What is Structural Engineer?

As Engineers, we like to assume. I didn't appreciate it much earlier, but I will tell you why we do that.  Most of the formulas we study during our Bachelors, well I have only completed my Bachelors yet, there's always some assumptions mentioned before a formula, Always.  Thin Beam Model Critical Buckling Load Now why do we assume if it's not the actual response. It makes our life easier, by that I mean the calculation time and effort for getting into something. And it gets the job done. As I earlier once wrote in my blog : Acceptable within the Engineering world, due to certain circumstances. Does it mean we are wrong, NO! Most of the assumptions give the limits too. One such assumption is the Engineering Strain .  A comparison. Engineering Strain is a straight line which indicates that the strain in a structure varies linearly although that is far from actual scenario. In actual life, or per experimentation, the strain doesn't vary linearly. It sorts of curve down as ...

A lazy Sunday afternoon on my apartment balcony, a friend sitting beside me on a bucket. Conversing rubbish most probably. As he got up to leave, the bucket he was sitting on crumbled. A normal occurrence with thin buckets. See, in my practice, that crumbling of bucket is called buckling. And rightly so, buckling came to my mind. So, what of it? Not that I have to design the bucket to resist my friend's weight. But you might agree with me on my intuition.  The formula for critical buckling load is quite eye catching. It's one of the easiest to remember, if you get what I mean. So, as you might have guessed it by now. My quest began to find the elastic modulus of the plastic.  First, I got a measuring tape to measure the dimensions. A bucket with a smaller diameter of 23 cm, large diameter of 32 cm and a Height of 32 cm. The bucket in question.  Those are actually the diameters and not radius as I wrote on my stickons. Taking pinned connection at the bottom, as it is not f...

The ill-condition error is the one we dread the most. One which can take days to solve, if we ever find it. Now I won't be able to help you with clearing this particular error at a snap. There are certain modelling techniques I follow to ensure an error free model. While modelling the structure, connecting all the elements node to node is a must. This is an FEA software, you need the transfer of reactions whether it be loads, deflection or moments. As per my experience in RC structures, most of the errors/warnings can be solved through this. Minimize use of the option of all floors or use with caution. It helps when others work on your model too. There goes the modelling basics, now let's get to the part of debugging. There are various kinds of errors, I might not remember all of it while I am writing this blog but I will try to answer the best I can. Well for starters, standard solver would be the best. Although it takes much longer to analyse, it does give the error locations...

As per tests, shear strength of a concrete does not increase in direct proportion with member depth. As per ACI, this phenomenon is called the Size Effect. Do mind that it is the contribution of Concrete only, and not including its reinforcement.  What this means is, a concrete block with X depth does not have twice the shear resistance of block with depth X/2.  As per ACI 318-19, How this acts in terms of one way and two shear can be seen from the code books. It's more dominant  in two way shear, a heads up. You can see from a simple calculation that the size effect factor of a 1000mm thick reduces the shear resistance of an element to around 63% of the original strength. But wait, if that's the case, won't the requirement for footings which take all the loads from the structure be too much. Clause 13.2.6.2 to the rescue. It permits the negligence of size effect factor for foundations. What a miracle. No it isn't. It's all calculated that's what I believe.  Now...

Structures are built to last. Most modern structures have a life expectancy much more than a regular person. So it's only natural to assume Engineers designed for it. We do design checks in this regard too.  It was not always a thing though, at least that's what I believe. And I will tell you why I think so. Civil Engineering is the oldest branch and has gone through some vey serious updates. My trade initially started with the Working Stress Method. It is also called the traditional method. In this, the design is based only within the elastic limit. Which means, the materials used for construction behaves in a linear elastic manner. You know how an elastic rubber works, it won't break unless stretched through its capacity. The philosophy is similar. As long as it is within the limit, it won't fail. But to make the structure not reach its limit, the materials required was much more. This, at times, leads in very un-conservative designs. This Method is good for critical ...

