運用邏輯關係評估變更設計之影響

Abstract

Changes or change orders represent modifications to the original project contract. As the complexity of a construction project increases, the occurrence of changes becomes unavoidable. The changes often have adverse impacts on both the duration and cost of a project. Such impacts may include direct impacts and consequential impacts. As defined by the Construction Industry Institute (CII) in 1990, direct impacts of changes are results experienced within the scope of the changed activity, and consequential impacts of changes are results of such changes experienced elsewhere on the project. In practice, compensations are normally granted only to the modifications on cost and duration for the activities that are directly affected by the change; and the existence of consequential impact is frequently overlooked. This investigation develops a model, LOGIC, which uses a logic-based approach to capture the direct and consequential impacts of changes. Restated, the LOGIC model proposes an innovative approach of integrating (and further expanding) existing logical relationships for evaluating change impacts. Three types of logic are adopted in the LOGIC model, namely: hard logic, soft logic and causal logic. Hard logic is the network logic that has only a fixed precedence relationship between activities. Soft logic is the logic that has more than one alternative relationship between activities. Depending on certain constraints (such as resource limitations), the soft logic is further divided into three subtypes, namely: SOFT link, OR link and EXCLUSIVE-OR link. Causal logic is the logic that indicates the influential relationship between activities that have no physically interconnected relationship. While the use of hard logic is to evaluate direct impact of changes, the soft and causal logics are used to assess the consequential impacts due to the changes. The strengths of the LOGIC model are demonstrated by its application to an example project.

Changes or change orders represent modifications to the original project contract. As the complexity of a construction project increases, the occurrence of changes becomes unavoidable. The changes often have adverse impacts on both the duration and cost of a project. Such impacts may include direct impacts and consequential impacts. As defined by the Construction Industry Institute (CII) in 1990, direct impacts of changes are results experienced within the scope of the changed activity, and consequential impacts of changes are results of such changes experienced elsewhere on the project. In practice, compensations are normally granted only to the modifications on cost and duration for the activities that are directly affected by the change; and the existence of consequential impact is frequently overlooked. This investigation develops a model, LOGIC, which uses a logic-based approach to capture the direct and consequential impacts of changes. Restated, the LOGIC model proposes an innovative approach of integrating (and further expanding) existing logical relationships for evaluating change impacts. Three types of logic are adopted in the LOGIC model, namely: hard logic, soft logic and causal logic. Hard logic is the network logic that has only a fixed precedence relationship between activities. Soft logic is the logic that has more than one alternative relationship between activities. Depending on certain constraints (such as resource limitations), the soft logic is further divided into three subtypes, namely: SOFT link, OR link and EXCLUSIVE-OR link. Causal logic is the logic that indicates the influential relationship between activities that have no physically interconnected relationship. While the use of hard logic is to evaluate direct impact of changes, the soft and causal logics are used to assess the consequential impacts due to the changes. The strengths of the LOGIC model are demonstrated by its application to an example project.