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BCGCM1005B Carry out measurements and calculations
Introduction
This unit specifies the competency required to carry out measurements and perform simple calculations to determine task and material requirements for a job in a General Construction environment.
To make understanding this unit easier, you should know something about:
Knowledge
- Drawings and specifications
- Materials used in construction
- Simple geometry measurements and calculations
- Costing for construction projects
Skills
The ability to:
- Read and interpret plans
- Measure and calculate manually and with a calculator
- Record measurements
- Communicate effectively
Key terms for this unit
Quantities
Recording
Plans
Area
Volume
Weight
Scale
Why measure?
All construction requires the use of accurate measurement and calculation of quantities. On big projects a quantity surveyor is often employed to do this work. For house construction, it is often the job of the builder or contractor to carry out this work.
The principles of measurement
When measuring, either materials or labour or both can be taken into account. For example, when a brick wall is measured, it is measured in terms of its area and not the number of bricks, weight of sand, cement and the number of bricklayers necessary to complete the wall.
Some of the main ways that building materials are measured include:
Count or/sets
No measurements are taken. The number of items required is considered. This is the case for items like basins, toilets, appliances etc. The number recorded.
Length
Only one dimension is required. Length is used to calculate the quantities for items such as skirting, pipes, gutters etc. Lineal measurement L/M
Two dimensions are required to calculate the area in square metres (m2). Items measured in area include such things as carpet, tiles, glass, painting, brick walls, roof tiles etc.
Three dimensions need to be taken to calculate volume. The unit for volume is cubic metres (m3). The types of material measured by volume include, concrete, topsoil and excavations.
Steelwork in a building is often measured in weight. They can be measured in number, m3 or m2 and then multiplied by a weight factor to give a quantity in tonnes (t). Some examples of materials measured by weight are; steel reinforcement, steel beams, columns etc.
The measurements
All measurements are taken using the metric system (metres, kilograms etc). All lengths are measured in millimetres (mm) and metres (m). All weights are measured in kilograms (kg) and tonnes (t).
The tools
Scale rule
Measurements from plans are often taken with a scale rule. The rule measures the lengths from the drawing and give measurements in full sizes. These can be used to take lengths not labelled on the plan. Common scales used are 1:100, 1:200, 1:500.
Rule
These can be one piece up to 1m long or folding. The folding 1m rule is the most commonly used tool for measuring or transferring distances of less than 1m. Non-folding rules are usually made of steel. Folding rules can be made of plastic or wood. You should select only good quality rules.
Tape measure
The most commonly used measuring tool is the tape measure. They may be metal-bladed retractable tapes of 3m to 8m or cloth tapes of up to 30m.
Longer distances are measured with perambulating wheels. These wheels have a set diameter wheel and as you walk with the wheel, measurements are taken by a revolution counter and a diameter measurement for part revolutions of the measuring wheel.
Using the measures
Length
Calculate timber lengths in multiples of .300 mm
A timber order for 50 x 19 DAR Oregon of
22/2.1
30/3.6
5/4.8
The total for this order would be 22x2.1m (46.2m) + 30x3.6m (108m) + 5x4.8m (24m) = 178.2m
Area
If a building floor plan measures 15.0 m x 12.4 m calculate the area of floor sheeting required when an allowance of 10% is made for waste in cutting.
The area is 15.0 x 12.4 = 186 m2 + 18.6 m2 = 204.6m2 of flooring required.
If a brick wall is built 15m long, 2.2m high, how many bricks would be required?
The wall is 15m x 2.2m = 33 m2. The quantity of bricks per m2 is 50. Therefore the number of bricks is 33 x 50 = 1650 bricks are required.
Volume
If a trench is excavated 20m long which is 600mm deep and 550mm wide, how much soil is removed from the trench?
The volume is 20m x .600mm x .550mm = 6.60 m3
Weight
If a concrete slab is to be 32m2, what will be the weight of reinforcing required when the reinforcing weighs 1.85kg/ m2?
The weight is 32m2 x 1.85 = 59.2 kg
When measuring and recording it is vital that the measurements are made and recorded accurately. Without such accuracy, estimates and final calculations may be wrong and lead to problems with costs and/or quantities of material available for construction.
Computers for Measuring and Calculating
Computers and calculators make both measuring and calculating more efficient. They also help in record-keeping. Many computer-aided drawing (CAD) systems allow items to be quantified from the plan. More sophisticated systems calculate quantities for orders and also take labour costs and estimates for total project costs into account. The calculators cost $20 or more, while computer software programs can cost up to $15,000.
Publications such as Cordells and Rawlinsons demonstrate how the estimated cost of construction can be calculated when the area of certain categories of construction is measured and multiplied by a cost factor. This is built on the superficial area method of estimating.