An-Najah Staff

Cost and time are interdependent by their very nature. However, cost and time are generally treated in isolation both informally and within the terms of the contract. In reality, cost and time interact throughout the construction cycle. Thus, cost and time models and modelling systems must facilitate the integration of cost with time. Recognition must also be given to the need to integrate cost and time, and suitable contractual procedures for utilising more advanced styles of modelling must be implemented. In this paper traditional and emerging models of cost and time are reviewed and the contractual context of cost and time integration is explored. This review seeks to ascertain if and why models and contracts have failed to satisfy this particular requirement, as well as the other requirements placed upon them. Key Words: Cost Models; Time Model; Integration and Modelling System.

Cost and time models have been developed for road and bridge projects using resource significance analysis, which is in turn based on the 80/20 rule. The work packages in these models are designed to relate to site operations. They serve as the basis for measurement, estimating, planning, valuation and control in civil engineering projects. For defined categories of work, a standard set of work packages have been developed which consistently contribute about 90% of a project's resource costs and hours. The resource significant cost and time models for bridges and roads predict cost to an accuracy of 4% Cv and 3% Cv respectively. The resource hours for a project can be predicted to an accuracy of 6% Cv for bridges and 3% Cv for roads. The bridge model contains 26 work packages and the road model contains 22 work packages. Coarser models have also been developed for situations where the road or bridge is only part of an overall project, with only a small loss of accuracy.