle platform where operations are done in a safe and housed conditions. The middle platform allows for the pouring of the concrete and fixing of the reinforcement. At the lower platform which is supported by rigid suspended scaffolds, it provides an access to the finishing on the newly formed concrete as it emerges from the upper platform. The climbing capacity offered by this system help reduce the use of crane and thus increasing the rate of concrete pour. The use of the slip form system is exceptionally diverse. Users in city centres frequently slip form for only eight hours a day. However, contractors in industrial areas look for the advantages of slip forming on a 24-hour basis therefore, using slip form help to reduce programme time on site (Taranath, 2011). Methods of Slip form Construction One of the methods recommended is to construct the core totally free from the floor construction. This allows the core to be exposed before the fixing of structural steel starts. Another method is to create the core on a floor on daily basis for five to ten days, then recess and construct the floor up to the same level as the core. This process is continuous and progresses throughout the project. The other method involves carrying on simultaneous operations of building of floor and slip forming. This is done on daily basis one floor at a time. This method should only be used if the core is not completely established by itself and it needs an additional horizontal support of the floor system. Most of the project uses the first slip forming method. This is usually because; the core is initially designed to have ability of outspreading from foundation to the top without leaning to the adjacent members of the floor. The core is built and designed to be stable and strong and act as an independent component which is able to resist wind and all the loads of the construction imposed during the construction operations. The horizontal plates can also be fixed occasionally to add extra strength during the construction. Some of this erected horizontal fixtures become of no use due to vertical shafts and the elevator openings (Binder 2006). Slip forming Process The slip form system operated by is of a hydraulic formwork system. Hydraulic jacks are purposefully fixed on located steel yoking frames to raise the formwork as the concrete is poured into the forms. The formwork system uses high steel plates that are held firmly by a framework built up from steel plates, trusses and bracing. The framework provides firmness to the slip form as well as providing support for timber floor hence forming working platform for placing of concrete, reinforcing of steel and slabs for doors and windows. The concrete is poured into the forms in layers. The rate at which the concrete is settled is regularly monitored to ensure that it is harmonized with the speed at which the forms are raised. Slip forming is executed on either a nonstop basis such as 24 hours per day or an uneven basis where pouring within one working day is done to a scheduled height. When the formwork is raised, reinforcement is held in the exact position by use of guides fixed at the top yokes. The reinforcement on the horizontal is strung under the yokes and is tied to the vertical reinforcement. The slabs for doors and windows are formed by use of timber or steel. These are fixed as the slip form continues and can be exposed from the irregular surfaces or use of allowances that are used in the provisions of connection between slabs, beams and the slip form walls. The formed concrete is visible from the bottom of the steel form plates and it is then treated as required (Robertson et al 1980). This section shows a typical slip form rig in position during a pour with the upper, middle and lower working levels The lower platform, supported on rigid suspended scaffold frames, provides access for the finishing trades to the newly formed concrete as it emerges from the upper platform. Typical section showing through slip form system for vertical structures Tapered Slip Forming The structural Systems are greatly involved in the construction of conical chimneys, Piers, cooling towers and other tall concrete structures that involve constant or varying wall thicknesses, widths and shapes. The process of using the slip forming is similar to the structural systems. Therefore, it requires adequate planning and logistics especially to heights that regularly make the use of cranes unfeasible (Binder & Foster 2006). Typical section showing slip form system for tapered structures 1-Upper spreading and working area 12-6 ton hydraulic climbing jack 2-Working area 13- Hydraulic jack pump 3-Droopy scaffold 14- Hydraulic turnbuckle pump 4-Radius screw 15-6 ton climbing rod extractor 5-Screw for adjusting wall thickness 16-3 ton climbing rod extractor 6-Screw for adjusting inclination 17- High pressure hose 3/8 7- Horizontal turnbuckles18-. High pressure hose 8-Spider beam 19- Distribution pipe 9- Lifting yoke 10- 3 ton hydraulic climbing jack 11-Jack rod Visual slip form of tapered structure Economics of slip form construction The organization of slip formed core in a building of the concrete walls is fundamental to linking with permanent walls which are required to function. This organization allows the walls to perform a double duty. The walls which are the structural physical wind barrier also provide an essential in carrying load carrying ability. At the same time it provides a fire separation nearby the stair and the elevator channels which is a requirement by the building code. These slip form concrete walls are positioned where permanent walls occur, such as walls around toilets, telephone cabinets, electrical rooms and vertical passages for electrical and mechanical systems. This adds value to these walls and is essential while cost guesstimating various structural framing alternatives. This is because the architectural separation walls do not form permanent fireproofing walls as compared to the framing systems (Michael 2012). Typically, slip forms are only four feet in height and are mostly used up to heights of 400 feet. This gives a form reuse aspect of 100 where no rearranging is required. In addition, the working areas and finishing scaffolds are among the form assembly hence excluding the requirement of scaffolding. This leads to low cost of forms per square foot of the surface area. This reduced construction time produces an extra savings of in-place construction cost. The simplicity of building and construction of structural steel floors and pillars is linked with the stabilizing slip form concrete core. This excludes instant links between beams and pillars which then reduces the cost of steel assembly that is below the standard estimated cost. Other economy allied to the slip form core building system includes the speedy fitting of stairs and elevators which are initially used for construction purposes. This helps the mechanical contractor to manage and save time while fixing vertical fixtures from the finishing scaffold. It also saves time for the slip form worker to fix all the steel inside the core together with the elevator separator beams through the slipping operations (Binder & Foster 2006). The slip form construction system has become feasible on even shaped structures in particular the four stories or bigger heights. Although it has found multiple applications on shorter structures, this method has been economically achieved in the past as compared to the cost of the conventional formwork. References Binder, G., 2006. 101 of the world's tallest buildings. Victoria: Images Pub. : Council on Tall Buildings and Urban Habitat Binder,G. & Foster, N.,2006. Tall building criteria and loading. Mulgrave (Vic.): Images Chew, M.Y., 2009. Construction technology for tall buildings. New Jersey: World Scientific Michael ,J.,2012. QR code for Planning for Tall Buildings. London. Routledge Parker,D & Wood, A., 2013. The Tall Buildings Reference Book. London: Routledge Robertson, E., Nakla,T., Gaylord,E., Mainstone,R., Council on Tall Buildings and Urban Habitat., 1980.Tall Buildings of Europe, the Middle East and Africa. New York: American Society of Civil Engineers Taranath, B., 2011. Structural Analysis and Design of Tall Buildings: Steel and Composite Construction. New York .CRC Press Read More