Calculating the amount of steel reinforcement required for various components such as concrete slabs, footings, columns, and beams is a vital step in determining the cost of construction. The design drawings serve as a foundation for estimating the rebar quantity in different structural elements. In this article, we will outline the process of computing the steel quantity for slabs, columns, and footings.
Calculate Steel Quantity for Slab
The task involves obtaining slab dimension and reinforcement details from design drawings, specifically as shown in Fig.1. The goal is to compute the number of steel bars required for the slab.
To do this, we will use two equations. Equation 1 is used to determine the number of main steel bars required and involves dividing the length of the slab by the center to center spacing of the main reinforcement steel bars and adding 1 to the result. Equation 2 is used to determine the number of shrinkage and temperature steel bars required and involves dividing the length of the slab by the spacing of these bars and adding 1 to the result.
It is important to note that the spacing used in equation 1 is the center to center spacing of the main reinforcement steel bars, while the spacing used in equation 2 is the spacing of the shrinkage and temperature steel bars.
Overall, the task involves obtaining the necessary information from the design drawings, applying the appropriate equations to calculate the number of steel bars required for the slab, and ensuring that the correct spacing is used in each equation.
Fig. 1: Types and arrangement of steel bars in one way slab
The cutting length for the main steel bars and shrinkage and temperature steel bars can be calculated using equations 3 and 4 respectively.
For the main steel bars, the cutting length is determined by adding the clear span of the structure (S), the development length (Ld) which can be found in Fig. 2, the inclined length, and two 45-degree bends.
The inclined length can be calculated using Equation 5, where D is equal to the slab thickness minus twice the concrete cover of the bar, and then multiplied by 0.45.
Similarly, for the shrinkage and temperature steel bars, the cutting length can be determined by adding the clear span of the structure (S), the development length (Ld), the inclined length, and two 45-degree bends.
It is important to calculate the cutting length accurately to ensure that the steel bars fit properly within the structure and provide the necessary strength and support.
Fig. 2: Bent up bars in slab
The given context talks about the process of ordering steel bars, which involves converting the length of the bars into kilograms or tons. This process applies to both main and shrinkage reinforcement, as well as temperature reinforcement, and utilizes the same equation. However, specific values such as the cutting length, number of bars, and bar diameter will differ depending on the type of reinforcement.
To calculate the weight of main steel bars, one can use the equation: No. of bars multiplied by cutting length multiplied by the weight of the bar divided by 162. This equation applies a constant factor of 162, which represents the weight of one steel bar in kilograms or tons.
It’s important to note that the weight of a steel bar is derived from its volume multiplied by its density, which is 7850 kg/m3. Therefore, the constant factor of 162 represents the weight of one steel bar that has a specific volume and density.
Overall, this process ensures that the appropriate amount of steel bars is ordered for a construction project by considering the required length and weight of the bars.
Calculate Steel for Footing
To calculate the amount of steel required for a footing, we first need to know the size of the footing and its reinforcement details such as bar size and spacing. This information can be obtained from the design drawings. Once we have this information, we can follow a series of steps to calculate the steel quantity.
The first step is to calculate the number of bars required for both directions using Equation 8, where we divide the length or width of the footing (minus the concrete cover for both sides) by the spacing and then add one. Next, we need to find the length of one bar using Equation 9, where we subtract the concrete cover for both sides from the length or width of the footing and add twice the bend length.
Once we have the number of bars required and the length of one bar, we can calculate the total length of bars needed by multiplying the number of required bars by the length of one bar. If the same size of bars is used in both directions, we can simply sum up the quantity of bars. We then convert this length into kilograms or tons by multiplying the cross-sectional area of the steel by its total length and by the density of steel, which is 7850 kg/m3.
It’s important to note that this calculation procedure is for a single reinforcing net. If the footing has a double reinforcing net, we need to use the same procedure again to compute the steel quantity for the other reinforcing net.
Calculate Steel Quantity for Columns
The task is to determine the column size and reinforcement detailing based on the design drawings, and then compute the quantity of steel required in the column using a set of steps.
To achieve this, one must carefully examine the design drawings to determine the appropriate column size and reinforcement detailing. Once these parameters are established, the next step is to calculate the amount of steel needed for the column.
This calculation can be done by following a set of steps that take into account the size of the column, the reinforcement detailing, and other relevant factors. By carefully performing these calculations, one can determine the precise amount of steel required to reinforce the column to the necessary specifications.
Overall, the process of determining the column size and reinforcement detailing, and then calculating the quantity of steel needed, is a critical part of the design and construction process for any structure that includes columns.
Longitudinal steels
To calculate the total length of longitudinal bars needed for a column, one should first add the column height to the laps for footing. This resulting length should then be multiplied by the number of longitudinal bars required.
To convert this length into either kilograms or tons, one can use the density of steel, which is 7850 kg/m3. This can be done by multiplying the cross-sectional area of the steel by its total length and then multiplying that product by the density of steel. The resulting value will give the weight of the steel in either kilograms or tons, depending on the preferred unit of measurement.
Stirrups
The provided equation, Equation 10, can be used to compute the cutting length of stirrups for a column. This equation requires the column width (w), column depth (h), and stirrup development length (Ld). The cutting length can be calculated by multiplying the sum of twice the difference between the width and cover (w-cover) and the depth and cover (h-cover) by 2, and then adding the stirrup development length (Ld).
To determine the number of stirrups required for the column, the column height is divided by the stirrup spacing plus one. This calculation gives the total number of stirrups needed.
The total length of stirrup required for the column can be estimated by multiplying the stirrup cutting length by the number of stirrups required.
Finally, to convert the total length of stirrup into kilograms or tons, the cross-sectional area of the steel is multiplied by its total length and the density of steel (7850 kg/m3). The total steel quantity of the column is the sum of the main and stirrup steels.