 Just like the topic of the blog suggests, the columns float. Well, not literally. It's just that these types of columns do not follow the typical path of load transfer in a building. The columns are in-fact rested on a beam or slab. So, they look as if those columns are suspended or hanged.  A floating column. Principle of a Floating Column. Well, the question then goes. Why do one need a column like that, isn't the simple geometry base plan enough for a building? The answer would be NO as per the Architects. What these columns give them is free reign over a room layout or any space in particular. Imagine a 3X3 grid column, a typical plan would consist of 4 small rooms, but if you remove the centre column you get one huge hall. I think I pretty much explained why Architects like it. They love it. But as the quote goes, " An Architect's Dream is an Engineer's Nightmare ". It's not exactly a nightmare, not the floating columns at least. But it's not typ...

Ritz, not Rizz and Eigen Vector are two ways of solving a Modal Analysis problem. It is what ETABS use while doing the Modal Analysis. Today's blog will be about the difference between these two. EIGEN-VECTOR : It determines the undamped free-vibration mode shapes and frequencies of the system. What free-vibration means in our term is that there is no external loads acting on it for any period of time, just the initial conditions. The idea of bending a ruler and allowing it to reverberate. The natural modes obtained through this provide an excellent insight into the behaviour of the structure.  But remember, it's the free-vibration response while the structures will be under various different loads. What should be done then? Here comes the Ritz Vector. RITZ-VECTOR : Research has indicated that the natural free-vibration mode shapes are not the best basis for a mode-superposition analysis of structures subjected to dynamic loading : Wilson, Yuan and Dickens, 1982. I stole this l...

Draftsmen draft. Just kidding. They do draft but they are better than that, well! Some are. The need for a draftsmen might be meek in an ideal European sense, with all the automations and sort. Even without the automations, a Structural Engineer is expected to be able to do the drafting himself/herself.  But I don't live in Europe, do I? And the need also arises due to the sheer scale of some projects. The main task of Engineers is to design and analyse the structures. And it does take time. Hence, the need for draftsmen. Now what does a Draftsmen do. They draft. They are expected to be good in drafting softwares, whether it be 2D, 3D or even 4D. Though I have never been a part of a 4D project YET. Some general softwares can be the CAD lineup, Revit, Dynamo, Sketchup and the list goes on.  They should have the knowledge as how it all works. Some cases are not always general, and they have to come up with alternatives, just like Engineers in this case. For example, I had to imp...

This is one of the coolest concepts I have properly learnt at my job. I do know I will learn lot more on this. It's the Stiffness Modifiers.  It is a modification factor that is generally used in the properties of cross-section such as Moment of Inertia, Shear Area, Torsional Constant etc. It can also be used for Mass and Weight as per requirement. Modifiers for a typical Beam. Now why is it used? As the loads act on the structure, it will tend to generate cracks on the tension zone. Thus, reducing the area of cross section and stiffness of the member. 1 means the structure would take all of the loads, while 0 won't be taking any. It is kind of a paradox; the structure would resist all the loads if it is not cracked, and we know it will crack. In other way, we want the structure to not take the load as it will eventually crack. Concrete is weak in Tension. As per codes, IS Code ACI Code Now I have two great examples for putting my case. One is related to a torsion modifier I st...

This is a photo I took during my visit to Indore. It's at the Devi Ahilyabai Holkar International Airport, but you could see this type of connections at every airport. I tried explaining my elder sis why is it so back then, but I might have been wrong. So here it is,  the correct answer. If you look closely at the connections, you can see that it's not welded or fixed like the smaller ones at the back. The reason is that it allows rotation on that particular connection. One might ask why would you allow rotation in the first place, isn't it dangerous? But wait, I will explain why is it so. Reactions in our world means how an object would respond to a certain load. If you squeeze a sponge, it gets flattened. So Reactions are basically responses. And if you don't want that particular response, you just allow it to be effected. Alright, it's not a very good explanation. I will try again. Take an example of catching a ball, the impact on your hand is nullified if you pu...

This is in Continuation to the ETABS_ 1 blog regarding the Shear Check of Beam.  The first post was only about the Shear Check. I rechecked the Beams for Shear and it passed as per my calculation. But the software showed otherwise. That was because of the additional external Torsion which I added to the beam. The Torsion in the Beam was added due to the Hollow Core Slabs which is supported on Beam ledges.  As per IS code , the torsion is converted to shear. Using clause 41.3, the equivalent Shear is calculated as, The torsion has been converted to Shear, it is therefore taken wholly by the Stirrups. Only the transverse reinforcement takes the torsion.  As per ACI 318-19 , the torsion reinforcement is provided in both the directions, clause ACI 22.7.6 But here's the catch, the point I am trying to make. There is an upper limit of the combination of Shear and Torsion that can be carried by the section. This is given in clause ACI 22.7.7.1a. This can also mean that the beam ...

