Rebar standees are reinforcing bar assemblies that support top mats of reinforcing bars in thick concrete members, such as footings and slabs. In this article, you will learn more about how rebar standees work, different types, and design considerations.
How Do Rebar Standees Work?
Many concrete applications include rebar, often known as reinforcing bar. Its primary purpose is to increase the tensile strength of the concrete, which will help it resist cracking and breaking. Concrete withstands breaking under tension better if it has a higher tensile strength.
Standees, generally fabricated from reinforcing bars, provide a common form of bar support. This especially holds true for heavy mats of reinforcement or supporting mounts located at relatively greater heights.
Different Rebar Standee Types
The most common rebar standee types include bend type 25, bend type 26, shape 27 and shape S6.
Bend Type 25
Bend Type 25 is primarily used in swimming pool frames, road, and highway paving. Other applications include patio and driveway construction as well as vineyards. For agricultural application, it assembles into a trellising system. The carbon-steel composite’s expansion coefficient is comparable to the properties of industrial-grade concrete.
Bend Type 26
While Bend Type 26 is the most stable standee due to the vertical load on the legs, its height is not adjustable. the same holds true for Shape 27.
Shape 27 provides a modified Bend Type 26 used by some fabricators, especially near slab edges. Because both feet point in the same direction in Shape 27, it tends to tip. The legs may require a tie-down. Migration of shape 27’s tendency to tip can occur by alternating the direction of the legs from one standee to the next.
Type 25, 26, and 27 are multiple-plane bend bars. They do not lie flat and thus are termed “special fabrication” in the industry.
Shape S6 allows for a single-plane shape that fabricators can bend on a standard tie bender. In addition, its height adjusts simply by spreading or moving the legs closer together. Tall standees have a tendency to twist under heavy loading. Thus, this may require lateral bracing.
Shape S6 allows for the dimensions “A” and “G” to be specified and is usually not the standard hook extension dimensions.
Legs A and G pull apart in the field, in a direction perpendicular to the original plane of the legs, to create the desired height of the standee similar to Bend Type 25. It’s important for engineers to properly specify the “B” and “D” sides. This ensures correct standee height once the legs are pulled apart or splayed.
The illustration below depicts the many types of bar supports found in foundation mats and footings. To prevent settlement or piercing into the base material, most reinforcement supports for these applications feature more expansive bearing surfaces on their base. Precast concrete blocks (Dobies) or “sand plates” on standard composite or steel supports can be used as supports.
The design of the support system for the top steel must provide for a large margin of safety, and many jurisdictions require that systems with heights exceeding 4 ft (1.2 m) be designed and stamped by an engineer.
There are no set rules for determining the size of the reinforcing bar to use while making a standee. Many detailers choose bar sizes based on their previous work. According to industry standards, the standee bar size should be about one size smaller than the bars to be supported. Of course, this can change depending on the spacing of the supporting steel, the number of top layers, and the standee height.
When engineers undertake an analysis, it should include a column stability analysis on a standee leg. In any case, it’s a good idea to cooperate with the bar placer when it comes to installing the reinforcement and bar support systems. The breadth of the standee should be sufficient to create a proper flat length along the top, preventing the supporting bar from rolling off.
Provided standees adequately brace against lateral and twisting movement, they can install to any depth. However, many engineers require some other kind of support when the support height exceeds about 6 ft (1.8 m). Scaffolding provides a common solution, as well as frames or trusses made of welded reinforcing bars or structural steel angles.