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The dilapidated failure of the twin towers of the world trade center in USA due to the terrorist attack on September 11, 2001, have put immense pressure on designers of future high rise buildings to explicitly ensure specified levels of safety against progressive collapse: impact, blast, fire, etc. The particular system where progressive collapse is triggered by the floor system, disengaging from its support over all part of the building, as appeared to be the case for the world trade center.
This research abstract brought a method involving evolutionary and "Pareto" optimization to analyze the load-path safety of high-rise commercial office buildings against progressive collapse under abnormal loading. The study was motivated by the progressive-collapse failure of the twin towers of the World Trade Center in New York on 11 Sep, 2001; consider the same as the best exemplary for being provoked. The assessment of load-path safety against progressive collapse is based on the degree of force redundancy that the structural system of a building has, optimal tradeoff surface formed by a population of conceptual designs for a particular office building project is established in the three dimensional space of capital cost and operating cost and income revenue. The "gray scale" filtering of the cost-revenue trade-off surface is employed to highlight the relative safety of the different building designs, thus design of buildings to withstand or delay progressive collapse under abnormal loading.
Factors that Promotes or Hinders Safety Levels in High-Rise Buildings:
ïƒ Cyclones, Tsunamis, Volcanoes
ïƒ Power Failure
There are so many natural calamities such as Cyclones, Tsunamis, Volcanoes but Earthquakes and Fire hazards are more devastating then them.
Earthquakes and Fire calamities have already acclaimed thousands of life in last 10 years. The figures death toll of 19th century and 20th century are not that authentic.
An earthquake is a rapid shaking of the Earth caused by the breaking and progressive shifting of rock beneath the surface of Earth. From thousands of years this process of shifting and setting is going on, these tectonic forces have shaped the Earth, These plates are locked together, fails to release the accumulating energy, and the huge plates that form the Earth's surface move slowly over, under and passes each other. Sometimes this shifting is slow and sometime it is so fast that people don't even come to know about the movement and calamities strike claiming hundreds of life. When the accumulated energy grows strong enough: plates break free causing ground to shake. Most earthquakes occur at the boundaries where the plates meet; on un-consolidated landfill and other unstable soil.
The dynamic response of building to earthquake ground motion is the most important cause of damage to buildings. The damage that a building suffers primarily depends not upon its displacement, but upon acceleration. Whereas displacement is the actual distance the ground and building may move during an earthquake and acceleration is a measure of how quickly they change speed as they move. The conventional approach to earthquake resistant design of buildings depends basically upon providing the building with strength, stuffiness and less elastic deformation capacity which are great to with stand a given level of generated force by earthquake.
Causes of Earthquakes
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Earthquakes are caused due to the over powering tectonic forces, which are caused due to the movement of tectonic plates in there respective directions with respect to each other. Elastic rebound has been clearly stated to explain the whole scenario of tectonic plates causing earthquakes, as according to the theory of elastic rebound "The movement of tectonic plates is escort by the sudden buildup of elastic energy beneath the plates at the occurring positions, the rock stores, this tectonic plates are bound by the strain energy and then later causes the earthquakes." These earthquakes are caused basically of the movement of tectonic plates and covering of larger distances in short span of time, and hence turning disastrous at the surface.
Movement of Active Tectonic Plates: Movement of tectonic plates and the forces around cause the earthquakes.
2. First Time Movement of Tectonic Plates: Tectonic plates never settle down they always floats in the mantle of the earth core but this floating movement is darn minuscule that it may never noticed by anyone but the settling down process causes the earthquake.
3. Eruption Power of Volcanoes: These eruptions are caused due to the pressure building up beneath the earth surface and when the volcanic blast when took place, sometime causes the movement of tectonic plates and causes the earthquakes.
4. Beneath and Explosions above the Surface:Â tunneling mining and various digging processes by man cause man made stress and sometime triggers the movement of tectonic plates causing the earthquake.
SEISMIC WAVES AND ITS TYPES
Â Â Â Â Â When the tectonic plates moves cause of the seismic waves then plethoric amount of tectonic energy released due to the collisions and settling down of the tectonic plates, some of these plethoric energy released by the collisions are used in the breaking down of the rocks and dividing of these small rocks in to the sand stones, since these seismic waves are capable of traveling through great distances so even a earthquake at farther distance causes catastrophe disasters , these waves continue to forward until they turns zero. Faster waves are p waves and slower are the s waves.Â
Primary, push waves "P waves":
Secondary or shake waves or S waves:
Tectonic forces produces due to the settlement of the tectonic forces causes the seismic waves to flow down and causes the destruction of human built structures causing to bolt down and claiming of human lives
ïƒ After the tectonic dispersion great energy release and so the seismic waves, when they reach the earth surface cause the destruction.
