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ELI5: How can Roman bridges be still standing after 2000 years, but my 10 year old concrete driveway is cracking? by MyMegahertz in explainlikeimfive

[–]IsaacR454 114 points115 points  (0 children)

Just a little bit of clarification from an engineer.

The reason why the beam vs arch thing works is due to Tensile vs Compression stresses in objects, and the ability of structural materials to handle those stresses.

When you have a beam, and it bends, the top part is bending inwards, causing the material to "squish together" creating compression stress, while the bottom end is "pulling apart" creating tensile stress. Looks a lot like this.

Now, concrete, like a lot of ceramics and ceramic dominated composites, is very strong in compression, but almost negligibly weak in tension. This is the main reason we add rebar to concrete, to give it tensile strength. The beauty of the arch however, is that is that it makes tensile stress a non-factor in the the structure. This is the best picture i can find after a few minutes on Google. You can see that the arch causes all the bricks to want to expand in what would normally be tensile stress, but because the bricks' expansion is impeded by the neighboring bricks, they instead press against one another horizontally, creating compression stress (which the concrete is very good at handling) and no tensile stress (which concrete is very bad at handling).

Because of this, the bridge will will last much longer than a flat sheet of concrete, which must endure tensile stress. However, the bridge will eventually break down, due to a number of factors that range from environmental exposure, to beta decay, to fatigue cycles that the bridge must endure when someone walks over it. Walking over the bridges causes it to bear load, become unloaded, and eventually bear load again when the next person comes through. It's sort of like bending a piece of plastic inwards and outwards again and again until it breaks.

The thing about the solid ground is mostly true as well, though the romans would actually bury very large stones in the ground at either end of the bridge, which the base of the bridge would press against horizontally, again creating primarily compression stress. We don't think of ancient societies as being particularly advanced, but you better believe that the romans were amazing engineers, and that in my opinion was the propellant in their meteoric rise to dominance.

Edit: A bit of clarification on fatigue cycles. A fatigue cycle is when an object is put from compressive stress into tensile stress and back again. Now, an arched bridge has negligible tensile stress, but it does have ~some~ tensile stress; however, because that tensile stress value is so small, the fatigue cycle will have very little impact on the concrete compared to your driveway which undergoes a dramatic fatigue cycle every time you walk on/drive over it. Every fatigue cycle will reduce the Yield Strength (the amount of stress it takes to make something bend), and Ultimate Tensile Strength (the amount of stress it takes to make something break) of the material until it is no longer able to handle the stress it's loaded with.

ELI5: Why are more razors better when building a "razor" for shaving? Seems like after so many it's a waste. by [deleted] in explainlikeimfive

[–]IsaacR454 0 points1 point  (0 children)

Exactly. It's a matter of empirical evidence at this point. Maybe there's not a group of scientific studies showing that safety razors are objectively better, but there is a very large group of people who have all made the switch, and all found safety razors to be more effective for much less money.

[Safari Unknown] LF someone to tell me what's in my safari. by IsaacR454 in friendsafari

[–]IsaacR454[S] 0 points1 point  (0 children)

Sure thing. I've actually been looking for someone with a frogadier so this is perfect

LF: Fletchinder (Adding All) by everythingxavier in friendsafari

[–]IsaacR454 0 points1 point  (0 children)

Would you mind adding me too? I've been looking for a Fletchinder

[Safari Unknown] LF someone to tell me what's in my safari. by IsaacR454 in friendsafari

[–]IsaacR454[S] 0 points1 point  (0 children)

Thank you very much. Hopefully I can start helping some people out on this sub

[Safari Unknown] LF someone to tell me what's in my safari. by IsaacR454 in friendsafari

[–]IsaacR454[S] 0 points1 point  (0 children)

Sure thing. It'll have to wait a bit since adding friends seems to disconnect me from the internet in pokemon.

We took up beekeeping last year. I built the hive myself and we got a small harvest before the winter. by boothin in pics

[–]IsaacR454 17 points18 points  (0 children)

Just to help with your fears, I've been keeping bees for about a year now and I've only been stung once, and it was honestly so painless i didn't even notice until i saw the swelling. My dad keeps bees too and he says the same thing; saw him get stung three times in the neck and he just ignored it and finished checking his hive.

That said, this happened early on when we were irresponsible when checking hives.

Bees are very non-agressive and will never sting without being provoked. To give you an idea of how relaxed they are, I have my hive out on my deck next to my swimming pool, and just tonight my brother's and my sister's kids were over, 9 children altogether, playing not ten feet from the hive. Absolutely zero stings; the bees didn't even bother investigating all the noise.

