搜搜考试网求一个英语文献,土木类的,
来源：学生作业帮 编辑：搜搜考试网作业帮 分类：英语作业 时间：2024/04/30 17:09:11
求一个英语文献,土木类的,
字数在3000-5000之间
忘记说了，我主要要路桥方面的，最好是道路的，
字数在3000-5000之间
忘记说了，我主要要路桥方面的，最好是道路的，
Factory construction
Factory construction ,the design and construction of single-storey building of large span often hundreds of meters long ,is a typical task of the civil engineer .Though architects often supervise these projects ,they succeed generally because the architect and the civil engineering designer work together ,with understanding of the client’s needs.
An earthy American. Who was probably a civil engineer , said Art engineer is a man who can do for one dollar what any fool can do for two . This is particularly true for civil engineering or building structures. For civil engineering structures like dams , piers , quays , breakwaters , roads or airfields the cost of the structure may well be 90-100 per cent of the total cost . For building structures it is usually not more than half , except in non-industrial countries, but for a hospital or similarly complicated building , the proportion of the cost of the structure can easily drop0 to 20 per cent of the cost of the cost of building without its mechanical equipment , because of the high cost of wall tilling , ducting for services , lift structures and so on .
It is therefore important for engineers to have an idea of the different ways that things can be built in different countries in earth , for example , which was once used in England for buildings of one or two storeys is not now used there , but in hot , dry countries like Arabia or Peru , it is perfectly suitable .Large churches have been built of earth in South America ,and earth buildings of four storeys have stood for a century in for example ,Jeddah ,Arabia .The Arabian method is of special interest because in many ways it would be a dangerous failure in a wet ,European climate .The walls ,about 60 cm thick ,are built of rubble (unshaped stones) laid in a mortar made of mud .At intervals of 1-3 m throughout their height they are interrupted by a layer of round poles laid for the full thickness of the wall .Where two walls join, these layers of poles cross each other and thus tie the two walls together .The few trees which grow in this area of Arabia are too small for construction so all building wood is imported ,and this seeming wasteful use of wood must have been felt to be truly essential ,and seems to have been reliable .In a wet climate the timber wound rot in forty years or less and in Britain its use in walls in this way has been forbidden for many years ,For single-story buildings ,mud walls even without stone or wood are completely satisfactory in Arabia and stand for centuries if the part next to the ground is of stone so that it does get washed away by the few rainstorms .In dry parts of the United States and Australia ,mud walls are accepted as normal construction and may be called cob walls.
In permafrost areas in the Soviet Union or Canada or Alaska ,ice has been used effectively for walling and roofing .In Sweden water power stations have been hollowed out of the rock, a method which has been found to be cheaper than normal construction ,Since the power scheme is at the foot of the dam ,it is usually convenient to place it in rock , and this is why it has been found cheap to put the water power plant in a tunnel.
Another unusual method of construction which has been used recently is the use of an air-inflated film .A small air blower keeps a slight pressure inside the film .The film is anchored to the ground ,and the pressure holds it up very cheaply .Balloon structures of this type have been .successfully used as temporary structures in Britain to provide urgent protection from the weather .They are also suitable for regions which suffer earthquakes .For instance in California ,a reservoir was built in about 1962 with a permanent air-inflated roof .This roof was not only light and therefore needed no foundations ,needed no foundations ,it was also cheap .In fact if an air-inflated roof is not tied down it will lift off the ground and lose air pressure .At the edges there is an upward load which must be held down by anchoring or weighting the edges .
Many thousands of kilometers of road have been built in dry parts of the United States with strengthened soil ,usually called stabilized soil .the material used for strengthening the soil can be any cheap local material, the ‘stabilizer’ .In an oilfield it can be waste oil .Near the sea ,particularly in hot countries, it can be sea water .Cement is commonly used in industrial countries ,but clays do not mix with cement ,and for clays it has been found that lime is a good stabilizer .
