10. Pillars Flashcards
What are pillars
Pillars are vertical supports that act to transfer deck loads down to the bottom structure. Additionally they tie the deck and bottom structures together, thus reducing hoggin and sagging. Generally placed under compressive load but could be tensile (full ballast tank) or side to side (chocking).
Scantlings
Made from materials possessing adequate compressive strength recommended by classification societies. The longer the pillar, the more prone it is to buckling under load, so longer pillar = larger scantlings.
Must be large enough for the operational needs. Number of pillars can be reduced but would need to increase scantlings and number of beams, frames, girders, brackets, etc. Can also replace pillars with bulkheads.
Pillar Geometry
Typically: round, square, octagonal, I-shaped.
First three are generally hollow but would be solid for some needs (like tanks to prevent ingress of contaminants).
Small solid pillars < 150 mm diameter.
Positioning of Pillars
Found under high stress areas (deckhouse, windlass, capstans, winches, machinery space).
Can either be placed directly in line with hatch side coaming intersection with deck girders, or offset only under the girders. If multiple pillars fitted over one another at the corners of the hatch opening = massed pillaring
Suitable strengthening is used between the pillars to ensure that the load is adequately transferred from one to the other
Pillars are required to support a load that is originating from an area encompassing several deck beams/longitudinals. In addition, these pillars must effectively distribute that load to an appropriately sized and strengthened area at the bottom of the structure. For these reasons, the top end (head) of the pillar is normally placed under a primary strength member. Thus the load is transferred from the deck, through the deck beams into the deck girder and finally down through the pillar. The bottom (heel) is positioned to fall on the intersection of a solid or watertight floor and a side girder. If these primary strength members are not in this position then suitable additional material including partial floors, extra side girders and brackets are fitted. The cutting of manholes and lightening holes under the heel of the pillars is generally avoided.
Pillar end attachments
Both the head and heel of a pillar are fitted with heavy doubling plates and are continuously welded. Where a pillar supports a deck girder, arrangements to prevent tripped of the structure are in the form of brackets welded to the girder. In areas subjecting the pillar to tensile loading, the bottom end of the pillar is also fitted with brackets in order to distribute the load over a larger area of support.
