Truss Spanning Adapter

hi i'm robin deyoung and i'm a structural engineer i'm going to show you the very simple formulas you can use to design a long truss so let's just imagine here we have a very long span of 30 meters and it's perhaps a roof that we're going to support on this and the way that you span such a long length rather than say with a steel beam is by designing a truss so you might have something along these lines here so we have the supports at the end we have a steel truss and it's spanning 30 meters so the first formula i want you to think about and remember this is particularly useful in an exam situation is that the depth is equal to the span over 15 now that's just an approximate figure so 30 divided by 15 is 2. so if you're creating a preliminary size of a truss what you want to look at is the length or the span over 15 or over 18 some something like that so that's the first formula i want