To some civil engineers ,metal construction in light alloy or steel is the most interesting of all structural engineering .A fairly recent development in Europe is the production of rectangular and square tubular steel section up to about 40 cm square and 1 cm wall thickness. They have been available in Europe since about 1965(much earlier in the United States)and will certainly form some of the fine welded structures of the future .The circular tubes used in the past produced beautiful welded structures .but rectangular sections are much easier to join because their meeting surfaces are flat not curved and their ends need to be cut and welded only lines.
One cause of delay in the development of new steels has been that welds have failed ,causing cracking .Civil engineers will not need to fear such failures if they make use of the specialist advice which is available in the country where the steel was made .International standards for steel are not helpful if the steel s in different countries are the steels in different countries are made from different materials .Since this is almost always so, technical advice on welding should be obtained from the country where the steel was made .
The light alloys, usually based on alumium ,have been so expensive that their use is only justified where weight is all-important as in the long jibs of mobile cranes ,in planes ,in lifting bridges or in the superstructures of ships or lorries.
For light industry which is not noisy ,the roofing and cladding generally consist of factory-made sheets ,of which hundreds of types exist made of corrugated or troughed of flat steel ,aluminium ,or asbestos-cement .the waterproof skin on the outside of some of them may also be of copper sheet ,tarred felt or steel .Some of these cladding or roofing units are expensive ,especially the sandwich units which contain a middle layer of highly efficient thermal insulator ,such as expanded polystyrene or glass fibre .
The insulation must be completely protected from the condensation of water out of the air from the hotter side of the cool insulating material .Thus in a hot climate the condensation will be on the inner face of the insulator and in a cold climate on its outer face .The insulation must be protected from moisture or it rapidly lose its insulating power as the moisture enters it. As it loses insulating power ,the condensation will increase ,more moisture will enter and the insulation will enter and the insulation will be completely lost ,quite apart from the dampness in the wall .
It is therefore essential to prevent not only moisture but also air from entering the insulation and this is done by a waterproof sheet of polythene or metal of other material , called as vapour barrier . It must be sealed at the joints to prevent air leaking through and condensation inside . The civil engineer should therefore ask whether the cladding is for use in a hot or a cold climate m and the maker will usually be happy to provide a possible buyer with all this information .
For noisy factories ,such as those which house heavy industry (car factories etc),cladding sheets are not good because noise passes through them .Any heavy walling is better because the deadening of sound depends on the weigh of the wall .Brickwork has been the unicersal in Britain in the past but modern civil engineering contractors have precast large concrete units of 4m-5m and placed them with powerful cranes .Such walls are quickly built provided that the organization of the site is good ,and the cranes are available and able to get to the lifting point, If the units are too large for one crane they are sometimes lifted by two cranes working together .The alternative is to reduce the height of the wall unit . keeping its length equal to the column spacing, since this construction is simple and looks good . If the crane is very small and the units are only about 15 cm high ,it may be advisable to lay a thin mortar joint between the units so as to keep out the wind , For the very large units. the mortar joint is less important since the joins are fewer.
It is most important to take some interest in the appearance of concrete walls because the designer’s reputation depends largely on the pleasant appearance of the factory ,and the walls are the immediately noticeable par of it . Many satisfactory ways of building concrete precast walling gave been worked out and if the engineer does not wish to think out his own solution he should apply to an architect or concrete specialist for advice .Some solutions are exceedingly simple ;for long ,horizontal thin walling units ,the edges can be cut off at 45*(chamfered )to make the horizontal lines show up . Large units can be cast with an exposed aggregate surface or with a surface or with a surface that has alternate square of exposed aggregate and ordinary concrete .For this sort of treatment ,architectural advice is helpful because of the pattern depends on the size of the squares in relation to the rest of the building .
