EARTHQUAKE, CONSTRUCTION & HUMAN LOSS
EARTHQUAKE, CONSTRUCTION & HUMAN LOSS
By R.K. Jain
We should endeavor that more and more persons are aware of the reasons and remedies of the Earthquake so that we can prevent huge loss of human life and other losses due to such happenings. This article is aimed at explaining occurrences of Earthquakes and the basic requirement to resist the deformation of your buildings due to such occurrences.
Few developers, presently in development of buildings and other structures wish to ignore the basic requirement of creating Earthquake Resistant Structures. There is a saying that you can wake up a sleeping man but it is difficult to wake up a person pretending of sleeping.
In the case of Earthquake, we have to create awareness twofold. One segment is the persons who are not aware of the Earthquake requirements but are associated with the affairs of Construction. These persons have to be given proper insight of the building detailing, to create building resistance to Earthquake.
Greater challenge is to convince the other segment viz. the persons who are aware of the basic requirements of Earthquake-resistant Structures and are the players in the building industries, at various levels but wish to ignore the Earthquake design and its implementation. Therefore, an urgent need of the time is to have Brain Storming Sessions on this subject, on all the levels of the construction industry.
A huge numbers of Engineers are at supervisory level and they are limiting their knowledge to the extent only for the placement of reinforcement bars as per the schedule created by the RCC Consultants. However, there is no harm of these engineers getting the brief knowledge of the basic requirement of Earthquake resistant members of the Structure, the Grade of Concrete and the location of reinforcement bars required for creating such resistance.
Earthquake is basically the movement of Earth, horizontally and vertically and in all other possible directions or the ‘earth vibration’, lasting for fraction of seconds to few seconds. Horizontal motions are much bigger than the vertical. It occurs due to the natural Earth disturbances or the man created disturbance of Earth. Thus, at a given area and at a given time, the Earth moves in different directions, a number of times in a second.
Even though the timings and the intensity of Earthquake have not yet been fully mapped by the scientists, a lot of conclusions have been drawn to understand the reasons of its occurrences. Cracks have been identified in Sub-surface strata Plates of Earth. Based on these studies, the Earth locations have been divided in to various Zones. Higher the Zone more is the intensity of Earthquake.
To understand the devastation Power of the Earthquake, a Scale, named as Ritcher, has been formulated. However, it is only a relative Scale, indicating only rough idea of the gravity of Earthquake.
Construction Engineers have formulated designs for the Buildings and Infrastructures that can resist these Earthquakes of varying intensity. These designs are based on the identified Zones and are aimed at having the least loss to the Buildings, Human beings, their belongings and the animals.
Key factor in designing of ‘earthquake resistant structure’ is that all the joints of the structure are created as ‘Rigid Joints’ and, in the eventuality of Earthquake; the shape of the joints should be capable of remaining the same. One may be curious as to why should the joints be rigid and not flexible.
If a man bends forwards or backwards, beyond a point, he falls to the ground because the ‘Center of Gravity’ of the body weight of the man goes beyond the base of the man. Likewise, during the Earthquake, the building tilts in a number of directions and at a number of times, in a fraction of seconds. If the Center of Gravity of the weight of the building goes beyond the base, the building is bound to collapse. The Rigid Joints restrict the sway of the building.
The weight of the Multi-story Buildings should be kept as light as possible and the building should act like a single/ monolithic Structure. The length of the building should be within permissible limit, say 3 times to its width.
Structural failures are due to formation of Plastic Hinges leading to easiness for the buildings to tilt. As opposed to these plastic Hinges, the Rigid Joint concept resists the building’s tilt, to keep the whole weight of the building within its base and to get the building regain its original shape. There is threefold task to reduce future Earthquake losses:
1) Strengthening the existing buildings that were not designed to resist the Earthquake.
2) Creating awareness in the mind of the persons related to the construction Industries who are creating the structures presently and, for some reasons, have not followed the rules.
3) Most challenging job is to convince the players of the Industries to spend extra fraction of cost, to create the Earthquake Resistant Structure.
Additional cost for creating Earthquake resistant building might be a very small amount and may be in the range of Rs.50/- to Rs. 60/- per Sq. Ft. However, cost for the Retrofit Techniques and or the strategies for repair of existing non-designed building may go from few hundred rupees per Sq. Ft. to as high as the demolition of existing building and creating a new one.
We should have the reinforcement, which should be as ductile as 14%. Thus, the reinforcement bars should be able to elongate to 14% more to its actual length, before forming cavity. Ductility based design requires quantitative estimates of deformations in post yield stage. Thus, the Concept of deformation based design methodology has to be used to achieve economical Earthquake resistant structures.
Seismic design procedures are more stringent. However, the designer goes into detailing of the requirement and considering practical problems, creates a good balance.
RCC designers normally also account for immediate occupancy, leading to eccentricity of the structure and structural stability at the initial stage. Vertical members are much more critical for designing the Earthquake resistance structures. Strengthening of horizontal members is necessary for increase in capacity of taking gravity loads.
While taking care of existing buildings for being Earthquake resistant, the designers use Retrofit Techniques and various other strategies of repair. One of the methods is the Bonded Laminates for improving structural performance and energy absorption. However, this technique does not improve the strength of the building but increases its stiffness. To understand the performance levels, we have to create damage modeling and thus improve the Structural strength. Seismic vulnerability of existing buildings is constantly been supervised by the construction Engineers.
Some of the important buildings, such as Hospitals, administrative Blocks, have to be designed such that the structures do not get disturbed during Earthquake. The basic design to protect these building, though bit costlier, is termed as ‘Base Isolation (Building resting on frictionless Rollers or on flexible pad), for low and medium height buildings.
Thus the Earthquake resistant buildings structures are safer to live in apart from the fact that the maintenance of these Earthquake resistant Buildings is also least. Therefore, over the years, these building become more economical and look elegant. The general awareness of the common man in this aspect shall be a big boon to the construction industry, as even the common man can ponder over these few questions, before making the decision to buy the flat or any other type of Properties.
It has already been observed that the buyers do not mind paying even Rs. 100/- per Sq. Ft more if they are assured of a better quality building. Thus, the Builders also tend to gain, in terms of their reputation and in terms of avoiding future Hassels.
