Understanding and quantifying the impact of changes on construction labor productivity: Integration of productivity factors and quantification methods.

摘要

Changes are a natural part of construction. Nevertheless, contractors and owners frequently fail to agree on the price of a change because they do not agree on how a project systematically responds to multiple changes. In addition, many in the industry are not aware of and in alignment on the available methods for quantifying productivity losses.;The studies on the subject of construction labor productivity can be divided into two groups: (1) studies that identify various factors affecting productivity, and (2) studies that try to quantify productivity losses due to certain factors or multiple changes. The first group of studies suffers from a lack of consistency in naming factors and defining the level of scope. This causes confusion and miscommunication. Though many have tried, there is still a need for a systematic synthesis of these factors. Many studies of the second group focus on the impact of only one factor at a time, overlooking the synergistic effects of change. Moreover, these studies have been questioned for their data reliability. The studies that did try to evaluate such synergism suffer from a lack of objectivity, clarity, and applicability.;This research attempts to improve that state of affairs. It has two objectives: (1) Identify the interrelationships of various productivity factors and integrate them visually into a big picture while re-defining and re-naming various productivity factors with consistency. (2) Analyze and evaluate all currently available studies, methods, and models for quantifying productivity losses due to changes extensively and intensively so that a reliable body of knowledge is assembled.;To achieve the first objective, the current research reviewed all productivity-related factors that have been identified so far, reduced them into 'major productivity factors', and grouped them into seven categories according to their features and relations to the entire system. Then cause-effect relationships between factors that lead to productivity losses were identified and weaved into one comprehensive system map. Two diagrams visualizing the integration of factors were generated and are presented here.;For the quantitative part, the existing studies were categorized largely into discrete and cumulative approaches. Comprehensive summaries of each of these studies are presented, enabling the most thorough critique to date of many of these studies. The productivity data of various studies are compared, and overall trends are drawn and discussed. Reliability and applicability of the data and models are evaluated. Strengths and limitations of each study are discussed in detail.