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Hi, I am not sure how to determine the direction of support reactions at point A and K. I know point A has a pin support, therefore, it can take in horizontal and vertical loads and point K has a roller support, therefore can only take in vertical load. But I am not sure in which direction the forces should be for both points. Help would be much appreciated.

  • 1
    $\begingroup$ The sum of the forces in your system have to be equal to 0 or else you system is accelerating. Take your sum horizontal at A, your sum vertical at A and your rotational about A. You can initially assume a direction for your reaction force and apply the appropriate signage. If at the end your reaction force is negative, it means you have assumed it in the opposite direction to what it is. $\endgroup$
    – Forward Ed
    Jun 23 at 4:55
  • $\begingroup$ I am not saying A is the best location, but sometimes a location can be chosen which simplifies the equations you need to work with. $\endgroup$
    – Forward Ed
    Jun 23 at 5:09
  • $\begingroup$ This seems like a homework problem, have you ever given it a try? Please show your effort, then ask questions, if any. $\endgroup$
    – r13
    Jun 23 at 11:48
  • $\begingroup$ Does this answer your question? Finding the reaction force at the hinge $\endgroup$
    – Abel
    Jun 27 at 20:10

1 Answer 1


I would assume the system is in equilibrium and point K is the support for the truss.

The truss is usually taken as a single unit in these calculations so creating a simple force diagram would assist immensely in reducing the apparent complexity.

Point A has a moment, point K doesn't.

The diagram would be like a beam of 20 length... Work it from there.


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