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Hot answers tagged structural-engineering

40

If you consider only the static forces then indeed the thickness might seem over-engineered. However, engine blocks are not statically loaded. They operate in the range of a few hundred to a few thousand rpm (Revolution Per Minute), so there are dynamic considerations here. Fatigue When materials are subjected to cyclic loading they exhibit a reduction in ...

30

This is to make sure they know what the foundation is made of. For all they knew there may have been an old tunnel underneath that would have collapsed when the new building is put on top. London is built on top of an old marsh, this type of soil is very prone to sinking and uneven settling, digging down and reinforcing the foundation alleviates that. It ...

25

That looks like a Pratt truss. These trusses have diagonals which go from the outer-top nodes to the inner-bottom nodes (i.e. they connect to the top chord on the node furthest from the center of the span, and to the bottom chord on the node closest to the center). This design means that the diagonals are under tension and the verticals are under ...

24

A specific reason for doing this is simply when there isn't enough room to do a bow or stern first launch. This is often the case when a ship or boat is built in a yard on a river or canal either because the hull is especially long or the channel it is being launched into is narrow. There is also the consideration that a sideways launch can be done from any ...

21

There are a few reasons why the footprint of large buildings are excavated and replaced. All of the old building must be removed - Typically, older buildings will have been built with weaker materials or less stringent building standards than are currently used. Depending on the age of the existing structure, complete plans may not even exist. This means ...

20

Because bridges and other structures are not static objects. They must be allowed to flex under varying loads and also accommodate changes in length from thermal expansion. The hinge pin allows changes in angle. and the sliding joint between the upper hinge plate and the flat plate on the bottom of the beam allows changes in length. If the connections were ...

19

While not an ideal situation, it is common enough that this type of cut/reduction of the beam as it comes to its support actually has a name. This is more often referred to as a coped or dapped steel I beam. There are various ways to transition from the full depth of the beam to the depth you may require at your support. Some examples are: Sometimes the ...

18

This is not a factor in practice: Water (and entrained solids) directed into a vertical pipe segment adhere to the sides of the pipe. I.e., there is no free-fall in a vertical waste pipe. Rather, liquids swirl around the side of the pipe (producing a self-cleaning effect known as scouring). Even if you managed to introduce a dense solid with insufficient ...

18

Down, Not Out Building foundations don't always have to spread the load out to a larger area. Sometimes the load only needs to be transferred to a stronger (harder) layer. This layer may be deep in the earth and have a softer layer on top of it. Layers Say you want to build a building in an area that has a lot of soft clay at the surface. This clay will ...

16

This is a textbook example of what not to do. We don't get into stress concentration at the cut off of the corner of the beam, or the fact that the two very different stiffnesses of the beams are a constant cause of differential deflection and vibration. The thin edge of the web sitting on the column cap is an unstable mechanism waiting to either kick the CC ...

16

You need to consider that the complete engine block has to withstand the reciprocating forces generated by each of the pistons and con rods moving as well as the rotational forces from the rotating crankshaft. The 1 litre 4 cylinder engine used in the Hillman imp was known for twisting under load especially once it was tuned as it was an aluminium block. One ...

15

Not everything scales linearly. In particular, the cross-sectional area of supports required scales faster than height of a structure, all else held constant. This explains why ants have tiny thin legs compared to elephants. An ant linearly scaled up to elephant size would not be able to stand, or would snap its legs trying. The same thing happens to ...

13

Parked vehicles vs moving vehicles Closely spaced parked (or slow moving) vehicles are definitely more onerous, as stated on page 89, Appendix 2.A, Clause 2.A.1 of the South African bridge design code TMH7: It is generally accepted and can readily be shown that except in the very small span range, the worst loading condition occurs under congested (...

13

The total length of the pipeline has little to do with the length that oil can be pumped in a pipe. This is because a pipeline is broken into many smaller segments between pumping stations. Stations are conveniently located either where required (see discussion below) or where another pipeline joins in. Pipelines are rarely one single pipe between point A ...

13

As grfrazee said, you won't know for sure until you do a finite element analysis. I was intrigued by this question as a colleague and I got into a discussion about this. While we both agreed the diagonal bracing would be better at resisting deflection, we wondered by what factor it would be better. We were really curious so we settled the debate and did a ...

