Taipei 101 - Structural Engineering Explained

Summary

This video delves into the structural engineering marvel of Taipei 101, a 508-meter tall building in Taipei, Taiwan. It highlights the building's resilience to typhoons and earthquakes, achieved through a combination of a mat foundation with bored piles, a concrete raft, and a superstructure inspired by bamboo's flexibility. Key features include a tuned mass damper to counteract wind forces, outriggers and belt trusses for stability, and a unique design that reduces wind impact by 40%. The video provides an in-depth look at the engineering solutions that make Taipei 101 an iconic symbol of architectural ingenuity.

Takeaways

• 🌐 Taipei 101 is an architectural marvel located in Taipei, Taiwan, and was the world's tallest building from 2004 to 2010, standing at 508 meters.
• 🌪️ The building is designed to withstand typhoons, earthquakes, and difficult soil conditions, including a magnitude 7.1 earthquake during construction and a category 5 typhoon in 2015.
• 🏗️ The foundation system includes mat foundation with bored piles due to the presence of soft soil and soft rock beneath the site.
• 💧 Slurry walls were constructed to prevent water and soil caving in during the foundation laying process, as the water table is just 2 meters below the surface.
• 🏢 The building's superstructure is inspired by ancient pagodas and bamboo, incorporating outriggers and belt trusses every 8 floors to mimic bamboo joints.
• 🛠️ The structure uses a combination of steel (420MPa) and concrete (70MPa) to optimize strength and reduce foundation costs.
• 🌬️ Wind tunnel tests led to the design of 'saw tooth' corners to reduce wind forces by up to 40%, improving the building's resistance to typhoons.
• 🏗️ A strong core and perimeter columns, including 8 'super columns' or 'mega columns', provide resistance to lateral loads from earthquakes and wind.
• 🔩 The building employs a Special Moment Resisting Frame (SMRF) with 'dogbone' detailing for ductility, designed to withstand 0.5-g ground acceleration.
• 🌀 A 726-ton Tuned Mass Damper (TMD) at the top of the building counteracts wind-induced sway, enhancing occupant comfort during strong winds and typhoons.

Q & A

What are the main challenges faced by Taipei 101 in terms of its structural design?

Taipei 101 faces challenges such as typhoons, earthquakes, difficult soil conditions, being near an active fault line, and a high water table just below the surface.

How does Taipei 101's design ensure flexibility to resist earthquakes and stiffness to resist typhoons?

The building uses a combination of outriggers, belt trusses, and a tuned mass damper (TMD) to provide flexibility and stiffness, allowing it to withstand earthquakes and typhoons.

What is the significance of Taipei 101's location in terms of its structural requirements?

Located in Taipei, Taiwan, which is prone to earthquakes and typhoons, the building's design had to account for these natural phenomena, leading to a structure that is both flexible and stiff.

What is the height of Taipei 101 and its current ranking among the world's tallest buildings?

Taipei 101 stands at 508 meters tall and is currently the 10th tallest building in the world.

What materials were used in the construction of Taipei 101, and what are their respective strengths?

The building uses steel with a strength of 420MPa (60ksi) for 80% of its steel content and concrete with a strength of 70MPa (10,000 psi).

Can you explain the foundation system used for Taipei 101?

The foundation system includes mat foundations with bored piles, slurry walls to deal with the high water table, and a concrete raft on top of 380 piles for the tower and 167 piles for the podium area.

How does the design of Taipei 101's superstructure contribute to its resistance against wind and seismic forces?

The superstructure design, inspired by bamboo, includes outriggers and belt trusses every 8 floors, a strong core, and perimeter columns to resist lateral loads from wind and earthquakes.

What is the purpose of the 'saw tooth' or 'double notch' corners on Taipei 101?

These corners were designed to reduce wind forces by up to 40%, as sharp corners on a square building can produce large crosswind forces.

How does the tuned mass damper (TMD) on Taipei 101 help in reducing the building's sway?

