Earthquake Engineering
There are many regions around the globe that are at constantly at high risk of being affected by seismic waves, otherwise known as earthquakes. The reason that earthquakes tend to happen in the same areas is due to the movement and position of tectonic plates that consist of the crust and the upper mantle. In total, there are about 7 major plates and many smaller ones. Areas that get shaken by high magnitude earthquakes often are the places that are aligned between 2 different plates that rub against each other which cause the rumbling. One example of such place is the great state of California, with beautiful and diverse landscapes, nice beaches, great weather…and the occasional violent earthquake. California lies on two tectonic plates called the Pacific Plate which moves upwards and the North American Plate which travels downwards (shown in the picture below). When these two plates come in contact and rub against one another, it causes very intense vibrations which are the cause of the shaking.
The first image shows the hazard of earthquakes (red is high risk). The second picture shows the direction of the North American Plate relative to the Pacific Plate along the west coast. You can see that areas that are on top of the edge of a plate have a higher risk of earthquakes.
Unfortunately, preventing an earthquake from occurring isn’t exactly possible since superman doesn't exist however, cities in high risk
areas can take measures to minimize the damage as much as they can. One of
the main consequences of earthquakes is the damage done to buildings. In some
cases, if the structure isn't strong enough, it can collapse completely. In
order to prevent this, engineers need to design and build structures in a
certain way to make them earthquake resistant. This is known as earthquake
engineering. There are also methods of strengthening existing structures known
as seismic retrofitting, however I’ll be talking about the former.
The process of building an earthquake resistant building
starts way before the construction and even the design. Before planning
anything out, engineers have to determine the seismic activity in the area
which they are building. One of the things they must consider is the
probability of a major earthquake occurring for the next couple of decades.
They also look at previous earthquakes to determine the risk of another one.
Once the first step is complete, they can move on to designing the building.
When creating a building in an area with high seismic activity, engineers tend
to avoid structures with unique shapes such as “t” shaped or hourglass
buildings since they would not be able to withstand the force of an earthquake
although they are visually appealing. One way of making a building earthquake
resistant is to make it triangular. This is not the primary choice since today
we have better technology and new methods, but since the shape causes the
center of gravity to be rather low and the majority of the weight of the
structure lies in the bottom portion, it can be a reliable way to reduce the
shaking of the building.
The main method that is used today is a base isolation
system. Its function is to physically separate the base of the building from
the floor using a mechanism.
There are different types of base isolations. One of them is
the spherical sliding bearing system which supports the building with rounded
and low friction bearing pad. The rounded bearing pad allows the building to be
less affected by the shock of the earthquake by allowing it to slide
horizontally smoothly.
This video explains and shows how the effects of an earthquake can be minimized in this base isolated building in LA
The second method is the lead-rubber bearing system which is
commonly used for earthquake resistant buildings. They are made by many alternating
layers of rubber and steel plates that are firmly compressed against each other.
The job of this block of rubber/steel is to move left and right very flexibly along
with the movement of the earthquake to allow the building to feel less of the
shaking. In other words, while a structure that has a fixed base (not resistant
to earthquakes) is susceptible to shaking violently due to the earthquake, an isolated
base structure remains less affected due to the mechanism that takes the shock
in between the ground and the structure.
Here we can see the function of the base isolation. The fixed-base building is clearly having a bad time compared to the isolated building...
Its a great thing that humans have discovered ways to prevent earthquakes and other natural disasters from causing too much damage to urban areas with large skyscrapers and structures. I guess our next goal is to find a solution for the possibility of an alien invasion...
