SOLIDWORKS, 3D CAD

National STEM Day - Part 1: Building a Truss with SOLIDWORKS

By Wayne White on November 8, 2018

I was fortunate to have the opportunity as a high school student to learn engineering and architecture through a program similar to STEM. I used this as a stepping stone to go to college for mechanical engineering. Then I found a great career with a large automaker and started really learning about practical applications. 

What is STEM, What's its purpose?

STEM stands for Science, Technology, Engineering and Mathematics. The purpose of STEM is to provide students with the necessary skills to understand technological challenges of the future. I really do feel that my high school experience in the STEM-like program helped to shape my career and future success. This experience is especially poignant and, as a new father, I hope that one day that my children will have every opportunity to learn math, science and more.

 >> Click here if you want to learn about your STEM type

In honor of National STEM Day, for the young minds among us, we’ll take a peek at some structural engineering. For this article I’ll be using a few STEM kits I purchased online (here is a kit I picked up for about $30) as well as SOLIDWORKS.

 

Project: Building a simple truss in SOLIDWORKS

Types of Forces:
  • Compression is the force that squeezes a material. If material is elastic, it will shrink. Materials strong under compression include wood, steel, reinforced concrete.  
  • Tension is the force that pulls material apart, the opposite of compression. Materials that are good in tension are wood, rope, steel. 
  • Bending is the force that bends a material, a combination of compression and tension.  
  • Shear is the force that tears a body. The direction of the 2 forces is opposite to one another. 

The book I'm using goes on to explain torsion, distributed, static, and dynamic loads, point loads, dead and live loads, etc. This is a great first pass before talking at length in school about summation of forces about a given point, and doing multiple matrices to solve for static equilibrium.  

Application of SOLIDWORKS 

I wanted to compare two simple things: (1) the truss above the bridge bed, and (2) the truss beneath the bridge bed. This is meant to be a simple comparison, but in any design competition there are variables and constants. For this problem I assumed that the span would be a constant, but I could vary number of elements and other aspects. Of course, every design competition is different, so pay attention to the rules! 

SOLIDWORKS does a great job with weldments. Weldments are basically shapes that don’t change across a length, such as extruded square tubing. To that end, there’s a great amount of control over the trim and how corners are applied. Additionally, we can create nicely formatted cut lists while using weldments. There’s a lot of great videos and blog articles out there that review editing weldments on our website, as well as our YouTube Channel so make sure to check them out! 

Here is the skeleton of what the truss will look like before the weldment is applied. 

skeleton of what the truss will look like before the weldment is applied

We’ve defined our own profile called STEM Profile that is the correct dimensions for the truss design. 

Truss design in SOLIDWORKS

Application of material is vital to the simulation study. In this case, ABS within our SOLIDWORKS material database will give us elastic modulus, Poisson’s Ratio and other important data that will impact our deflection and stress results. 

important data that will impact our deflection and stress results

Let’s add in SOLIDWORKS Simulation- super simple- if you have SOLIDWORKS Premium or the Simulation Suite, just click your command manager and SOLIDWORKS Add-ins, Simulation. 

SOLIDWORKS Simulation

Because we used weldments, we can use a special element type within Simulation called beams. This allows for quick work so long as we define our joints effectively. We are assuming that the joint won’t fail. We are also assuming that the profile of the weldment is solid. Of course, these assumptions are not entirely accurate. However, if the cross section is a constant, we should be able to vary the structural shape and see the direct comparison. 

5

In our result, we see a dramatized version of deformation and stress as the actual deformation would be too small to see.

example of deformation in SOLIDWORKS Simulation

That’s great, but what about other design ideas? 

Modifying our shape for the lower truss analysis is quick work. Again, we’re keeping our span a constant. 

modifying the shape for the lower Truss in SOLIDWORKS

We apply the same constraints and loads, 50 pounds directly normal to the top of our structure. 

8

So, what do we see? 

It looks like the upper truss wins in this test with about 60% less deflection. Not bad for a first iteration. We could continue forward with other iterations, shapes, supports, and see the impact of our change. 

If you like math and technology, this could be a good path for you to get into structural or mechanical engineering. There are a lot of math, static calculation and matrices coming your way! 

Continue to Part 2