The TMD, a 726-ton pendulum, counters the wind force and reduces the building's sway during typhoons, enhancing occupant comfort and stability.

What is the role of outriggers and belt trusses in Taipei 101's structural system?

Outriggers tie the core and perimeter systems together to resist overturning forces, while belt trusses form a belt around the building, distributing tensile and compressive forces to the exterior frame columns.

How does the design of Taipei 101 ensure safety during seismic events?

The building is designed to stay up under a 0.5-g ground acceleration, with a strong core and perimeter columns filled with high-strength concrete to control drift and resist seismic forces.

Outlines

00:00

🏙️ Introduction to Taipei 101's Structural Engineering

This paragraph introduces the video's focus on the structural engineering behind Taipei 101, a building that has faced significant challenges such as typhoons and earthquakes. The building's location in Taipei, Taiwan, and its status as the 10th tallest in the world are highlighted. The video promises to delve into the building's design, including its foundation system, which had to accommodate difficult soil conditions and a high water table. The materials used, such as 420MPa steel and 70MPa concrete, are mentioned, setting the stage for a detailed exploration of the building's structural components.

05:01

🏗️ Foundation and Superstructure of Taipei 101

The second paragraph delves into the foundation system of Taipei 101, which includes slurry walls and bored piles to handle the soft soil and water table challenges. The tower's 21-meter deep basement and the use of a concrete raft to transfer loads are discussed. The superstructure's design, inspired by ancient pagodas and bamboo, is described, including the use of outriggers and belt trusses every eight floors to mimic bamboo joints. The building's resistance to wind and seismic forces is introduced, with mention of wind tunnel tests and the innovative 'saw tooth' corners that reduce wind forces by 40%.

10:02

🌪️ Wind and Seismic Resistance of Taipei 101

This paragraph discusses the wind and seismic forces that Taipei 101 is designed to withstand, including the building's location in a high typhoon zone. The building's core and perimeter columns are highlighted as crucial for lateral load resistance. Details of the building's super columns, braced core, and the use of special moment resisting frames (SMRF) are provided. The design philosophy of prioritizing wind resistance over seismic ductility is explained, along with the use of 'dogbone' details for ductility. The paragraph also covers the structure below level 26, including the sloping super columns and the integration of floor beams and core columns.

🛠️ Outriggers, Belt Trusses, and Mass Damper

The final paragraph explains the role of outriggers and belt trusses in台北101, which are designed to resist overturning forces and distribute tensile and compressive forces. The design of the outriggers, inspired by bamboo joints, and the belt trusses that connect perimeter columns are described. The paragraph concludes with a discussion of the building's tuned mass damper (TMD), a 726-ton pendulum that counteracts wind forces and increases occupant comfort during strong winds. The TMD's operation during a category 5 typhoon and its safety measures during earthquakes are also mentioned, emphasizing the building's innovative engineering solutions.

Keywords

💡Structural Engineering

Structural engineering is a sub-discipline of civil engineering focused on the design, analysis, and maintenance of structures. In the context of the video, structural engineering is crucial for understanding how Taipei 101 was designed to withstand natural forces such as typhoons and earthquakes. The video discusses how the building's design, including its foundation system and superstructure, is a testament to the ingenuity of structural engineering.

💡Typhoons

A typhoon is a powerful tropical storm with heavy rain and strong winds. The video highlights the challenges posed by typhoons to tall structures like Taipei 101, which is located in a high typhoon zone. The building's design incorporates features to resist the lateral forces generated by these storms, such as the use of 'saw tooth' corners to reduce wind forces by up to 40%.

💡Earthquakes

An earthquake is the shaking of the Earth's surface caused by the sudden release of energy in the Earth's crust. The video mentions that Taipei 101 was designed to withstand earthquakes, including a magnitude 7.1 earthquake during its construction. The building's superstructure, including its outriggers and belt trusses, plays a critical role in absorbing and distributing the forces from seismic activity.

