Skyscrapers are products of civil engineering. Experts are predicting that buildings will go over 3200 feet high. And there could be a one-mile skyscraper by 2050. Planners are also predicting over 6 billion people will be living in the city.
In fact, California and Stanislaus County Project Management is coming up with plans to accommodate more people in the cities thanks to brilliant skyscraper engineering.
One classic skyscraper is the New York Empire State Building. The slender 96-story building was built in the 20th century and overlooks Central Park. But what is impressive is the footprints at the ground level.
Another iconic landmark is the Skidmore, Owings & Merril. According to the structural engineer (Bill Baker), this building will stand the test of time.
So, how do engineers make more for less?
The design and construction of skyscrapers
One concept about skyscraper engineering is that a building must support its weight. In addition to that, it must protect the occupants from fire and should resist winds. Yet, the skyscraper should provide a comfortable climate, and all floors must be accessible.
The basic design
Given the high cost of construction, skyscraper engineering ensures there is no single chance of failure. The building should be in a position to resist all loadings. But if it fails, there’s a question of lack of foresight.
One aspect of skyscraper engineering is the special substructure. The pit that holds the substructure must go all the way to bedrock. But first, the topsoil must be removed to build a foundation.
Loading and vibration
One fascinating fact about skyscraper engineering is that the weight of the building comes from the material itself. From a technical perspective, the weight of the structure should be greater than the weight of the furniture, people, etc. The vertical tubes can come in different categories like:
- Sheer walls
- A tube design
- Steel frames
- Concrete cores
Another important aspect of engineering is the wind loading speed. Since the wind pressure increases with weight, tall buildings come with live or dead loads. Other factors that affect the vertical and horizontal load come from unpredictable sources like an earthquake.
This is a classic concept in skyscraper engineering. It entails a large steel box with a few boxes inside. Because steel is a strong material, the skyscraper can be built with vertical and horizontal support throughout. While this may look like a simple method, it has drawbacks.
More material is needed to reduce the distance between the support members. And this is quite uneconomic for tall buildings that go beyond 40 stories. Of course, the unused floor spaces can be reduced using more steel.
Steel offers superior strength because it’s an alloy of iron and carbon. And it’s no wonder it’s used in large scale construction. Steel is resilient, strong, and durable. In the late 1960s, a renowned engineer of Bengali descent came up with a formula that allows skyscrapers to reach a new height.
Fazlur Khan is believed to be the father of the tubular design of skyscrapers. He first introduced the concept while working at Merrill’s Chicago Office and Skidmore Owings. And any skyscraper that was introduced after 1960 used the same skyscraper engineering principles.
According to Khan, a framed tube is a simple design that can be adapted to circular, square, rectangular, and freeform shapes. His construction engineering principles further categorized the design into two:
- Braced tube / Trussed tube design
- Bundled tube
The braced tube features spaced exterior columns while the bundled tube was tied together to resist lateral forces. For example, the Willis Tower in Chicago used the bundled tube design by using tubes of different heights. Keep in mind that the tube units can have different shapes and can be bundled into different units.
But the beauty of Khan’s engineering is that it used concrete or steel to reach lofty heights. More interestingly, the composite of concrete or steel could reach a height of 828 meters. According to Khan, the amount of steel used to create the tubular design is half that of the steel frame.
Shear walls are strong and have high stiffness. They can support gravity loads and can resist horizontal loads. And that’s why they are unique in skyscraper engineering applications. So, what’s a sheer wall?
From a skyscraper engineering perspective, sheer walls can resist the axial load and any movement induced by the lateral load. In simple terms, a sheer wall increases the rigidity for load resistance.
In the construction of skyscrapers, the shear walls can be seen as vertical elements for resisting loads introduced by earthquakes and wind. This explains why the walls come in different shapes like irregular cores or rectangular shapes.
Over the last few years, the use of shear walls in skyscraper engineering has gained popularity – for good reasons. They are common in the construction of a service apartment or office blocks. And this system is effective as it allows for the construction of a 35-story building.
From a statistical standpoint, no building with shear walls has ever collapsed due to elements like an earthquake or strong winds.
Reinforced concrete (RC) Shear Walls
Reinforced concrete walls start from the foundation and go all the way to the height of the building. In one statement made by structural engineer Mark Fintel – you cannot have a strong building that can withstand earthquakes without RC sheer walls. Another important thing to note is that sheer walls must be symmetrical to reduce the ill-effects of twists in buildings.
Confusing the wind
In the real world, you may be wondering what prevents the skyscrapers from swaying. It’s all about taming the wind. If you happen to check a building like the Grand Hyatt on a windy day, you may notice the skyscraper creaks a bit when the wind moves back and forth. But this is not a structural problem.
In any skyscraper engineering, the wind has been an important factor to consider. Since the first skyscraper was opened in the late 1880s, engineers have to think about wind loading.
So, how does a tall building like Burj Khalifa withstand the wind? It rises 2717 feet into the sky and has remained the world’s tallest building. As the altitude increases, the building should be designed in a manner that it can conquer the wind.
