Plants and equipment are often used in construction works to save time, labour and cost. Plants used in the construction industry are many and they include: pile driving equipment, tower crane, concrete mixers, pumps, excavators, scaffolds, demolition plants, hoists, compressors, bulldozers, power tools etc. The use of plants and equipment in construction works always come with large costs and these are factored at the billing stage of the project. Large companies may have necessary equipment available to them but smaller companies when given a project may be in the need to hire or buy necessary equipment. The decision to buy or hire an equipment is guided by some factors listed below:
Factors to determine whether to buy or hire an equipment
1. What will the machine do?
2. Will skilled operator have to be employed?
3. Working life of the machine.
4. Power source.
Plants/equipment are mechanical instrument. To ensure that they stay longer in service, endeavour to
1. Keep the plants clean always.
2. Keep them in good working condition.
3. Regularly maintain them.
4. Use machine for the work they were made to do.
5. Keep statutory records of the equipment.
Plant/equipment cost rates
The cost to the builder of the use of plant/equipment comes about as follows:
1. Initial cost
2. Scrap value
3. Estimated life period
4. Depreciation
5. Licence and insurance
6. Repairs and maintenance
7. General overhead (cost of admin)
8. Profits
How to determine total cost of plant per hour: Total cost of plant per hour includes cost of the plant, cost of operation of the plant, overhead and profit.
How to determine cost per hour of a plant/equipment
To determine the cost per hour of a plant, it is necessary first to determine the total working hours per year by the following process
Total number of weeks in a year = 52 weeks
Assuming holiday period = 3 weeks
Maintenance period of plant = 2 weeks
Time to transport plant to site = 1 week
Idle time/breakdown = 8 weeks
Total working hours in a week = Total number of weeks – (holiday period + maintenance period + transport period + idle time) = 52 – (3 + 2 + 1 + 8) = 52 – 14 = 38 weeks.
Working days per week = 5
Working hours per day = 8
Working hours per week = 8 x 5 = 40 hours
Assuming half-day work on Saturdays = 4 hours
Total working hours per week = 40 + 4 = 44 hours
Total working hours per year = total working hours per week x total working week per year = 44 x 38 = 1672 hours
If the cost of plant per year = N 1,000,000
Cost of plant per hour = cost of plant per year/number of hours per year = 1,000,000/1672 = N 586.09 per hour
How to determine operation cost per hour of a plant/equipment
To use an equipment in a day, the following costs are involved:
Machine operator: 8 hours @ N 1,000 per hour = N 8,000
Diesel per day = N 9000
Oil per day = N 2,000
Grease or rags = N 500
Total cost per 8-hour day = N 19,500
Cost per hour = cost per day/number of hours in a day = 19,500/8 = N 2,437.5
Total cost per hour = cost of plant per hour + cost of operation of plant per hour = 586.09 + 2437.5 = N 3,023.59
Add 10% overhead = N 302.359
Total = N 3,325.949
Add 10% profit = N 332.595
Total = N 3,658.544
How to determine production capacity of a plant (using concrete mixer for example)
154 m3 of concrete is required to be produced and placed in foundation in 6 days, check whether a 0.35 m3 capacity mixer would be suitable to do the job.
Actual production time of the equipment assuming 80% actively working in a day = 0.8 x 8 (hours per day) x 6 (days) = 38.4 hours
Required output of the mixer per hour = volume of concrete/ total number of hours = 154/ 38.4 ≈ 4 m3 of concrete per hour.
Mixing cycle of concrete is as follows:
Loading time to mixer = 1 minute
Mixing time in mixer = 3 minutes
Discharge time from mixer = 1 minute
Total = 5 minutes = 0.0833333 hours
This implies that using the mixer, one batch of 0.35 m3 concrete is completed in 0.0833333 hours
In one hour, 0.35/0.08333333 = 4.2 m3 of concrete would be produced.
This value (4.2 m3) is greater than the calculated required output (4 m3) per hour for the mixer. This implies that the mixer can produce 4.2 x 38.4 = 161.28 m3 of concrete in 6 days which is higher than the required value of 154 m3. Therefore, the mixer is adequate for the work. Where the mixer capacity is less, it may be required to go for a larger mixer or increase the number of days of the work.
Thanks for reading!
