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Showing posts from 2016

Ductility In Structures

Have you ever participated in a marathon? Or have you ever practiced for one? The only way you can finish a marathon is high stamina and a constant comfortable pace. If you run too fast, the energy in your body will drain out quickly and you will get tired within first 10% of the run. But if you maintain your own comfortable speed, where you heart beat is not too high then you could finish the marathon without even getting too tired. The key is glycogen stored in the body. On an average a person can store up to 2000 calories of energy that is readily available and then once this glycogen is consumed body starts burning fats to get energy which leads to fatigue. The key in marathon is to consume this glycogen efficiently and so you have to run at a comfortable pace.  Image credits: HALHIGDON Similar to this concept, in structural engineering, a building has to perform under large forces without breaking itself to pieces. As we discussed about different sources of energy d

Earthquake vs Energy Dissipation

 In this blog post, I will try to explain in simplest words possible as to what happens to a building during an earthquake.  Imagine this: You are travelling in a car which I am driving. I applied a sudden brake. You will experience a serious "jerk" and most probably curse me after that. But that sudden "jerk" also called as deceleration is experienced because your body changed the velocity from 100 feet/second to dead zero in 3 seconds. That is equivalent to gravitational acceleration applied in horizontal direction. This is called inertial force. There was a change in state of motion of your body.  "A body at rest stays at rest and a body in motion stays in motion unless an external force is applied to change the state of body" - Newton's first law of motion.  A force experienced by a body is equal to: Force = Mass x Acceleration When earth shakes, it gives these impulses at the base of the building. Let us look at an accelerat

Response Spectrum Analysis - I

"Response" is what an object, living or nonliving, gives to a certain situation. It can be passive response or active response but it doesn't matter. What matters is how the buildings respond to earthquakes. Let us say for an example, you take a pendulum and you pull it to a certain height and leave it for free oscillation. What you will see is the mass attached at the end of the pendulum moving back and forth constantly, such motion is simple to understand as it is clearly visible to your eyes. The time a pendulum takes to complete one oscillation is called the time period of a pendulum. This factor, "time period" is very important characteristic of a building, it can tell you everything about the building, every ins and outs. Coming back to pendulum and time period, when you plot the motion of pendulum with respect to time it will give you a sinusoidal curve called the response of the pendulum to the disturbance. It will look something like this: Angl

Taiwan Earthquake 2016

Every time an earthquake strikes, we learn something new from it. As a structural engineer it is always difficult to explain people as why a building collapsed. The only reason is we cannot predict earthquakes. But wait I am not done here, yet..!! Let us take a deep breath and jump into the possibilities of failure of buildings in the city of Tainan which is located just at a distance of 48km (30 miles) from the epicenter. Let us take a look at USGS map of the affected zone. Now the earthquake was a very strong earthquake of category 7 which describes the wave velocity of 20 cm/s and a peak acceleration of 0.22g. One more thing to keep in mind is that the earthquake was a shallow earthquake which means that the intensity of the earthquake might have amplified.  Talking about the building collapses in Tainan, we cannot directly blame at design engineers and the only reason I am saying this is because Taiwan has been famous for earthquakes and not small intensity but the la

Building a 3000m tall building..!! Is it possible?

Fun stuff...!! A 3000 m tall building is definitely possible. Let us say we have infinite sum of money. Just for the sake of simplifying things so that we can focus on engineering. Challenges? 1. Wind A structure this tall will be under a giant amount of wind force and I am not saying that it is not possible to resist, we can resist it, but with intelligent engineering. In such cases wind tunnel tests are conducted and the shape of building is put up in such a fashion that we can reduce the wind forces. For example, the current tallest building of the world, Burj Khalifa is standing under the same principle.  As Will Baker (Bill Baker) says that, the design of the tower is such that it confuses the wind force. The wind force increases as the height of the tower increases, and if the building height is like that of Burj Khalifa, than the allowable deflection is 3m or so which can make the people inside the building uncomfortable. So what they have done is, they have regularly changed