DATA COLLECTION
The data for this case study were collected as part of an ongoing study of construction labor productivity (Thomas and Mannering 1987). The goal of the research is to test a productivity measurement technique that provides a daily assessment of the problems affecting production without the need for continuous on - site work measurement methods.
The technique relies upon both quantitative and qualitative data. An independent observer visits each case study project daily and classifies the day according to a predefined set of more than 25 site factors of conditions that potentially affect productivity. These factors include disruptions, one of which is material management; work content and constructability issues; construction methods; environmental conditions; and other management aspects. The data set can then be partitioned according to the desired classifications and examined to determine the impacts of one or more factors. The measure of impacts is determined by comparing daily productivity data from the pertinent subsets of the data base. The mechanics of how these variables are measured are described below
Productivity Measurement
Ineffective material management leads to the inefficient use of craft labor. Construction labor productivity is the measure of the effect. A simple, but effective productivity measurement technique has been developed (Thomas and Kramer 1987) and successfully field tested by three commercial contractors in the Midwest. An important attribute of the technique is that the data accurately reflects the changes in the way the work is executed. Construction labor productivity is defined as:
labor productivity = work – hours ......................................................................................(1)
units of output
This definition is often called the unit rate. This measurement scheme can be readily applied to task or crew level work - one of the important project management needs identified by the CICE Project (BRT 1982)
Identification of Adverse Conditions
An adverse condition is a situation that has been identified in the literature as not being associated with good work force management practices or one that probably has a negative impact on construction labor productivity. The identification of adverse conditions is critical in explaining abrupt changes in labor productivity. The approach used for this case study relies on the identification of specific events and conditions that are described in extensive written guidelines (Thomas et al.1987). Data collection focuses on the work of construction crews rather than on individuals or on the site as a whole. The approach has been field tested on more than 30 labor - intensive activities on 23 commercial construction projects in central Pennsylvania and the Tayside region of Scotland. The procedures are currently being tested by 12 researchers in the United States and 7 foreign countries.
The identification of an adverse condition that likely affects productivity is determines daily and relies upon the judgment of an independent observer. The observer is interested only in those aspects that seriously affect the work for at least several hours or more. Minor disruptions that are part of the normal working day are of no concern unless they perpetuate throughout the day so as to be abnormal. Adverse conditions are thus identified only if they are severe and known to have been present for most or all of the day.
Traditionally, researchers have relied on work measurement techniques to assess material management problems. However, many well - recognized work measurement techniques like work sampling and foreman delay surveys are also highly subjective. Even the measurement of delays using stopwatches and video photography are not an adequate measure because the effects of many material management problems are inefficient handling and distribution methods, not pure delays. These quantitative methods were considered inadequate for the purpose of this study. Instead, a qualitative measure was adopted as a way to document the presence of adverse material - related conditions.
The qualitative approach used herein is a unique departure from work measurement concepts. The observer documents the existence of known events and conditions that are clearly not associated with accepted standards of good project management. These are usually factual occurrences, and because one is interested in only the major disruptions, they can be easily identified. The observer's evaluation is based on the daily observance of the work, daily measurements of progress, daily assessments of the working environment, and discussions with the crew foreman at the end of the shift. Typical examples of adverse material management conditions or events that have been identified on commercial construction projects include:
Organization of storage areas
Extensive multiple - handling of materials
Materials improperly sorted or marked
Housekeeping
Trash and debris obscuring access to and movement of materials
Planning of material deliveries
Material expediting not coordinated with the erection sequence
Remobilization and refamiliarization after a lengthy delay (O' Connor 1968)
Material availability
Running out of materials
Crew slowdowns in anticipation of material shortages
Rework when materials arrive
Material handling and distribution
Materials misfabricated
Extraordinary and inefficient methods needed to distribute materials
The criteria used to define an adverse condition is whether the condition existed for several hours or more, affected most or all of the crew, resulted in the consumption of additional work - hours, required crew redeployment, or resulted in a changed construction method. In reality, the method has proven to be very accurate because the conditions cited above are usually a matter of fact and invariably prevail for most or all of the day.
The final verification that a condition is adverse is made by the researchers in consultation with the observer. On average, four to six hours is spent in reconciling the data from each project. During this process, varied factual and subjective evidence is studied, including progress photographs, diaries, and work schedules, Because progress and productivity are not known until after the disruption has been initially identified, the researchers are able to control the temptation to classify the day as being disrupted simply because the productivity is poor.