# Deflection of a Perfect Strut Under Point Forces

• dichotomy
In summary, the conversation discusses the possibility of a perfect strut bending laterally when compressed by two imaginary point forces acting on its centroid. The speaker argues that ignoring practicality, such as precise alignment and impeccable geometry, there is no reason for the strut to bend dramatically. However, the other speaker points out that several factors, such as end restraints, moment of inertia, and load applied, can affect the likelihood of the strut buckling and deflecting laterally.
dichotomy
hello all, first post here so don't bite.

if a perfect strut was compressed by an 2 imaginary point forces acting exactly on its centroid, and ignoring outside effects, would it bend laterally, and why so? when I say perfect, i mean ignore all consequences of practicality, ie. the alignment is precise to the eg. atom, and the bar is of impeccable geometry along its length.

i was having a debate about this for at least 20 minutes with someone, and I saw no good reason why it should (ignoring material failure for the moment), since the point forces acting on the centroid produce no moment/horizontal component to cause the strut to bend in such a dramatic manner.

What? Be more clear. If one of the components of a load is perpendicular to the centroidal axis (beam, bar, slab, etc...), then there would be bending!.

Last edited:
In your perfect example, I guess there is no real reason for the column to buckle. You would then have to deal with compressive failure. If there is no moment at the ends or eccentricity to the load and the material is perfectly homogeneous, it should be in perfect compression. I had to take a quick look back in one of my books to make sure the Euler equation for buckling is derived assuming that there is an applied moment at the end of the column.

dichotomy said:
hello all, first post here so don't bite.

if a perfect strut was compressed by an 2 imaginary point forces acting exactly on its centroid, and ignoring outside effects, would it bend laterally, and why so? when I say perfect, i mean ignore all consequences of practicality, ie. the alignment is precise to the eg. atom, and the bar is of impeccable geometry along its length.

i was having a debate about this for at least 20 minutes with someone, and I saw no good reason why it should (ignoring material failure for the moment), since the point forces acting on the centroid produce no moment/horizontal component to cause the strut to bend in such a dramatic manner.

You have to know several different things before you can answer that question.

1) end restraints (it is common to assume that both ends are pinned or free to rotate)
2) moment of inertia of the section (about both axes)
3) unbraced length of the strut in compression
4) the amount of load applied

As the strut length gets longer, the section gets smaller, or the applied load gets larger, the strut will be more likely to buckle and deflect laterally. Assuming the section is sized appropriately, it will not buckle and will not deflect lateraly.

## 1. What is deflection of a perfect strut under point forces?

Deflection of a perfect strut under point forces refers to the bending or displacement of a structural member, such as a beam or column, when a concentrated load or force is applied at a specific point along its length.

## 2. What factors affect the deflection of a perfect strut under point forces?

The deflection of a perfect strut under point forces is affected by the magnitude and location of the applied force, as well as the properties of the strut such as its length, cross-sectional area, and material stiffness.

## 3. How is the deflection of a perfect strut under point forces calculated?

The deflection of a perfect strut under point forces can be calculated using the equation δ = PL^3/(3EI), where δ is the deflection, P is the applied force, L is the length of the strut, E is the modulus of elasticity, and I is the moment of inertia of the cross-sectional area.

## 4. What is the relationship between the applied force and the deflection of a perfect strut under point forces?

The deflection of a perfect strut under point forces is directly proportional to the applied force. This means that as the force increases, the deflection also increases.

## 5. How can the deflection of a perfect strut under point forces be minimized?

The deflection of a perfect strut under point forces can be minimized by using a material with a high modulus of elasticity, increasing the cross-sectional area of the strut, or decreasing the length of the strut. Additionally, adding supports or bracing can also help to reduce deflection.

• High Energy, Nuclear, Particle Physics
Replies
10
Views
3K
• Astronomy and Astrophysics
Replies
30
Views
4K
• Other Physics Topics
Replies
69
Views
11K
• Introductory Physics Homework Help
Replies
1
Views
4K
• Engineering and Comp Sci Homework Help
Replies
2
Views
2K
• Introductory Physics Homework Help
Replies
1
Views
2K
• Science Fiction and Fantasy Media
Replies
12
Views
3K
• Special and General Relativity
Replies
32
Views
5K
• Special and General Relativity
Replies
264
Views
29K
• Nuclear Engineering
Replies
4
Views
3K