FAQ >> FACTORS BEHIND THE SELECTION OF CONSTRUCTION EQUIPMENTS

FACTORS BEHIND THE SELECTION OF CONSTRUCTION EQUIPMENTS

The selection of the appropriate construction equipment is an important part of job planning. The contractor has many different options to choose from, which makes the selection even more complicated. A planner has to choose the alternative that provides the best value from a cost and schedule perspective.

Selection of equipment for construction projects generally involves two classes of factors or considerations-hard factors and soft factors. Examples of hard factors include technical specifications of the equip- ment, physical dimensions of the site and constructed facility, and cost calculations. As can be noticed, hard factors are tangible in nature. On the other hand, soft factors are mostly intangible, qualitative and informal in nature. Some examples of soft factors are safety considerations, company policies regarding purchase/ rental, market fluctuations and environmental constraints. The soft factors influence decision-making to a large extent.

A number of researchers have worked to develop a method to assist in equipment selection and, consequently, different models have evolved over the years. For example, there are optimization model, graphics model and database-centred models to select tower cranes. Different expert systems have also been developed to assist in equipment selection. Finally. there are artificial intelligence-based models. Harris and McCaffer (2001) have developed their equipment selection model based on multi-attribute decision-making. Dynamic programming-based models have also been developed for equipment selection. A number of computer programs have been developed to assist in the equipment-selection process.

Similarly, commercial software is available that offers solutions for the selection and location of a specific crane model and for lift planning (Meehan 2005). Examples are Compu-Cranc and LPS (NCI 2006).

Cranimation and Tower-Management (Cranimax 2006), LiftPlanner (LiftPlanner Software 2006) and MethoCAD (Progistik 2006). These software packages, commonly used by engineering and construction firms, address mainly the technical aspects of crane location and lift planning.

In the following paragraphs, we discuss some of the factors that govern the equipment-selection decision. It may be difficult to come up with a set of decision variables that are applicable for the selection of all types of equipments used in construction, and hence, only a few common decision variables are discussed. The specific decision variables for a particular class of equipment selection are discussed subsequently.

Economic Considerations

The economic considerations such as owning costs, operating labour costs and operating fuel costs of equipment are most important in selection of equipment. Besides, the resale value, the replacement costs of existing equipment, and the salvage value associated with the equipment are also important. The economics of equipment selection and replacement issues are dealt with in detail in later parts.

Company-specific

The selection ofcquipmcnt by a company maybe governed by its policy on'owning' or'renting': While emphasis on 'owning' may result in purchase of equipment keeping in mind the future requirement of projects，the emphasis on 'renting' may lead to putting too much focus on short-term benefits. This may explain the situa- tion of a construction company opting for two 30 m3/h batching plant owned by the company and currently idle, instead of the required one 45 m3/h batching plant that it can get on rent. It is clear that the company wants to deal with the 30 m3/h batching plant keeping future projects in mind, even though going for the 45 m3/h batching plant option at present may have been economical.

Further, if the company project forecast says that there will be considerable number of projects involving a particular type of construction equipment, say X, for the next couple of years, then the decision would be to buy only this type of equipment.^construction company specializing in a particular type of construction, such as tunnelling, will have a tendency to procure only those equipments that are used in tunnel construction. The equipment-selection decision also depends on the amount of outsourcing the company does to execute its projects. A company opting to subcontract a majority of their project work will tend to keep low equipment asset.

Site-specific

Site conditions-both ground conditions as well as climatic conditions-may affect the equipment-selection decision. For example, the soil and profile of a site may dictate whether to go for a crawler-mounted equip- ment or a wheel-mounted equipment. If there is a power line at or in the vicinity of site, one may go for a fixed-base kind of equipment rather than a mobile kind of equipment. Similarly, climatic conditions such as the presence of strong winds, visibility level and noise level may affect equipment-selection decision. Further, the access leading to the site may also affect the decision. Heavy traffic congestion near a site may lead to a decision to produce the concrete at site and, hence, selecting a concrete batching plant rather than relying on ready. mix concrete. Similarly, if there is only a narrow road leading to the site, it may have a bear- ing on type of transportation equipment selected for the site.

Equipment-specific

Construction equipments conic with high price tags. While it may be tempting to go for the equipment with low initial price, it is preferable to opt for standard equipments. Such equipments are manufactured in large numbers by the manufacturers, and their spare parts are easily available, which would ensure minimum downtime. Besides, they can also fetch good salvage money at the time of their disposal.

It is a general tendency to go for such equipments that can bring in'uniformity' in the type of equipments that are already available with the company. For example, a company would like to go for a uniform type of engines for different machines such as excavators, dumvers and tractors.

The size of equipment selected is also an important consideration. Although the unit production cost may be cheaper for equipments of large size. it is also true that large equipments require correspondingly larger sizes of matching equipments. Thus, downtime in one primary unit may lead to downtime in dependent equipments also.^trade-off between unit production costs versus size must be obtained. and as far as possible, equipments of similar sizes should be selected for the project.

Besides the above factors, the versatility (whether it can perform more than one function) of equipment, the adaptability for future use, the past experience with the equipment, and the interaction with other equip- ments are also to he noted.

Client and Project-specific

The owner/client in a certain project may have certain preferences that are not in line with the construction company's preferred policies as far as equipment procurement is concerned. The schedule, quality and safety requirements demanded of a particular project may in some cases force the company to yield to the demands of the client.

Manufacturer-specific

A construction company may prefer to buy equipment from the same manufacturer again and again, and that too from a specific dealer. This may be to bring in uniformity in the equipment fleet possessed by the company or because the company is familiar with the working style of the manufacturer and the dealer. Long association may not only result in cheaper price, but it also ensures prompt services by the manufacturer with regard to the company.

Labour Consideration

Shortage of manpower in some situations may lead to a decision in favour of procuring equipment that is highly automated. Further, the selection of equipment may be governed by the availability or non-availability of trained manpower. The company may not be inclined to select some sophisticated equipment if it finds that there is limited availability of manpower to operate the same.

In the following sections, we briefly describe some common construction equipments that can be seen in most of the construction sites these days.

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