Questions tagged [moments]

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7
votes
3answers
989 views

Calculating moment of inertia for a hollow discontinuous circle?

This is a pretty simple problem, but I'm just not sure how to go about it. I want to find the moment of inertia of a discontinuous hollow circle. But since the shape is so irregular, I'm not sure how ...
4
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3answers
2k views

is bending moment on roller supports at beams zero?

isn't the bending moment supposed to be zero on roller supports at beams? then why isn't it zero here in this picture at x=2?
3
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2answers
3k views

Determine the moment of inertia of a filled circular sector

Does anyone know how to determine the moment of inertia of the filled circular sector shown below? Apparently I have to use $dA=r\ d\theta\ dr$, $y= r\sin(\theta)$ and end up getting $I_x=\frac{r^4}{...
3
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1answer
1k views

A way to calculate the magnitude of the moment

In my engineering textbook, I didnt understand the example given to explain the magnitude of the moment. It asks to calculate the magnitude of the moment about the base point O of the 600-N force in ...
3
votes
1answer
132 views

Skewing of joints using virtual work

Given ist the following framework: $$E=210 \frac{\text{kN}}{\text{mm}^2}$$ $$ EA \to \infty $$ $$ I_1 = 80000\text{cm}^4 $$ $$ \frac{I_1}{I_2} = \frac{3}{4} $$ $$ I_3=I_1 $$ Using the principle of ...
2
votes
1answer
299 views

What are the principles (if there are any) behind the conservation of bending moment in frame analysis?

I notice from this question that the moments at joint connection are somehow "conserved", or being "transferred" from one element to the others. In other words, there are no "missing moment". Note ...
2
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2answers
4k views

Transfer of moments in beams with internal hinges

We have a beam with 1 internal hinge just like the picture. We know the internal hinge can not transfer moments between AB and BD. We know the 30 kN force makes some moments on BD & AB. If B (...
2
votes
1answer
94 views

Why is the bending moment equation for a uniformly distributed load (w) across a length x on a structure given by w(x)(x/2)?

So for any structure, simply supported beam, three hinge frame, cantilever etc. where there is a uniformly distributed load. For example, for a simply supported beam with uniform load of w along the ...
2
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1answer
3k views

Sheet Metal Bending: stuck on calculating the minimum radius required

I'm used to calculate the minimum radius required for bending operations on both aluminum and steel sheets, given the following parameters: https://imgur.com/a/7akHC Problem statement: For a sheet ...
2
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4answers
297 views

Moment and Torque at a Single Point

As far as I know, moments/torques occur when forces applied are not in line. However, I often see moments/torques being applied at a single point in free body diagrams. How can moment/torque be ...
2
votes
1answer
183 views

Structural mechanics - computing bending moment

I am having difficulties trying to work out one problem. I've attached a picture explaining the situation - the task is to determine internal forces in C but the bending moment M(x) doesn't seem to ...
2
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0answers
31 views

Optimization: Most efficient way for multiple people to move boxes

We are moving house in a few weeks and have a couple of people helping moving the boxes. My previous experience from moving is of queues building up in small hallways and people getting tired from ...
2
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0answers
31 views

Most efficient way for finding the rotation angles after moment distribution (Cross method)?

First of all, I have taken a look at the Grinter's method, which is similar to Cross, but balancing angles instead of moments. My question assumes that we are using the Cross method, and not the ...
2
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0answers
19 views

Shift of joint in kinematically indeterminate system

Given ist the following system: $$EI=100000\frac{\text{kN}}{\text{m}^2}$$ $$EA\to \infty$$ I'm suppossed to find the horizontal and vertical shift of joint g. My first approach was to use the ...
1
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2answers
4k views

Force required to rotate an object on a plane - moment of inertia?