                              If you look at it the right way, that's the whole of Seismic Analysis as per ASCE 7-10. 10 means the year of publication, the latest is 7-22. There are three important factors here, R = Response Reduction Factor, Omega = Overstrength Factor and Cd = Displacement Amplification Factor. Today I will be writing about the later one. Now it has to be seen as per Linear and Non-Linear Analysis. After a certain level of strain, the structure goes into a state of Non-Linearity, where there is more strain/deformation in structures over the increase in stress. In a perfectly elastic state, the change in uniform. If one wants to do linear elastic analysis of a structure under full seismic loading, the resultant forces will be significantly large, as seen in the graph, and the design of the structure will be uneconomical. We are not taking advantage of the of ductility and inelastic energy dissip...

To be honest, I don't really know much about Skyscrapers, not as a Structural Engineer. But what do I know a 100 %. So this blog is more like a rant about my interest in it.  Skyscrapers are super tall structures. You can see it in almost every top cities, I have only been to one YET. It is possibly the best way of utilising the minimal overly priced plot of land in a city. And it has been a game changer since its introduction. It makes the city skyline pretty too, in a way. A building is considered a skyscraper if it's taller than 160 meters, with more than 50 percent habitable. What this means is that more than 50 % of the building should be occupiable by humans. Take for example, The Eiffel Tower is a gigantic structure of 300 meters, but people can't stay there, hence a tower. The other 50 % could be aesthetics, to make it look cooler and dominant. This I learnt from the B1M podcast. To the Design aspects. At a height of more than 160 m, the winds play a crucial role. T...

Forces here means Reactions. Forces just sounds way cooler. The reactions are the responses by the structure to a load. It can be Axial Forces, Shear, Moment and Torsion.  Now what is Stiffness? It is the ability of a member to resist deformation under bending. It highly depends on the Moment of Inertia around the axis of Bending. Please be reminded that it's the Area Moment of Inertia and not Mass Moment. For a Solid Rectangular Cross Section, Moment of Inertia = b*h^3/12. Onto the deliveries, below is an ETABS model of the same plan with two different thickness profile.   A. Raft of equal thickness.   B. Raft of different thickness. B has a raft of 400 mm with a thickening of 1500 mm near the edges. This thickened portion will support the wall from above.  Now we analyze the model for the same loads and loading combination over the same process. I have taken the M22 case for comparison, but any other reaction would have been fine. A. B. As we can see, the reactions...

Suppose you have a foundation at two levels. The foundation of the structure is at two different heights/elevation, A and B. And the two are connected by a wall.  The scenario. The wall will start from the lower foundation B and so it will be monolithically connected with it. Thus, you will have to model it accordingly.  Whereas A can be modelled and designed in two different ways: The two approaches. One where you place the foundation over the wall. But then the foundation would be able to move sideways in case of horizontal forces, like the first image below. To avoid the horizontal movement, it is designed to be monolithic by providing the required reinforcements. And it becomes a normal wall slab connection design, the third image below.                                    Another way to go through it is by placing the foundation on the top level of the wall. Case II among the two appr...

 I have been super busy the last three weeks. We had a submission, a Detailed Design submission, you don't have to know what that is. So, I didn't have enough time to sit down and pen my thoughts carefully. I have the resources though, both theoretical and application wise.  Today's blog is an update that I have completed my first project as a Structural Engineer. It is a mall at Sharjah, by the name ALJADAH. You can google, it's pretty, at least Architecturally. It wasn't the smoothest of projects, that's what my mini bosses told. It's my first project, who am I to judge? I learnt few things down the process. I got to learn technical structural things, but also the working of a corporation. But maybe, it is what it is.  Ow! why do you have to google it. I will attach the image here. See how pretty it is. But it was such as dreadful for us Engineers. I don't understand the Architecture urge to make changes as fast as they do. Some interesting takeaways f...