This article will discuss the input parameters in the Distributed Loads table and gives some worked examples on how to input distributed loads into Calcs.com for structural design applications.
Input Parameters
| Parameter | Description |
|---|---|
| Start Location (A) | The distance from the left end (zero point) of the beam where the load begins. Measured in feet. |
| End Location (B) | The point where the load ceases to act, measured from the left end (zero point) of the beam. Measured in feet. Use ‘L’ for the right end of the beam. |
| Tributary Width (C & D) | The width of the area from which the member obtains its load. See the explanation below for details. |
| Load Magnitude (E) | The pressure magnitude, entered in Pounds per Square Foot (PSF). Click the cell to open a table where you can select the load type and enter the value. |
Understanding Tributary Width
Every structural element has an area from which it obtains its load. As with any other area, this can also be expressed as a product of length and width. The length of this area is usually either the length of the element itself or the length of the distributed load (B-A from the table). Tributary width is simply the width of this area. To better illustrate this concept, consider a floor that is supported by members spaced ‘s’ ft apart.
Key Concept: For most cases, the tributary width is the same as member spacing.
- The starting and ending tributary widths will be different
- You’ll need to enter different values for Total Start Tributary Width and Total End Tributary Width
Load Magnitudes
When you click on the Load Magnitudes cell, a new table will appear (see below).
- First Column: A drop-down menu from which you can choose your load type.
- Second Column: You can input the magnitude of the load in Pounds per Square Foot (PSF).
Examples
Example 1
Task
Input a live load of 40psf on a floor joist with a member spacing of 1.33ft.Method
1
Set the Range
Enter 0 for Start Location and L for End Location to apply the load to the full beam.
2
Define Tributary Width
Input the member spacing (1.33ft) into both the Start and End Tributary Width cells.
3
Apply Load Magnitude
Click the Load Magnitudes cell, select Live Load from the dropdown, and enter 40 in the magnitude field.
Example 2
Task
Input a dead load of 10psf on a ceiling joist with a member spacing of 2ft.Method
1
Set the Range
Enter 0 for Start Location and L for End Location to apply the load to the full beam.
2
Define Tributary Width
Input the member spacing (2ft) into both the Start and End Tributary Width cells.
3
Apply Load Magnitude
Click the Load Magnitudes cell, select Dead Load from the dropdown, and enter 10 in the magnitude field.
Example 3
Task
Input a roof live load of 20psf and a dead load of 15psf on a rafter with 1.33ft member spacing.Understanding Load Orientation (Rafters Only)
Understanding Load Orientation (Rafters Only)
In the calculator for rafters, you will notice that there’s an additional column in the distributed loads table (as shown in the image below).
This column refers to the orientation of the line of action of the specified load. There is a drop-down menu from which you can choose either gravity or allied.
This column refers to the orientation of the line of action of the specified load. There is a drop-down menu from which you can choose either gravity or allied.- Gravity: The load always acts vertically downwards. e.g. weight force
- Allied: The load acts perpendicular to the surface of the structural element. e.g. wind
Method
1
Set the Range
Enter 0 for Start Location and L for End Location to apply the load to the full beam.
2
Define Tributary Width
Input the member spacing (1.33ft) into both the Start and End Tributary Width cells.
3
Apply Multiple Load Magnitudes
Click the Load Magnitudes cell to open the load table. Add two rows:
- Select Roof Live Load and enter 20 in the magnitude field
- Select Dead Load and enter 15 in the magnitude field
