Questions tagged [structural-beam]

A structural element whose length greatly exceeds both its width and height, which are of the same order of magnitude.

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66 views

How do I account for damping on structural vibrations?

I want to know what terms to add to the differential equation for structural vibrations to account for structural damping. Not external damping, but internal damping. I consider the transfer of energy ...
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Fundamentals of body deformations (recommend some books? soft robots?)

I'm researching about soft robots but most of the papers I've found have a very complex theory, which is making my progress quite slow. I was wondering if any of you who have some background on ...
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Tower of building blocks

Why does a tower of building blocks (cubes) fall? Theoretically, as long as the center-of-mass is above the blocks' bottom faces, and as long as one does not shake the tower too much, it should not ...
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Shear stresses in a rectangular beam

To find the shear stress at point A in the beam above using the equation τ=VQ/(It), how do you decide which value of thickness to use? Is it correct to use a value of 100 mm because the cut segment at ...
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29 views

Why does the LASER beam quality factor (M^2) use squared value?

Why does the LASER beam quality factor (M^2) use squared value? Why not using just M? i.e., Why define beam quality factor as $M^2 = \frac{BPP_{Real}}{BPP_{fundamental}}$ not $M = \frac{BPP_{Real}}{...
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31 views

Intuitive approach to cantilever deflection based on beam length

A high schooler like me asked a question on here regarding the equations used for cantilever deflection, inquiring about derivations. It turns out the derivation is learnt in the first or second year ...
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Does Maxwell's reciprocal theorem apply to a beam with spring supports?

So Maxwell's reciprocal theorem applies to elastic structures, for example rigidly supported beams: "the deflection at D due to a unit load at C is the same as the deflection at C if a unit load ...
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1answer
34 views

Using preload to resist bending moment on an unfixed cantilever beam

I have a cantilever beam that is resting against a wall (not fixed) and will not slide (strictly looking at bending moments). The beam of length = 0.3m is under a distributed load of 4000N and a ...
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How does stress “propagate” in beams?

I'm studying structural mechanics and I have been stuck on a thought. I drew a very simple cantilever beam situation. If I make a fictional cut like in my fig.1, I will be in the situation of the ...
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25 views

Do I have to compute the second moment along principal axes to calculate the maximum deflection of a cantilever beam with irregular cross-section?

Do I have to compute the area moment of inertia along the principal axis of the cross-section, in order to find the maximum beam deflection of a cantilever beam with a random polygonal cross-section? ...
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51 views

Timoshenko Beam with sliding boundary conditions at angle

I would like to calculate the effective stiffness of a structure which can be represented as follows: (Image source: Link to paper with image.) The yellow part is flexible and the blue is a rigid-...
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15 views

Confusion between statically determinate and indeterminate beams

Why is it that statically determinate beams can take some degree of misfits without any generation of strains or stress, but not statically indeterminate beams?
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1answer
38 views

Differential Equation - Why do beams break?

I've never studied physics before and I'm a Maths major. But I do have a physics-related differential equation question which I need help on. Given the beam deflection equation: $$F(x) = EI \frac{d^...
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Best location for supports of a horizontal beam?

What are the best locations for placement of $y$ supports for a beam of length $x$? This seems like a very basic physics question, but I have been unable to find the answer. Perhaps I am not sure ...
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31 views

More formal definition of admissible functions and expressions of $T_{m}$ and $V_{m}$ with the Rayleigh-Ritz Method

In this textbook I'm reading on the Rayleigh-Ritz method, they define an admissible function (in the context of finding natural frequencies and modes of vibrating beams) as a function which doesn't ...
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Design an Experiment based on Castigliano’s Theorem to Determine Young’s modulus of the Unknown Member

The question states: "You need to design an experiment based on Castigliano’s theorem to determine Young’s modulus of the vertical member (unknown material) without destroying the structure." Is ...
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51 views

Thrust coefficient wind turbine

I am having issues with computing the thrust coefficient of a wind turbine. I have available some field measurements: air density, wind speed, blade dimension and root bending moment of 1 blade (out ...
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40 views

