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1500 questions
11
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4 answers
Why were engineers negligent in the 1981 Hyatt Regency walkway collapse?
I was recently reading up on the 1981 Hyatt Regency walkway collapse. It was a tragic loss of life and haunts many to this day.
The linked article does a better job of summarizing things, but here's a summarized version of what led up to the…
user16
11
votes
4 answers
Should I reject a concrete mix design for having too high of a compressive strength?
I usually design precast concrete members for the common concrete strength of f'c=4,000 psi at 28 days. Occasionally, a mix design will be submitted that has a very high strength. In one case, the mix that was submitted had a history of cylinder…
hazzey
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11
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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):
$$P_{cr} = \dfrac{\pi^2EI}{L^2}$$
However for $n > 1$, as shown below the buckling…
pauloz1890
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11
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2 answers
External diffusion: calculation of surface concentration
I am struggling a bit with an external diffusion problem. I am trying to calculate the concentration at the surface (as well as surface reaction rate) and would like some help or guidance.
Here is what I have thus far.
The reaction taking place,…
Mierzen
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11
votes
6 answers
Why isn't heatpump technology used for solar collector panels and boiler tanks?
All solar collector and boiler tank systems that I can find on the market use a liquid to circulate the heat between solar collector panels (or PVT panels) and boiler tanks. Is there a reason why they do not use expandable gas and a compressor…
Louis Somers
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11
votes
9 answers
Aluminum weight saving
"Aluminum saves weight! Its 3 times lighter than steel!"
Also its 3 times weaker and 3 times softer. When comparing stiffness and strenght to weight ratio, aluminum isnt any better than steel of comparable grade.
Yes, 7000 grade expensive aluminum…
Soliton
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11
votes
3 answers
Could a gold/{second metal} crown be created that would pass the Archimedes test cost effectively?
Many people are familiar with the story of Archimedes submerging a crown in water to identify if the volume of the crown was consistent with the volume of the same amount of gold. The test was to see if a lighter cheaper metal (like silver) was…
James Jenkins
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11
votes
2 answers
Soil swelling and mass/volume relationships
Given moisture content, Specific gravity of solids, initial volume, and weight. I'm asked to compute the moist unit weight, dry unit weight, and degree of saturation of this compacted soil. This is already done. This compacted soil sample was then…
Gon
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11
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2 answers
Why do air entrainment admixtures improve the freeze-thaw resistance of concrete?
It is stated on here that:
Air-entraining admixtures cause small stable bubbles of air to form uniformly through a concrete mix. The bubbles are mostly below 1 mm diameter with a high proportion below 0.3 mm. The benefits of entraining air in the…
egg
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11
votes
1 answer
How do Thumb instructions compare to ARM instructions for performance?
A colleague mentioned that Thumb instructions were significantly slower than ARM instructions (this was for an AT91SAM7S32 processor). Is this true? What are the performance benefits of one instruction set over another?
Patrick
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11
votes
4 answers
Why are most jigsaw blades designed to cut on the up stroke and have teeth that point towards the shank?
Why are most jigsaw blades designed to cut on the up stroke with teeth that point towards the shank? Why are reverse teeth jigsaw blades less popular?
Adam
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11
votes
3 answers
Why doesn't stovetop glass crack from thermal shock?
I have a feeling that if my stovetop was made out of regular glass, it would have cracked from rapid cooling/heating a long time ago – especially if you consider accidental water spills. What kind of glass is able to withstand such abuse?
(I am just…
Vasiliy Sharapov
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11
votes
2 answers
What made bronze the first widely used (non-ornamental) metal in human civilization?
I recall learning about the bronze age in school. Why was bronze so important to the technological development of humans? Why not some other metal?
James Jenkins
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11
votes
3 answers
Why are mass-produced metal parts machined by rotating the part against a stationary tool?
There's a TV programme called "How It's Made" which often shows automation of mass-produced machined parts. Very often, it seems that metal parts are machined (especially drilled) by rotating the part against a stationary tool rather than holding…
Lefty
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11
votes
2 answers
Why are three way bridges rare?
It's true that most bridges are "two directional."
But three way bridges are pretty rare, globally. I can understand why there wouldn't be many for rivers, but if bridges are designed based on the lie of the surrounding ground, why wouldn't there be…
Tom Au
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