Reinforced cement concrete or the RCC frame buildings are those type of building in which reinforcement of steel rod is used along with the cement concrete to provide additional strength to the frame of the building. Ever since the reinforcement of concrete came into existence it has been considered to be the best in its business. Reinforced cement concrete buildings are supposed to be the best for the handling of vertical as well as horizontal loading within the permissible limit. But it has been discovered that even after availing with concrete and reinforcement, some buildings could not withstand against forces and collapse within their permissible limits. The answer to this failure can be signified if we study the proper reasons and factors that is affecting them.
Most common causes of the collapse of R.C.C. frame buildings
1.Improper consideration of the building codes
The most relevant cause behind the collapse of RCC frame buildings are basically due to the ignorance of the architects and engineers about the content of the relevant earthquake resistant building code.
2.Softness of the base soil
The softness of the base soil RCC frame building can cause the relative displacement of between the individual column foundations vertically and laterally. Moreover if the soil is sandy and water table is high it may liquefy. Furthermore the liquefaction may resemble sinking, leaning or tilting effects on the structure.
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3.Soft first storey
Soft first storey buildings are the buildings with open plinth area. Now a day’s most of the multi-storey RCC frame buildings are provided with open ground storey for the purpose of parking. These open ground storey introduces severe irregularity of sudden change of stiffness between the ground storey and upper storey due to the absence of infilled wall. The effect of irregularity is so much so that the stiffness factor of the building increases by three to four times.
4.Bad structural system
The structural system adopted by using floating column for the reason of higher FSI is very undesirable in earthquake zones of moderate to high intensity as in zone IV and V. This is because it will induce large amount of vertical earthquake force even under horizontal earthquake ground motion due to the overturning effect.
5.Heavy water tanks on the roof
Heavy water tanks on the RCC frame buildings add large lateral inertia force on the building frame due to the whipping effect under seismic vibrations, but remain unaccountable for the design.
6.Lack of earthquake resistant building
In India the violation of code provision for erecting a building in earthquake zone has seen a downfall after the catastrophic earthquake that took place in Kachchh in the state of Gujarat. But the presence of ignorance and lack of proper earthquake resistant design of RCC frame buildings are still residing. It can be stated that the buildings are designed against lateral load in the transverse direction.
7.Improper dimensioning of beam and column
In most of the constructions it has been seen that the dimensions of the columns and beams are in adequate as per the IS code. Moreover the beams and columns did not have proper dimension for the installation of reinforcement.
8.Improper detailing of the reinforcement of the RCC frame buildings
In most of the collapses and severely damaged buildings it was found that the detailing is below satisfactory level of lateral shear requirement in the concrete of the joint as per the IS 4326-1976 and IS 1393- 1993.
9.Short column detailing
The collapse of short column RCC frame buildings under shear due to improper detailing has been a major cause of the collapse of RCC frame buildings. It is normally seen in those cases where the column is surrounded by walls on both sides such as up to the window sills and then to the spandrel portion above the window, but it remains exposed in the height of the windows. In such cases the shear stress in the beams is much higher than the normal length column and fails in shear.
A well symmetric building is less prone to torsional failure as compare to asymmetric one against lateral forces. In technical words, the non-coincidence of centre of mass and centre of rigidity causes the torsional failure and subsequent collapse of the building. In today’s time aesthetics of a building has made a greater position in the minds of both dwellers and constructors. Thus the aspect asymmetry has a lot to do with the aesthetics of the building but when the importance of their stability and durability comes into discussion than engineers and architects should consider these factors properly.
11.Pounding damage of the adjacent building
Pounding damage is a kind of damage that is seen due to severe impact between adjacent building under earthquake shaking if the adjacent blocks of a building are of different height with floors at different levels and with inadequate separation. Delhi is a living example, which is more prone pounding damage during an earthquake due to its haphazard constructions.
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12.Inadequate stability of the infill walls
The collapse of the infill walls is a major cause of the collapse of the RCC frame buildings during the horizontal earthquake forces. This is because the infill walls are not properly attached to the columns or top of the beams for the stability against out-of–plane bending and this result in cracking and falling of the RCC frame building walls and subsequent falling of the later.
13.Poor construction quality
The quality assessment of a constructional project is very important in order to attain proper durability, strength, efficiency, value for money and most importantly safety of the dwellers. Often in low budget constructional projects, it is found that the quality of construction is under mind because various reasons like corruptions, practice of poor quality constructional materials, usage of alternates which do not satisfies the requirements of the construction and presence of inexperience. There are numerous other factors which contribute to the poor construction quality and these results in the collapses of the RCC frame buildings.