Factory design is interesting to most civil engineers because it includes the design of many important services ,and the engineer is the main designer ,not a mere helper as he is for a multi-storey building .He must design the roads and the drains ,possibly the water supply and the heating or air conditioning and provide the power and telephone cables and gas pipes .If possible he will try at least to get main roads and drains in position before the main construction starts .This will make the site much easier to travel over ,and by keeping it driver will probably reduce the damage to vehicles .
Provided that a factory is of one storey it can usually be well lit from the roof except in hot climates ,but if it is more than one storey high .day-lighting of the lower storeys in any large-span building becomes difficult or impossible .For this reason ,some US factory designers have built factories without windows ,entirely air-conditioned ,and as spans increase this will become unavoidable for the internal rooms .In fact it is now quite common to place bathrooms internally so that they do not waste the valuable space for windows that would be more useful to a living-room .In temperate climates, the air-conditioning equipment should be designed to provide cooled air in summer and warm air in winter .
Roof lighting can be through transparent sheets in an ordinary sheeted sloping roof, or through a saw tooth roof which would be north-facing in northern continents or south-facing in southern . A monitor roof enables the lights to be either vertical or on the roof slope and also provides excellent ventilation ,Glass is still the commonest material used for admitting light because it is the cheapest .but in hot country it is unsuitable .In a sheeted roof occasional sheets may be replaced with a translucent or transparent material .either glass fiber which is translucent , or one of the transparent plastics materials ,Which may be colorless of tinted red , yellow ,etc All these large sheets can be corrugated to allow them to span over distances of about 2 m.
One difficulty in every building for heavy industry is the arrangement of the supports for an overhead crane . The crane is carried by a bridge across the building ,and the bridge runs on rails ,one along each wall .These two rails are carried on crane beams which pass the full length of the building carried on the main columns ,usually at about 10 m above ground level , so that the crane can command the whole of the work area. This means that the roof structure and the columns cannot be fully detailed until the main design of the crane is known .Crane makers are usually happy to give details of the dimensions of their cranes and bridges to structural engineers ,so this does not usually cause much delay .However ,each column must be designed to carry about there quarters of the crane weight plus three quarters of its hook load ,as well as half the bridge weight .The roof columns also carry the structure load ,as well as half the bridge weight .The roof columns must also carry the structure load (which is much smaller )and they will be about 10 m long plus the crane height .
The columns will be eccentrically loaded since the part of the column above the must be off-center from the crane grider .Precast concrete columns have been successfully cast to carry cranes beams of this type thought it was once thought that would be too big and complicated for recasting .A successful design for the overhead crane and its supports will help the reputation of a civil engineering designer.
A structure is the part of a building that carries its weight , and for at least half the world’s civil engineers , structures are most of civil engineering . We should also remember that anything built is a structure (From an aeroplane engineer’s point of view,an aeroplane also is a structure .)A structure may be a dwelling house, or a pyramid in Egypt, the statue of Christ on the Andes .or a dam built by beavers across a Canadian river . A building is a structure with a roof and much of civil engineering structural design is the design of building structures. The building as a whole is designed by an architect , particularly in a densely populated area . For water engineers,sewage-treatment engineers , and municipal engineers , structures are not always an important party of their work though even a road or a pipe is a structure they both carry load .
Every structural design includes the foundation design . The structural design itself includes two different tasks , the design of the structure , in which the sizes and locations of main members are settled , and the analysis of this structure by mathematical of graphical methods of both , to work out how the loads pass through the structure with the particular members chosen . For a common structure such as a building frame . many methods have been developed for analysis , so that the design and analysis will be relatively easy and may need to be performed only once or twice .
But for any unusual structure the tasks of design and analysis will have to be repeated many times until ,after many calculations ,a design has been found that is strong ,stable and lasting .Cheapness does not enter into the quality of the design though it is important since a costly structure will probably not be built and the designer’s fee will therefore be smaller .
