COMMUNICATING ABOUT FORMWORK
Dr J D Bapat
This post is a summary of an excellent article by: Mary Bordner Tanck, Concrete International, January 2009, pp 53-56.
The communication among the architect, structural engineer, general contractor, formwork designer and contractor is one of the most important issues on any concrete construction project. The main goal of the formwork drawings is to convey to the contractor how to build it. Good communication on a project can take many forms but drawings are the principal means of communication. It can be a huge help, especially on fast-track jobs, if the CAD files on formwork layout are shared with the contractor. This has the benefit of expediting the formwork layout and eliminating the need for extensive shop drawing revisions. It is important that items such as slab edges, beam faces, work points and anchorages are properly dimensioned.
The design live loads, live load reductions and superimposed dead loads should be noted in the contract documents. The reshoring designer needs these values to produce a safe design. When a pour strip is required (for example, on a post-tensioned slab), the engineer should indicate whether the cantilevers on each side of the pour strip can support their self-weight and any superimposed dead and live loads or if they are required to be backshored until the pour strip is closed.
There are many details that need to be conveyed by the formwork designer for the contractor to construct a safe formwork system. Of particular importance are bracing sizes and locations as well as the specifications for the materials and components to be used. The more detail a designer provides, the lower the risk of errors, both in the design and in its realization in the field. The shop drawings should give field superintendents all the information they need, including the locations for potential problems, so the risk of missing a key item is significantly reduced. The drawings can also help the formwork designer and field personnel work together to address potential problems. Depending on the formwork designer’s scope of work, the location each beam edge relative to a grid line and relative to adjacent beams should be shown. These dimensions can help the contractor lay out the job so that material can be moved to the appropriate location the first time, saving the contractor time, money, and crane usage. The formwork designers need to very clearly communicate the materials required for shoring, reshoring or backshoring. When timber is used, the grade and species of each timber member should be clearly called out on the plan.
When responsibility is passed onto the contractor for critical items such as cantilever spans, framing over an opening or slab framing along column lines, the risk of problems increases significantly, as forms may be cobbled together in the field with little regard to connections, safety factors or back-span conditions. The sequencing can be crucial to the success of a shoring and reshoring design.
The members of the project team should share a common goal: to get the structure built safely, on time and within the budget.
The readers are advised to go through the original article to know more details.
