# Reaction forces for structure

• member 392791
In summary, the conversation discusses the process of solving for unknowns using equations and moments, particularly in the context of a loaded beam with two supports. It is suggested to pick one of the reaction points and write a moment equation for it in order to simplify the calculation process. The importance of taking moments about an axis rather than a point is also emphasized. One participant discovers and fixes a sign error in their calculations.

#### member 392791

My problem here seems that I can't figure out how to solve for my unknowns. I have 3 equations for force, and I'm not sure if that equation I have for the moment around the origin counts as 3 new independent equations if I split them up into i, j, and k components. If that is allowed, then I have 6 equations and 6 unknowns, which should be solvable. Otherwise, I only have 4 equations and can't solve this thing.

Is my analysis of the moments ok as well as the forces present on my FBD? I figured the rings cannot oppose motion in the directions where the hole of the ring is perpendicular to the force, thus has no reaction force.

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When writing moment equations, it's usually a good idea to pick one of the locations where an unknown reaction occurs. Look at it like solving a loaded beam on two supports: the sum of the forces involves both R1 and R2, but by writing a moment equation about one of the reaction points, say point 1, there is no moment produced by R1 but the resulting equation contains only R2, which can then be calculated. R1 is found by plugging R2 into the force equation.

You have your force equations involving the reactions. Instead of writing a moment equation about the origin, pick one of the reaction points and write a moment equation for it.

Best to take moments about an axis rather than a point.

If I take the moment about the X-axis, does that mean the moments caused by all forces that originate at points on the axis (A_y and A_z) go to zero, or is it that the moment caused by forces that act along the x-axis (B_x) go to zero, or is it something else??

I did the moment around point B, I get Cy = -Ay, which if I put into the summation of F_x equation, I get 1200 = 0, so something is wrong here

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Solved it. I just made one sign error in the matrix on one of my determinants!

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## 1. What are reaction forces for a structure?

Reaction forces for a structure are the forces exerted by a structure's supports or connections in response to external loads, such as weight or applied forces. These forces help to keep the structure in equilibrium and prevent it from collapsing or deforming.

## 2. Why are reaction forces important to consider in structural design?

Reaction forces are important to consider in structural design because they help determine the stability, strength, and overall integrity of a structure. By understanding the reaction forces, engineers can design structures that can safely support the intended loads and maintain their shape and function over time.

## 3. How are reaction forces calculated?

Reaction forces can be calculated using the principles of statics and the equations of equilibrium, which state that the sum of all forces and moments acting on a structure must equal zero for it to remain in equilibrium. By analyzing the external loads and the geometry of a structure, engineers can determine the magnitude and direction of the reaction forces at each support or connection point.

## 4. What factors influence reaction forces in a structure?

Several factors can influence reaction forces in a structure, including the type of support or connection, the geometry and shape of the structure, the magnitude and direction of external loads, and the materials used in the construction. The location and distribution of loads also play a role in determining the reaction forces.

## 5. How can reaction forces be reduced or minimized in a structure?

To reduce or minimize reaction forces in a structure, engineers can use various techniques such as redistributing loads, adding additional supports or bracing, changing the geometry or shape of the structure, or using different materials. By carefully analyzing and optimizing the design, engineers can minimize the reaction forces and ensure the stability and safety of the structure.