I have a rectangular shape with uniform mass, approx 6m x 1m. It rotates around an axis in the centre of its width but 1m from one end. The axis has some friction but this is not known. What I need ...
1
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3answers
111 views

Statically determinate structure by adding moment

I'm considering the problem below. It's a setup with a roller joint and a pinned joint with a hinge between the two rigid links. Since there are now 3 unknowns for 3 equations and a zero moment at the ...
1
vote
3answers
3k views

Transfering moment through internal hinge

My professor says, the internal hinge can not transfer moment: But can we calculate $\Sigma M_A=0$ for whole beam ( without cutting it or something) this way?: $\Sigma M_A=0 ===\Rightarrow M_A+(D_y ...
1
vote
1answer
720 views

polar moment of inertia for compound shape

I have a shape that I'd like to calculate the polar moment of inertia for: the diameter is 600mm; the hexagon in the middle sides are 70mm each; the holes around the hexagon are 130mm from the center ...
1
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2answers
579 views

Flexural modulus for a beam fixed at one end

For a beam supported at both ends with a mass in the middle, the flexural modulus is given by: $$E_b = \frac{F L^3}{48I d}$$ with I as the area moment $$I = \frac{1}{12}wh^3$$ How does the ...
1
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3answers
224 views

Different measured strain in beam experiencing pure bending

I have a beam experiencing a pure bending moment. The setup is similar to this image from these lecture notes (with different values). Using the flexure formula, we can determine that the stress (and ...
1
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2answers
68 views

2nd Moment of Area of a ring

This is my first question here. I am having trouble finding the 2nd moment of area of a ring with a thickness 't' and radius 'r'. I seem to be a factor of 2 out. What I do is I consider an area like ...
1
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1answer
548 views

Is radius of gyration same for both types of moment of inertia?

We know that moment of inertia is commonly known as second moment of area. Which is $\int_{}{} y^2 dA$. However there another moment of inertia called as mass moment of inertia given by $\int_{}{} r^...
1
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2answers
1k views

Maximum torsion shear stress in cylinder

I am trying to figure out am I doing this calculation correctly. To get the maximum shear stress for a solid cylindrical pipe I need two formulas: Moment of inertia = pi/2*r^4 Not sure what this ...
1
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1answer
25 views

Rubik cube torque experiment - Correct equations and experiment set up?

Background I am attempting to experimentally find out the average torque required to rotate a single face of a Rubik cube. Little to no data is available as it varies from cube to cube. Some people ...
1
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1answer
25 views

How to determine the fixed end moment?

I was trying to compute the fixed end moment for the beam (given below) using equilibrium equation for x, y displacement and moment but there are 4 unknown variables reaction and moment at both ends ...
1
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3answers
105 views

Is there a 6th equilibrium equation for a static beam?

For a scholarship exam I'm taking, it takes simple enough ideas and then messes with them in crazy ways. In this question four of the equilibrium equations I'd use to solve this are linearly dependent....
1
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1answer
86 views

Is there a moment at a point between two connected sliders, when one is subjected to a force? (schematic shown)

Background: I'm designing a machine that uses an actuator to push an object. The connecting component may not take certain bending forces, therefore I'm trying to evaluate the system with a free body ...
1
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2answers
2k views

The internal normal force, shear force and moment

How do I determine the internal normal force, shear force and moment at the point C? $V_c = 0$, $N_c = 0$ and $M_c=3.75 kN/m$ I have already done this: Where is the problem?
1
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1answer
136 views

Shear force and bending diagram un-uniformly distributed load

I already got great help on this topic, but I'd like to make sure that I get it. For example, take a beam of length 6 meters, left side fixed support and right side rolled support. There is a load of ...
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2answers
305 views

Moments of inertia, rods mechanism

I need some assistance understanding moments of inertia. I am doing some review for an upcoming exam, however I am slightly stumped by this question. I have already tried googling "moments of inertia" ...
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0answers
30 views

Does anybody know where this calculation for the mass moment of inertia for an eighth of a circle comes from?

These attached photos describe flaps which are a portion of a circle and equations are attached as the mass moment of inertia, but there are no descriptions. I am using this for part of my research, ...
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4answers
75 views

If an aircraft's wing blows air downwards, how is the momentum conserved in level flight?