13

We use engineering strain even though it is not the "correct" value because in most cases, specifically in the elastic regime, engineering strain differs negligibly from true strain. For linear elastic, Hookean materials, it is generally the case strain at the elastic limit is very small. Even the strongest steels, for example, have an upper limit when cold ...

13

Euler buckling occurs because the world isn't perfect. So that theory assumes that there is an initial infinitesimal deviation along the column (assuming the column is in fact not perfectly vertical*). This deviation causes a bending moment along the beam, which increases the deviation, which increases the bending moment, which increases the deviation... ...

12

I do not know, I've never been there and I have no other information other than what is in your question. However, ... I'd say that best guess, until somebody who knows more presents, is your suggestion of now-unused telephone booths. On the wall are two plates. These are at the same height in each case and consistent with connecting a telephone. Other ...

12

Assuming the joints are welded, for the top gate to deform as you draw it the vertical bars will have to bend into an "S" shape. The flexibility in bending will be proportional to the cube of the length, if everything else is the same. The stiffness of the three sections of the top gate will be proportional to $1/1^3 = 1$, $1/0.6^3 = 4.6$, and \$1/0.4^3 = ...

12

Here is how I visualize what is physically happening (for steel sections): As you get closer to the connection to the gusset, all the force needs to be transferred through the bolts, so the stress has to flow toward the connected portion of the angle. In the limit, (L = 0) the net effective area would simply be the net area of the connected portion of the ...

12

Whenever one speaks about removing a structural element (column or beam), the initial hypothesis must always be: NO! GOD NO! WHAT ARE YOU DOING! The second hypothesis must always be: No. No. No. No. That being said, it can be done. But it is not trivial and requires a serious investigation by a structural engineer. This is a "last resort" issue. ...

12

The vibration, loading, and fatigue aspects have already been addressed, but a wide range of operating temperatures is another factor. A typical consumer engine can be deployed in anything from say -50F to 120F (-45C to 50C), and some blocks will crack when operated or even stored at those extremes. An engine operating at those extremes will experience ...

11

You can never make something earthquake proof, but there are many things that can be done to resist earthquakes. There are long-span bridges built in earthquake zones. For example, the Akashi Kaikyo bridge in Japan is currently the longest span bridge in the world and is in a severe seismic zone. It is designed to withstand a magnitude 8.5 earthquake. In ...

11

That is due to necking. When a bar is under tension, two opposing mechanisms take place: The bar loses cross-sectional area since it attempts to retain its volume while being stretched (see Poisson's ratio). Once the bar begins to suffer plastic deformations, it undergoes stress hardening and it's elastic modulus rises. So long as the increase in elastic ...

11

This marketing video shows moments of their construction. At 0:40 you can see them all upright. They aren't painted, but you can tell it's the same installation. At 1:37 and 1:46 you can see guys drilling into the boulders From 2:16 to 2:24 you can see the base is also being drilled and, most clearly, steel rods are being slid into the rocks. So it is ...

11

In itself putting paper inside a glass will make very little difference. Glass is a brittle material and tends to fail by shock and point loading. Its static tensile strength is actually pretty good. What will help is packing paper between the glasses as it will help prevent them coming into contact with each other and dampen vibration and impact forces. ...

10

You might be interested in the National Society of Professional Engineers' page of professional liability resources, which has a section for insurance. There are quite a few entities offering professional liability insurance for engineers; NSPE surveyed 18 of them last year with questions like: Question #6: What percentage of your total book of [...

10

Design life can be one of two different things, and they aren't interchangeable. A reference to '100 years design life' might mean that it's designed for a '1-in-100-years' loading case (wind load, or tidal surge, or whatever). This is solely about a means of quantifying the magnitude of loading. It is actually nothing whatever to do with the durability of ...

10

I live in Brazil, so the relevance of my answer to your US experience is somewhat questionable. This is exacerbated by the fact that Brazil is almost 100% concrete, with very few steel or wooden structures (including buildings). That being said, some of these concepts are location-agnostic and others may apply to the US as well. Firstly, as mentioned by ...

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