💡Foundation System

A foundation system is the base of a structure that supports the weight of the building and transfers it to the ground. The video explains that Taipei 101's foundation system includes mat foundations with bored piles due to the soft soil and stiff colluvial soil at the site. The foundation system is essential for the stability of the building, especially considering the high water table and the need for a 21-meter deep basement.

💡Outriggers

Outriggers are structural elements that resist overturning forces in a building. In the video, outriggers in Taipei 101 are described as vertical braces that tie the core and perimeter systems together, helping to reduce the rotation of the core under lateral loads. This feature is particularly important for a tall building like Taipei 101, which needs to withstand strong winds and earthquakes.

💡Belt Trusses

Belt trusses are horizontal structures that encircle a building, helping to distribute forces across the building's frame. The video explains that Taipei 101 uses belt trusses at every eight floors to gather and transfer the weight of the building to the super columns. These trusses play a vital role in the building's lateral stability and resistance to wind and seismic forces.

💡Super Columns

Super columns, also known as mega columns, are large, heavily reinforced columns that provide additional strength and stiffness to a building's structure. The video describes how Taipei 101 has eight super columns filled with high-strength concrete, which are crucial for controlling drift and resisting the lateral loads from wind and earthquakes.

💡Mass Damper

A mass damper is a device used in tall buildings to reduce the sway caused by wind and seismic activity. The video details the tuned mass damper (TMD) installed at the top of Taipei 101, which acts like a giant pendulum to counteract the building's movement. The TMD increases occupant comfort during strong winds and typhoons by reducing the building's sway.

💡Vortex Shedding

Vortex shedding is a fluid dynamics phenomenon where vortices are shed from the sides of bluff bodies (like buildings) as the fluid (such as wind) flows past them. The video mentions that Taipei 101's design includes 'saw tooth' corners to mitigate the effects of vortex shedding, which can cause large alternating forces on a building and lead to significant motion.

💡Composite Steel and Concrete Floor

A composite steel and concrete floor is a type of floor construction that combines steel and concrete materials to create a stronger and more efficient structure. The video notes that Taipei 101 uses composite steel and concrete floors, which are typically 135mm thick. This type of floor construction is beneficial for high-rise buildings as it provides both strength and flexibility.

Highlights

Taipei 101 is an architectural marvel designed to withstand typhoons, earthquakes, and difficult soil conditions.

The building is currently the 10th tallest in the world, standing at 508 meters.

80 percent of the steel used has a strength of 420MPa, and the concrete used is of 70MPa strength.

The foundation system includes mat foundation with bored piles due to the presence of soft soil and soft rock.

A 21-meter deep basement was required for the tower due to the high water table.

Slurry walls were constructed to prevent water and soil caving in during foundation construction.

The tower's main foundation consists of 380 piles, each with a diameter of 1.5 meters.

The superstructure is inspired by ancient pagodas and bamboo, featuring outriggers and belt trusses every 8 floors.

The building has a square core with 16 box columns braced by moment frames.

Eight 'super columns' or 'mega columns' are filled with high-strength concrete to control drift.

Wind tunnel tests led to the design of 'saw tooth' corners to reduce wind forces by up to 40%.

Special moment resisting frames (SMRF) are used, with 'dogbone' detailing for ductility.

Outriggers and belt trusses are used to resist overturning forces and distribute lateral loads.

A 726-ton Tuned Mass Damper (TMD) at the top of the building reduces sway and increases occupant comfort.

The TMD pendulum is 6 meters in diameter and is made up of stacked steel plates.

The building is designed to withstand a 0.5-g ground acceleration during earthquakes.

Taipei 101's engineering solutions make it a remarkable icon in the field of architecture and engineering.

Transcripts

Hi guys this is structures explained and in this video we will be learning about structural

engineering behind Taipei 101.

Before we get into the video, please consider subscribing to the channel and hit the bell

icon to get notified for new videos.

