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New Slip Form method for lighthouse construction
Lighthouses are generally constructed in isolated locations where infrastructure facilities are minimum. Until now the Directorate General of Lighthouses and Lightships had been using conventional methods like wooden shuttering to construct lighthouses. This process was time consuming and site engineers depended on local labour. To overcome these problems, the Directorate introduced the Slip Form method to build the superstructure of lighthouse towers. The Slip Form method has been developed by Swedish Technologies for constructing chimneys, cooling towers etc.
Slip Form means a continuously moving form, moving at such a speed that the concrete when exposed has already achieved enough strength to support the vertical pressure from the concrete still in the form so as to withstand lateral pressure caused by wind, inclination of walls and so on. The Slip Form is moved by hydraulic jacks spaced at equal intervals lifting the forms about 1" at a time every 5 to 10 minutes depending on the required sliding speed. An average sliding speed of 9" an hour is achieved in slip forming during construction.
The Slip Form method was introduced for the first time in the construction of the 30-metre high lighthouse at Vodarevu in AP.
Structures constructed with Slip Form are hollow from inside. However, the lighthouse tower structure requires an RCC spiral staircase along the inner periphery of the tower and a top slab for housing LH equipment. This was the bottleneck for taking up the LH tower construction by the Slip Form method. It was overcome by providing two cantilever beams on either side to support the staircase flight. Thus, the Slip Form process was devised to suit the indigenous need for a staircase inside the lighthouse tower.
New Slip Form method for lighthouse construction
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