High-Rise Buildings

As those who follow my articles know, especially after the earthquake, because of the pain in my heart due to the loss of life, and also because of the personal love of rent and, in my opinion, a collective almost immoral level of carelessness and shamelessness that the country has been dragged into in terms of construction, my articles on these issues are usually critical.

Although I am a civil engineer myself, let's just say that due to my disappointment in the contracting sector, I realized that this business cannot be solved by engineering anymore.

That's why I've been saying in a few of my articles that we need to build low-rise buildings with tunnel formwork type concrete shear walls, especially in residential buildings. 

The general opinion is that earthquake loads are lower in low-rise buildings than in high-rise buildings and therefore, if sufficiently robust and low-rise buildings are built, if the ground conditions are also suitable, such buildings are safer. 

The calculations actually prove this statement.

The reason why I say that we should build tunnel formwork style buildings in residential buildings is not because high-rise buildings are bad. 

I say this because we as a country, with this point of view and within the established order, unfortunately, we cannot do these things as we should.

When we have engineers who do not know how to do projects properly, without even doing a proper ground investigation and with poor workmanship, just for the sake of rent, and when there are unscrupulous contractors and corrupt public cadres in these matters, I have recently started to think like this because I cannot find any other solution.

However, in order not to be misunderstood, let me tell you about some of the features of high-rise buildings in this article.

During my years as a project engineer, I had also done projects of such tall buildings. 

And for those days, there were quite high buildings like 200 meters among the projects I worked on.

In fact, these high-rise buildings, i.e. skyscrapers, can be quite safe structures for earthquakes with a good design. 

In other words, high-rise buildings can actually be quite robust in terms of resistance to earthquake loads.

In this article, I will not touch on other problems of high-rise buildings that I think are problematic.

Without going into too much detail, let me try to explain why high-rise buildings can also be safe.

First of all, I should start by explaining how earthquakes affect buildings.

As you know, the effect of this natural phenomenon we call earthquake is the shaking of the earth's crust for a certain period of time. 

This shaking is just like shaking a cake on a tray in your hand left and right.

Or do you know how to fry an egg?

When the egg reaches a certain consistency, I shake the pan back and forth a few times to make sure the egg doesn't stick to the pan. Something like that.

Under the ground, rock masses fracture at some point due to tectonic movements and the tremor caused by this fracture spreads in waves to distant places. 

When I say far away, I mean as far as an earthquake in Malatya that destroys Hatay. So it can be kilometers away.

In fact, there has been a one-time big movement somewhere underground.

But the spreading effect of this movement reaches us in the form of waves.

It is the job of geological or geophysical engineers to measure or calculate the intensity and density of these waves. 

However, depending on the geological structure of the layers underground, the waves that propagate differ. Sometimes the wavelength shrinks as it passes through one layer, then increases when it enters another layer.

The whole wave propagates like this in all directions until it is damped.

When there is an earthquake somewhere, seismic devices can measure the epicenter and magnitude of that earthquake even in America. In other words, earthquake waves set off from Malatya and reach even America.

For us civil engineers, the forces that these waves create on the structures we build are much more important to us.

Therefore, we are more interested in the acceleration created by the waves of the earthquake exactly where we will build the structure rather than the magnitude or intensity of the earthquake according to the Richter scale.

What is acceleration? 

You know when you step on the gas in a car with a powerful engine and your back sticks to the seat? 

This is what acceleration does. 

So maybe we can say the speed at which the vehicle accelerates. The faster the vehicle accelerates, the more acceleration it creates on you. That's why you stick to the seat in a vehicle with a very powerful engine.

Earthquake waves also have accelerations, just like the vehicle example.

These accelerations create forces on the building, mostly in the horizontal direction, in proportion to the mass of the building.

The formula is simple, maybe you all remember it from high school. 

F=m.a

In this formula, "a" is the acceleration, "m" is the mass and "F" is the force acting.

The building keeps shaking this way and that way, each time according to the oscillation of the earthquake wave.  

This shaking occurs mostly in the horizontal direction and at certain frequencies as the earth's crust moves left and right. 

There can also be earthquakes acting in the vertical direction, but you need to know that all these tremors are irregular tremors that vary with each earthquake.

These tremors can be likened to an accelerating effect, like someone pushing us from behind while we are swinging on a swing.

In other words, the earthquake waves are not like calmly swinging from side to side on a swing, but like someone pushing us from behind every time and in both directions, giving us a force to accelerate.

And these pushes are not regular. Sometimes there is an irregularity, such as when a force is applied in one direction and suddenly a force is applied in the other direction, with different forces each time.

