Planning Towards a Safer World
Text by: Sabiha Essa Khan
Natural disasters have always been one of the most uncertain and unknown enemies of human life. Earthquakes, cyclones, hurricanes or Tsunamis, all pose great challenges to the very existence of mankind and have been taking many lives since the humans came into origin. Earthquakes are considered to be one of the most dangerous natural calamities which occur due to the sudden breaking and shifting of large sections of Earth’s rocky outer shell which generate heat energy inside the surface of earth and jolts over the surface of earth. The resultant jolts could be of high or low intensity and frequency depending on the amount of energy waves. An earthquake of severe intensity (more than 7 on the Richter scale) can release energy of 10,000 times as great as that of the first atomic bomb. Recently our neighboring country, China faced one of the most devastating earthquakes of its history which killed thousands of innocent people. Like in any other part of the world, our country too has had many instances when it had to face terrifying earthquakes, paying a huge price in the form of loss of precious human lives, infrastructure and economic growth. The most disastrous of all earthquakes that our country faced was of 8th Oct 2005 in which more than 70,000 people died. Where the tragic incident didn’t forgive the elders, it didn’t spare the lives of innocent children either and killed more than 17,000 children. Investigations until now have revealed that the major reason for the rise in death toll amongst children was mainly due to the collapsing of school buildings. The reasons for collapsed buildings have mainly been found to be the use of low quality construction material, unplanned selection and construction of the school sites. Investigation into this has revealed that buildings were never made keeping the higher seismic risks of these locations.
It’s very rightly said that “Earthquake don’t kill people, buildings do”. With all the ongoing frequent episodes of earthquakes in different parts of the world, scientists and engineers are trying to study the impact of earthquake on buildings and other structures. They are continuing their research by scrutinizing how structures respond to earthquakes and using that gained knowledge, for improving the ability of structures to survive major earthquakes. In some countries, many lives along with millions of dollars have already been saved by these scientific advancements. Designing and constructing large structures has always been a challenge which gets compounded when they are to be built in earthquake-prone areas. There are certain regions of Pakistan, including Karachi, which lie on the seismic belt and are very much at risk of frequent, uninformed earthquakes. Keeping this fact in mind and the previous irreparable loses of human lives, we must gear up our energies in building safer and earthquake or seismic resistant buildings and structures like bridges, dams etc.
The seismologists or the earth scientists work to identify the places which are more prone to receive earthquakes. They design maps indicating the faulty zones with unresisting, poor construction, flood plains, areas at risk of landslides or to soil liquefaction. With the help of such maps, the construction planners design zoning restrictions for preventing the construction of hazardous structures in earthquake prone areas. Unlike our country, while designing and constructing any building, Architects and engineers around the world give much importance to the safety and seismic resistance of their built buildings. But since it’s an expensive task to achieve, their efforts can’t be used in making all the buildings seismic free but some dams and public buildings of higher importance, e.g., schools, hospitals, densely populated residential areas etc. However, with extensive researches it has been found that the cost of repair is a fraction of the cost of earthquake-proofing of these buildings.
Seismologists started to research on earthquake during 1880’s and in 1940 they were able to create instruments which could be installed in buildings in order to measure their response to the jolts of earthquake. The information provided by these instruments not only helped in calculating the intensity of earthquake and understanding the forces produced by shaking of earth, but it also helped in defining the building codes. The building codes help in formulating the front line safety measures against future earthquake damages to the public life. In many countries the earthquake recording instruments are installed in all major constructions of the buildings like schools, hospitals, dams and other structures.
Seismic Resistant Buildings
An earthquake resistant building is the one which safely withstands the rapid and forceful shocks or jolts of earthquake without being damaged or collapsed. This is generally achieved by carefully choosing a suitable structural configuration of construction tools like beams, columns and interlinkages between them. The basic aim behind constructing safer buildings is to strengthen the building to resist the earthquake generated forces acting on it. This can be done by de-coupling the building structure from seismic ground motion. Such buildings generally comprise of shear walls, a shear core, and cross-bracing. For smaller or medium sized buildings, the common strengthening procedure consists of bolting buildings to their foundations and providing supportive stronger walls. In order to strengthen the structure against the displacing forces, the walls are made up of reinforced concrete with steel rods and bars implanted in it. The walls can be further made and resistant to rocking forces by reinforcement of the diagonal beams in a special technique known as cross-bracing. The shear core is made in the centre of the building, mostly in the region of an elevator shaft or stairwell. Specially made shock absorbing devices, known as base isolators can also be used which are bearings consisting of alternate sheets of steel and flexible material like the synthetic rubber. They act to take up some of the lateral movements which can be an important cause of damaging buildings.
For taller and larger buildings, it’s important that they must be secured deep inside the ground. They require a strongly reinforced framework with powerful joints than an ordinary building which makes them resistant to shocks and elastic enough to bear the displacing forces of earthquake.
According to engineers, lighter the building, lesser the loads it would have, especially when the weight is higher up. The roof of any building should also be made light-weight. If the lateral resistance of the construction is expected from the diagonal bracing then it should also be made equal all around in both directions, increasing the strength good enough to bear the weight in tension as well as compression. This can be done by using bolted or welded connections which can resist more force than the load bearing capacity of the brace, care should be taken that it should not fastener with loads more than the design load. The loads of the construction should go down to the ground in a stronger and firm manner.
