Cost Impact of Float Loss on a Project with Time-cost Trade-off

[[abstract]]雖然非要徑上之作業在浮時範圍內之延遲並不會影響整體專案完工日期，不過常會因其衝擊原資源使用計畫造成專案成本之增加而導致紛爭，因此相當多研究致力於提供了一個有效且可靠的方法來進行浮時耗用之成本評估。然而，近年來的研究多以假設專案內各作業工期均為固定不變，或僅以作業成本為基礎來進行分析模擬，而較少於浮時耗用之成本評估過程中考量時間-成本之權衡互易與資源整合之關係。本研究首先以基因演算法建立一個與傳統要徑分析法結合之可變動作業工期資源整合最佳化模式（CPM-Modified Resources-Integrated Optimization Model），此模式中假設各作業工期與不同種類資源之使用效率呈現二次方函數關係，而允許各作業工期可以變動調整以趨近實際，在專案總成本最低之目標下藉由該模式演算，可以得到資源最佳配置方案及作業的最佳時程。接著透過與浮時耗用後最佳作業時程（optimal after-impact schedule）之比較，進一步評估浮時耗用之成本。本研究並藉由一個案例來測試該模式的有效與性能。本研究發現；當最佳作業時程中的浮時作業一旦受到干擾時，即會導致成本的增加，故唯有將浮時耗用的成本納入考量，才能使浮時的分配管理更加的合理。本研究中所提供之客觀量化且能精確評估非要徑作業浮時耗用成本的方法，除了可以讓專案管理者在施工階段規劃浮時與資源之使用，並有助於在非要徑作業遲延所致紛爭發生時，進行浮時耗用之成本分析與責任釐清。[[abstract]]Although delays to non-critical activities within the float do not always affect the overall completion time of a project, they commonly cause disputes over the impact cost and apportionment resulting from the complexity of resource utilization in construction projects. Therefore, considerable attention has been focused on providing an effective and reliable method for analyzing the effects of float loss. Several recent studies have proposed various methods; however, most of these methods are based on the assumption of a fixed duration for each activity or activity-based cost simulation. Few studies have considered the trade-off between time and costs and the integration of project resources.First, this research introduces a critical path method (CPM)-modified resource-integrated model using genetic algorithms (GAs). Under the assumption of a non-linear quadratic relationship between resource efficiency and working duration, the proposed model incorporates the adjustment of activity durations and resource allocation into the CPM to identify the optimal realistic schedule. Subsequently, the quantification of the impact of float loss can be determined definitively by comparing the baseline schedule with the after-impact schedule. An application example was conducted in this research to test the validity and performance of the proposed model.This research suggests that the utilization of float is not free when the optimal schedule is disrupted. Float apportionment will never be reasonable unless the cost associated with float loss is taken into consideration. The proposed method provides an objective approach in which the impact of within-float delays on non-critical paths can be evaluated accurately. Thus, it enables managers to plan the use of float and evaluate the resource utilization plan during construction and facilitates the analysis of the impact on cost and apportionment associated with delay claims in construction projects