Succeeding a technical civil engineering interview and then winning that dream civil engineering job is not that easy. It is even more challenging if it is a structural engineering job interview. However, this is not that difficult either if you focus the correct structural design points in the right way. You should not ignore the simplest of structural engineering principles as many times that will be the points that you will be tested on.
Today am writing about a very simple thing that a civil engineering graduate or a fresher in civil engineering or structural engineering should think of. I am choosing a simple topic as many even from site engineering is asking me to help shift to design in this pandemic times. These blogs should help the site engineers too who aspire to have some structural design training.
I keep on hearing questions from students and civil engineering professors on what they have to do so that the civil engineering freshers are job ready. What the civil freshers lack is logical thinking ability. They are never encouraged to practically connect to what they learn.
I will clarify this gap in civil engineering education by stating one simple example in this civil engineering blog. This will give you a good idea on what kind of things you need to focus to be job ready and more importantly, helps you become independent civil engineers appropriate to your level of experience. I will plan to write more structural questions similar to this in the subsequent blogs that will help a MTech civil fresher or a BE civil fresher to cover the gaps in education
What is a simply supported beam?
I have seen a variety of answers to this question. Some of the answers I have seen in the near past is listed below.
· Simply supported beam rests on 2 walls on either side.
· Simply supported beam has no hogging
· Simply supported beam needs bottom steel
· Simply supported beams have a bending moment of wl2/8
· A simply supported beam will have only upward reaction at the support
While these answers are not wrong, these kinds of answers do not communicate that you have a civil engineering subject knowledge. If you have to stand out from the crowded civil engineering job market, you should be positively different and able to present the answer with authoritative civil engineering knowledge and understanding.
What is a more correct explanation to this question above?
For that you have to know a few more simple points in structural engineering. This is not a rocket science. It is fairly simple. I will try to explain this in the simplest way that I know.
Degrees of Freedom
As we know, anything in the structural engineering world has 3 dimensions. To simplify let me state it as length, width and thickness. Now you can call the length as height when it is a column or call depth as thickness when it is a slab. These are not important. What I mean is any thing has 3 dimensions. Let us consider an axis in each of these directions and these are the 3 axes, x, y and z that we use to represent an axes system. Now a free-floating node in this world can move in 6 ways. 3 translations in each of these x, y, and z directions and 3 rotations about these axes. So total 6 ways. This is what we mean by 6 degrees of freedom.
Fixed beam vs simply supported beam
Before getting in to simply supported beam, let me explain what is a fixed beam. If you arrest the movement of a node in all these 6 ways completely then we can say it is fixed. If it is possible to arrest its movement completely is some thing we have to discuss separately.
In a fixed beam, you are restraining the ends from moving. That is the meaning when we say fixed. As you know, a force is developed in a beam when an external load is applied on it and when it is not allowed to move. If you allow to move, then the structure won’t have a force developed in it, however it won’t be stable. It won’t remain in a place or it will deflect and you will have all the instability issues. So, you have to have a structure that can be used and we need that to be stable. My point is that, the support moment that is developed in the column beam junction is due to this restraint. The restraint or the fixity there induces internal resistance and hence you get internal forces there. If it were free to move, there would not have been any moments at the support.
The simply supported beam is restrained only in one direction. Or restrained only not to fall down. That’s why text book says that there is only an upward reaction for a simply supported beam. Saying that alone will not be an answer that conveys your understanding of degrees of freedom.
See the video for a better understanding.
So, what is a simply supported beam?
If you answer about degrees of freedom and the fixity and then answer all the other answers I had written at the start of the blog, then it is fine. If you say any of those with out demonstrating your structural understanding ability, none of these answers would help you win a civil engineering job or structural interview.
Is a beam fixed when connected to columns?
Many will say yes, it is fixed. When I agree to it, there is something more that you should know about this. Students learn fixed beams in text books and also moment distribution method for analysis. However unfortunately the curriculum, don’t try to connect these and explain the structural significance in detail. These are the reason that the gaps in civil engineering education is existing. I will explain this structural point in detail. The fixity is depending on the stiffness or the inertia. So, when the size of the column increases, the inertia and the stiffness of the joint increases and hence the fixity and the restraint. So, the fixity is very relative.