Typhoons, earthquakes, difficult soil conditions, site present near an active fault line, Water

table just below the surface, all applied to a structure more than half a kilometer

tall.

Taipei 101 is an engineering and architectural marvel.

The structure witnessed an earthquake of magnitude 7.1 during the construction and recently,

a category 5 typhoon in the year 2015.

Hence the building must be flexible enough to resist an earthquake and stiff enough to

resist a typhoon.

Taipei 101 is located in Taipei, which is the capital of Taiwan, located in east Asia.

It is currently the 10th tallest building in the world at 508 meters and was the tallest

building in the world from 2004 to 2010.

The project consisted of a 5 storied retail mall and hundred and one storied office tower.

If we see the site in plan the yellow portion is for the tower and blue for the retail mall.

80 percent of steel used in the building is of 420MPa strength or 60ksi while concrete

used is of 70MPa strength or 10,000 psi.

Now let us look at the foundation system used for the building.

Here we are seeing the buildings section with ground level and basements for podium and

tower.

Soft soil in the form of clay, and stiff colluvial soil is present just below the site of Taipei

101, which has low load bearing capacity.

Soft rock in the form of sandstone is present beneath 40 to 60 meters, hence it required

mat foundation with bored piles.

The tower required a 21 meter deep basement.

Water table at site is 2 meters below ground which would create huge uplift forces on the

foundation of the building.

Hence slurry walls were constructed to lay the foundation below the tower.

Slurry walls are deep walls constructed on site to prevent water and soil caving in while

construction of foundation and excavation.

These walls surround both the tower and the podium and are 1.2 meters thick and upto 47

meters below ground.

Main foundation of the tower consists of 380 piles of 1.5 meter diameter and 167 piles

for podium area.

They were spaced 4 meters apart in staggered rows for tower portion.

A concrete raft of thickness 3 to 4.7 meters capped the piles and transferred loads from

columns and walls above.

Use of steel in the superstructure minimised the building weight which reduced the cost

of foundation.

Now let us understand the SUPER STRUCTURE of the tower.

The building is 508m above ground and resembles ancient pagodas.

It takes inspiration from Bamboo which is flexible and light, yet strong.

The bamboo has joints at intermediate locations which are mimicked by the building in the

form of outriggers and belt trusses at every 8 floors.

We will learn about outriggers and belt trusses in the later part of the video.

This separates the building into 8 identical modules.

At the top of 8th module sits a 9th module which has a smaller footprint.

This module supports a spire and contains equipment and an observation deck.

Below the 8 repetitive modules, a 25 story base, shaped as a truncated pyramid is present.

This base provides an improved overturning resistance and lateral stiffness compared

to a straight block.

The story height of each floor is 4.2 meters and retail floors below are 6.3 meters.

The floor is composite steel and concrete, typically 135mm thick.

Now let us know about the WIND and seismic FORCES acting on the building and ways the

building resist them.

Taipei 101 is present in a high typhoon zone which experiences winds of 156 kilometers

per hour with 100 year return period.

The building is impacted by alternating crosswind forces due to vortex shedding which means

wind passing the building separates from the sides producing alternating whirlpools.

Large forces can result when the time period of the building matches with the period of

vortex formation.

These winds can also damage the facade and partitions.

Wind tunnel tests were conducted which showed that sharp corners of a square building produced

large cross wind forces.

Hence ‘saw tooth’ or ‘double notch’ corners were provided which reduced the wind

forces by upto 40%.

For resisting the lateral load from earthquakes and wind a building needs a strong core and

perimeter columns.

Let us see a typical plan of the building above level 26.

The building has a square core made up of 16 box columns in four lines, which are generally

fully braced by moment frames between floors.The braced core is encased in concrete walls from

foundation to the 8th level.

The core box columns were filled with concrete of strength 69MPa till level 62.

The building has 8 ‘super columns’ or ‘mega columns’ which are steel boxes filled

with high strength concrete.

They are present on the perimeter of the building, 2 on each face.

