How to Measure the Weight Limits of Steel Trusses
There are numerous variables that must be considered to determine the weight limit of a steel truss. Some factors include the span length, the amount of lateral bracing, acceptable movement and bending and bowing. The American Institute of Steel Construction offers a matrix of basic weight limits but if your conditions do not exactly fit the load tables, you must compute the stresses for each beam in the truss under varying conditions. You can accomplish this by one of two ways, according to Dr. Michael Engelhardt, professor of civil engineering at the University of Texas: either become a civil engineer or use the West Point Bridge Designer software program (see References) that allows you to test the weight limits of all the load bearing components in trusses used to make a bridge. The software program is relatively small, takes only minutes to download and is fairly simple. Does this Spark an idea?
Other People Are Reading
Instructions
-
-
1
Go to the West Point Bridge Designer site and download the 2010 version of the software program to your computer. The site offers both PC and Macintosh programs.
-
2
Click on the "About" button. On the next screen, click "How it Works."
-
-
3
Review thoroughly how the designer software works. The page is referred to as a Help section but in fact it's a printable tutorial. When clicking on such chapter headings as the Overview, How To and Bridge Design, the right side of the window pops up a detailed narrative to familiarize you with the program. It is recommended that you first begin with one of over a dozen pre-designed bridge options that are known to be structurally sound before embarking on determining the weight limits of trusses you have in mind. Print what you need and close the smaller open windows.
-
4
Choose "Load a Sample Bridge" design and click the "Okay" button. Select a sample bridge design that you think might closest represent the type of truss you want to use to determine the weight bearing capacity of the truss you have in mind. You can select from the 10 options. As you click on each, it will give you a visual structural preview of the bridge so you can see what it looks like before selecting one that may be representative of the truss weight limits you want to determine. You can also choose between a solid carbon steel truss and a hollow steel truss. Once you've selected the bridge type, click "Okay" and the screen will display the bridge with trusses, each corresponding to an index on the right side of the page. You will also be shown a toolbar that allows you to add or remove trusses.
-
5
Play around with removing or adding different trusses and then select "View." That will assign a number to each truss member. Click on "Test," then click on "Load Test Results." You will be presented with a table showing the compression force and compression strength exerted on each member of the bridge and the tension force and tension strength of each bridge component, including the trusses. It will also indicate whether or not the status of the design is capable of handling the proposed load. Keep in mind that although this simulator is showing the weight bearing capacity for trusses and components of a bridge, the same load bearing capacities apply no matter what you're building--although there may be additional factors to consider if it's a 100-story high-rise building.
-
6
Start from scratch and design your own bridge with trusses located at your discretion to model the use you have planned. Using a similar method as above, you can determine the test load results for your trusses.
-
1
Tips & Warnings
Print the Help pages to easily guide you through the steps and use of the tools. You will find it extremely helpful, especially the first time using the program.
If you plan on using and printing the Help pages as a tutorial, there are a lot of pages to download, so have an adequate supply of printer paper on hand.
References
- Photo Credit Bridge image by Luke Haverkamp from Fotolia.com
