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Types of rebar spacers or reinforcement chairs & design of rebar spacers

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Rebar alias reinforcing bar should be enclosed in concrete to the exact depth (known as cover) to enhance the strength of the concrete structure when designed.

Rebar chairs and related supports belong to the standard devices which are utilized to prop up the rebar or detach it from the concrete form in order that the rebar is encircled by concrete to retain the certain cover.

While construction work is going on the job site, Rebar Spacer or steel chair is mostly found in raft or mat foundations. It is normally shaped as Z or inverted U type reinforcement to equally detach the top and bottom mesh reinforcement or to arrange adequate space among the meshes. While setting up the main mesh reinforcement throughout construction, steel chairs can retain the spacing uniformly and retain the mesh reinforcement in exact position before and after concreting.

Several types of chairs and other supports are found for various applications. The exact support for any project is based on various factors like the type of surface below the concrete, the type of concrete formwork, and the design specifications.

Standard Rebar Chairs: These types of chairs are extensively used to pick up the rebar off the ground. These are mostly utilized on foundation footings, concrete slabs, and other flatwork. The chairs are formed with metal or plastic or other non-corrosive material. They add strength to the structure. They are lightweight, inexpensive, and easily set up.

Also Read: Some useful guidance to place reinforcement in RCC staircase

Standard steel chairs are equipped with plastic feet to resist spot decay on the concrete surface. The stainless steel chairs are also available and they are non-corrosive and mainly utilized when plastic is not accepted into the concrete or when the weight is heavy for plastic chairs.

Spacer Wheels: Spacer wheels are mainly applied on columns, walls, beams, pre-cast formwork, and round formwork. These are formed with plastic and the wheels contain internal webbing, or framework to retain the rebar at the center of the wheel. Since the wheel is round, it can't overturn like chairs when the rebar is shifted. Spacer wheels are strong and light and make nominal surface contact, and they are accessible with various rebar sizes.

Multi-Level Rebar Chairs: Multi-level chairs are useful for mats or other configurations that entail multiple layers of steel. The multi-level chair is arranged at multiple heights, facilitating you to set up a bottom layer, an intermediate layer, and a top layer, keeping spacing among all of the rebar layers. These chairs generally come with good strength and maintain perfect concrete flow in among the spacers. This solution can save time and money since no support fabrication is required.

Tip or Round Cap Rebar Spacer: A tip or round cap spacer is suitable when rebar is set up vertically and needs bottom or top concrete cover. The cap is set up at the end of the rebar and contains a thin, elongated tip that supports the rebar and places it at an exact height. The tip is also created to facilitate better concrete flow to resist breakouts.

The rebar chairs are designed based on the following standard raft details:

Standard Raft Section

• Raft thickness: 2000mm
• Main Mesh Reinforcement:
• Bottom: T32-200mm both ways
• Top: T25-200mm both ways

Load Calculations - The load is measured on the basis of the weight of the rebar reinforcement in the raft as follow:

• T25: 0.0378 kN/m length
• T32: 0.0632 kN/m length

An extra 1.5kN/m2 live load should be taken into consideration for any construction loads.

The rebar weight is computed with the following formula :-

Types of rebar spacers or reinforcement chairs & design of rebar spacers

Here, D stands for diameter

To get more details on how to work out the weight of rebar, go through the following link. www.thestructuralworld.com

Types of rebar spacers or reinforcement chairs & design of rebar spacers