ïƒ the damages caused by the seismic waves could be in the various forms such as dissolving of human made buildings in earth surface , cracking down and displacing from the previous place
ïƒ Sometimes after the earthquake the surface tilts at certain slope.This causes plain land to tilt causing excessive stresses on buildings, resulting in damage to buildings.
incorrect assessment of soil nature cause the more damage even if the earthquake is not that much big
ïƒ This induces excessive stresses and causes cracking.
For Earthquake Resistant Buildings: -
The step which has to be taken is to make the ceiling and terrace or roof as light as could be possible. This thing or target can be easily achieved by using steel sheets putting the slope ranging between 2 to 14 degrees. If no slope is required than a flat roof can also be made of the galvanized processed steel with appropriate toppers used to hang the steel together and can be done easily. Even a roof with nearly zero slope could be provided with a 2 degree slope to decrease the chances of stagnation of water and other liquid or waste. Then an concrete piece can be put on the roof, this concrete slab should only be of 5inches, and should weight under 200kg/sqm. Such a concrete piece will be sturdily in the concrete frame and will not be able to move a single inch ion any circumstances and not even collapse. If no slope is required than a flat roof can also be made of the galvanized processed steel with appropriate toppers used to hang the steel together and can be done easily. Even a roof with nearly zero slope could be provided with a 2 degree slope to decrease the chances of stagnation of water and other liquid or waste. Then, floor-boards or tongue-and-groove chipboard can easily be screwed to the joints, however in Motels, if we have a building that will behave very well in an earthquake, but nothing can be guaranteed to be able to resist any possible earthquake, but buildings like the ones proposed here by Steel would have the best possible chance of survival and would save many lives, providing greater safety from an earthquake Apartment buildings, Offices, concrete floors may be needed.
Fire Calamities: -
The buildings these days are generally high-rise and even super high-rise buildings, specifically in the Gulf and Far Middle East regions, raises new fire safety impasse and concerns for those authority peoples increasing there safety concerns, Fires in newly developed sites have, from many years have been considered as a serious problem for building authorities and even for building insurers, but its not a serious issue of safety of public, till now there were relatively few fire deaths in such fire calamities. There is a trend of even more high-rise buildings, specifically in the Gulf and Far East Middle region, and have been ended in a numerous times of significant fires hazards in the high-rise buildings which have claim thousands of deaths and showed up the impasse facing by authorities of fire brigades when handling such disastrous events , several times, helicopters were needed to handle such fire suppression and hazards and to rescue the public life .
Some of the taller buildings of Far East are:-
ïƒ Al Burj/Nahkeel Tower 1400m high
ïƒ Murjan Tower, 1022m high
ïƒ Tower of Russia, 612m high
Hazard and Risk Assessment
One main problems these days has put immense pressure on building industry, they have analyzed and put altogether there considerations that how much a taller building is vulnerable to fire calamities. Waste wood can cause big fire calamities in the newly build building as there were no proper disposal techniques for those timber piece. The packaging has also emerged as the biggest reasons for the fire calamities in high rise building. It is a kind of deadlock emerged as the huge difficulties of risk.
Fire Safety Problems
The fire caused in the building do not differ radically from, conventional single floor buildings. The main difference arise in the amount and area damaged by the fire and problems that are caused during the workforce working, causing impasse in the recovering of people hang in the fire and even for the rescue workers during tackling these hazards
The fire causes can involve fire causing factors such as electrical short circuits risks of smoking, waste burning, overly used equipments which released heat and cause sudden fires, as such the risks causing fire in the taller buildings include:
1. Catastrophe equipments, lifts, other management systems and their failure some time causes the fire.
2. Storage of raw building materials and trash inside the building cause fire.
3. Amorphous buildings in taller building structure itself causing fire.
4. Use of equipments run on fuel which may cause fire if there fuel is loosened by any reasons.
5. Waste storage and some times in car parking causes most of the time not revealed.
Implying Sprinklers to Control Fire: -
Types of Sprinkler
ïƒ Non Sodden sprinklers: - These are the most common systems and are used in buildings where there is no risk of freezing. They react quickly as they are always filled with water. Wet systems are required for multi-storey or taller buildings for less claims of life.
ïƒ Cooled Sprinklers: - As alternate systems can have their pipes full of water for the summer and be drained down and filled with air under pressure for the winter, This is important for buildings that are not heated.
