Duct Banks & Manholes
Duct banks present an excellent prefab opportunity. By prebuilding cages with rebar and conduit preinstalled, countless hours can be saved on the jobsite. Examples shown are for concrete encased reinforced duct banks, but the same principals apply to nonreinforced and / or encased.
Manholes are another example of a prefabricated assembly. There are very few contractors that pour in place. Detailing before release of the manufacture will get terminators of the correct number and location as well as holes for ground wires, support embeds, and pulling eyes cast in place, as well as specified lids. Services of a licensed structural engineer may be required for loading calculations, although many precast manufacturers provide this service in house.
Manholes are another example of a prefabricated assembly. There are very few contractors that pour in place. Detailing before release of the manufacture will get terminators of the correct number and location as well as holes for ground wires, support embeds, and pulling eyes cast in place, as well as specified lids. Services of a licensed structural engineer may be required for loading calculations, although many precast manufacturers provide this service in house.
The Tools
- Several trailers to move completed assemblies to trench.
- Equipment for placing prefabricated cages in trench.
The Best Practices
- 20' lengths of conduit eliminates half the gluing labor and half the linear shrinkage loss.
- Unless you wish to become adept at tying rebar, a rebar fab shop can prefabricate to your specifications.
- Determine the specified lap length required by specification and order horizontal bars equal to 20 feet plus lap minus.
- Duct templates can be used as an alternative to the many spacer offerings.