For the typical multi-storey structure in a city ,whether it is to be used for offices or dwellings ,the most important member which the engineer designs is the floor—for two reasons :it repeats all the way up the building ,and it has the greatest effect on the dead load of the building .The dead load ,in fact ,as pointed out in ‘foundations’ ,can be fairly exactly calculated by assuming that the floors are the only dead load .
These floors are generally of reinforced or prestressed concrete because they resist fire better than steel or wood ,an important consideration for a tall building .There arte tow main types ,the solid floor and the hollow-tiled(or ribbed)floor .In the ribbed floor ,as the drawing shows ,part of the lower half of the slab is hollow , a great advantage because this concrete would not strengthen the floors ,but it is more difficult to cast them with holes through them unless these holes are care-fully planned beforehand .It is generally safe to cast a hole through a solid slab by adding a few extra bars of 12mm diameter in the concrete all round it ,though when there is time ,holes should be properly designed .
Suspended structures are among the most interesting at the moment because the first large ones were recently (1966) completed in London ,and possibly other great cities .In all these structures ,the columns or stanchions are made fewer and larger so as to reduce the buckling effects on them and to increase their effective length .In two that were recently built in London ,there is only one column ,in the center of the building ,and this is a hollow concrete tower some 12 m square which carries the lifts ,stairs ,ducts ,pipes and cables within it or attached to its wall .The tower may be called the core of the building and on its top is a bridge overhanging in all directions ,from which high-tensile steel bars drop to carry the floors below .These bars are very thin and can be hidden in a door frame or window frame so that for such a building there need be no noticeable obstruction to sight or horizontal movement in any direction outwards from the core .
But this is only the beginning of suspended construction .If it is successful and if the world’s large cities continue to become more crowded ,the idea will grow ,and the 60-syorey skyscrapers of New York will be tiny compared with the vast 300-storey structures of the world’s future cities .
It seems possible and even likely that the whole city may be one or a few of these vast buildings ,carried on pairs of towers 1,000 m high joined by lightweight bridge structures ,possibly suspension bridges .To reduce sway and buckling ,the columns will be massive ,probably not less than 30 m square ,and the floors will hang from the bridges by thin high-tension steel suspenders in the same way as a suspension bridge deck hangs from its cables .
没具体数,不知道差多少?
Factory construction ,the design and construction of single-storey building of large span often hundreds of meters long ,is a typical task of the civil engineer .Though architects often supervise these projects ,they succeed generally because the architect and the civil engineering designer work together ,with understanding of the client’s needs.
An earthy American. Who was probably a civil engineer , said Art engineer is a man who can do for one dollar what any fool can do for two . This is particularly true for civil engineering or building structures. For civil engineering structures like dams , piers , quays , breakwaters , roads or airfields the cost of the structure may well be 90-100 per cent of the total cost . For building structures it is usually not more than half , except in non-industrial countries, but for a hospital or similarly complicated building , the proportion of the cost of the structure can easily drop0 to 20 per cent of the cost of the cost of building without its mechanical equipment , because of the high cost of wall tilling , ducting for services , lift structures and so on .
It is therefore important for engineers to have an idea of the different ways that things can be built in different countries in earth , for example , which was once used in England for buildings of one or two storeys is not now used there , but in hot , dry countries like Arabia or Peru , it is perfectly suitable .Large churches have been built of earth in South America ,and earth buildings of four storeys have stood for a century in for example ,Jeddah ,Arabia .The Arabian method is of special interest because in many ways it would be a dangerous failure in a wet ,European climate .The walls ,about 60 cm thick ,are built of rubble (unshaped stones) laid in a mortar made of mud .At intervals of 1-3 m throughout their height they are interrupted by a layer of round poles laid for the full thickness of the wall .Where two walls join, these layers of poles cross each other and thus tie the two walls together .The few trees which grow in this area of Arabia are too small for construction so all building wood is imported ,and this seeming wasteful use of wood must have been felt to be truly essential ,and seems to have been reliable .In a wet climate the timber wound rot in forty years or less and in Britain its use in walls in this way has been forbidden for many years ,For single-story buildings ,mud walls even without stone or wood are completely satisfactory in Arabia and stand for centuries if the part next to the ground is of stone so that it does get washed away by the few rainstorms .In dry parts of the United States and Australia ,mud walls are accepted as normal construction and may be called cob walls.
