- #1
steve321
- 25
- 0
hi!
i have a bunch of questions where I'm suppose to indicate if a structure is statically determinate
i have way to do this that usually gives me a decent answer. i go with r > 3n means it's indeterminate, and r = 3n means it's determinate. r represents reaction forces, and n represents the # of parts in the structure member.
just by memory i have an idea of how many 'reaction forces' there are. if there's a pin (the little triangle), i stick in two forces. if it's a roller (the little wheel thingy) i pop in one, and if the bar appears to be fixed to a wall i stick in three forces. if there's a hinge you draw four arrows but only count two of them. (or at least this is what the book seems to do)
then, the number of 'bars' in the drawing represents the number of structures, although if the structure has a bunch of connecting horizontal members you seem to split those into two for some reason.
anyway as you can see i have all these little shortcuts that help me get the right answer, but i don't know what exactly I'm doing.
first, what exactly is a determinate structure? i know it's something that doesn't have any more supports than it needs, and has few reaction forces (enough to solve).. but what does this mean? how does this translate into any practical application? is a determinate structure stiffer? more stable? easier to _____? i don't understand why i need to know this magical, intangible property of a structure.
second, i don't really understand the connection types. the pin and the fixed bar both seem to be the same thing from what i can tell, and i have absolutely no idea what the 'roller' represents in real life, nor do i understand what the triangle on the little circles represents. likewise i don't understand 'internal hinge' from 'pinned truss node', those both look the same.
if anyone could point me in the direction of an article that explains this clearly, or summarizes what exactly I'm doing, that would be a huge help. i hate doing things without understanding them.
i have a bunch of questions where I'm suppose to indicate if a structure is statically determinate
i have way to do this that usually gives me a decent answer. i go with r > 3n means it's indeterminate, and r = 3n means it's determinate. r represents reaction forces, and n represents the # of parts in the structure member.
just by memory i have an idea of how many 'reaction forces' there are. if there's a pin (the little triangle), i stick in two forces. if it's a roller (the little wheel thingy) i pop in one, and if the bar appears to be fixed to a wall i stick in three forces. if there's a hinge you draw four arrows but only count two of them. (or at least this is what the book seems to do)
then, the number of 'bars' in the drawing represents the number of structures, although if the structure has a bunch of connecting horizontal members you seem to split those into two for some reason.
anyway as you can see i have all these little shortcuts that help me get the right answer, but i don't know what exactly I'm doing.
first, what exactly is a determinate structure? i know it's something that doesn't have any more supports than it needs, and has few reaction forces (enough to solve).. but what does this mean? how does this translate into any practical application? is a determinate structure stiffer? more stable? easier to _____? i don't understand why i need to know this magical, intangible property of a structure.
second, i don't really understand the connection types. the pin and the fixed bar both seem to be the same thing from what i can tell, and i have absolutely no idea what the 'roller' represents in real life, nor do i understand what the triangle on the little circles represents. likewise i don't understand 'internal hinge' from 'pinned truss node', those both look the same.
if anyone could point me in the direction of an article that explains this clearly, or summarizes what exactly I'm doing, that would be a huge help. i hate doing things without understanding them.