Rebar Required Intensity
- mert.goktas (Unlicensed)
The determination of Rebar Intensity values is essential for Slab Design, particularly in areas where columns and shear walls intersect with the slab.
The previous page provides the calculation details for Rebar Intensity, while this page lists the individual operations conducted during the calculation process.
Navigate to Slab Result in the BDS tree view and select the relevant floor. Make the following settings.
Direction: Direction 1
Result Case: 1.2D + 1.6L
Type: TopRebarArea
The direction we want to look at is Direction 1. Set the result case to "1.2D + 1.6L", which we think is the most critical case.
The result type should be Top Rebar Area.
The yellow rectangles surrounding the columns represent the density rectangles. For a more detailed explanation, please follow this link: [Top Slab Reinforcements]. This link will provide you with a comprehensive explanation and further information regarding the density rectangles associated with the columns.
In order to perform the calculation, we need to specify a column. Let's select column C2, which corresponds to the upper left corner column.
Now, let's proceed to the results observed on the CAD side.
As per the CAD results for column C2, we can observe 3 Top Rebar Area result strips. To determine the reinforcement design value of the C2 column, we need to draw lines between the strips in the Slab Design section and perform manual calculations.
For this purpose, we need to draw lines each strip that extends to the Slab edge. The length of the area scanned by the strip is measured from the middle distance to the middle distance of the drawn lines. It is important to note that only the distances within the yellow rectangle (density square) are considered as the scanned area.
This process allows you to calculate the impact of the strip, read as a unit distance, on the overall design. Based on the provided screenshot, it is evident that Strip 2 (Value=0.7319 in²/ft) scans an area measuring 16,875 inches.
Rebar Intensity (Area/Unit Width) | ||
Layer | Analysis Source | Column |
1st | Aecbolt | C2 |
Distance (in) | Strip Area (in^2/ft) | Result |
17.625 in | 0.8025 | 14.14 |
16.875 in | 0.7319 | 12.35 |
4 in | 0.3069 | 1.23 |
Total = 38.5 in |
| Total = 27.72 |
Required Intensity → | 27.72 / 38.5 = → | 0.720 (in^2/ft) |
The "Required Intensity" value that was calculated above is utilized for Slab Design in BDS. Using this value, the reinforcement calculation for the slab area that covers the C2 column can be performed.
To access the Slab Design section, please navigate to the BDS tree view and select the relevant floor (in this case, the 5th floor).
Next, navigate to the "Top Reinforcements" section and select the "Column Strip Reinforcements" option. From here, you can compare the required value with the rebar area values obtained from the Slab analysis.
By clicking on the "Compare Required Rebar Area" button, the value that appears for the 1st Layer of the C2 column under the "Aecbolt Results" section should be the same as the value we found earlier.
With the obtained value for the reinforcement calculation of the slab area covering the C2 column, you can proceed with the analysis.
What does "Required Intensity" mean? How would you define "Provide Intensity"? And what is the connection between these two concepts?
Let's delve into the example of column C2. In the context of this column, "Required Intensity" refers to the calculated rebar area that is necessary to ensure sufficient reinforcement, as per the guidelines outlined in the "Building Code Requirements for Structural Concrete (ACI 318-14)" Design Code.
If you define a reinforcement and its range in the design software BDS (Building Design Suite) that falls below the specified "Required Intensity" value as per ACI 318-14, BDS will issue a warning indicating a failure, and the corresponding value will be highlighted in red.
We have designated the use of #6 rebar, spaced 4 inches apart, within the slab area corresponding to column C2. This configuration allows for a total area of 1,320 in^2/ft (square inches per feet) for the slab area of column C2.
For the slab design to be considered structurally sound, it is essential for the "Provide Intensity" value to be equal to or greater than the "Required Intensity" value. (1.320 in^2/ft > 1.229 in^2/ft)
Why is the value different between Aecbolt Results and Required Intensity?
The BDS software offers the option to control the punching shear for the corresponding floor through the "Slab Design" page in the BDS tree view.
If the necessary reinforcement and appropriate spacing, which would provide an adequate "Provide Intensity," are not defined in the Top Reinforcements section for the reinforcement area of C2, a warning message will be displayed, similar to the screenshot. Upon receiving this warning, it indicates that we need to increase the amount of rebar.
Additionally, below the summary spreadsheet, there is a Flexural reinforcement spreadsheet available for further reference and analysis.
By clicking the "Increase Top Reinforcement" button on the "Flexural Reinforcement" spreadsheet, the C2 column will experience an increase in the "Flexural Rebar Required Intensity" value for Direction 1. Specifically, this value will change from "0.721" to "1.23" (0.721 → 1.23).
Why is the Safe Required Intensity value different from the Aecbolt Required Intensity value?
I want to design Slab with only Safe Results or only Aecbolt results. Is it possible?
Yes, it is possible to design a slab using either the "Safe" or "Aecbolt" analysis in the design process. Both methods provide different approaches and algorithms for analyzing and determining the structural integrity of the slab.
If you prefer to rely solely on the "Safe" slab analysis result, you can utilize the calculations and recommendations provided by that analysis method to design the slab. Similarly, if you choose to use the "Aecbolt" Local (slab) analysis results, you can base your design decisions on the outcomes and suggestions generated by that analysis.
If you decide to utilize both the "Safe Results" and "Aecbolt" analysis together in the BDS software, the software will calculate the required intensity based on the most critical value obtained from the two analyses. This approach ensures that the design incorporates the highest level of safety and structural integrity by considering the most demanding conditions identified by both analysis methods.
To make this adjustment, navigate to the Slab Design in the tree view. Select the Analysis Results Sources as in the figure.