英国研究生论文 Project Scheduling Construction Essay 屋面工程的生产率

Definition of productivity

Within these several decades, many researchers have defined the productivity term in their studies in a number of ways. The term productivity has different meanings to different people. Many individuals automatically think only of labor unions when the term “productivity” is mentioned. Others associate capital expenditures with the term. Each of these interpretations is only partly correct (Adrian, 1993). Many researchers have attempted to define precisely the meaning of productivity and below are some of it that referred from their studies:

Oglesby et al. (1989), presented that productivity can be defined as “in-place value divided by inputs”. Some researchers have defined it as works-hours divided by the equivalent quantity of work. In construction, productivity normally can be understood as work quantity divided by man-hours (or work-hours) consumed to accomplish the work.

Productivity = Work Quantity Man-hours

According to Dolman, Parham, & Zheng, (2007), productivity is a measure in order to know how much output is produced per unit of input.

Diewert & Lawrence, (2006) presented that productivity can be defined as the level of economic output per unit of input and also per worker. Productivity is important to the wealth and well-being of a nation and give efforts to improve productivity occur at all levels of society.

Thomas and Mathew, (1986) presented that no standardized productivity definition had been established in the construction industry. It is difficult to define a standard productivity measure because companies use their own systems which are not standardized. Association simply illustrates the productivity between an output and an input. The form has been widely used and existing in literature over the years in construction industry is; Productivity = Input/Output

2.3 Measurement of productivity

There is controversy surrounding productivity that rooted in the differences in data collection. It is due to incorrect in assuming productivity measured uniformly and that all published productivity values have the same basis (Whiteside, 2006). Overall conception of productivity is difficult to express or to measure. It is sometimes expressed either in terms of output from labor or from services or from capital invested. These parts of expressions often do not give an accurate picture of the overall position. Although, there are measurements of some or all of the inputs and outputs of the industry but they still failed to combine these measurements into any satisfactory measure of efficiency. In fact, the ratio is easy to compute if the unit uses a single input to produce a single output (Choy, 2008).

Although there are numbers of publications exist on construction productivity, there is no agreed upon definition of work activities nor a standard productivity measurement system. Most of researchers have concluded that it is difficult to obtain a standard method to measure construction labor productivity because of project complexity and unique characteristics of the construction projects (Oglesby et al. 1989). The uniqueness and non repetitive of operation in construction projects make it is difficult to develop a standard productivity definition and measure (Sweis, 2000).

Factors influence productivity in construction

Lim et al., (1995) has studied that factors affecting productivity in the construction industry in Singapore, indicated the problems affecting productivity were difficulty with recruitment of supervisors, difficulty with recruitment of workers, high rate of labor turnover, absenteeism from the work site and communication problems with the foreign workers. Olomolaiye et al., (1996) also studied that factors affecting productivity of craftsmen in Indonesia show the findings indicating craftsmen in this country spent 75 % of their time working productively. There are five specific productivity problems were identified such as lack of materials, rework, absenteeism, lack of equipment and tools.

Kane et al., (cited in Herbsman et al., 1990) has classified the factors affecting construction productivity into two main groups which is technological factors and administrative factors. The technological factors involved those related to the design of the project and the administrative group factors are related to the management and construction of the project. Technological factors are comprises of sub-groups such as design factors, material factors and location factors. Administrative factors are comprises of sub-groups, such as construction methods and procedural factors, equipment factors, labor factors and social factors. Based on Heizer and Render (1990), they classified that factors influencing site productivity into 3 groups which are labour characteristic factors, project work conditions factors and non-productive activities. Olomolaiye et al., (1998) also stated that factors affecting construction productivity are rarely constant and may vary from country to country, from project to project and even within the same project which are depending on circumstances. They classified the factors influencing construction productivity into 2 categories which are external and internal. That means its representing those outside the control of the firm’s management and those originating within the firm. The external factors included the nature of the industry, construction client knowledge of construction procedure, weather and level of economic development. The internal factors included management, technology, labor and labor unions.

Choi, (2007), stated that based on his finding, weather and poor communication prove to be the greatest impediment to roofing productivity, whereas the field workers pointed out that roof pitch, height and age of the roof along weather were major causes for lack of productivity in their job at site. He also stressed that roofing contractor generally not consider safety as a high priority in their business.

Metrics – an overview

According to Melnyk et al., (2004), they stated that metrics are fulfill with the fundamental activities measuring (evaluating how we are doing), educating (communicating what is important and how we intend to deliver value to our customers) and directing (flagging potential problems by size of gap between the metrics and standards). Ideally, metrics are consistent with the way operation delivers value to the customers. Based on Melnyk et al., (2005), they presented that metric is a verifiable measure which consists of three elements such as; a) the specific measure, b) the standard (the numerical values that identifies the minimum threshold of performance, and c) the environment which the activity or person being measured operates.