Pole Footings and Foundations

Generally the poles, columns and masts supplied by GPA are either base plate mounted (circular, octagonal or polygonal on a steel flange, or directly buried into the ground if under 15 m in height. In certain applications the poles are directly mounted onto an existing structures.

Base plates are bolted onto Foundation Bolts (sometimes referred to as rag or anchor “Bolts”) which varying in diameter from 16, 20, 24, 30, 36, 42 & 48 mm. Foundation bolts are either generally U-shaped for sizes 24 mm and under with thread on each end 148 mm or 247 mm apart. For larger bolts sizes they will be either straight or the non-threaded end will have a cog or “j” bend. All bolts supplied by GPA are hot dipped galvanized.

The foundation bolts are anchored into the ground by embedment into concrete footings. The concrete footings are generally a Pile Footing. A Pile Footing is where concrete is poured into a cylindrical excavation. Where ground conditions dictate, (because of water levels, soil type or rock), Pad Footings are utilised, which are a rectangular concrete shape and are wide rather than deep. In both types of footings reinforced steel foundation structures ( called “Cages)” are installed into the footing excavation, at least 100 mm from the top, bottom and edges of the excavation.

diagram1

Bolts are usually welded into the Cage in their required configuration prior to dispatch to the installation site, and are complete with two nuts and two washers on each thread end and a galvanised steel template to match the pole base plate configuration. Bolt assemblies consist of various configurations made up of either 2 U bolts or up to 24 or more individual bolts. Bolts of 24 mm and under are generally configured in a square pattern on a 233mm or 350mm Piece Circle Diameter (“PCD”), and for Bolts above 30 mm and greater a circular pattern of 350mm PCD or more. Once the bolts are welded into the cage a nut and then a washer will be placed onto the threads. Once this is complete on all the bolts the template is then placed onto the bolts followed by the second washer and then the remaining nuts tightened down ready for transport to the installation site.

Pole Foundation Installation

Before commencement of installing the pole and fittings, by suitably qualified and experienced installers, the following should be in place.

  1. Completed geotechnical review of site soil conditions to confirm soil load bearing capacity.
  2. Engineering to certify of suitability of footing for the installation site.
  3. Site Safety Plan
  4. Suitable equipment at site to receive cages and unload depending on the size of the cages either forklifts, truck with hiab or crane.
  5. Confirmation of final floor level and foundation bolt projection.
  6. Site prepared so that surface runoff cannot drain over or pond adjacent or on the foundations.
  7. Excavatation to the required dimensions with at least 100 mm cover to all reinforcing bars.
  8. Soil to be free of organic matter and excessive moisture.
  9. Insert form work for concrete pour (in very sandy condition form tube or form work may have to be utilised).
  10. Concrete supplied to be to be certified as adequate by an relevantly qualified engineer and laid to AS 3600 and as 2159 with 100 mm minimum cover to all reinforcing bars

Place temporary form work (supports) across the footing excavation (see Diagram 1 above) to support the cage and anchor bolt arrangement at the correct height for the final floor level. The supports shall be adjusted to provide for all nuts to be level, checked with a spirit level. This will help to ensure that the foundation for the pole will provide the basis for vertical installation of the pole. Foundation bolts should be set so that they protrude approximately 120 mm out of the concrete for M24 and below size bolts and at least 150 mm for M30 and above. The protruded thread is necessary to allow for nut, washer, baseplate (as template is removed before installation) and sufficient distance beneath the baseplate for the other nut and washer and grouting.

The protruded thread should be greased and capped or covered to ensure that the bolt threads are not damaged during the concrete pour and before installation of the poles.

Electrical and communication conduits are then installed by a relevantly licensed installer and any other required services must be installed into the footing by qualified persons, prior to the pouring of the concrete. The protrusion of these conduits and other services should be at least level with the top of the foundation bolts. Conduit should be sealed at both ends.

Pouring Concrete

Concrete must be poured into place and compacted immediately after mixing. Transfer of the concrete into the excavation has to be immediate so the concrete is poured before its initial set.

Concrete should be applied in layers of no more 250 mm at a time. With each layer properly compacted before pouring the next one. Compaction should proceed immediately after placement. Compaction is normally done by the use of mechanical vibrators the purpose is to expel any air bubble from the concrete pour.

Curing is the final critical requirement after placement. Curing is the process of the concrete drying at the right speed to ensure the maximum strength of the concrete. The longer concrete takes to cure or to set completely the stronger its inherent strength. Concrete curing speed is slowed by keep concrete damp ideally concrete curing should take 7 days in warm conditions and at least 9 days in colder conditions.

The instructions included in this document have been written for guidance purpose only for the assembly of the equipment therein described. Galvanised Poles Australia is not liable for any direct, indirect or consequential loss or damage to property person that may arise at law as a result of following these instructions. Copyright © 2014 Galvanised Poles Australia.

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