New answers tagged

6

To visualize part of Nmech's answer: in the image, the washer actually greatly increases the contact area of the bolt head. The bolt head looks pretty big: But most of that is the shaft, which obviously does not spread out load on the material. So the actual contact area looks like this: Comparatively, the bolt head on the washer looks like this: That's a ...


3

The short answer is: They are permitted/allowed to do work. Sometimes they can do (they have skills) at least some of the labor. Usually they don't get involved with the actual labor. The last part is the most important - IMHO- and there are many reasons for that: there is literally not enough time (usually engineers need to see the larger picture and ...


25

I will expand on DKNguyen answer, because to my knowledge also the two reasons are: reduce contact/bearing stresses (having a significant effect on thin finishes live galvanisation) change the joint tightening characteristics (see joint diagram). reduce contact stresses on surfaces. The basic idea is that since contact stress is defined as: $$\sigma = \...


5

A Civil Engineer is a person trained on how to solve problems or put things together (build) using his/her brain and express his/her thoughts/ideas on the papers (reports, drawings) for the persons in trades to carry out (build), using their trained knowledge and skill for the specific trade, which usually requires physical strength. Actually, many engineers ...


0

The sound rock (if determined by an engineer) should be able to support the building weight and the gravity load induced by the occupant without the significant settlement that typically identified as the bearing failure or the differential settlement that may cause/trigger the structural failure due to the bearing failure. In general, serviceability concern ...


1

Yes, per the design code (ASCE 7 & IBC) the formula could be used for estimating the fundamental period of buildings during a seismic event if the construction of the building meets the criteria indicated in the code provisions. See P 1-56, https://www.seismicreview.com/January_2017-Errata-1.pdf However, as the seismic design and evaluation are quite ...


9

Except for special applications, most washers are made of dead soft steel, which deforms under the compressive load imposed by a tightened bolt head. As the washer smooshes, it minimizes stress concentrations caused by bumps under the bolt head and surface flaws in the part the bolt is running through.


23

It is for spreading out the stress. But it is also for giving the bolt a bearing surface to turn on. The washer always goes on the side (nut or bolt) that is being turned. It prevents it from marring up the work surface and also changes the tightening characteristics. I don't know the specifics of that though but that's what I was told by a toolmaker. Always ...


1

The bolt elongation length is (in all likelihood ) what is referred to as Effective length in the following image Figure 1: Effective bolt length (source: Resonic) The physical significance, is the part of the bolt that is in tension, and effectively generates the clamping force. Additionally that length can be used to estimate the spring constant of the ...


0

Hookie's Law defines the linear elastic relationship of material within the elastic range in the stress-strain curve. $F = kx$ $k = EA/L$, so $F = EA(x/L) = EA\epsilon$, and $F/A = \delta$, so $\delta = E\epsilon$ Now we can generalize the "Hooke's Law" to cover the stress ($\pm\delta$), on an element of "homogeneous isotropic" material, ...


0

This problem is most easily handled using the "table" form as shown below. The result can be verified by selecting a more convenient reference line, to eliminate the potential mistake made in sign convention, as shown below. Final checks: $y_{c(A)} = y_{c(B)}$ Due to effect of substraction, the neutral axis must shifting above the centerline of ...


1

Circular hollow sections were standardised a long time ago and in inches for historical reasons. This should be obvious if you look at a complete list and convert the units. The question is better asked the other way around: Why should we change the standard diameter from 60.3mm to 60.0mm, which would an additional cost for the manufactorers, when the 0.3mm ...


0

This is more for a historical aspect (not about state of the art) If you search for Eupalinian aqueduct on Wikipedia, you will find a reference for the first tunnel excavated from both ends through the use of geometry (and it is actually the second ever excavated in recorded history). The tunnel was approximately 1 km long and it was build in 6th century BC (...


2

The forces on section b-b are calculated below. $\sum F_J = 0, R_I= +8.33$ Draw section diagram with member forces indicated as shown in graph below. Write the external equilibrium equations for the section: $\sum F_X = 0, F_{BA} + 0.8F_{EG} + F_{HG} = 0$ -----(1) $\sum F_Y = 0, F_{BD} + 0.6F_{EG} - 8.33 = 0$ -----(2) $\sum M_I = 0, 6F_{BA} + 8F_{BD} + ...


1

What you need to do is instead of section b-b (sectioning AB,BD, GE, GH), you need to take another section cc (sectioning AB,BD, DG, FG). Then the second step is, to calculate the reactions at J or (preferably) I. Then you take a section (e.g. a-a in my example below) and you draw the forces for each rod Then the final step is to write equation for each ...


0

Because 3d printing a hard case solution, will create a hard barrier which will affect the weight measurement, you'll probably need to consider some sort of flexible isolation method. A quick (and not so eye pleasing solution) if a) the project does not need to be submerged in water b) if you are not so much bothered about appearances is to consider ...


0

Friction is the resistance of instantaneous bonds between the molecules of the two contact surfaces against their sliding. Any effort or force trying to slide one of the surfaces against the other will cause a reaction exactly equal and in the opposite direction of that force. (static friction) This static friction will keep increasing equal to applied force ...


0

The keys are 1) the wheel must in contact with a surface, 2) having the noraml force pushing it against the surface, 3) the friction is always in the reversed direction of the motion. In the case shown in the picture, there could be no friction because conditions 1 and 2 above do not exist. Or there could be two frictional forces, one pointing backward ...


2

The easiest way to find is the direction of friction between two contacting bodies is to consider the direction of sliding (i.e. relative movement). The key concept is that there needs to be relative movement between two surfaces (during the rolling of the wheel there is no relative movement, therefore in the direction of movement of a free rolling wheel ...


0

it is called free float. And Einstein used it as an intuition leading to his theory of general relativity. In a small local spacetime no physical ebservation or experiment can tell the difference between weightlessness and free float. the picture is from A Jurney into Gravity.. by John A Wheeler. It is said that he considered this was one of his the happist ...


0

In the so called center of mass frame the gravitational forces of the constituents sums to zero per definition. That's the reason why we describe two body problems as (1) motion of the center of mass, and (2) relative motion with respect to the cantor of mass.


2

The classic example of a frame of reference in which gravitational forces disappear is called a freely-falling reference frame. This is what you get when in deep space, or in orbit around the earth, or when falling off a tall building or down a mine shaft on earth. In a freely-falling reference frame, pendulums do not swing because all the (mg) terms vanish.


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