DUCTILE DETAILING & 4 VIRTUES OF SEISMIC RESISTANCE

Updated: Jan 11


Did you know what Are the Most Important Seismic Resistance Considerations When Designing a New Building? There are many. However, there are four key considerations that are often regarded as the 4 virtues of Seismic Resistance. These seismic considerations are called as virtues since the fact that, if the building possess these results or qualities after the considerations, the building will be seismic resistant. As we all know these qualities or virtues will come in the building when the structural engineer adopts these considerations while designing the structure.

Seismic resistance is something which needs to be planned for in the structural design of any type of structure. This structure can be anything from a small single-story dwelling to a high-rise building.

The first step towards seismic resistance is to make sure that the design of the structure is as per the building codes. In India, the codes for seismic resistance are IS 1893 2016. Though it is simple to state this, adhering to IS 1893 involves application of experience.

Let us quickly discuss what is seismic resistance first before discussing the virtues.


What is Seismic Resistance?

The ability of a building or a structure to perform during earth quake is what we all structural engineers desire. The ability of structure to withstand an earth quake is what we call as performance.

Designing an earth quake PROOF building is not possible. There are 2 reasons for this.

We have limitation in understanding the intensity of expected Earthquake as it is a natural phenomenon and we don’t have any control on it. So how do we make a building seismic proof?

Even if we knew the expected intensity, if we try to make a building earthquake proof, it won’t be economic or functionally feasible as the member size will be extremely high to meet the seismic demand. Because we cannot have an earthquake proof building, engineers arrived at a design philosophy that if followed will give the building certain amount of seismic resistance with acceptable level of damages. This design philosophy based on experiments, trials and studies considers less than 15% of expected seismic forces. If you do this, you can achieve the below mentioned conditions

Mild Earthquakes - No cracks and damages

Moderate Earthquakes – Reparable cracks may occur.

Severe Earthquakes – Irreparable cracks may occur but no collapse

Very severe Earthquakes – Collapse but gradual so that occupants can be evacuated.


What are the 4 Virtues of Seismic Resistance?

I have listed the 4 virtues below.


Good Structural Configuration


In fact, the better performance starts with the structural scheme of the building. A good structural scheme is possible when the Architectural scheme is great as well. This can happen when the structural consultant is on board early in the design development stage and the architect and the structural engineer work together in achieving this robust scheme. Robust scheme means a scheme that performs well during a seismic event. This can be achieved by adopting the below mentioned points


Regular geometry:

Regular geometry is really important for a good performance during earth quakes. I have already mentioned about significance of geometry is another blog. You can see it here


Avoiding cantilevers:

Cantilevers perform poorly during earth quakes and should be avoided as much as possible in the design. This is a shared responsibility with client and the architect. Another reason that a structural engineer should be on board the project during architectural scheme development stage itself.


Proper position and sizes of structural members:

Proper scheme of the building is extremely important for the overall wellness of the structural configuration. The structural scheme decides how the members interact and behave during earth quakes.


Proper orientation and position of columns and shear walls:

Orientation of columns properly is important to resist seismic forces. Most large buildings will need additional bracings in the form of shear walls to relieve the columns from seismic forces. All this needs to be carefully planned and configured.

I have already mentioned about shear walls in another blog. You can see it here


Lateral Strength