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Showing posts from 2014

Structural Health Monitoring

Monitoring, a very common term used in - I think every field present today. But monitoring what? The answer is a "system". Why do we need to monitor? To check for the changes happening in the system as the day passes by and to remain prepared for the future changes. For example let us talk about health monitoring. What do you do when you feel sick? You go and see a doctor. What does doc do? He examines you and from the diagnosis s/he prescribes you some medicine. But is that it? No, he calls you again and again till s/he feels that your are good to go. When does he leave you? When s/he is certain that you are perfectly fine and there are no more negative changes happening in your body, till then s/he "Monitors" you.  He checks every other day or week or may be month, just to see the changes that are going through in your body. If s/he stops monitoring your health in such a way, then I am pretty sure it will take longer to get yourself some cure. So this is the imp

9/11 Remembering World trade centers

Today, exactly 13 years ago, two planes crashed in the two towers of the World trade center. WTC1 and WTC2. This attack of terrorists is one of the most dangerous attack of all time. Being a structural engineer it is of prime importance to study such a case. A flight, Boeing 767, very small and tiny in front of the tall towers was the reason behind the collapse of the structure.Let us study some important aspects behind the collapse, like the time difference between the collapse of two towers, collapse type and structural failures. 1. Structural Design To understand the failure of any structure in a better sense, it is first important to study the structural integrity and the behavior of the structure itself. You can only know how the column or a beam will fail when you load it and understand it's deformation patter as well as it's load path. Similarly it is important to study the structural design or the structural system of the two towers of world trade center

Arch Bridge..!! When? Where? & Why?

Want to travel across a valley? Want to cross an ocean? Want to span from one end to another? Whatever might be the need, bridge is required for that need. But it is a preliminary decision taken on the basis of budget, location, type of soil and surrounding to built a particular type of bridge. This can result in a most commonly used simply supported bridge or a suspension bridge or a cable stayed bridge or an arch bridge. Today we will be discussing about arch bridges. How they are designed? Where they shall be used? Why they are used?  First let us ask a basic question to ourselves. What is an arch? Arch is a member which takes majority of the stresses in compression while spanning a gap. The definition of a column and arch is very near to each other except the last words "spanning a gap". (Yeah, these last two words created majority of the complications in structural engineering). It can be of any shape, a parabolic, catenary, straight lines, etc. But how can w

Madness - Tensegrity - Bridge construction

I was bored after coming from work, I wished to refresh my mind so that I can do some work so I downloaded a game called Bridge construction from Google play. At first I though the game would be easy and it was easy in the beginning. But then I started realizing about what can I learn from the game. As within a limited budget I had to construct a bridge. Also using the limited type of material. So I really gave a thought. I started thinking about how can I construct a best possible bridge, should I use a truss or suspend it using a cable. I started making influence line diagram to find out the relative maximum force that can possible act in certain region of bridge. It was fun and a good learning experience. Let me share some of the thoughts that I gave on the application. In the structure above, I need to cover the total valley length of 60m and I was allowed to use concrete and wood with a support at 25m from one side. I just erected a concrete column at the assigned

Indeterminacy - A curse or A boon

A course in structural engineering starts from a particular type of structural analysis called determinate structural analysis. Here you study anything regarding determinate structures, whether it may be a simply supported beam, a 3 hinged arch, a truss. Everything is determinate and that means number of unknowns is equal to the number of equations. That is great, you see the unknowns, form the equations and figure out the value of the unknowns. As simple as that. But this isn't everything about structural engineering. When you design a building or a bridge, there is more to it than just a determinate structure.  Let us take a simply supported beam and a fixed ended beam.In case of a simply supported beam, you apply the load and the amount of the load carried by the beam is equal to the strain energy stored in the beam. Let us assume a beam with a load capacity of 100 kN. When you load the beam, then it will be deflected by a certain amount (x). So the work done by the load

Possible types of failures in a steel structure

We, structural engineers design all the members of a building, whether it might be a column, beam, a tie member or a strut anything, but we design it to resist certain forces. We predict a load, calculate forces in different members and design them member to resist a particular load. But sometimes because of some undetermined or unpredicted load the forced in certain members increase to a value which it cannot withstand and the LObmember fails. But what are the different possibilities of failure? How can a member fail? Don't worry, here is what we are going to talk about. The possible types of failures in steel structures. Steel is a ductile material and to build a structure using steel is like setting up a huge Jigsaw puzzle. You have 1000 different members and you need to connect them and tada..!! Your structure is up. But it is not as simple as it is visible. Steel being a very strong material  leads to slender members. Now you can imagine the difficulties associated with it

The elastic bending effect

Why does a beam bend? Have you ever asked this question to yourself? Did you get any answer? I know that it's difficult to find an answer about this phenomena. But let me try to explain this to you.  Consider a free falling I section from the top of a building. If it falls freely what do you think will happen? It will remain straight because all the particles are moving at the the same velocity at a particular instant of time and the acceleration is equal to the gravitational acceleration. Here I am considering the case of vacuum or else air resistance will induce some external forces. But now consider that the beam is supported at two ends. What will happen? The thing is, the particles which do not have direct support experience the gravitational force and they will try to move down. But the particles who have direct support beneath them, they will not move, they are reluctant. This thing causes internal forces and the two supported ends because of the strength of

Charlie Chaplin and his buckled stick

Charlie Chaplin, one of the most famous character in the history and you will always find him with his stick. But wait, have you ever seen his stick when he rests on it? The stick in the picture above describes one of the most fundamental characteristic of a column in the field of structural engineering, called "Buckling of Column". But why did it buckle? What made the stick to bend instead of taking the load straight down the ground? Well, here we are to discuss about the event. Buckling is called an instability occurred in a structure because of excessive loading. In 1757, mathematician Leonhard Euler derived a formula for calculating the maximum load carried by a slender column. But what do we mean by slender? When the longitudinal dimensions of the member are much greater than the cross section of the member then it is called a slender member and remember you should use the word slender while describing the compression in column not when there is any tension