Stirrups play a crucial role in reinforcing concrete structures, particularly in countering shear failure and securing longitudinal bars. Understanding how to determine the cutting length of stirrups is fundamental to successful construction.
Various shapes of stirrups are used in construction, each with its unique cutting length. Let’s explore the process of calculating the cutting length for different stirrup shapes.
Rectangular stirrups are among the most commonly used shapes, particularly in beams and columns. Let’s take a detailed look at how to calculate the cutting length for a rectangular stirrup.
Let’s break down the process into simple steps:
Step 1: Determine the Dimensions
Start by studying the size of the beam or column on the construction drawings. In our example, we have a rectangular column with dimensions 300 mm × 600 mm.
Step 2: Bar Diameter and Concrete Cover
Check the diameter of the bar intended for the stirrups. Typically, an 8 mm diameter is used for stirrups. Also, consider the concrete cover, which is the distance between the outer surface of the stirrup and the nearest edge of the concrete. In our case, it’s 25 mm.
Step 3: Calculate the Outer Length of the Stirrup
To find the outer length of the stirrup, subtract the concrete cover from each dimension. For the length (A), it’s 300 – 25 – 25 = 250 mm. For the width (B), it’s 600 – 25 – 25 = 550 mm.
Step 4: Determine Hook Length
In our example, there are two hooks in the stirrup. The total hook length is 18d, where ‘d’ represents the diameter of the bar. Here, it’s 18 × 8 mm = 144 mm.
Step 5: Calculate Bend Length
Inspect the diagram to identify the bends. In this case, there are three 90° bends and two 135° bends. The total bend length is 12d, where ‘d’ is the bar diameter. So, it’s 12 × 8 mm = 96 mm.
Step 6: Calculate the Cutting Length
Finally, calculate the cutting length of the rectangular stirrup using the formula:
Cutting Length = Perimeter of stirrup + Hook Length – Bend Length
In our case : Cutting Length = 2 × (250 + 550) + 144 – 96 = 1648 mm or 1.648 meters.
By following these simple steps, you can accurately determine the cutting length of rectangular stirrups for your construction project. This ensures that you have the right amount of materials and helps maintain the structural integrity of your beams and columns.