Euler beam equation sign confusion

Euler beam equation is defined as follows: $$M=-EI{\frac {d^{2}w}{dx^{2}}}$$ There is a negative sign, so if the second derivative of the deflection is negative, the moment is positive. When the ...
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1answer
92 views

Deflection of L bracket [closed]

I want to calculate the deflection for an L bracket like https://imgur.com/a/0PabX0T to determine how thick I will need to make the steel for a workshop shelf. I have done the calculation using the ...
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2answers
183 views

Cantilever Beam Deflection with load in middle of beam

How can I calculate the deflection of a Cantilever beam if there is a load at different points on the beam? My current scenario is the following → I have a ruler that I have modelled to be cantilever ...
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Cantilever beam with a mass at different positions and resonance frequency [duplicate]

I have a Cantilever beam attached to vibration generator at the bottom. I have a piece of blu tac of some mass and I move it down the ruler. Whilst moving it down I notice the resonance frequency of ...
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1answer
184 views

Calculate impact force. when A beam starts to fall down with one end hinged and hits an object [closed]

A beam of 10 Kg and length 12 meter starts to fall from initial vertical position with one end hinged. When Beam's center of mass is dropped 5 meter from earlier position, Beam hits an object with ...
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1answer
80 views

Resonance Frequency and Centre of Gravity

Is there a relationship between these 2 As of now I am moving a piece blutac up and down a ruler to change my COG. I have connected the base of my ruler to a vibration generator and am measuring the ...
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1answer
209 views

Dependence of resonant frequency on the length of a ruler

Why does the resonance frequency of a ruler increase when the length is lower? I have a relationship from experimenting but I want to know why. I have a vibration generator hooked up to the bottom ...
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2answers
60 views

A question about the vertical part of the beam

I am solving beam type of problems finding reactions, moments...my question is how do I represent the F2 force that is acting on the vertical part of the beam (on the stick). Usually there is only a ...
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1answer
155 views

Finding distance of forces for maximum bending moment

I'm having a hard time looking for the distance ($x$) on which the forces must be located for a maximum bending moment. The reaction forces in $A$ and $B$ are dependant of the value of $x$, and so ...
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2answers
203 views

Can someone explain how does the -4222.50kN jump happen in the Shear Force Diagram of the beam [closed]

This the the problem https://beamguru.com/online/beam-calculator/?save=02461c5130daee73a8c73a51060e2adc Now I did the reaction forces correctly $R_a$ and $R_b$ and it matches with the ones the ...
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1answer
369 views

Why is the shear force of simple beam “half-positive” and “half-negative”?

Why is the shear force of simple beam "half-positive" and "half-negative"? As given here: Perhaps it's because the forces have to sum somehow? But does it make empirical sense that the force ...
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2answers
205 views

Why can we assume long structural members to be in plane strain?

In plane strain, the strain in one direction is assumed to be zero. It is taught that if we have a structural member that is very long in one direction compared to the others, the strain in the long ...
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2answers
915 views

Is a square tube more resistant to bending than a round tube?

In considering tubular forms for aircraft construction, I am reasoning that a square form (or I-beam) would be more resistant to bending (if the load is directly perpendicular and in the plane of the ...
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1answer
33 views

How to derive different maximum bending moments and sheer forces of a beam fixed at both ends?

I know how to derive the maximum bending moments and sheer forces of simply supported beams, but I'm having problems deriving these quantities of the beam fixed at both ends with an eccentric load. ...
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1answer
96 views

Compute the stress curves for the half-circular arch beam

I'm very new to static mechanics and need some help to check my solution. We have that, $$R_A+R_B=0,$$ so given the equilibrium $$P r/2 + R_B 2r=0,$$ we find that $R_B=-p/4$ and $R_A=p/4$. Now, for ...
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1answer
136 views

Lagrangian Involving an Integral

This is my first post here, so do let me know if I am asking anything or in any manner improperly! I am trying to construct a Lagrangian for a dynamic Euler-Bernoulli beam (with one end cramped) with ...
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2answers
148 views

Beam momentum positive/negative sign

Could anyone explain to me why the momentum of this isostatic beam in $A$ is negative instead of positive? Why isn't it as simple as $+FL-FL/2 = +FL/2$?
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1answer
139 views

In a truss, where is the reaction force acting on?

