Welcome to my blog post about "Rebar in Concrete Footings". As a concrete contractor specializing in concrete construction, I understand the importance of reinforcing concrete footings with rebar.
In this post, I will be discussing the various types of footings used in concrete construction, including slab, foundation, pier, deck, and column footings.
I'll explain the different types of rebar available, recommended sizes and spacing of rebar, tying vertical wall reinforcement, code requirements, and how to calculate the amount of rebar needed for a specific type of footing.
Rebar is a vital component in concrete construction that enhances the strength and durability of concrete footings, making them more resistant to tensile and compressive forces. By using rebar, you can prevent structural failure and ensure that your building is strong and long-lasting.
Using rebar for concrete footings is important for several reasons:
Rebar, short for reinforcing bar, is a steel bar or mesh of steel wire used to strengthen and hold the concrete in tension. It's essential in footings because it helps to distribute loads and resist cracking and shifting, ensuring the overall stability and longevity of the structure.
Types of rebar
Rebar sizes and grades
This table serves as a general reference, and the specific rebar size requirements for a particular project should be determined by consulting a structural engineer or following the appropriate building codes and design specifications.
|Footing Type||Suggested Rebar Sizes|
|Residential Wall Footings||#4, #5|
|Column Footings||#5, #6, #8|
|Deck Footings||#4, #5|
|Slab Footings||#4, #5|
|Grade Beams||#5, #6, #8|
|Retaining Wall Footings||#5, #6, #8|
|Bridge Pier Footings||#8, #9, #10|
|Industrial Footings||#6, #8, #10|
What size and type to use:
The size and type of rebar used in concrete slab footings will depend on the specific requirements of your project, including the size of the slab, the load it will support, and local building codes.
Common rebar sizes range from #3 to #6 for slab footings, with #4 being the most commonly used.
As for the type of rebar, steel rebar is the most common choice due to its excellent strength and durability. However, other types of rebar, such as fiberglass, stainless steel, galvanized, or epoxy-coated rebar, can be used depending on the specific needs of the project, including corrosion resistance or specific environmental considerations.
How many rebars to use in the footing:
The number of rebars used in a slab footing will depend on the footing's dimensions, the spacing of the rebar, and the required reinforcement.
Most slab footings 24" wide have 2 or 3 bars laid in a flat horizontal position throughout the entire footing length.
The placement of rebars in the footing:
In slab footings, rebars are typically placed in a grid pattern, with both horizontal and vertical bars intersecting at regular intervals. This grid provides a balanced reinforcement throughout the slab, ensuring adequate tensile strength and crack resistance.
Horizontal rebars, also known as main bars, are placed parallel to the length of the slab, while vertical rebars, or distribution bars, run perpendicular to the main bars. The rebars should be supported by chairs, spacers, or bar supports to maintain proper positioning and concrete cover during the concrete pour.
How far apart should rebar be in a slab footer:
Rebar spacing in a slab footer will depend on the size of the slab, the load it will support, and local codes. Generally, rebar spacing in slab footings ranges from 12 to 24 inches, both for horizontal and vertical bars.
How to install rebar in slab footings:
To install rebar in slab footings, follow these steps:
It is essential to consult with a structural engineer or follow local building codes to determine the appropriate number of rebars and spacing needed for your specific application.
The placement of rebar in foundation footings involves several steps to ensure proper reinforcement of the footing and foundation. Here is a general guideline on how to install rebar in foundation footings:
The most commonly used rebar size for concrete deck footings and sonotubes is #4 (1/2-inch diameter) or #5 (5/8-inch diameter) rebar. These sizes provide adequate reinforcement and tensile strength for typical deck applications.
In a sonotube, vertical rebars are commonly used to reinforce the concrete. The number of rebars needed depends on the diameter of the sonotube and the load requirements of the deck. A common configuration for deck footings is to use 4 vertical rebars evenly spaced around the interior of the sonotube.
For larger sonotubes or higher load requirements, you might need to increase the number of rebars or consult a structural engineer for guidance.
In addition to vertical rebars, you may also need horizontal stirrups (circular or square-shaped) within the sonotube to provide additional reinforcement, especially in areas prone to seismic activity. The horizontal stirrups are placed at regular intervals along the length of the vertical rebars, with the spacing determined by the specific needs of the project.
Incorporating rebar into pier footings is crucial for reinforcing the concrete and ensuring the structure's stability and durability. We typically advise using at least two pieces of #4 rebar (1/2-inch diameter) placed vertically in an 8-inch-diameter concrete pier that supports a structure.
This reinforcement provides additional tensile strength to the pier, reducing the risk of cracking and improving its load-bearing capacity.
For larger-diameter piers, it's essential to increase the amount of vertical rebar to maintain the necessary reinforcement. In these cases, it's advisable to use four or more pieces of vertical rebar, depending on the pier's diameter and the load requirements of the structure.
