7 Actionable Tips on How to make Earthquake Proof Buildings?

7 Actionable Tips on How to make Earthquake-Proof Buildings?

7 Actionable Tips on How to make Earthquake-Proof Buildings?

"Is it Possible to make earthquake-proof-buildings"?

"Earthquake-proof-building" or "Earthquake-resistant building"- Which one we should need to focus on?

What are the must-have features of these type of structure?

These are just some of the most common questions civil engineers at various level (Beginners, Intermediate) have and in this exclusive guide, I'm helping you to answer all these questions.

I will also answer "How can we minimize the effect of Seismic force?"

If this is your first time here at Civil049seminar, Please comment below with 'yes' and like our facebook page to get notified regularly.

Back to the topic,

Due to the Earthquake forces structures founded in ground, experiences motions at its base. This phenomena makes the structure unsafe and unstable also.

3 Golden Rules about "EARTHQUAKE PROOF BUILDINGS"

So, It is necessary to ensure superior stability, strength, and serviceability with acceptable levels of safety by adopting the suitable design and detailing of the building.

Let me clearly explain the effect of seismic forces on the buildings with an example-

You may have observed that:

When the bus is in motion the whole body of the passenger is also in the state of motion. But the lower part of passengers body (Body part which makes contact with the bus) comes to rest when the bus suddenly stops.

But due to the inertia force, the upper part of the passengers tends to stay in the state of motion- that's why the passengers tend to lean forward when the vehicle suddenly stops.

Now compare this phenomenon with earthquake and buildings.

When Earthquake strikes the ground, the base of the building moves with the ground surface but the roof of the structure tends to stay in its original position.

Since the roof and the base of the building are connected by the wall, columns, and beams are- they drag the roof along with the base of the building.

Here the concept of inertia forces arises.

This inertia force can be calculated by the formula,

[ F=m*a ]

Where,

F = Inertia force,

m = mass of the roof of the structure,

a = acceleration.

How many of you can describe the basic concept of 'Earthquake-proof buildings'?

- Please comment below with your answer.

The reason why I'm curious about your answer because I want to give you the best information about "Basic-to-advanced-features-of-Earth-resistant-buildings".

EARTHQUAKE-PROOF VS EARTHQUAKE-RESISTANT

The aim of the engineers is not to make a building "Earthquake-Proof" but to make an earthquake resistant building.

One thing you have to understand that we should focus on structures which prevent loss of life in an earthquake that doesn't mean that the structure won't have any significant damage.

Because if we construct an earthquake-proof structure then it will be too expensive & robust. Instead, Engineers tries to design structures that can survive during high seismic forces without showing any significant failure or building collapse (Severe damage is acceptable).

There are many factors which we should look upon to attempt such a design approach.

Previously I discussed 7 characteristics of the earthquake-resistant structure- CHECK IT HERE.

From choosing the right type of building material to the Size of the building everything matters when safety and stability of the structure is our first priority.

In this post, I'll be sharing 7 actionable tips in terms of requirements and design parameters to make the building Earthquake-resistant.

1. Soil Profile

Design of an Earthquake-resistant-building begins with the study of the soil profile.

Strength or stiffness, bearing capacity, types of soil (sandy, clay, etc), consistency, density, Texture & structure- these are some of the parameters of soil on which details of the construction are dependents.

Such as, What type of framing will be used in the structure?

Is it going to be a steel structure or Reinforced Concrete?

Which type of foundation is most suitable?

and many more...

Nowadays new research on 'Soil Liquefication' has been opened up.

"Soil Liquefication" refers to the process by which the strength or stiffness of the soil is weakened by the movement of earth surface (caused by Earthquake).

In this process, soil acts like a plastic compound and begins to move like a viscous liquid.

Understanding the soil nature or profile helps to maximize the performance of "Earthquake proof buildings".

2. Building Configuration

Building configuration factors such as uniformity, symmetry, shape, etc are needed to be identified to enhance the performance of buildings.

It's highly recommendable to minimize the torsion and stress concentration of the building.

For an example, it is more advised to construct a simple rectangular and symmetry structure (in terms of mass and rigidity) rather than buildings with a very complex design in the plan, elevation or even in mass.

"Simple is better than complex"

But what if it is not possible to make a symmetry and simple structure in the plan or even in elevation?

Well, in that case, special care (such as detailing of reinforcement) should be taken to minimize the torsional and other effects induced by earthquake forces.

As per Indian Standard code, Buildings with shapes like L, T, Y, and E should be designed separately by providing isolation section at adequate parts.

These separations are not recommended for the buildings having minor asymmetry in the plan.

2.1 The lightness of the structure

As I have already mentioned that the seismic force is a function of mass, structures should be as light-weighted as possible with taking care of structural safety.

One little tip is that: Always design the upper storeys and roofs as light as possible.

3. Ductility

Ductility refers to the ability of the structure to resist large deformation without failure which is also the backbone of Earthquake Resistant Buildings.

During the ground vibration, buildings show a tendency to sway back-and-forth.

Rigid structures are more likely to collapse during an earthquake as it isn't flexible enough to withstand deformity.

Mild-Steel is a good example of ductile material

More uses of ductile material means more ductile structure.

Mild Steel is one of the most ductile material whereas plain concrete is an example of brittle material.

Thus the design process for structure needs to prevent the ductile failure and it can be achieved by providing reinforcing steel.