A truss, its free body diagrams and also of the pin at C is shown in the figure. Ay and P, in figure II may be equated because they are acting in opposite direction on the same body(the whole truss), ...
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84 views

Gaussian Beam propogation in a fiber

If we suppose that a Gaussian beam traveles in the fiber with diagonal end as it shown in the image, so I have several questions: 1- Do we get in the end of the fiber Evanescent field (Total ...
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30 views

How Gaussain beam exaclty be after diffraction between two mediums?

How it will be the refraction of the Gaussian beam, does one of its sides will go in distortion, and which equations can predict this distortion? Sure I have to use Snell's law to know the angle but ...
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1answer
50 views

Writing a two variable function$ f(x,t)$ in terms of Dirac-Delta $δ(x)$ function and a function $P(t)$?

How to write a two variable function $f(x,t)$ in terms of Dirac-Delta $\delta(x)$ function and a function $P(t)$? For example; I read something in a book. You can find the following picture. But ...
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111 views

In a beam, when there is a UDL present on a small portion, why do we add a UDL above and below of the remaining beam?

In the above image, I need to find the deflection at point C and D of the simple supported beam. Macaulay's method is to be used. To solve this, on part BC a UDL of 1 kN/m is introduced both above ...
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1answer
548 views

How the length, flexural rigidity and position of attached mass affects the period of oscillaion of cantilever?

Hey everyone, I'm a highschool student from New Zealand and can someone please explained to me with physics principles in words: Why increasing the length of cantilever increases the period of ...
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2answers
4k views

Understanding positive and negative shear strength sign

Shear strength is a force that tries to keep stuff in equilibrium, when another force tries to break/bend/modify a structure. This "another force" (external force) may also produce a moment. In the ...
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1answer
81 views

Moment on a body and on a simply supported beam

Consider a body on a frictionless floor being acted upon by a force F as shown in figure. Force acts on its centre of mass. (Centre of mass and centre of gravity coincide in this case, ie, both lie on ...
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Finding Shear Force in a Beam [closed]

I have the following question: The question is asking for the shear force at point C. To work this out, I've determined the reaction force at point A. To find the shear force, the book then sums the ...
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60 views

Simple beam deflection of cantilever beam

Recently I had need to prove the beam deflection equation for a simple cantilever beam with a point load at the end. The equation would be in reference to the Euler-Bernoulli theory taught in most ...
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3answers
954 views

Poisson's ratio in analytical beam deflection equations

After looking at some of the analytical expressions for analyzing beams, I noticed that none of the equations depend on the material's Poisson ratio. Some analytical expressions can be found in https:/...
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1answer
251 views

Why are there no vertical normal compressive stresses when a horizontal beam has a vertically applied load?

In a beam with a a single vertically applied load and a single vertical reaction force, as well as a reaction moment, for example, this one: We would typically consider the normal stress ($\tau_{xx}(...
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2k views

Is the Young's modulus the same for compressive and tensile test?

I want to know the Young's modulus for a compressive test, but I have just a tensile test. Are they of the same value?
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375 views

Does the resonance frequency of a cantilever beam depend on whether it is bending in-plane?

What is the in-plane resonance frequency equation for a single-beam cantilever of rectangular cross-section that is fixed on one end and has a mass M attached to the other end? Below are the only ...
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1answer
110 views

Why it is better to have two legs than four?

I cite from the available on internet book "Structures or why things don't fall down" written by J.E.Gordon. ...from the structural point of view two legs are better than four, and the centripede is ...
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1answer
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Why is beam forming more energy efficient than a straight up omnidirectional signal?

Someone tried to explain the process of beam forming to me, and how beam forming is far more efficient than an omnidirectional signal of similar amplitude. This seemed obvious at the time: the power ...