Westpoint bridge designer is software that has been written to allow people to enter a competition but you can download and use it for free in schools regardless.
The software allows the user to construct a variety of bridges for a variety of situations, it seems very open ended and easy to get in to. You quickly get drawn into the software and want to improve your work.
The ‘test’ mode creates short film of your bridge under load and shows where struts are under compression and tension and shows buckling and failure. Great stuff.
Oh yes .. it’s free