Rebar is essential for reinforcing concrete columns, as it helps resist tensile forces that can cause buckling or bursting. To create a rebar "cage" for a column cut four vertical No. 4 rebar pieces to span from the top of the column to the bottom of the footing.
Bend the last six inches of each bar at a 90-degree angle to form an L shape, allowing three inches of clearance above and below the rebar.
Next, cut No. 3 rebar to create rectangular stirrups that will encircle the vertical bars, spaced one foot apart vertically. Bend the stirrups and secure the overlaps with securing ties (wire).
Insert the vertical bars into the stirrups, tying the top and bottom ones first to establish the cage's shape. Ensure the L-shaped bottom points away from the column center.
Slide the remaining stirrups into position and tie each corner to an upright bar. Place the completed cage in the footing using dobies (small concrete blocks) to maintain spacing, with three inches of clearance from the footing bottom and the column top.
Pour the footing with the rebar cage in place, and when it dries, build the column forms around the rebar.
The code requirements for rebar being used in concrete footings vary depending on the jurisdiction and the specific building codes in your area.
However, there are some general guidelines provided by the American Concrete Institute (ACI) that serve as a basis for many local building codes:
VERTICAL REBAR REINFORCEMENT:
Calculating the amount of rebar needed for a concrete footing requires knowledge of the footing's dimensions, the required rebar size, and the spacing between the rebars. Here's an example of a foundation footing to estimate the rebar needed for this type of footing:
Calculate the Perimeter of Your Concrete Foundation. Suppose you have a foundation that is 120 feet long and 50 feet wide. To calculate the linear footage of your footing, remember that a linear foot is a one-dimensional measurement, not to be confused with a square foot. You need to add all sides lengths of your footing instead of multiplying the length by the width.
Here's the formula: 50 + 50 + 120 + 120 = 340 linear feet. Now, let's determine how much rebar you need for this length.
Typically, footing rebar requirements include one rebar for every 8 inches of footing width. If your footings are 16 inches wide, you'll need two rods across the width of your footings.
To calculate the total rebar needed, multiply the linear footage of your foundation (340) by the number of rebar sticks required across the width of your footings (2). This gives you 680 lineal feet of rebar.
Rebar is typically available in lengths of 10, and 20, feet. To determine how many rods you need based on these available rebar lengths, you can divide 640 by 10 (64 bars) or 640 ÷ 20 for 32 bars, the amount you choose will depend on your desired length.
For more help calculating how much rebar in footings you need, try this rebar calculator.
Tying the rebar together is an essential process to ensure the proper positioning and spacing of the rebar within the concrete. This helps to maintain the structural integrity and strength of the footing.
There are several methods used today to tie steel rebar in footings, including manual tying, loop wrap and saddle tie, and using rebar tying tools. Here's an overview of these methods:
Manual Tying: Manual tying is the traditional method of tying rebar, which involves using a tie wire to bind the intersecting rebars together. Here are the steps for manual tying:
Double Loop Ties: Rebar loop ties are pre-formed wire ties (with loops on each end) designed for a quicker and more efficient method of tying rebar. They come in various lengths and can be used with a yo-yo tie tool. To use a loop snap tie:
Battery-Powered Rebar Tying Tool: Rebar tying tools, such as battery-powered rebar tier machines, are designed to make the process of tying rebar faster and more efficient. These tools automatically wrap and twist the tie wire around the intersecting rebars, significantly reducing the time and effort required. Here's how to use a rebar-tying tool:
Setting vertical rebar in footings is crucial for providing structural stability and reinforcement to your concrete basement walls. Here are some basic guidelines to follow when setting vertical rebar in footings:
Bending rebar can potentially weaken it if not done correctly. When rebar is bent beyond its specified bend radius or subjected to excessive force, it can lead to stress fractures or cracks, which may compromise its structural integrity.
However, if the bending process is performed according to the recommended guidelines and with the appropriate tools, it will maintain its strength and continue to provide the necessary reinforcement for concrete structures.
Here are some tools commonly used to bend rebar:
Here are different methods commonly used to cut rebar:
Yes, it is possible to put too much rebar in a concrete footing, which can lead to issues with the overall performance and structural integrity of the footing.
What are beam corner bars used for? Beam corner bars are rebar that is placed in the corners of the beam to provide additional support and strength to the structure. The size and spacing of beam corner bars depend on the weight and size of the structure being supported. Proper placement of beam corner bars ensures that the load is evenly distributed, preventing cracking and structural failure.
Is rebar used in precast concrete? Rebar is placed in precast concrete footings to reinforce them and provide additional support.
It's essential to consult with a structural engineer or refer to your local building codes for the specific requirements related to rebar in concrete footings in your area.
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