In permafrost areas in the Soviet Union or Canada or Alaska ,ice has been used effectively for walling and roofing .In Sweden water power stations have been hollowed out of the rock, a method which has been found to be cheaper than normal construction ,Since the power scheme is at the foot of the dam ,it is usually convenient to place it in rock , and this is why it has been found cheap to put the water power plant in a tunnel.
Another unusual method of construction which has been used recently is the use of an air-inflated film .A small air blower keeps a slight pressure inside the film .The film is anchored to the ground ,and the pressure holds it up very cheaply .Balloon structures of this type have been .successfully used as temporary structures in Britain to provide urgent protection from the weather .They are also suitable for regions which suffer earthquakes .For instance in California ,a reservoir was built in about 1962 with a permanent air-inflated roof .This roof was not only light and therefore needed no foundations ,needed no foundations ,it was also cheap .In fact if an air-inflated roof is not tied down it will lift off the ground and lose air pressure .At the edges there is an upward load which must be held down by anchoring or weighting the edges .
Many thousands of kilometers of road have been built in dry parts of the United States with strengthened soil ,usually called stabilized soil .the material used for strengthening the soil can be any cheap local material, the ‘stabilizer’ .In an oilfield it can be waste oil .Near the sea ,particularly in hot countries, it can be sea water .Cement is commonly used in industrial countries ,but clays do not mix with cement ,and for clays it has been found that lime is a good stabilizer .
To some civil engineers ,metal construction in light alloy or steel is the most interesting of all structural engineering .A fairly recent development in Europe is the production of rectangular and square tubular steel section up to about 40 cm square and 1 cm wall thickness. They have been available in Europe since about 1965(much earlier in the United States)and will certainly form some of the fine welded structures of the future .The circular tubes used in the past produced beautiful welded structures .but rectangular sections are much easier to join because their meeting surfaces are flat not curved and their ends need to be cut and welded only lines.
One cause of delay in the development of new steels has been that welds have failed ,causing cracking .Civil engineers will not need to fear such failures if they make use of the specialist advice which is available in the country where the steel was made .International standards for steel are not helpful if the steel s in different countries are the steels in different countries are made from different materials .Since this is almost always so, technical advice on welding should be obtained from the country where the steel was made .
The light alloys, usually based on alumium ,have been so expensive that their use is only justified where weight is all-important as in the long jibs of mobile cranes ,in planes ,in lifting bridges or in the superstructures of ships or lorries.
For light industry which is not noisy ,the roofing and cladding generally consist of factory-made sheets ,of which hundreds of types exist made of corrugated or troughed of flat steel ,aluminium ,or asbestos-cement .the waterproof skin on the outside of some of them may also be of copper sheet ,tarred felt or steel .Some of these cladding or roofing units are expensive ,especially the sandwich units which contain a middle layer of highly efficient thermal insulator ,such as expanded polystyrene or glass fibre .
The insulation must be completely protected from the condensation of water out of the air from the hotter side of the cool insulating material .Thus in a hot climate the condensation will be on the inner face of the insulator and in a cold climate on its outer face .The insulation must be protected from moisture or it rapidly lose its insulating power as the moisture enters it. As it loses insulating power ,the condensation will increase ,more moisture will enter and the insulation will enter and the insulation will be completely lost ,quite apart from the dampness in the wall .
It is therefore essential to prevent not only moisture but also air from entering the insulation and this is done by a waterproof sheet of polythene or metal of other material , called as vapour barrier . It must be sealed at the joints to prevent air leaking through and condensation inside . The civil engineer should therefore ask whether the cladding is for use in a hot or a cold climate m and the maker will usually be happy to provide a possible buyer with all this information .
