HowtoBuild.cc presents – Concrete Form Design

The form work that we create for concrete construction must be designed to  be strong enough enough to support the plastic concrete until it has hardened.

If one fails to provide for adequate form strength form failure will cause most unfortunate results. Concrete forms must be designed for the total of the combined weight and stresses that they will be subjected to. These stress includes the weight of the forms themselves ( not insignificant when building using steel forms ) the weight of the plastic concrete in the form work once poured, the additional weight of the men working on the pour along with their equipment and materials, and any effects from the applicataion of mechanical vibrators

Quite obviously each of these factors will vary considerably with each project and some care must be taken to consider each one on each new form design.

For commercial reasons the ease with which a team can erect and take down  concrete formwork is also important factor in the design of your forms.

On occasion it maybe more economical to design and plan for platform and ramp structures to provide access for the workmen and their heavy equipment separate to the concrete formwork itself.

Hydrostatic Pressure & Concrete Form Design

When plastic concrete is placed in forms it exerts some “hydrostatic pressure” on the form support. We commence basic form design  therefore but reviewing the maximum pressure produced during placing the concrete, which in turn depends on the rate at which the concrete is placed and the temperature. The volume rate that you place the concrete affects the pressure exerted on the forms because this rate affects how much hydrostatic pressure build up follows.

The pressures associated with hydrostatic head increase continuously until the concrete takes its initial set ( normally in around ninety minutes ) However at lower temperatures the initial set will occur far more slowly. This is why we must factor into account the temperature at the time of placing concrete.

By knowing these two external factors and the material that the form will be constructed from it is is possible to calculate and good preliminary concrete form design.