As a general rule, a rebar cage for a drilled shaft consists of longitudinal bars that are distributed with equal spacing along the perimeter of a cylinder. To reinforce these bars, steel is placed transverse to the bars, attached with ties, clamps or welds.

Drilled Shafts: US DOT , IDOT. IOWADOT, MODOT, NYDOT, PENNDOT. CDOT,WISCDOT, KANSASDOT, KYDOT, OHIODOT, NJDOT

The American Society for Testing and Materials (ASTM) specifies several steels that can be used for reinforcing drilling shafts, availing in the Annual Book of ASTM Standards.

Most of these ASTM steels are also designated by the American Association of State Highway and Transportation Officials (AASHTO) as appropriate for use in building rebar cages for drilled shaft construction.

Generally, the steel that is usually available for these cages is AASHTO M 31 (ASTM A 615) in Grade 40 or Grade 60.  If welding is necessary, then weldable steel, such as ASTM A 706, can be used.

Longitudinal Rebar

The main role of the longitudinal reinforcing steel in rebar cages for transportation structures is to resist stresses due to bending and tension.   The reinforcements must be strongest within the top diameters of the ground line, diminishing rapidly with depth.  The highest number of longitudinal bars will be required in the upper section of a drilled shaft, with some bars eliminated as the depth increases.   As a general rule, longitudinal bars should be spaced evenly around the rebar cage. If there are six or more bars in a symmetrical cage, then the bending resistance is almost equal in any direction.

There should be sufficient clear space between the longitudinal bars, as well as the transverse bars or spiral loops to allow free passage of the concrete through the cage.

This is particularly important because drilled shaft concrete is placed without vibrating the concrete.

Transverse Rebar

There are four primary purposes of transverse reinforcement bars in rebar cages during drilled shaft construction.

1. Resisting the shearing forces that act on a drilled shaft.
2. Holding the longitudinal steel in place during construction.
3. Providing the drilled shaft with enough resistance against compressive or flexural stresses.
4. Confining the concrete in the core of the cage to give the drilled shaft post-yield ductility. Transverse reinforcing steel is provided in one of three forms: ties, hoops or spirals.

Sizing Hoops or Crush ring

To assist in the fabrication of the rebar cage, sizing hoops are often constructed.  These hoops also ensure that the finished cage diameter is correct. The sizing hoop functions as a guide for the fabrication of the rebar cages and is often made of plain rebar or thin rolled-plate stock.  Sometimes called a “gauge hoop,” a sizing hoop can also be made with a lapped splice or with the ends of the hoop butt-welded.

Sign Structure Rebar Cages

Overview:

Adaptive signal control technology (ASCT) adjusts the timing of red, yellow and green lights to accommodate changing traffic patterns and ease traffic congestion. Outdated traffic signal timing incurs substantial costs to businesses and consumers. Real-time management of traffic systems is proven to work, yet these systems have been deployed on less than 1 percent of existing traffic signals. FHWA is now working to bring these technologies to the rest of the country.