During an earthquake, one ductile structure is going to absorb more seismic energy than a non-ductile building.

Even the shear walls are needed to be designed to be ductile. Steel bars are to be provided in shear walls in vertical and horizontal grids.

Remember: Minimum reinforcing steel for the wall is 0.0025 times of the cross-sectional area of the wall, along with horizontal and vertical directions.

4. Bearing-Walls

Masonry bearing walls are constructed to fill the vertical gaps between floor and column. It is also required to define floor area into functional spaces(rooms).

These masonry walls play an important role in resisting the vertical movement of the column.

During an earthquake, when the column receives horizontal forces, walls are the one element that resists the undesired horizontal movement of the column.

Thus the importance of these walls is high.

Since masonry walls are brittle in nature, it requires some additional work to enhance the performance during the seismic attack.

Here I have mentioned some of the most important factors that will enhance the performance of masonry wall under earthquake forces.

• Make straight and symmetrical walls in the plan as much as possible.
• Masonry walls built in mortar shall not be greater built of greater height than 15 meters.
• Uses of openings in the bearing wall should be as low as possible as it reduces their lateral load resistance.
• The minimum thickness of any part of the wall is 150mm.
• Reinforcement should be provided in longitudinal as well as the transverse direction in the plane of the wall.

5. Lateral load resisting system

The intensity of an earthquake can be reduced significantly by introducing damping, energy dissipation capacity, and ductility into the structure.

A good earthquake-resistant building is the one which have both strength as well as ductility.

Various components of the structure and their connections should be designed to have the ductile failure- this will enable the structure to withstand sudden failure.

There are some load resisting systems to resist lateral forces induced by the earthquake.

1. Shear walls
2. Simple moment resisting frame
3. Ductile moment resisting frame
4. Hybrid system (consists of ductile moment resisting frame as well as shear walls).

ⅰ ) Shear wall is a great way to dissipate seismic energy through flexural yielding as it is highly capable of resisting lateral forces on its own plane.

This type of walls is nothing but a reinforced concrete wall cantilevering vertically from its base.

It should extend from the base of the building to the top of it or to a lesser height as per design consideration.

Studies show that buildings built in shear walls of height about 85% of the total height of the structure are more advantageous. 

ⅱ ) In simple or ordinary moment resisting frame, induced moments at the structural members and joints are carried by this space frame.

But it is not capable of meeting the requirement for ductile behavior. In order to achieve the detailing of ductile behavior the "Ductile moment resisting frame" is introduced.

Detailing of ductility are given in (As per Indian Standards)-

• IS CODE- 4326 (Earthquake resistant design and construction of buildings)
• IS CODE- 13920 (Ductile detailing of reinforced concrete structures subjected to seismic forces)

This type of framing system can survive a large intensity of an earthquake.

ⅲ ) The last but not least Dual system is designed to resist the total lateral forces in proportion to their lateral stiffness.

It has been observed that 25% of the total base shear can be withstood by its own.

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6. Seismic Zone

Consideration of the seismic zone is required for the advancement of structural design so that building can undergo seismic forces with minimal damages.

As per Indian standard,  the total land area is divided into four zone

(2002 edition): 

1. ZONE 2
2. ZONE 3
3. ZONE 4
4. ZONE 5

Where zone 2, 3, 4, 5 defines the low-risk zone, moderate risk zone, High-risk zone, Very high-risk zone respectively.

Based on the intensities sustained during the damaging past earthquake, this zone classifications are arranged.

Seismic Zone of India (% division by land area)

From the above image, it can be seen that almost 60% of the land area of India lies under an earthquake-prone zone.

Depending upon the Seismic zone (in which the building lies), some parameters are required to fulfill as per the standard code.

As per the ASCE (American Society of Civil Engineering) division, in very high seismic zone structure's height is restricted to 50m.

Level of detailing for ductility should be based on the location and Seismic zone.

In Eurocode part 1:2004, detailing of ductility is available for different structural members such as beams, columns, and walls.

7. Reduction of Earthquake effects

Frequency and the intensity of an earthquake can be reduced by adopting these technologies.

'Seismic dampers' and 'base isolation system' are used to prevent damage from earthquake effects.

In both technologies, most of the seismic energy is absorbed. Thus effects of earthquake get reduced.

Base Isolation System

The basic concept of this technology is to isolate the 'super-structure' from 'foundation'.

The entire weight of the building resting on frictionless rollers for which no force is transferred to the building due to ground vibration.

This helps in further inducing flexibility and damping to the structure.

Learn more about: Base isolation system

Seismic Dampers

The aim of this approach is as same as the base isolator to improve seismic performance by installing dampers.

Have you seen shock absorber in a bicycle?

-It is used to soak excess vibration.

Similarly, the purpose of this dampers is limiting excessive vibration.

When earthquake energy is transmitted through these dampers, they absorb the most of it and thus reduce the undesired motion of the building.

Most common types of Dampers are tuned mass dampers, viscous dampers, friction dampers, etc.

All of these factors must be considered to achieve nearly Earthquake proof buildings.

Conclusion

Well, it is highly expected that a building or structure will face many earthquakes of small intensity and one or two earthquakes of high magnitude.

It is an engineer's duty to reduce the effect of the earthquake and thus will have less damage.

Most of the very important points we have covered in this post about "7 Actionable Tips on How to make Earthquake-Proof Buildings"?

I hope you liked this article.

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