When planning the installation of building column and their appropriate dimensions, the ratio of the length to the diameter is very important (i.e. – length ÷ diameter). This is called the slenderness ratio. If the column is too long and has a small diameter, then it will have a high slenderness ratio. In this case, it will look very thin and seem to be flimsy and will have the tendency to buckle. If the opposite is true, i.e. it is short and has a larger diameter, then it will appear very thick and will have low slenderness ratio.
There are some important strength related issues regarding the slenderness ratio. If the slenderness ratio is less than 10 (for example if the column has a diameter of 250mm then the length can be up to 250 x 10 = 2500mm/2.5m) then the column does not require reinforcing steel and may simply be filled with concrete.
If the slenderness ratio falls between 10 and 15 (for example with a 250mm diameter column the length is between 2500mm (250 x 10) and 3750mm (250 x 15), then the column should be reinforced with steel. This must be extended below the column, into the concrete foundation and out of the top of the column, into the member the column is supporting.
If the slender ratio is bigger then 15, a structural engineer needs to be consulted.
In all instances where the column may experience strong horizontal force, i.e. adjacent to a driveway where a vehicle could bump into the column, reinforcing steel should be used in the column irrespective of the slenderness ratio.
Fibrecem building columns are effectively permanent structures and should not be used as structural elements without filling with the correct strength concrete and reinforcing as required.
Place the base component in the correct position on top of a solid foundation base (i.e. concrete) which is sufficiently strong to carry the intended load of the column.
If the base is not fully level, then use a thin layer of river sand and cement to ensure the base sits solidly on the concrete base.
if the column is to be reinforced then drill through the base component into the foundation material and insert steel reinforcing starter bars approximately 600mm long into those holes. The lower part of the starter bars should be coated with general purpose epoxy before inserting into the holes so that they will rigidly adhere to the foundation material. The depth of these holes should be at least 15 times the diameter of the steel bars (i.e. if you are using a 10mm steel bar, drill a hole 12mm in diameter at least 150mm deep.)
Once the steel is in place fill the base with good quality concrete and allow a day for the base to dry.
If the steel reinforcing is being used erect this now and tie onto the started bars.
Erect the building column so that it stands vertically on top of the column base. Install support bracing or struts that will hold the column vertically in position while the concrete is being poured. These struts should be sufficiently strong to prevent the column from moving or tilting.
Once the column is secured in a vertical position it is ready to be filled with concrete. The concrete should not be very wet or runny. A drier mix that is still workable is recommended. Technically the concrete should have a maximum slump of 50mm. This is achieved when 31 litres of water are added for every 50kg of cement (1 bag) used in the concrete mix.
The concrete in the column should be poured in lifts of about 1250mm at a time. Use a vibrator to ensure the concrete settles properly, particularly if steel reinforcing is being used. Do not hammer the sides of the column to make the concrete settle as this will damage the column.
Pour the subsequent lift of concrete no less than 6 hours following the previous lift.
If any concrete spills on the outer surface of the pipe, clean it off before it hardens.