For noisy factories ,such as those which house heavy industry (car factories etc),cladding sheets are not good because noise passes through them .Any heavy walling is better because the deadening of sound depends on the weigh of the wall .Brickwork has been the unicersal in Britain in the past but modern civil engineering contractors have precast large concrete units of 4m-5m and placed them with powerful cranes .Such walls are quickly built provided that the organization of the site is good ,and the cranes are available and able to get to the lifting point, If the units are too large for one crane they are sometimes lifted by two cranes working together .The alternative is to reduce the height of the wall unit . keeping its length equal to the column spacing, since this construction is simple and looks good . If the crane is very small and the units are only about 15 cm high ,it may be advisable to lay a thin mortar joint between the units so as to keep out the wind , For the very large units. the mortar joint is less important since the joins are fewer.
It is most important to take some interest in the appearance of concrete walls because the designer’s reputation depends largely on the pleasant appearance of the factory ,and the walls are the immediately noticeable par of it . Many satisfactory ways of building concrete precast walling gave been worked out and if the engineer does not wish to think out his own solution he should apply to an architect or concrete specialist for advice .Some solutions are exceedingly simple ;for long ,horizontal thin walling units ,the edges can be cut off at 45*(chamfered )to make the horizontal lines show up . Large units can be cast with an exposed aggregate surface or with a surface or with a surface that has alternate square of exposed aggregate and ordinary concrete .For this sort of treatment ,architectural advice is helpful because of the pattern depends on the size of the squares in relation to the rest of the building .
Factory design is interesting to most civil engineers because it includes the design of many important services ,and the engineer is the main designer ,not a mere helper as he is for a multi-storey building .He must design the roads and the drains ,possibly the water supply and the heating or air conditioning and provide the power and telephone cables and gas pipes .If possible he will try at least to get main roads and drains in position before the main construction starts .This will make the site much easier to travel over ,and by keeping it driver will probably reduce the damage to vehicles .
Provided that a factory is of one storey it can usually be well lit from the roof except in hot climates ,but if it is more than one storey high .day-lighting of the lower storeys in any large-span building becomes difficult or impossible .For this reason ,some US factory designers have built factories without windows ,entirely air-conditioned ,and as spans increase this will become unavoidable for the internal rooms .In fact it is now quite common to place bathrooms internally so that they do not waste the valuable space for windows that would be more useful to a living-room .In temperate climates, the air-conditioning equipment should be designed to provide cooled air in summer and warm air in winter .
Roof lighting can be through transparent sheets in an ordinary sheeted sloping roof, or through a saw tooth roof which would be north-facing in northern continents or south-facing in southern . A monitor roof enables the lights to be either vertical or on the roof slope and also provides excellent ventilation ,Glass is still the commonest material used for admitting light because it is the cheapest .but in hot country it is unsuitable .In a sheeted roof occasional sheets may be replaced with a translucent or transparent material .either glass fiber which is translucent , or one of the transparent plastics materials ,Which may be colorless of tinted red , yellow ,etc All these large sheets can be corrugated to allow them to span over distances of about 2 m.
One difficulty in every building for heavy industry is the arrangement of the supports for an overhead crane . The crane is carried by a bridge across the building ,and the bridge runs on rails ,one along each wall .These two rails are carried on crane beams which pass the full length of the building carried on the main columns ,usually at about 10 m above ground level , so that the crane can command the whole of the work area. This means that the roof structure and the columns cannot be fully detailed until the main design of the crane is known .Crane makers are usually happy to give details of the dimensions of their cranes and bridges to structural engineers ,so this does not usually cause much delay .However ,each column must be designed to carry about there quarters of the crane weight plus three quarters of its hook load ,as well as half the bridge weight .The roof columns also carry the structure load ,as well as half the bridge weight .The roof columns must also carry the structure load (which is much smaller )and they will be about 10 m long plus the crane height .