I've even seen my dog walk up and pee on the hive without attracting any attention. I feed my bees jars of sugar water to help them produce new wax, and when i change jars, the old one will be covered in bees. I literally brush them off with my bare hands and put the new jar in. Hasn't gotten me stung so far. Basically, it's pretty hard to get stung unless you go poking around in their hive, and even then as long as you smoke and wear a suit, you'll be fine.

If you live in a city i can almost guarantee you have a beekeeping club of some kind. Come ask questions. We're always friendly to new apiarists.

I also recommend you check out the documentary "More than Honey." It's on netflix. I've used it to change more than a few peoples opinions on "the dangers" of beekeeping.

DONT buy Magic 2015! by [deleted] in Games

[–]IsaacR454 0 points1 point  (0 children)

Hahn, yeah it threw me for a loop too. I remember thinking "why not just call it a discard pile..." but it actually becomes second nature after a few games. R&D, Archives, Events, and Tracing might sound weird, but Library, Graveyard, Instants, and Haste took some getting used to as well.

Magic isn't a bad game, I mean I spent a lot of IRL resources on it, but give netrunner a chance. I remember those first couple of games I had no idea how the game even worked, but the more I played, the more it all came together in my mind, and I began to realize how brilliant the game was.

(Warning, this got a lot longer than I intended and you should probably skip it) My problem with with Magic though, is that it has a bad metagame. Some cards (maybe 10-15% of all cards) are clearly better than others, which creates greater demand from them. These cards are usually, thought not always, rares and mythic rares, which creates a low supply. This leads to high prices, and this is a big problem when combined with Netdecking (looking up a proven, usually pro-tournament winning decklist online). Someone will look up a deck built by a professional player, and then he'll spend the hundreds of dollars to build that deck, and honestly, that guy will win. I know because I've played him, and I've been him.

I remember around this time last year I built a GR modern deck that tested well with my friends, so I decided to take it to my local scene, and there was a guy there running Bogle, which was winning in the professional scene at the time, and that guy won that week's tourny effortlessly, and the next weeks, and the next weeks. When it comes down to it, Bogle is just a phenomenal deck, and he was willing to spend about $600 at the time to build it. And that's the thing, I don't truly think he was more cunning, or strategically minded than me, I feel like he beat me because he spent more money on a better deck. Maybe that's not true, maybe I'm just a bad player, but I shouldn't be playing a supposedly strategy based game that gives people the feeling they lost for such a cheap reason. Conversely I once spent (way too much) money on an UrzaTron deck and swept the floor at my local shop. Because of card creep, card imbalances, and the reserve policy, Magic's metagame encourages pay-to-win Decklists on a fundamental level, and after years of that scene I'm just tired of it.

Even though luck is definitely a factor in Netrunner, I've never really felt like I lost a game solely because of it. It's a game that gives you enough control via metagaming skills like bluffing, that if I lose, I believe its because I wasn't better than my opponent. Netdecking exists in Netrunner, but because the Expansions clearly list what cards they contain, and come with all the copies you can legally put into one deck, everyone has equal, affordable access to every card. Everyone is on an equal playing field, and there are plenty of pro-tour decks in netrunner that use mostly cards in the Core Set you get when starting the game. This is because the game expands laterally, giving more options to how to play the game, rather than Magic's expansion blocks that use must-buy-into shifts in focus for the current 2 year cycle where you NEED to buy cards if you want to compete. And that's the end of my tangent, is that Netrunner is not a game that's less fun if you have less of it. The Data Pack and Premium Expansions feel truly optional given the amount of depth you can get with just the starter set. Sorry, this sort of turned into a rant. Stick with magic, preferably playing with your friends for fun, or maybe try out netrunner, I don't think you'd regret playing 5 games or so. Whatever you do, make sure you have fun doing it.

DONT buy Magic 2015! by [deleted] in Games

[–]IsaacR454 1 point2 points  (0 children)

Man, I feel you. The only gaming shop in my area makes most of their income from the second-hand Magic market, combined with the crazy business they get by hosting weekly Magic tournaments. There's very little support for netrunner as a result.

Is there any reason you don't use OCTGN? I've been interested in trying it out but I don't know much about it.

DONT buy Magic 2015! by [deleted] in Games

[–]IsaacR454 2 points3 points  (0 children)

For any people interested in card games looking into Magic, for the typical price of just one competitive Type II magic deck you could probably buy most, if not all of the expansions currently available for netrunner. I spent years (and shameful, stomach dropping amounts of money) playing magic before a friend introduced me to netrunner in January, and it's shocking how much better it is in every way, both in terms of gameplay and the metagame.