placing reinforcing bars pdf
Placing of the Reinforcing steel is often done by ironworkers on major construction projects; however, most contractors are responsible for at least a portion of the reinforcement. It is essential to the performance of the structure that it be positioned correctly and maintained in that position while the concrete is placed.
The placement drawings should be followed precisely while putting in reinforcements. The detailer will specify the number of bars, bar lengths, bends, and placements at this point. Although there are several pdf formats for this subject, we have covered it in this article.
Cover
One of the most significant reasons for correct placement of the reinforcing steel is to obtain the appropriate quantity of concrete cover. Concrete cover refers to the amount of concrete that is placed between the surface of the concrete member and the reinforcing steel.
When it comes to preventing corrosion of reinforcing steel, cover is hands down the single most critical aspect. Cover is also required in order to guarantee that the steel will form strong enough connections to the concrete in order to enhance the structure's strength.
In most cases, the specifications for the project will include a listing or an illustration of the criteria for minimum cover. The ACI 318 Building Code will specify the minimum cover required for cast-in-place concrete in areas where it is not specifically stated.
Positioning
It is essential to keep in mind that the blueprint for the building relies on the steel being installed in the appropriate locations in order to function properly.
Serious concrete structural failures can be caused by, and have been caused by, improper installation of reinforcing steel. For instance, if the top bars were lowered or the bottom bars were raised by half an inch more than what was specified in a slab that was 6 inches deep, the load-carrying capacity of the slab would be reduced by 20%.
It is not an acceptable approach for placement to position reinforcement on top of a new layer of concrete, and then to pour additional concrete on top of it.
You are required to make use of reinforcing bar supports, which can be fabricated from plastic, precast concrete, or steel wire. To accommodate the wide range of reinforcing bar sizes and positioning options, chairs and supports can be purchased at a variety of heights. In most cases, the cost of plastic attachments is significantly lower than that of metal supports.
There are three tables in either the Ready Reference Reinforcing Steel Resource Guide published by the Concrete Reinforcing Steel Institute or the time-tested Placing Reinforcing Bars book. These tables display the majority of the currently available supports in the various materials and describe the circumstances in which each can be utilized most efficiently.
It is not sufficient to just place the bars on the supports. To prevent reinforcing steel from moving about during construction activities and the laying of concrete, it is necessary to secure the material. Tie wire is typically used for accomplishing this task. The coils of tie wire weigh either three or four pounds each.
For ease of access, the wires are either stored in a wire holder or wound onto a reel that is strung from the worker's belt. The wire is normally a black, soft, annealed wire that has a gauge of 1612 or 16. However, stronger reinforcement may require wire with a gauge of 15 or 14 in order to retain the rebar in the correct position.
In the industry of concrete reinforcing, a wide range of ties, which are essentially wire twists used to link intersecting bars, are utilized. These ties include snap ties, saddle ties, and everything in between. Placing Reinforcing Bars by CRSI provides an illustration of the various sorts of ties as well as a description of the circumstances in which each type is most effectively utilized.
PVC ties should be utilized when securing epoxy-coated bars together (available from American Wire Tie). There is also the option of purchasing proprietary snap-on ties, such as the Speed-Clip Rebar Tie manufactured by Con-Tie Inc. This is a straightforward tool for manually attaching rebar in parallel or at any other angle desired. There is no need for any tools.
When tying bars, it is not necessary to tie each junction; instead, it is typically adequate to bind every fourth or fifth intersection.
Keep in mind that the tie does not contribute any strength to the structure; therefore, more ties are only required when there is a possibility that the steel could become moved during the laying of the concrete. Make sure the ends of the tie wires are kept away from the surface of the concrete, where they could rust, since this will prevent corrosion.
When working with preassembled mats or reinforcing steel, you must tie sufficient intersections to ensure that the assembly is solid enough to be placed; normally, this includes every intersection around the outside and every other intersection in the middle of the mat. Tack welding the junctions, which would diminish the cross section of the bars, is normally not allowed for this same reason.
Placement tolerances
Even while the bars should be placed in a position that is as near to the required one as is practically practicable, there will still be some variation.
Tolerances for rebar location are displayed in the table below according to ACI 117, which is titled "Tolerances for Concrete Construction and Materials." Don't forget what this means: an ACI 117 tolerance is the allowable variance from a given dimension. To put it another way, it indicates how far the rebar deviates from what is shown in the plans.
If the clear gap that must exist between the edge of a reinforcing bar and the face of a concrete beam that is 6 inches wide is specified as 2 inches, then the tolerance must allow for no less than 1 5/8 inches.
A tolerance of three inches is allowed for the position of the longitudinal bars. This is because the specific position is not necessary so long as the right cover is maintained and the specified amount of bars are included. The reason for this is that the precise position does not matter.
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