If the requirement of the construction is that the weight is to be opposed with the help of resisting beams then enough care should be taken to make sure that the joints are burly enough than the beams. Usually, the beams fail earlier than the columns and the columns cannot fail if made with pure concrete material. In this scenario too, the rigid framing should be made all around and in both directions.
If the building or structure resistance needs to be achieved with the help of resisting frames, then special care should be taken from the foundation to first floor level. If the design demands a higher clear height of the construction with open holes in the walls, then the columns at this level need to be stronger than at higher levels. The beams at first floor and the columns from ground to second floor would also have to be capable enough of opposing the turning loads these columns distribute to the frame. For giving permanence to the columns at the feet, fixed-feet with many bolts into big foundations can be used. This can also be done by having a grillage of steel beams at the foundation level in order to oppose the column moments. The steel grillage can also be used to keep the foundations of the building in its place. If the beams in the frame is being bent to achieve a little more strength at their highest stressed points, with no losing resistance and giving good resistance to the joints and the columns then it would alter the resonant frequency of the whole frame. In that case if the building was vibrating due to the effects of shock waves, then this vibration will tend to be damped out. This is due to the phenomenon of ‘Plastic Hinging’.
The floors of the building need to be connected to the framing in a tough and supple manner, without being able to shaking loose and falling. The floors should be lighter in weight and should go all around each column, fastening to all the supporting beams or walls. According to scientists, an important way of decreasing the vulnerability of big buildings is to separate them from the floor using bearings or dampers. However, this method is very expensive, not appropriate enough to be used for low and medium rise buildings and low cost buildings.
During earthquakes, the majority of deaths and injuries occur due to the damaged or collapsed buildings and other structures. These losses can greatly be minimized through documenting and understanding how structures react to earthquakes. However, achieving such knowledge requires a long-standing commitment due to the fact that large overwhelming earthquakes take place at irregular and often long intervals. For keeping a well maintained and effective track of earthquakes, recording instruments must be in place and waiting, ready to capture the response to the next temblor whenever it occurs. The latest information gathered by these instruments can then be used for making improved designs for earthquake-resistant buildings and structures with the help of which the loss of life and property can be reduced in future earthquakes.
There is a great need for the government as well as the non-governmental relief agencies to give serious considerations to this fact that modern scientific knowledge and its tools has greatly enabled us to built safer, earthquake resistant buildings by using which we can save our present and future generations to come.
Natural disasters have always been one of the most uncertain and unknown enemies of human life. Earthquakes, cyclones, hurricanes or Tsunamis, all pose great challenges to the very existence of mankind and have been taking many lives since the humans came into origin. Earthquakes are considered to be one of the most dangerous natural calamities which occur due to the sudden breaking and shifting of large sections of Earth’s rocky outer shell which generate heat energy inside the surface of earth and jolts over the surface of earth. The resultant jolts could be of high or low intensity and frequency depending on the amount of energy waves. An earthquake of severe intensity (more than 7 on the Richter scale) can release energy of 10,000 times as great as that of the first atomic bomb. Recently our neighboring country, China faced one of the most devastating earthquakes of its history which killed thousands of innocent people. Like in any other part of the world, our country too has had many instances when it had to face terrifying earthquakes, paying a huge price in the form of loss of precious human lives, infrastructure and economic growth. The most disastrous of all earthquakes that our country faced was of 8th Oct 2005 in which more than 70,000 people died. Where the tragic incident didn’t forgive the elders, it didn’t spare the lives of innocent children either and killed more than 17,000 children. Investigations until now have revealed that the major reason for the rise in death toll amongst children was mainly due to the collapsing of school buildings. The reasons for collapsed buildings have mainly been found to be the use of low quality construction material, unplanned selection and construction of the school sites. Investigation into this has revealed that buildings were never made keeping the higher seismic risks of these locations.
It’s very rightly said that “Earthquake don’t kill people, buildings do”. With all the ongoing frequent episodes of earthquakes in different parts of the world, scientists and engineers are trying to study the impact of earthquake on buildings and other structures. They are continuing their research by scrutinizing how structures respond to earthquakes and using that gained knowledge, for improving the ability of structures to survive major earthquakes. In some countries, many lives along with millions of dollars have already been saved by these scientific advancements. Designing and constructing large structures has always been a challenge which gets compounded when they are to be built in earthquake-prone areas. There are certain regions of Pakistan, including Karachi, which lie on the seismic belt and are very much at risk of frequent, uninformed earthquakes. Keeping this fact in mind and the previous irreparable loses of human lives, we must gear up our energies in building safer and earthquake or seismic resistant buildings and structures like bridges, dams etc.
