38 votes

What are those large poles for that are always in front of US stand-alone store buildings?

They are called bollards. Their function is to provide safety for pedestrians from traffic, distracted drivers who may encroach into the sidewalk, or runaway cars e.g a driver who inadvertently ...
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29 votes

What are those large poles for that are always in front of US stand-alone store buildings?

They are called Bollards. But these aren't defensive as suggested. Look closer. There's no curb. This is a new style of store (from the architecture) and curbs have been eliminated for ADA reasons ...
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26 votes

Why are some public benches made with arm rests that waste so much space?

I am not sure about this particular design. But in public places, the benches are designed to provide temporary comfort but discourage using them as a vagrant or homeless hang out, hence designed ...
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23 votes
Accepted

Why are three way bridges rare?

Most bridges (and overpasses) are built to cross over something. With a few notable exceptions, most of these "somethings" are relatively long perpendicular to the desired crossing direction and ...
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23 votes
Accepted

Why does a gear have extra holes?

Different gears have different drivers for having holes. One way you can categorize gears is by whether they are used primarily for transferring: motion: transferring angular position and angular ...
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18 votes
Accepted

Why does a jumping rope have no bending stiffness and compression stiffness?

TL;DR: The bending and compression (buckling) stiffness is so small because the second moment of area of the fibres is small. Bending stiffness It does have a bending stiffness however it is really ...
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14 votes

Is there a theoretical bound to how tall a structure can be built?

Pedantic Answer First You specifically eliminated most constraints that would make this anything other than an theoretical exercise. You did specify that it had to be "built" though. By building ...
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12 votes

Why does prestressing in trees make them stronger?

How To Read the Graphs The graphs are plots of stress versus position. Stress is the force per unit area exerted on a material. Positive values are tension and negative values are compression. The ...
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  • 1,167
11 votes

What is the practical limit on the number of storeys in residential buildings built with monolithic reinforced concrete?

Any limit is going to be hard to quantify. There are a lot of factors that have to be weighed when choosing the basic material type. The short answer is that the limit has already been chosen for ...
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11 votes
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How do the columns in the 'magic mountains' sculpture stay up?

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 ...
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11 votes
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What is the advantage of statically indeterminate structures?

For example, take a look at the following static systems. Assume they have the same length and the same (constant) cross-section. Thus an equal allowed bending moment $M_u$. The first system is ...
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  • 1,186
11 votes

Why are some public benches made with arm rests that waste so much space?

Benches are not usually engineered as such. They are being made by furniture designers, (landscape/interior) architects etc. Now generally these professions put a lot of work into making their items ...
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10 votes
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How did this building's windows get like this?

The building is in a place (Halton Hills, Ontario, Canada) where the relative humidity is about 100% in the summertime (see part Climate in this https://www.britannica.com/place/Toronto) The building ...
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9 votes
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Is a permanent platform that is hanging and moving a dead load or a live load?

What is the difference between a Live or Dead Load? A Live Load is typically a moving load. This can be vehicles on a bridge or occupants and vehicles in a building. Dead loads are (relatively ...
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9 votes

How different is using styrofoam rather than empty cans when pouring concrete?

I suspect that the reason to use it is that the cans and the associated empty space is cheaper than actually having solid concrete (and may be partly necessary to reduce the weight of the concrete and ...
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  • 3,587
9 votes
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Where did I go wrong conceptually when attempting to calculate the maximum force on a truss at a given joint?

The reason is that you assumed that the elements around node $\text{D}$ will be the first to fail. That is not the case. Indeed, it is the elements under compression ($\text{AB}$ and $\text{BC}$) that ...
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9 votes

What are those large poles for that are always in front of US stand-alone store buildings?

Bollards and other defensive oriented structures significantly predate the 2016 Nice attacks. They have been in place at the construction of many buildings in the US and across the world for decades ...
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  • 191
9 votes

How did this building's windows get like this?

OP states that the staining is not always present. here is a possible reason for it: If the building is air-conditioned and has single-glazed windows, then the outside of the window glass might be ...
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8 votes

Why are three way bridges rare?

Multi-way bridges are rare for river crossings for the reasons you describe; however, they are seen as a component of highway interchanges, usually when left entrances/exits are present or access ...
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8 votes
Accepted

Why are hyperboloid towers not popular anymore?

Meet Vladimir Shukhov, a Russian architect who first developed hyperboloid structures. He was born in 1853, died in 1939, and created over 200 hyperboloid structures in the intervening years. He was ...
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  • 2,485
8 votes

What concerns would I need to consider for building a swimming pool of gold coins?

The weight of the gold would be about 52,110,000kg, over 900 meters square of floor area. This is about 82.4psi of floor pressure, or, under standard gravity, 57.9kN/m^2 live load. This is only an ...
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  • 1,106
8 votes
Accepted

Does the length of a beam change upon deflection?

The dimensions of the beam and magnitude of the deflection are important here. In most structural applications, it's reasonable to assume the length of a beam is unchanged by a small deformation. One ...
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  • 3,211
8 votes
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What angle - for a strut - provides the greatest vertical strength/support for a cantilever?

Assumptions The angle between the wall and the strut is $\theta$ $a$ is the depth of the table top $P$ is the weight on the table top, applied at the edge furthest from the wall The strut will fail ...
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  • 356
8 votes

Why does a gear have extra holes?

In addition to the other answers such as weight reduction and inertia, there are other possibilities: Often there can be a precision machined hole for timing purposes. A common solution for some / ...
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  • 14.1k
8 votes

How did this building's windows get like this?

To add to the other answer: When ledges protrude out from the wall then the water, and dirt, falls away from the wall surface. Also, the underside of the ledge usually has a drip channel or groove to ...
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  • 14.1k
7 votes

How to calculate deflection of a simple beam with a load in the center?

I am specifically thinking of a wooden beam... Wikipedia suggests I also need to know "Area moment of inertia of cross section" but I have no idea how to obtain this. If you're using standard wood ...
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  • 3,587
7 votes

Seeing through walls and noninvasive structural integrity metrics

Depending on the region and structure of building the techniques might vary. Below are few suggestions Termite inspection is another popular method to determine the structure integrity of building. ...
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7 votes
Accepted

Given the tensile strength of a rod, how do you calculate the max weight that can be hung from it?

You're hanging it from a rod supported by both ends - and need to use the bending equations. For this case (case 7 in the link), the max weight is: $$W_{max} = \frac{\pi d^3 \sigma}{8L}$$ $\sigma$ ...
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  • 5,313
7 votes

Why does a gear have extra holes?

It could be for combination of reasons. lubrication: the holes will both pump and let the lubricant pass through. Reduced angular momentum reduces backlash and adds to gearbox responsiveness. ...
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