Why, if arch’s are the best for bearing loads are the majority of modern structures made with using 90 degree angles?



Seems like they would be better for areas with earthquakes, hurricanes, and high wind while also being more durable in general.

In: Engineering

Because modern building techniques dont rely on tension destribuition in localised spots as instead tension forces are distributed throught the steel beams on the inside of the buildings.

Also has to do with regionalism, places where there was such architecture tend to show modern examples of old techniques, in example in Italy and Portugal romanic arches are more comon in the south and gothic arches in the north, in Ohio or Montreal neither are common

Arches are the best at bearing loads, but are not the more practical. Advances in materials and design make it so we don’t need to use _the best_ system.

If a Ferrari is the best for going fast (for argument sake) why would you ever buy a luxury car? Shouldn’t pizza delivery deliver in a Ferrari to save time?

Aches have a huge advantage if you build in a material that has high compression strength but low tensile strength. That means strong if you compress them but week if you try to pull them apart. An example is concrete, bricks, stones you put together with or without mortar

The advantage is a lot lower if you have material that can have high compressive and tensile strength. Examples are steel, reinforced concrete.

You have a lot of arches in old stone building because that was the only way you could build it and support the load. Today you can do the same with horizontal steel or reinforced concrete beams.

There is a relatively well know the quote

>Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.

The general meaning is that building something strong is not hard the problem is if you what to build is at a reasonable cost. For a building, there is also the amount of usable space, windows sizer etc.

There is a lot of prefabrication today where you move the part to the building site and assemble there both steel and reinforced concrete. The flat part is simple to make and simpler to transport

It is not hard to build stuff that survives earthquakes, hurricanes, and high winds. It is hard to do that at a reasonable cost and having a large internal volume.

So arches are a lot less needed today than in the past because we can build strong enough without it at a lower cost. If you see a short arch it is likely for the visual, not the strength.

But they are still used when it is the best option like if you build a [concrete bridge with a ](https://en.wikipedia.org/wiki/List_of_longest_arch_bridge_spans#/media/File:Qinglong_Railway_Bridge.jpg)[445-meter](https://en.wikipedia.org/wiki/List_of_longest_arch_bridge_spans#/media/File:Qinglong_Railway_Bridge.jpg)[ span](https://en.wikipedia.org/wiki/List_of_longest_arch_bridge_spans#/media/File:Qinglong_Railway_Bridge.jpg)

Arches can be good if you don’t care about the depth required for a structure to work.

Look at all the buildings you see where there are arches as the primary structural system – the floor to floor heights are **enormous**. This is because you need a huge depth of structure to work, especially around the perimeter.

Once we developed structural durable materials capable of taking tension (ie steel) we moved to structural systems that are much more efficient, and require a much shallower structure. Instead of a 20 foot tall arch you can have a two foot steel beam system. This enables high rise construction.

Masonry arches, the type of arch you see in buildings, are also very very heavy compared to structural systems we use today – so for multiple floors require enormous foundation systems.

They’re also not great in earthquakes – the enormous mass means they pick up enormous earthquake forces, but aren’t very ductile so have bad failure modes when trying to dissipate those forces.

The cases where you do still see them are things like bridges where the height of the structure isn’t often a critical concern, and in these cases can be efficient structures.

Arches are great in static compression, but an earthquake can make them crumble.

Once you start adding rebar for stability and tensile strength, it is more efficient to make multiple levels with columns and beams and slabs. Arches are still pretty good if doing only one big space.