An aircraft's wing generates force of lift by directing the oncoming airflow down. How is this momentum balanced when the aircraft is not climbing, but maintains level flight?
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0answers
47 views

Pin, Slot, and Spring Equilibrium

I am checking to see if this is done correctly, the slot is a little confusing for me. B is a pin in a slot, solve for the spring constant (k) so the 50 lb force applied does not move pin B Solving ...
1
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2answers
491 views

Buckling of a cantilever with midway support

I'm trying to understand the implications for buckling and column sizing in the drawings below. A 3000mm 120x60 RHS steel column supports a 350mm horizontal steel beam. The column base and right side ...
0
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3answers
28 views

BMD of the beam joined at intersection

4 beams are supported by the column at one side, another side is jointed together at the intersection. I have assigned UDL of 20 kN/m on all the beams. 2 beams are longer (3m), 2 beams are shorter (2m)...
0
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1answer
45 views

Question in finding the direction of forces in a truss

This question primarily involves finding the direction of forces in a truss. Let's give a scenario in Method of Joints One source I found says that in finding the direction of the source, it would be ...
0
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2answers
124 views

Maximum induced bending stress within the beam

The Maximum induced bending stress within the beam. Given that: $$\frac{My}{I}$$ The beam depth is 300mm, the width is 150mm. The beam is an I section beam with a 5mm wall thickness. My ...
0
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2answers
2k views

Shear force and bending moment for continuous span

It's given that L1 = 5m, L2 and L3= 7.5m, w = 8.9kN/m , I am asked to find the bending moment using these coefficient.. Prior to this , i need to have the value of shear force first.Shear force = ...
0
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3answers
853 views

Second Moment of Area for slanted triangle?

Consider this triangle with its centroid at $C$: Then this is how I believe we can calculate the Second Moment of Area along the $x_{C}$ and $y_{C}$ axis: $$\begin{align} I_{xc} &= \frac{bh^3}{...
0
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3answers
65 views

How to derive fixed end moment of a beam fixed at both ends with a point force not in the center

So this is as far as I have gotten. The formulas written in green are the formulas that I have to find/ derive but I am hitting a wall. I know I am supposed to integrate but I am not sure where to go ...
0
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2answers
46 views

Torque required to start rotating a wheel about its center

Assuming i have a circular disc of a significant mass and diameter. Neglecting friction, if a motor is put at its center how do i calculate the torque required for the wheel to just start to rotate? ...
0
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2answers
69 views

How can I find deflection in a member that doesn't have a constant area moment of inertia?

I'm trying to calculate the maximum deflection in a simply supported member with a uniformly distributed load. The trouble is this member does not have a constant area moment of inertia. I've drawn a ...
0
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2answers
308 views

Resolving moments and forces

The calculations for a design I am doing are making me go round in circles. I have simulated the design but I cannot seem to resolve this mathematically and it is really bugging me! Below is an ...
0
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1answer
89 views

How to solve for moment with uniform distributed load

How do we get the moment when there's a distributed load? For example, the picture below has 9[(60)(18)]. I get that 60 is the distributed load and 18 is the total length of the load, my question is ...
0
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2answers
216 views

Finding the force in a cable of a rigid system

QUESTION (see attached image file): I got stuck when trying to find tension for part A; see my working below. and help me solve.
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2answers
86 views

moment of inertia forces and torque

I did some calculations to find out the moment of inertia and physical qualities of some metal. I am using typical medium carbon steel. I'll use a density of 7.8 g/m^3 until I get better numbers. ...
0
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1answer
20 views

Moment placed off-centre on a rotating body

Imagine a body which is allowed to rotated around its centre of gravity. I place a rotating moment, $M_d$ on a point which is a distance d from the body's centre. $M_d$ is only required to put the ...
0
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1answer
118 views

Calculate deflection of a beam with an arbitrary shape

I have a beam with rectangular cross section, but rather an strange shape in the length wise direction as seen below: So I have taken out the symmetry part of it: And it actually has some nice ...
0
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1answer
50 views

Are there different moments of inertia for shapes and bodies?

I'm confused by this. There is a moment of inertia for a shape, let's say circle: But if you make it 3D, you have a new moment of inertia: Is there any connection between these two?
0
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1answer
753 views

Problem while solving for the moment of a cantilever beam

As in the first image, Moment at any point between C and B should be 0. But when I try to solve it by substituting equal and opposite forces at end C so that anti-clockwise moment of $F(l-a)$ and ...