Contractors today have more options than ever before in selecting form and shoring materials and systems. Steel, aluminum, plastic, lumber, and engineered wood products are readily available, and elaborate forms can be assembled and disassembled piece-at-a-time or ganged in large units. Development of new form and shore systems has been made possible by lighter and stronger materials, improved connectors and fasteners, efficient materials-handling equipment, and more sophisticated engineering by manufacturers and contractors. The key to proper selection is understanding the driving forces behind the increased use of engineered forming and shoring systems: economy, contract language and federal regulations, and environmental responsibility.
Formwork and shoring typically represent more than 50% of the cost of cast-in-place structural concrete, with form and shore costs often as high as 60% to 70% of the structural costs. That means owners often pay at least as much for the temporary structure used to mold and support the concrete as they pay for the permanent concrete and steel. For example, a Midwest contractor reports that by using a custom forming system, parking garage floors can be built for about $11 per square foot for the structure only, but the beam and slab forms will account for more than $6 of that the total amount.
When it comes to getting an edge in competitive bidding, there are more options for innovation and differentiation in formwork, shoring, and materials handling than in buying and installing the concrete and steel. Further, if one assumes a fairly uniform productivity among skilled, motivated workers, the difference in form and shoring costs will come from the selection and volume of materials; the amount of labor needed for assembly; disassembly and moving; required equipment; and, of course, the number of times the forming materials can be reused.
The critical reuse factor is only partly under the contractor's control. Durability and required maintenance of form and shore materials are critical, but even more important is the regularity of structural dimensions throughout the building. Uniformity of beam depth and width, column spacing, and column cross section define the degree to which forms can be reused as is or economically reconfigured as work progresses. Much of concrete's attractiveness as a structural material is that nonstandard dimensions, sizes, and shapes are possible, but increased formwork cost can result when exercising that flexibility. Experienced designers recognize that unless the form or function of the project requires a wide variety of formed structural shapes, attention to details and dimensions that allow for repetitive forming and shoring can have more impact on overall construction cost and duration rather than optimizing structural cross sections alone.
A contractor's investment in form and shore materials and equipment can be amortized further by reusing it on a subsequent project. Here again the uniqueness made possible by structural concrete works against the likelihood of using custom-made forms on a subsequent job, putting a premium on standardized components that can be reassembled into new configurations. Although estimators imagine the ability to ship form and shore materials from one project to the next, reality is somewhat different. When that “next and perfect” project is not ready, materials are cleaned and repaired minimally onsite, loaded up, and shipped back to a storage facility.
Now off the project budget, corporate overhead is incurred at the yard in unloading, removing nails, sorting out cracked, bent, and broken parts, oiling, and restacking. Although there is hope that the forms can be used on another project, the longer the forms remain in storage the more likely it is that they will be moved outside and exposed to the elements. The longer they are stored, the more likely pins, connectors, bolts, and other accessories get separated and storage becomes a burden. The ideal opportunity for reuse has to occur before the materials wear out, before rehabilitation costs get prohibitive, or before the forms are forgotten.
Note, too, that form and shore materials have to be purchased early in the project, well before any substantial work has been completed. From an accountant's point of view, this means considerable expenditure of funds prior to any significant payments from the owner. Depending on the contractor's cash situation, leasing or time payments may be better options.