Selection of Roof Casting Formwork Systems for the Bird Island Project: Case Study

Formwork is a major contributor to profitability-or the lack of it-on most large and complex concrete jobs. Furthermore, formwork has major consequences for the project schedule, as well as all related trades, such as ironworkers and cement finishers. Consequently, selecting a formwork system and planning its field operations must consider the effects of the system on the overall project. However, due to competitive pressures and limited recourses, contractors seldom have the time to think through the construction phase specifics, and enter bids with carryover estimates adjusted for inflation. This may result in significant difficulties in meeting the project requirements. The paper illustrates the complexities involved in the selection and deployment of a formwork system through a study of the concrete formwork selection on the Bird Island Flats Tunnel project. This $290 million project was a part of the Central Artery/Tunnel project in Boston, Massachusetts. Because the conventional shoring methods could not produce the output needed to meet the project schedule and budget, the contractor solicited proposals from formwork manufacturers and chose the system from CONESCO Industries. This study has two objectives: first to identify the issues involved in the selection and sequencing of a custom-made formwork system and second to formulate a detailed analysis method to improve decision-making. The study shows that the planning of the formwork method involves two important decisions: First, the selection of a formwork system, and second the decisions regarding the sequencing and quantities of the formwork to be used on the project. The study presents the quantity/cost analysis for selecting a formwork system, and then illustrates the value of simulation in optimizing the sequencing scheme for the formwork operations. The study shows that indirect project cost plays an important role in the overall analysis, and that selection and sequencing of a formwork system can be improved using a time-cost trade-off technique.