Iterations

As an engineer, Iterations is a part of you. Until you have the required experience, it is one of the best ways to learn and understand the trade. I do believe Senior Engineers require their share of iterations too.

For me, it's the endless analysis of structural models. 

Don't mind my naming of the files.

Lucky for us, we have software to do the work for us. Now you might ask why we don't just do the work with the codes and the books, the manual way. In a way, it is nearly impossible to design a whole structure just by hand calculations. It would take too much of our time and the transfer of Reactions might not be accurate. REACTIONS are what the building/structure would experience when it is subjected to different loads. I did explain, ever so slightly about the loads in my first blog.

As a rookie, my task is to check whether the reactions are within the allowable limits. For this, the first task is to model the building in the software, then the model is subjected to the loads. The first model is usually an estimated one, one from the previous experience. Then we run the test for that particular structure. There can be different checks. One of it is the Punching Shear Ratio Check. 

Going Civil Engineer here, a foundation of a building is of different types, according to the requirements. One type is Raft Foundation. It is a thick concrete slab resting on a large area of soil. It is generally used to support structures where the soil condition is poor, or for building with higher loads i.e, commercial or high rise b. A Foundation takes all the load from the structure above and transfers it to the ground buildings. Hence, these require larger area to disperse the loads.



The type of Raft Foundation I analyzed is the Thickened Plate Type Raft Foundation, where the weights/Reactions are much higher at the Columns. The thickness of the slab at the point of Columns are thicker. The thickness of the Raft is 500 mm. The thickened sections are modeled as Drops.

The colourful boxes represent the thickenings at the point of Columns.


In this check, I have to check the effect of Punching Shear on the Raft Foundation. Punching is caused by the concentration of load on a small area. Imagine a paper being pierced by a pencil and a highlighter, the pencil would easily pass through the sheet of paper. One way to avoid the piercing is to have a thicker sheet of paper, and that would be our approach on this too. Analogous to the pencil experiment, a column can punch through a slab/foundation if not given enough depth and reinforcement. The column increases the Shear in the foundation and ultimately pierces through it. 

As the load is not similar in all the columns, the punching offered would be different too. Hence, we require different drop sizes too. The ratio is between the capacity and demand. Hence it should be less than 1. I change the sizes till I get the ratio less than 1.





Check 1, many drops have ratio more than 1.



Check 6. 

As you can see, the punching Shear Ratio got reduced due to the size increment. The increase should be gradual so as to comply with the cost. My Drop sizes vary from 1200 mm to 2000 mm. In a similar way, there is a check for Drop Punch where we increase the lateral dimension of the Drops, like the highlighter in my silly example. 

The concepts I explained is as per my understanding and I am always open for a healthy discussion. 

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