The seismologists or the earth scientists work to identify the places which are more prone to receive earthquakes. They design maps indicating the faulty zones with unresisting, poor construction, flood plains, areas at risk of landslides or to soil liquefaction. With the help of such maps, the construction planners design zoning restrictions for preventing the construction of hazardous structures in earthquake prone areas. Unlike our country, while designing and constructing any building, Architects and engineers around the world give much importance to the safety and seismic resistance of their built buildings. But since it’s an expensive task to achieve, their efforts can’t be used in making all the buildings seismic free but some dams and public buildings of higher importance, e.g., schools, hospitals, densely populated residential areas etc. However, with extensive researches it has been found that the cost of repair is a fraction of the cost of earthquake-proofing of these buildings.
Seismologists started to research on earthquake during 1880’s and in 1940 they were able to create instruments which could be installed in buildings in order to measure their response to the jolts of earthquake. The information provided by these instruments not only helped in calculating the intensity of earthquake and understanding the forces produced by shaking of earth, but it also helped in defining the building codes. The building codes help in formulating the front line safety measures against future earthquake damages to the public life. In many countries the earthquake recording instruments are installed in all major constructions of the buildings like schools, hospitals, dams and other structures.
Seismic Resistant Buildings
An earthquake resistant building is the one which safely withstands the rapid and forceful shocks or jolts of earthquake without being damaged or collapsed. This is generally achieved by carefully choosing a suitable structural configuration of construction tools like beams, columns and interlinkages between them. The basic aim behind constructing safer buildings is to strengthen the building to resist the earthquake generated forces acting on it. This can be done by de-coupling the building structure from seismic ground motion. Such buildings generally comprise of shear walls, a shear core, and cross-bracing. For smaller or medium sized buildings, the common strengthening procedure consists of bolting buildings to their foundations and providing supportive stronger walls. In order to strengthen the structure against the displacing forces, the walls are made up of reinforced concrete with steel rods and bars implanted in it. The walls can be further made and resistant to rocking forces by reinforcement of the diagonal beams in a special technique known as cross-bracing. The shear core is made in the centre of the building, mostly in the region of an elevator shaft or stairwell. Specially made shock absorbing devices, known as base isolators can also be used which are bearings consisting of alternate sheets of steel and flexible material like the synthetic rubber. They act to take up some of the lateral movements which can be an important cause of damaging buildings.
For taller and larger buildings, it’s important that they must be secured deep inside the ground. They require a strongly reinforced framework with powerful joints than an ordinary building which makes them resistant to shocks and elastic enough to bear the displacing forces of earthquake.
According to engineers, lighter the building, lesser the loads it would have, especially when the weight is higher up. The roof of any building should also be made light-weight. If the lateral resistance of the construction is expected from the diagonal bracing then it should also be made equal all around in both directions, increasing the strength good enough to bear the weight in tension as well as compression. This can be done by using bolted or welded connections which can resist more force than the load bearing capacity of the brace, care should be taken that it should not fastener with loads more than the design load. The loads of the construction should go down to the ground in a stronger and firm manner.
If the requirement of the construction is that the weight is to be opposed with the help of resisting beams then enough care should be taken to make sure that the joints are burly enough than the beams. Usually, the beams fail earlier than the columns and the columns cannot fail if made with pure concrete material. In this scenario too, the rigid framing should be made all around and in both directions.
If the building or structure resistance needs to be achieved with the help of resisting frames, then special care should be taken from the foundation to first floor level. If the design demands a higher clear height of the construction with open holes in the walls, then the columns at this level need to be stronger than at higher levels. The beams at first floor and the columns from ground to second floor would also have to be capable enough of opposing the turning loads these columns distribute to the frame. For giving permanence to the columns at the feet, fixed-feet with many bolts into big foundations can be used. This can also be done by having a grillage of steel beams at the foundation level in order to oppose the column moments. The steel grillage can also be used to keep the foundations of the building in its place. If the beams in the frame is being bent to achieve a little more strength at their highest stressed points, with no losing resistance and giving good resistance to the joints and the columns then it would alter the resonant frequency of the whole frame. In that case if the building was vibrating due to the effects of shock waves, then this vibration will tend to be damped out. This is due to the phenomenon of ‘Plastic Hinging’.
The floors of the building need to be connected to the framing in a tough and supple manner, without being able to shaking loose and falling. The floors should be lighter in weight and should go all around each column, fastening to all the supporting beams or walls. According to scientists, an important way of decreasing the vulnerability of big buildings is to separate them from the floor using bearings or dampers. However, this method is very expensive, not appropriate enough to be used for low and medium rise buildings and low cost buildings.
During earthquakes, the majority of deaths and injuries occur due to the damaged or collapsed buildings and other structures. These losses can greatly be minimized through documenting and understanding how structures react to earthquakes. However, achieving such knowledge requires a long-standing commitment due to the fact that large overwhelming earthquakes take place at irregular and often long intervals. For keeping a well maintained and effective track of earthquakes, recording instruments must be in place and waiting, ready to capture the response to the next temblor whenever it occurs. The latest information gathered by these instruments can then be used for making improved designs for earthquake-resistant buildings and structures with the help of which the loss of life and property can be reduced in future earthquakes.
There is a great need for the government as well as the non-governmental relief agencies to give serious considerations to this fact that modern scientific knowledge and its tools has greatly enabled us to built safer, earthquake resistant buildings by using which we can save our present and future generations to come.
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