Ever wondered why steel buildings seem earthquake-resistant? Read on to find out the reason.
When earthquakes happen
Before you can fully grasp how steel buildings are able to survive earthquakes, you need to understand the phenomenon itself.
Earthquakes happen because of the tectonic plates that cover the Earth’s surface. Each plate has a tendency to move relative to another; this can be caused by centrifugal forces (due to the rotation of the Earth), gravitational forces (from the Moon and Sun) as well as convection forces (coming from the Earth’s core). However, the movement is hindered by friction. In times when the stresses between the plates are very intense, friction no longer suffices and the movement of plates become inevitable. The plates either move against each other by bumping or sliding or come together. Most times, the movement is unnoticed because it is not considerable—changes that measure a millimetre or so are not bound to draw attention. But there are also times when movement is more apparent, causing physical changes that are not only seen but also felt.
It is important to note that earthquakes have both vertical and horizontal components. This means it can move the surface not only up and down, but also side to side.
How earthquakes affect buildings or structures
It is not the vertical motion that usually causes damage or brings about the ruin of a building or structure. All structures, even those which are not constructed well, can handle vertical loads. One proof of this is the ability of all buildings to carry their own weight without falling apart. Another proof is the ability of existing structures to withstand heavy rains and snow. Moreover, there is the ability of buildings to be expanded vertically—existing structures can be made higher with the addition of new floors and the latter will not necessarily compromise the former’s stance.
If buildings and structures can deal with vertical loads like the aforementioned, then they can handle vertical movement caused by earthquakes. What these cannot handle are horizontal loads, unless they were constructed with these loads in mind.
The swaying motion of earthquakes, particularly the strong variety, can do a lot of damage to existing structures. Structures that are more vulnerable to damage are those that have more weight and height.
The more weight there is (as contributed by additional storeys and walls for partition), the more force the structure is subjected to. The more force there is, the more likely a collapse will occur. Consequently, the higher the building and the more weight it has, the more extensive the damage in the event of an earthquake.
How steel buildings resist earthquakes
Buildings and other structures will be able to resist earthquakes if they are built with consideration to possible sideways loads. Also, they are less likely to fall apart and crash if their foundations were strengthened prior to adding additional weight.
There are some buildings that resist earthquakes better than others, and one of these are steel buildings. Compared to buildings made from other materials, steel buildings are known to behave well during earthquakes. The ability of steel buildings to resist earthquakes can be attributed to three things: low weight, flexibility and ductility.
For buildings to endure amid the damaging effects of earthquakes, they have to be light. The lighter the structure, the better it will behave during an earthquake; this is because low weight means less loads. Steel buildings are considered low weight because they are lighter compared to buildings constructed with other materials. With lower mass comes lower seismic design forces, and in turn, better adaptability to sideways loads.
The flexibility of steel is also responsible for the buildings’ notable behaviour during earthquakes. Steel structures are not as stiff as those made with other materials, and thus do not attract larger forces. If forces applied in the structure and its foundations are lower, then the steel building is less likely to fall apart or be damaged.
However, it is the ductility of steel buildings that makes them most impressive. Steel itself is a ductile material—it is durable, designed and manufactured by qualified professionals. But the way steel buildings are constructed also add to the structure’s ductility. Steel structures are made of smaller sections, which are created to form plastic zones. In the event of an earthquake, only the said zones will be affected. Excessive seismic effects will be absorbed because more energy dissipates through the plastic zones of the building.
Considering how well steel structures behave in the midst of an earthquake, you should not worry too much about industrial steel building prices. After all, what you get after the purchase is an investment worth every penny.