# Questions tagged [beam]

Questions about the theory and applications of structural elements designed to resist bending.

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### Can I remove one or both of these support posts in my basement? [closed]

Below is a picture of two supporting posts in my basement. The posts are directly underneath the kitchen/dining room. Would it be feasible to remove one or both of the posts? What would the cost ...
1k views

### Derivation of beam slope for a cantilever beam

I am trying to derive the maximum beam slope formula $\theta = \dfrac{wL^3}{24EI}$ for this cantilever beam: What method can I use for this derivation? So far I can only find simply supported beams ...
153 views

### Why is this box girder made of lattice on one side only?

Here's a zoomed piece of this image from Wikipedia That's a close-up of a tower holding a railroad bridge. A and B are two of the four columns in the tower's corners. I assume that they are placed ...
3k views

### Buckling: Do buckling mode shapes of n > 1 occur in reality?

In the buckling of columns we know that: $$P = \dfrac{n^2\pi^2EI}{L^2}$$ The smallest value of P occurs when $n=1$ which gives a simple buckling shape (one wave): $$P_{cr} = \dfrac{\pi^2EI}{L^2}$$ ...
180 views

### Finding My, Mz in Complex/Asymmetrical Beam Bending

So I have done a three point loading test on a piece of bone. I have been able to obtain the Second Moments of Area $I_{xx}$, $I_{yy}$, $I_{zz}$. As well as the centroid. I also have the data from ...
1k views

### How is shelf deflection determined?

Question: How is shelf deflection determined? More specifically, how is the deflection determined when one or more edges of the plate have reinforcing edging applied to them? I have been able to find ...
153 views

### What is the name of this section?

I am trying to identify the section designation so I can determine it's properties. I have looked under "C 150 x 100 x 40" but I can't find its properties or what it's correct designation. What is ...
884 views

### Why is there a moment at the cross section end when you cut a body?

I just started mechanics of materials, and it seems that my knowledge from statics has gotten rusty over the summer. But there was a new concept introduced in the first example problem today. There ...
5k views

### Is it acceptable, with reinforcement, to notch a floor joist more than 1/6 of the depth?

IBC 2308.8.2 states a rule of not notching more than 1/6 the depth of a wooden joist (emphasis added): Framing details. Joists shall be supported laterally at the ends and at each support by solid ...
4k views

### Unbraced Length for Lateral Torsional Buckling vs. Yield Strength

The AISC 360-10 Specification for Structural Steel Buildings gives provisions for calculating the maximum unbraced length of a compression flange that separates yielding moment from lateral torsional ...
3k views

### Strength of a welded steel gate with vertical bars vs. crossed diagonal bars

Looking for some hints on how to create a rough estimate for the following problem. Given two steel gates with the same dimensions, same material - e.g. everything is the same. The only difference ...
29k views

### How to deal with a point force acting right on the hinge of a beam?

I have been attempting to solve a question where there is a point force acting on the hinge of a beam. Here is the problem: I am not sure how to deal with the 2 kN point force at $C$ ($C$ and $E$ are ...
1k views

### Large deflection of a cantilever beam with distributed normal load

I have a strip of stainless steel encastree'd at one end to which is applied a constant pressure on one side, and I need to know what the deflection equation y = f(x) is at equilibrium. If the ...
1k views

### How to rate a davit beam?

What forces are relevant when it comes to a davit lifting arm with a support? I'm not sure how to take the weight of the davit into account or how to calculate the max stress/strain on the system. ...
148 views

### Is the order of operations in jacking a cable relevant?

If you have a prestressed concrete beam or slab and are jacking a cable from both ends, does the order of operations alter the result? For a symmetric curve, the tension diagram along the cable's ...
4k views

### How do you select the correct area to consiser for first moment of area calculations?

I have just begun studying mechanics of materials and I am struggling to understand intuitively how to select the area in first moment of area calculations. I was hoping someone has a relatively easy ...
241 views

### Sum up the loads at same position on a deflected beam

I am computing the deflection of a beam. If the length of the beam is 10 m and I have load at the position 4 m from left with force 5 N. Now I add another load at the exact same position with force ...
2k views

### Does the length of a beam change upon deflection?

I have made a Python program in which I have computed the deflection of a beam. I am plotting the deflected beam and am now asked to show the length of the beam. If the beam is not deflected, it is ...
3k views

### Plotting deflection of a beam

I have a formula to compute the deflection of a beam. When I have computed the deflection I get a vector with non-negative elements representing the deflection in each position on the beam. When I ...
149 views

### Effects of constructed tubular/annular beam upon moment of inertia

I would like to construct a hollow beam using either 2"x4" or 2"x6" structural lumber.1 My thought is to take 4 boards and butt them against each other in order to form a square beam2 with a hollow ...
3k views

### Is the Qmax of an T-Beam equal if calculated both above and below the neutral plane?

I was doing a question involving a T-Beam question wrong since I was selecting the wrong area to use for $Q_{max}$ when trying to maximise the shear stress. $$\large{\tau}= \frac{VQ}{It}$$ A friend ...
3k views

### Effective length for lateral torsional buckling in a laced strut

When loaded vertically, a beam experiences compression in its top flange and tension in its bottom flange. The top (compression) flange would tend to buckle vertically much like a column, however, the ...
5k views

### At what point does an I-beam becomes a H-beam?

According to BS5950, a beam section can be classified as plastic, semi-compact, compact or slender. For the same section area, a H-beam can take axial compression (without buckling) better than an I-...
6k views

### Why is it unwise to choose cylindrical horizontal beam

I heard that it is unwise to choose cylindrical horizontal beam. My question is why?
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### How do I calculate the forces on a desk and its legs?

I have a design for a desk, and I'd like to not just guess at how strong it'll be, but I can't find an explanation on how to figure out all the forces involved that doesn't assume I already know a lot ...