Having trouble calculating reaction forces for this truss.

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Comfy
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Homework Statement


Calculate reaction forces for truss. Truss is attached in picture.

Homework Equations



ΣFx=o
ΣFy=0
ΣM about reaction point=0

The Attempt at a Solution


attached in picture
 
Attachments
  • Handwritten support reactions worksheet with equilibrium equations: sum of Fx = 0 gives Hx = 0, sum of Fy = 0 gives Ay + Gy + Hy + Ey - 8.5 = 0, and three moment equations about points A, G and E.
    1462768412577-223762192.jpg
    10.8 KB · Views: 600
  • Photo of handwritten work on lined paper showing joint equilibrium equations for a truss, with sum of forces in x and y set to zero and sums of moments written in several rows.
    1462768369827508814578.jpg
    17.5 KB · Views: 567
  • Handwritten sketch of a truss on lined paper with pinned and roller supports at the ends, labelled joints 1 to 6, panel lengths 9.11, 26.6, 26.6 and 9.11, and a 53.2 span dimension; a hinge is marked near one joint.
    1462768436719370329048.jpg
    31.8 KB · Views: 611
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Comfy said:

Homework Statement


Calculate reaction forces for truss. Truss is attached in picture.

Homework Equations



ΣFx=o
ΣFy=0
ΣM about reaction point=0

The Attempt at a Solution


attached in picture
Unfortunately, the attached images are almost entirely illegible. :frown:

If you want some help, either write out your calculations or post better images. :wink:
 
SteamKing said:
Unfortunately, the attached images are almost entirely illegible. :frown:

If you want some help, either write out your calculations or post better images. :wink:
This truss is statically determinate now, and should be solvable, right? That is why I don't understand why I am having trouble solving for the support reactions.
 
Attachments
  • Handwritten sheet of moment and force equilibrium equations for a truss, with sums of moments about points A, B, C and K and vertical force balance, involving unknowns A_y, G_y, B_y and terms such as 80A_y and 275/4.
    20160509_001153.jpeg
    16.8 KB · Views: 581
  • Handwritten derivation on paper: sum of moments about A equals zero gives -700 + 792 by + 590 Gy - 800 Ay = 0; Ay = -225/4 + 9 By + 10 Gy; sum of forces in y gives -225/4 + 9 By + 10 Gy - 10 Gy - 9 By + 225/4 = 0, annotated 'all this cancels out?'
    20160509_001201.jpeg
    9.5 KB · Views: 584
  • Hand-drawn truss diagram on paper with joints labelled A to K, a roller support at A, a hinge at H, and a roller support at G and K, with member lengths 9.41, 26.6, 26.6, 9.41 and 53.2 written on it.
    20160509_001214.jpeg
    21 KB · Views: 593
  • Handwritten support reaction equations on lined paper: sum of Fx = 0 = Hx; sum of Fy = 0 = Ay + Gy + Hy + ky - ... ; sum of MA = 0 = 8Hy + 80ky + 88Gy - 550; sum of MG = 0 = 550 - 8ky - 80Hy - 88Ay; sum of ML = 0 = 8Gy + 450 - 72Hy - 80Ay.
    20160509_001352.jpeg
    11.8 KB · Views: 572
Comfy said:
This truss is statically determinate now, and should be solvable, right? That is why I don't understand why I am having trouble solving for the support reactions.

What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
 
SteamKing said:
What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I
SteamKing said:
What makes you think this
SteamKing said:
What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
I have 4 equations Sum of forces in y direction and the
 
Comfy said:
I

I have 4 equations Sum of forces in y direction and the
Your last post came out garbled. Can you repeat?
 
SteamKing said:
Your last post came out garbled. Can you repeat?
I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
 
Comfy said:
I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
You can write only one equation involving the sum of the forces and one equation summing the moments about one convenient reference point.

You cannot write, for example, one moment equation where you sum moments about point A and another equation where you sum moments about point H.

This beam is statically determinate:


Free-body diagram of a horizontal beam with a uniform downward distributed load w across its full length, and upward reaction forces labelled R at both ends.

​

This beam is statically indeterminate:


Diagram of a three-span continuous beam A to B to C with supports at A, B and C, a uniform downward load q over the full length, reactions R_A, R_B, R_C, and spans marked L and L.

​

Both beams are loaded in a similar fashion, except the latter beam requires an extra equation in addition to the equations of static equilibrium in order to solve for the reactions at the supports. In the case of the latter beam, we must know how the beam deflects under load, and we cannot calculate that unless we know some additional structural details beyond the spacing of the supports.