Saturday, April 19, 2014

Builders Plant - Output and Cycle Times

Output and Cycle Times ~ all items of plant have optimum output and cycle times which can be used as a basis for estimating anticipated productivity taking into account the task involved, task efficiency of the machine, operator's efficiency and in the case of excavators the type of soil. Data for the factors to be taken into consideration can be obtained from timed observations, feedback information or published tables contained in manufacturer's literature or reliable textbooks.

Typical Example ~

Backacter with 1 m3 capacity bucket engaged in normal trench excavation in a clayey soil and discharging directly into an attendant haulage vehicle.

An allowance should be made for the bulking or swell of the solid material due to the introduction of air or voids during the excavation process

This gives a vehicle waiting overlap ensuring excavator is fully utilised which is economically desirable.

Builders Plant Costing

Plant Costing ~ with the exception of small pieces of plant, which are usually purchased, items of plant can be bought or hired or where there are a number of similar items a combination of buying and hiring could be considered. The choice will be governed by economic factors and the possibility of using the plant on future sites thus enabling the costs to be apportioned over several contracts.

Advantages of Hiring Plant:

1. Plant can be hired for short periods.

2. Repairs and replacements are usually the responsibility of the hire company.

3. Plant is returned to the hire company after use thus relieving the building contractor of the problem of disposal or finding more work for the plant to justify its purchase or retention.

4. Plant can be hired with the operator, fuel and oil included in the hire rate.

Advantages of Buying Plant:

1. Plant availability is totally within the control of the contractor.

2. Hourly cost of plant is generally less than hired plant.

3. Owner has choice of costing method used.

Typical Costing Methods

Builders Plant - Economic and Maintenance Considerations

Economic Considerations ~ the introduction of plant does not always result in economic savings since extra temporary site works such as roadworks, hardstandings, foundations and anchorages may have to be provided at a cost which is in excess of the savings made by using the plant. The site layout and circulation may have to be planned around plant positions and movements rather than around personnel and material movements and accommodation. To be economic plant must be fully utilised and not left standing idle since plant, whether hired or owned, will have to be paid for even if it is non-productive. Full utilisation of plant is usually considered to be in the region of 85% of on site time, thus making an allowance for routine, daily and planned maintenance which needs to be carried out to avoid as far as practicable plant breakdowns which could disrupt the construction programme. Many pieces of plant work in conjunction with other items of plant such as excavators and their attendant haulage vehicles therefore a correct balance of such plant items must be obtained to achieve an economic result.

Maintenance Considerations ~ on large contracts where a number of plant items are to be used it may be advantageous to employ a skilled mechanic to be on site to carry out all the necessary daily, preventive and planned maintenance tasks together with any running repairs which could be carried out on site.

Builders Plant - General Considerations

General Considerations ~ items of builders plant ranging from small hand held power tools to larger pieces of plant such as mechanical excavators and tower cranes can be considered for use for one or more of the following reasons:-  

1. Increased production.

2. Reduction in overall construction costs.

3. Carry out activities which cannot be carried out by the traditional manual methods in the context of economics.

4. Eliminate heavy manual work thus reducing fatigue and as a consequence increasing productivity.

5. Replacing labour where there is a shortage of personnel with the necessary skills.

6. Maintain the high standards required particularly in the context of structural engineering works.