The first thing you’ll note is that the building rises high in stalks. It brings somewhat an odd-looking design that prevents the air from being organized into whirlpools. This also prevents the formation of vortices that stop the tower from moving side to side. But even with such a unique skyscraping engineering design, the building will still sway about two meters at the top.
Another landmark that confuses the wind is the Taipei Tower. It stands a second distant of 1667 feet. Between the 88 and 92nd stories, you’ll find a giant pendulum. It’s designed to battle typhoons and windstorms. It swings gently to balance the tower and ensures the comfort of the occupants.
The New York Citi Group has also employed a unique mechanism to combat the wind. It has a tuned mass damper that is designed to reduce the impact of the wind on the scraper. As the wind pushes the building in one direction, the damper will swing to the other side. What this skyscraper engineering means is, you’re adding a component to deal with the wind rather than the building itself.
The wind specialists and structural engineers work meticulously to alleviate stress and ensure the comfort of occupants.
And just like a guitar string, buildings are inclined to vibrate, so you should ensure the frequency lines out just right. A key goal of skyscraper engineering is to disrupt an organized flow of wind.
If not addressed, strong winds can cause serious structural damage. Another key aspect of skyscraper engineering is that buildings follow the 100-year return rule. This means that the speed of the wind is expected to change once in a century. After the time lapses, designers should increase the strength by 60%.
But despite these measures, strong winds can still cause damage to windowpanes or a myriad of other issues. For instance, a light breeze may feel like a hurricane on the top floors. But if a skyscraper is engineered properly, you don’t expect excessive motions. An occasional creaking is normal.
Shock absorbers for supertalls
A great aspect of skyscraper engineering is the use of dampers. They work like counterweights that help to stabilize the structures. The engineers attach about 300-800 tons of steel to interfere with the local wind patterns. There are two types of dampers:
- Tuned mass dampers – these are more of swinging pendulums
- Slosh dampers – they consist of a large pool of water that helps to absorb vibration
Generally speaking, a damper consists of a piston and head filled with silicon oil. When the building moves in a horizontal motion, the damper transforms mechanical energy into heat.
With skyscraper engineering, architects use cleaver technologies to mitigate the effect of earthquakes. And as a result, the occupants can come out unharmed. Other tactics include:
Use of pendulum power
This is another unique aspect of engineering that allows you to spend enormous mass at the top of the structure. Each pendulum is tuned to match the vibrational frequency of the building.
For example, the Taipei 101 building uses a pendulum power to mitigate the effects of strong winds and earthquakes. At the heart of the system, there are eight suspended steel cables.
In many high-rise buildings, you’ll find a core wall construction. The rocking core wall refers to reinforced concrete that runs through the heart of the structure. This kind of construction can withstand earthquakes and strong winds. For extremely tall buildings, the rocking core wall should be 30 feet and can be between 18-30 inches thick.
Carbon fiber wrap
Another aspect of skyscraper engineering is adding base isolation systems. The reinforced fiber plastic wrap mixes carbon fibers with other materials to create a lightweight but incredibly strong structure.
When using this method, the engineers wrap the material on concrete to create an epoxy gap between the material and concrete. You can also create a mummy-wrapped beam that has incredible strength.
The levitating foundation
For many years, engineers have been using base isolation to protect buildings from the effects of an earthquake. This involves floating the building above the foundation.
How concrete is poured
Let’s face it: we haven’t moved beyond steel and concrete in technological advancement. Generally, skyscraper engineering allows a building to support much weight with less material. The truth is, concrete continues to gain massive power due to the unique chemical composition.
Skyscraper engineering ensures that you combine concrete and high-strength steel in different ways. But the most technological advancement is the use of unique designs.
Unlike ordinary concrete, the concrete used in skyscrapers has to be reinforced. For example, the Burj Khalifa building had to take more than 300,000 cubic meters of concrete. A mixture with high comprehensive strength had to be made.
Building a high-rise building requires that you rethink the materials you use. Concrete that is reinforced with microfibers can have massive strength to withstand strong winds.
The elevator conundrum
The traditional elevator can run for a limited 1600 feet because the wire can’t reach higher than that. What this means is that super-tall buildings can take valuable floor space.
Given that many people cannot climb more than a few stairs, the elevator conundrum is an invention of the skyscraper. A key aspect of skyscraper engineering is that the building requires more elevators. This means that there has to be a dedicated area for shaft ways. And this is where a conundrum comes in.
Many tall buildings like the John Hancock Center and the World Trade Center Tower use express elevators. So, engineers can place conundrums on top of each other to save space.
Some buildings like the Petronas Towers have double elevators that allow more people to reach the top. The only downside with double elevators is that all people have to stop when a few want to get to a specific floor.
Without cables being confined in an elevator cabin, you can have a bus system with multiple cabins. And just like airplane cabins, an elevator can be pressurized to help in the transition of higher altitudes. They can also move faster to reduce the waiting time.
Skyscraper engineering continues to be one is one of the greatest achievements in the world.