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Design of beam using Working Stress Method (WSM)

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W orking stress method is one of the oldest design philosophies, and now it is applicable at very fewer places. Nowadays, other methods are used instead of working stress method as they rule out the limitations of WSM. The alternative methods that are used are Limit State Method and Ultimate Load Methods which uses loads factors and ultimate strength in the design.   In it, we start with the analysis part, which is practised in the Mechanics of Solids. The first task is to find bending moments, shear forces, reaction forces at the supports, axial forces, etc. Let us look at the bending stresses first as they produce both types of stresses (compressive and tensile).  The theory of bending ( plane section remains plane before and after bending) is applicable. Still, one thing to note is that this theory is applicable only when the perfect bond between two different materials exists and no-slip occur between the material.   Stress-strain Distribution:    Since it i...
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Design Philosophies for design of RC structures

T o have a properly designed structure which fulfils all the requirements like proper durability, functioning, etc. We follow certain design philosophies. Every philosophy has some set of assumptions, and based on the premises, some ideas are suggested. So, let us start one by one. Working Stress Method (WSM) : Now it is an outdated method, and it is used occasionally. Today, it is used in a place where the complete analysis of the structure is complex, and no risk is allowed like an overhead water tank, chimney, etc. This traditional method has the following assumptions: The material behaves elastically, means stress-strain linear relation will be applicable. The adequate factor of Safety is applied so that the working load is well below the material strength. Here, we raised a term factor of Safety ( FOS) which is given by                     FOS =  Strength of material / Allowable strength of the material Since in this metho...
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Behaviour of Concrete under compression and tension

T he behaviour of concrete is different when it comes to compression and tension. Usually, concrete performs very well under compressive stresses, but when it is subjected to tensile stresses, its performance is considered inferior. Let us look one by one how concrete behaves under different stresses and what are some terms related to it.  The behaviour of concrete under uniaxial compression: IS 456:2000 has stated that to test the compressive strength of concrete specimen of 150 mm cube should be tested after 28 days of curing. Then the testing on the concrete cube is performed. The loading test of the concrete cube is strain-controlled, and the uniform strain rate applied is 0.001 mm/mm/min.  IS 456:2000 also recommends testing of 3 samples and the average value of maximum stress should be noted as compressive strength.  Now many people may ask why we perform the strain-controlled test and why not stress-controlled test. The answer to this question when we perform a st...
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Characteristic Strength of Concrete

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C oncrete uses different constituents like coarse aggregate, fine aggregate, water, plasticisers, etc. All of the components come in different variety, and thus the concrete prepared from the same mixture and taken from the same tray can have significantly varying compressive strengths. This variation can be controlled by assuring quality control at the site. Some ways to have reasonable quality control on the concrete mix can be the following: Controlling the size of aggregates by proper sieve analysis.  For coarse aggregates, there are tests like flakiness test and elongation test. For fine aggregates, bulking of sand should be in a reasonable range. Water content should be proper. Mixing of components should be uniform. The graph becomes more and more flatter when quality control is more miserable at the site. If quality control is better, then a sharp peak can be observed. One thing can be concluded that if more specimens are near average compressive strength, your mix is bette...
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