On beam and truss diagrams, what do the triangle/circle symbols reprsent?

Question

For instance, in the picture at: http://upload.wikimedia.org/wikipedia/commons/1/18/Beam_in_Bending.png
there are symbols at the bottom left and right of the beam. What do these symbols mean? To they refer to how that point may move (fixed vs free)? Is there a site with a reference of these symbols if there are more than these two?

Thank you

Answer 1

Any basic statics book should have your answer. Try books by Popov or Shigley or Roarke.



The triangle on the slashes mean "Fixed and Pinned" or allowed to rotate only.

The circle on the slashes is a "Roller" support or allowed to roll and translate in one direction.

Slashes only means "Cantilevered" or "Clamped" or fixed in all degrees of freedom.

The only thing left (for beam diagrams) is "Guided" which allows translations but no rotations and is basically a double roller, sometimes one on each side of the beam.



Note, sometimes the basic roller diagram is a triangle on circles.



Think: circles are wheels, triangles are hinges, ground is slashes.

Answer 2

The triangle means it is pin-connected, so it would have two force vectors preventing movement, an x-direction vector and a y-direction vector.



The circle means it is free sitting on top of a roller. In this case, you would only have a y-direction vector, because it would be free to move left and right (even though it usually doesn't, but this allows for expansion because of heat)

Answer 3

The triangle represents a support that can resist the vertical and the lateral reactions from the truss loading.



The circle represents a roller support than can only resist vertical reactions.

Answer 4

The circles indicate rollers on which the beam is mounted and the triagle is a pivot. The idea is that the beam is free to flex and move as it expands.

Answer 5

From memory the triangle is the fixed point, from which you take the moments from in a simply supported beam.



I say from memory college was a long time ago