These super columns were built up to level 90 of the tower.

They were filled with concrete of strength 69MPa from bottom of basement till level 62.

These columns controlled drift as large portions of drift is created at lower stories due to

overturning rotations.

The interstory drift and overall lateral motion were limited to Height by 200.

Super Columns were built from 50 to 80mm thick steel plates with welded splices.

Highest dimensions of the column are at 3 meters by 2.4 meters and vary along the height

of the building.

Internal cross ties resist bulging of the column.

Shear studs link concrete and steel together and rebars strengthened the concrete.

The building was designed to be stiff for resisting the wind forces first and then checked

for seismic ductility and seismic strength.

The steel framing used in the building is Special moment resisting frame also known

as SMRF.

Ductility was provided by using reduced beam section or ‘dogbone’ detail.

Steel moment frames along each sloping face of the building works in parallel with the

braced core and outriggers to counter seismic forces.

The building is engineered to stay up under a 0.5-g ground acceleration.

Now let us see the typical plan of the tower below level 26.

Below this level, super columns slope with the building’s profile as shown in the section.

Two columns of size 2 meters by 1.2 meters are added toward the center of each facade,

while each corner is supported by an additional 1.4 meters square, sloping box column.

Main floor girders shown in yellow connect each super column through moment connections

with a core corner column, along the same line.

Rest of the floor beams are shown in green in these typical plans below 26th level and

above 26th level which support the composite floor.

We can also see locations of stairs and shaft openings for elevators and utility services.

Now let's talk about Outriggers and belt trusses used in the building.

Outriggers are as the name suggests are extra structural members to resist the overturning

forces.

Boats and cranes as shown in the picture use outriggers to counter the overturning forces.

In structures, outriggers basically tie two structural systems together, which are core

and perimeter systems.

When subjected to lateral loads, the column restrained outriggers resist the rotation

of the core, causing the lateral deflections and moments in the core to be smaller than

the system without the outriggers.

The external moment is now resisted not by bending of the core alone, but also by the

axial tension and compression of the exterior columns connected to the outriggers.

Belt truss as the name suggests, forms a belt around the building connecting perimeter columns.Belt

trusses are often provided to distribute the tensile and compressive forces to a large

number of exterior frame columns.

.

In Taipei 101, belt trusses below level 27 are two stories deep at levels 9, 19 and 27.

For upper floors, the belt trusses are single story deep, every 8 floors tying main perimeter

columns by cross bracing.

These belt trusses gather and transfer perimeter weight to two super columns on each face.

Outriggers in Taipei 101 were formed by vertically bracing two adjacent floor girders through

occupied space, every 8 floors, just like bamboo joints.

Two minor outriggers connect the core’s central columns with sloping I-shaped columns.

This floor was dedicated to storage and mechanical equipment as open space is occupied by trusses.

Now let us talk about the Mass Damper used in the building.

At the top of the building between 86th and 92nd floors, is a huge pendulum which is called

a Tuned mass damper or just TMD.

This pendulum counters the wind force and reduces sway of the building in the typhoons.

The occupant comfort is also increased during strong winds due to the damper.

This damper uses building motion to push and pull giant shock absorbers to convert motion

to heat by forcing fluid through small internal openings.

When the building sways the mass will tend to move in the opposite direction.

This removed energy from the building due to wind oscillations and reduced movement.

The pendulum is of 726 tons and 6 meters diameter.

It is built up from stacked steel plates and weight is equal to 0.24 percent of the total

building weight.

Recently a typhoon of category 5 caused the damper to sway a record 100 centimetres or

39 inches.

Two additional 7-tonne dampers control the oscillations for the 60-m-tall pinnacle rising

from the hundred and one level.

In the event of an earthquake the sudden shock locks the mass for safety during seismic events.

Taipei 101 is a very special building in the world of engineering and architecture.

Its ability to take on every challenge thrown by nature is remarkable and it will remain

an icon for years to come.

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