ïƒ Air filled Sprinklers: -They are always filled with air under pressure all of the time and the water is controlled by the valve controlling the water in it, the head of the sprinkler opens only when the smoke detectors detects any smoke, and drop in the air pressure of the valve, opens the valve and water comes out of the valve to control the fire caused. These systems are implemented only where, when there is no specific administrations to monitor the hazardous situations.
ïƒ Pre Sprinklers: - pre systems are initially filled with air and water is provided in the pipes only in the case of the detection of smoke by automatic detectors.
Other Natural Calamities: -
Tornados and Cyclones: - Tornados and Cyclones are basically the winds locked in self spinning and during their spinning they took each and everything I between there way and creates doughnut clouds which are very destructive capable of wiping out the whole city, they took each and everything such as animals, humans, vehicles, tones of trees and waste and capable of causing severe damages.
Volcanoes: - Volcanoes are basically ejaculation of hot lava from the earth crust due to the over powering pressure in the mantle crust and could create a possible disaster scenario if a tall building is near by with less exit openings.
Tsunami: - A tsunami waves are basically stockpiles of water which are caused due to the earthquake inside the sea and some time due to the movement of the tectonic plates. Tsunamis occur suddenly and often they are extremely dangerous to costal tall buildings and even for city centers buildings since tsunamis generally have such a huge range of wipe outs.
Power Failure Management: -
Standby power generating system conforming shall be provided. The buildings shall be equipped with suitable means for automatically starting the generator set upon failure of the normal electrical supply systems and for automatic transfer of all functions required by the at full power within 60 seconds of such normal service failure. Building supervisions and administration should be able to manual start and transfer features shall be provided at the central control station.
An on-premise fuel supply sufficient for not less than two hours full demand operation of the system shall be provided, thus standby system shall have a capacity and rating that would supply all equipment required for to be operational at the same time including fire pumps required to maintain pressure. Fire pumps are required to have their own transfer switch. If in case generator is not sized to run fire pump or pumps depending on whether pumps are connected in series or parallel, then a diesel engine fire pump will be required for the backup pump if backup pump is required.
Â Recommendations: -
High rise building: -
ïƒ For this purpose the buildings are supposed to have 15 meter height for each floor and proper staircase management for each floor.
ïƒ Every tall building should have 2-3 optional staircase management and this ratio must be increase proportionally with the height of the building.
ïƒ The handrails fitted on side of every staircase must have minimum height of 90cms and if there is some gap between these handrails then it must not be greater than 10cm.
Guard rails: -
ïƒ Every concrete piece of veranda and balcony above any interior and exterior space which are 200centimetres and below should be provided with par safety walls and guard rails which must be less than 120centimeters of height and such guard rails should be subtle fixed and firmly into the walls and concrete structures and may also be fitted into the walls, grilled metals and the sequence implemented.
Fire Escape Stairway: -
ïƒ Every tall building should have an optional easy fire escape stairway that must be proved useful in the hazardous situation.
ïƒ These fire escape stairways should be provided in myriad numbers and should be leading to open space in shortest span of time.
ïƒ There must be some emergency openings in those staircase side walls if the evacuation taking more time than those emergency openings can be used.
ïƒ External fire escape stairway shall have straight flight not less than 75cm wide, with 25cm steps and must not be less than 25cm of height; this high rise should be limited to some specific numbers.
ïƒ The height of those handrails fitted by side of staircase should be in between range 100cm and not more than the 120cm.
ïƒ Debarring the use of spiral staircase in the taller building cause they took so much time during the evacuation.
Lifts for high-rise Residential Apartments: -
ïƒ Every tall building having more than 15 floors should be fitted wit ha lift capable of carrying either 15 persons at a time and must be enough spacious to carry to loaded stretchers at a time
ïƒ Every building dwelled with more than 15 floors should be provided with at least one lift as in accordance to the act number 48 standard for all taller buildings.
Evacuation to the Terrace: -
ïƒ If a taller building is having more than 15 dwelling units or floors then there must be some management to the terrace itself, because in case if the lift and staircase felt useless and damaged by fire than the evacuation can be made to the terrace from where with the help of helicopter the life could be saved.
Design Plan Followed For the Taller Buildings: -
ïƒ When these taller buildings are constructed a specific plan and strategy made after the research should be followed and must be implemented effectively.
ïƒ When these buildings are built designer must keep that what seismic waves can do during the consecutive occurring of fire and earthquake, so the area code according to the national report for seismic waves tendency should be very clear and specific plans and strategy must be implemented while building such high buildings.