When our building starts to sway under the influence of these tremors, its natural periods, which are related to its length, rigidity and mass, come into play. 

I have previously explained the natural period with the example of a sapling planted in the ground or a plastic ruler.

When the shaking frequencies of earthquake waves coincide with the natural periods of our building, if the building resonates, its collapse will be inevitable.

But if the frequencies of the earthquake waves and the natural periods of our building do not match, then there is nothing to fear. 

When you design reinforcement and concrete that can withstand the acceleration of the earthquake and the possible loads on the building, no matter how high your building is, it will be designed to be resistant to earthquakes.

It is possible to calculate the natural periods of buildings and, if necessary, make some changes in the design to make a more suitable natural period structure.

In some cases, these adjustments can be made by placing a weight on the top of the buildings.

In fact, when this weight is designed as a moving weight, it can also be useful in terms of absorbing earthquake loads.

In short, it is possible to envision different designs for this purpose. 

I guess this is a bit technical. But in essence, 

Thoroughly check the ability of the building's ground to transmit, amplify or attenuate seismic waves in a possible earthquake,

✓ good calculation of the highest possible acceleration of the earthquake waves that will be transmitted by this earthquake according to the magnitude of the earthquake that may occur on a nearby fault line

Taking care that the frequencies of earthquake waves and the natural periods of the building we will construct do not coincide

✓ also in case of a design resistant to lateral and vertical loads caused by earthquakes,

You can accept that any building, no matter what height, can be safe against earthquakes.

In saying this, of course, some presuppositions cannot be overlooked.

First of all, it is not possible to be sure of the magnitude of a possible earthquake. 

It is possible to make some predictions based on historical records and on-site geographical examinations and shifts on fault lines, but these predictions are not certain. 

In other words, when we say that our building is strong, we cannot ignore the fact that it has been designed according to possible risks.

We also cannot rule out the possibility of a hidden fault that has not been detected so far. 

Faults behave in the same way as a crack in the windshield of a car moves across the windshield, sometimes it is not clear which way it will go. 

Because they are big cracks in the tectonic plates underground. 

Tectonic layers are likely to be exposed to many factors, from their thickness to the mobility of the magma beneath them, as well as the direction in which the cracks that form on them will move.

In other words, there is no guarantee that an earthquake will not occur tomorrow, even in a place that we say is very safe today, there has never been an earthquake here.

A final factor is the properties of the earth's layers between the center of the earthquake and your structure to transmit earthquake waves. 

If these studies have not been carried out well in time, it may not be of much importance that you have gotten a geological report by drilling where you have built your building. 

Such effects can only be revealed through large-scale geological surveys.

Such impacts can only be revealed through large-scale surveys in the region. This means that it is necessary to conduct research that can only be done by the state.

In short, the subject is quite deep. A lot of research has been done so far, but there is still a lot of work to be done.

Based on the records of earthquakes that have happened so far, it is possible to build high-rise buildings with good engineering work, since the possible earthquake wave periods and accelerations are known.

Nevertheless, if there are effects on the building that we cannot take into account in a possible earthquake, then there is nothing left to do.  

However, I can say this. High-rise buildings can be even more durable than a two-story building if they are well designed.

In fact, in high-rise buildings, an elevator tower in the middle and a frame consisting of columns and beams around it can give much better results than a structure consisting only of concrete curtains. 

This is because elevator towers consisting only of concrete walls work differently in terms of earthquake loads, while the surrounding frame consisting of a column and beam system works differently under earthquake loads.

Since these two support each other in high-rise buildings with a good design, they give much better results together.

Of course, it is necessary to connect the two systems at the top with a large tie beam. This tie beam, as I call it, should have a depth perhaps as much as the height of the floor.

In a very tall building, sometimes it can be useful to consider tie beams on the mezzanine floors. Since such intermediate floors can already be used as technical floors in high-rise buildings, there is no problem in terms of tie beam design.

The design of high-rise buildings requires a lot of engineering knowledge, from the special design of elevator shafts consisting of concrete curtains according to buckling.

Anyway, with good engineering, no matter what you design, there is no problem.

I think our problem is that we don't give importance to engineering and science.

That's why I still haven't given up on my idea.

The solution is tunnel-molded buildings, low-rise. Yes, they are ugly and they all look alike. But at least they are durable.

If my friends who are architects design nice looking buildings using tunnel formwork, why not. It is also possible to make beautiful buildings with tunnel formwork.

Let's say that's all for now. 

Stay with science, you cannot be wrong.

Love and respect to everyone from Moscow