Day 124 – Bridge Breaking



Engineering Physics – I finally built my bridge testing apparatus.  A bottom beam sits on two bathroom scales.  Another beam slides on threaded rod which is attached to the bottom plate, and by tightening the nuts on the rod, the top beam compresses the bridge truss and bottom beam against the bathroom scales.

The bottom picture shows the bridge truss that withstood the greatest force.  Lots of bridges failed at glue joints which surprised me. I need to look into that for next year.

Day 116 – Bridge TRU Results

Engineering Physics – Today I received the results from the Thompson Rivers University.  As you can see, there is a pretty big jump from the 6 to the rest of the contestants.  My students are further down the list. I’m confident that one team’s design was solid but their construction was a bit off – some of the popsicle sticks were a bit crooked and the bridge likely twisted and failed because of the twisting.

Day 110 – Two Bridges for TRU


Engineering Physics 12 – Two groups finished their bridges and wanted to be a part of the TRU bridge competition.  The top bridge was designed based on the group’s first attempt where they analyzed the failure mode(s) and reinforced those areas. I can get behind that kind of iteration design at this level.  The bottom design is known as being a strong structure, based on web searches.  There aren’t a lot of unknowns in long-running bridge competition that doesn’t change the design parameters…  In any event, they worked hard on the build and did their best to pay attention to small details.  We’ll see how they do.

Day 102 – More Clamps


Engineering Physics – Students continue to work pretty well on their bridges.  I’ve brought in as many clamps as I can, but more clamps would be mo’ betta.  I’ve suggested that students go out and get their own packages of binder clips, which work very well.  I upgraded our glue to Lepage.  When I get the chance we will try to find its shear strength compared to the Staples glue.

Day 100 – TRU Bridge Contest


Engineering Physics – Students are now challenged with designing their own truss/bridge, which they will put in the Thompson Rivers University Bridge Contest.  Some students are experimenting with Bridge Designer software, others are working on their own designs based off of what we’ve already studied. Some groups are doing web searches for past TRU contest winners…

Day 98 – Breaking Bridges


Engineering Physics – Today we broke the bridges that students made. The previous attempt to break them was messy: I was hanging a bucket from the bridge where the bucket contained sand and hanging masses.  The buckets weren’t heavy enough so we then started stacking textbooks on top of the brides.  Once we got to 40 kg I called it off, as I didn’t want spilt sand and textbooks all over the place.

I built this bridge press in about 30 minutes, plus another hour for going out and buying the threaded rod.  The nuts gradually press the top beam down on the bridge and we monitor the bathroom scale for how much force is applied. Students used their phones to video record the scale because once the bridge breaks, the reading drops instantly.

There weren’t many broken popsicle sticks, almost all of the failures were with the glue. We used Staples washable white glue because it was cheap, but I wonder if the “washable” part makes the glue a lot weaker.


Day 90 – Popsicle Bridge


Engineering Physics 12 – Students started working gluing together their first popsicle bridge.  They were given specific plans and instructions on their build and I handed out three different truss designs: Warren, Pratt and Howe.

The idea here is that they will have some practice in clamping and properly assembling a bridge.  The next step after this will be for them to use their knowledge of truss/joint analysis to design and build their own bridge for the TRU bridge contest.