The columns will be eccentrically loaded since the part of the column above the must be off-center from the crane grider .Precast concrete columns have been successfully cast to carry cranes beams of this type thought it was once thought that would be too big and complicated for recasting .A successful design for the overhead crane and its supports will help the reputation of a civil engineering designer.
A structure is the part of a building that carries its weight , and for at least half the world’s civil engineers , structures are most of civil engineering . We should also remember that anything built is a structure (From an aeroplane engineer’s point of view,an aeroplane also is a structure .)A structure may be a dwelling house, or a pyramid in Egypt, the statue of Christ on the Andes .or a dam built by beavers across a Canadian river . A building is a structure with a roof and much of civil engineering structural design is the design of building structures. The building as a whole is designed by an architect , particularly in a densely populated area . For water engineers,sewage-treatment engineers , and municipal engineers , structures are not always an important party of their work though even a road or a pipe is a structure they both carry load .
Every structural design includes the foundation design . The structural design itself includes two different tasks , the design of the structure , in which the sizes and locations of main members are settled , and the analysis of this structure by mathematical of graphical methods of both , to work out how the loads pass through the structure with the particular members chosen . For a common structure such as a building frame . many methods have been developed for analysis , so that the design and analysis will be relatively easy and may need to be performed only once or twice .
But for any unusual structure the tasks of design and analysis will have to be repeated many times until ,after many calculations ,a design has been found that is strong ,stable and lasting .Cheapness does not enter into the quality of the design though it is important since a costly structure will probably not be built and the designer’s fee will therefore be smaller .
For the typical multi-storey structure in a city ,whether it is to be used for offices or dwellings ,the most important member which the engineer designs is the floor—for two reasons :it repeats all the way up the building ,and it has the greatest effect on the dead load of the building .The dead load ,in fact ,as pointed out in ‘foundations’ ,can be fairly exactly calculated by assuming that the floors are the only dead load .
These floors are generally of reinforced or prestressed concrete because they resist fire better than steel or wood ,an important consideration for a tall building .There arte tow main types ,the solid floor and the hollow-tiled(or ribbed)floor .In the ribbed floor ,as the drawing shows ,part of the lower half of the slab is hollow , a great advantage because this concrete would not strengthen the floors ,but it is more difficult to cast them with holes through them unless these holes are care-fully planned beforehand .It is generally safe to cast a hole through a solid slab by adding a few extra bars of 12mm diameter in the concrete all round it ,though when there is time ,holes should be properly designed .
Suspended structures are among the most interesting at the moment because the first large ones were recently (1966) completed in London ,and possibly other great cities .In all these structures ,the columns or stanchions are made fewer and larger so as to reduce the buckling effects on them and to increase their effective length .In two that were recently built in London ,there is only one column ,in the center of the building ,and this is a hollow concrete tower some 12 m square which carries the lifts ,stairs ,ducts ,pipes and cables within it or attached to its wall .The tower may be called the core of the building and on its top is a bridge overhanging in all directions ,from which high-tensile steel bars drop to carry the floors below .These bars are very thin and can be hidden in a door frame or window frame so that for such a building there need be no noticeable obstruction to sight or horizontal movement in any direction outwards from the core .
But this is only the beginning of suspended construction .If it is successful and if the world’s large cities continue to become more crowded ,the idea will grow ,and the 60-syorey skyscrapers of New York will be tiny compared with the vast 300-storey structures of the world’s future cities .
It seems possible and even likely that the whole city may be one or a few of these vast buildings ,carried on pairs of towers 1,000 m high joined by lightweight bridge structures ,possibly suspension bridges .To reduce sway and buckling ,the columns will be massive ,probably not less than 30 m square ,and the floors will hang from the bridges by thin high-tension steel suspenders in the same way as a suspension bridge deck hangs from its cables .
没具体数,不知道差多少?