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High rise buildings: frames and tubes
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A large number of high-rise buildings use shear walls to provide lateral stability. A development of the shear wall is the core structure in which a number of shear walls are placed together, usually enclosing lifts, stairs or services to form tubes or other plan shapes. Compared to a single wall the core or shaft structures have ‘flange’ as well as ‘web’ parts to resist horizontal forces. However the overall shear and bending moment patterns in shear wall and core structures follow that of a cantilever. In practice there is a difficulty because of the need to provide openings in the core structure for service runs. With only small openings the core structure will not be affected but larger openings will require strengthening round the openings, especially at sharp corners. Most core structures are of poured concrete construction in which additional reinforcement may be placed as necessary but cores may also be built in reinforced or unreinforced masonry. Where a high-rise concrete frame of cast-in-place construction is used, it is natural to connect the frame with shear walls so that they interact with each other.
A further increase in stiffness against horizontal forces can be provided in steel buildings by using a shear truss and frame with belt trusses. In this system deep horizontal outrigger trusses are connected to the central shear trusses which are vertical, and to a horizontal belt truss in the perimeter of the steel frame.
In order to prevent bending moment being passed over into the perimeter columns, the connection between them and the belt trusses can be a pinned one. There are certain best locations for the belt trusses: if two belt trusses are used they would be best placed somewhere near the half and three-quarter points in the height of the building; if only one belt truss is used, it would be best placed somewhere between these two positions, although in practice the highest belt truss is often placed at the top of the building.
The most effective way of resisting horizontal loads, for any given plan area, is to use a cantilever with a solid section; however hollow tubes are more efficient in that they are almost as stiff but use very much less material than a solid section cantilever. The direct stresses of tension and compression and the shear stresses are those connected with a pure cantilever. Solid sections are not practical forms and hollow sections without openings are generally only feasible for towers and other such uses. However high-rise buildings can still be designed to exploit the inherent efficiency of tube action by an adequate choice of form. The purpose, if tube-type systems are used, is to increase the plan area of the tube as much as possible that is to increase the effective section area of the cantilever, and to make the structural behaviour as close as possible to that of the hollow tube without openings in it. As window openings are necessary for the building, the perimeter structure is weaker and more flexible than that of the pure tube. However buildings do have the compensating advantage of being stiffened by the floors, which act as a series of horizontal diaphragms and prevent deformation of the cross-section of the building throughout its height.
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Notes:
direct stress напряжение, усилие (растяжения или сжатия)
| outrigger truss | выносная ферма | |
| pure adj. | простой | |
| sharp adj. | острый | |
| shear moment | момент сдвига | |
| shear truss | ферма жёсткости | |
| solid section | сплошное сечение | |
structural behaviour работа / поведение строительной конструкции
Ответьте на вопросы к тексту.
1. What is used to provide lateral stability in high-rise buildings?
2. What is a difficulty in providing strength of the core or shaft structures?
3. How can this difficulty be overcome?
4. How are most core structures built?
5. What can be done to increase the stiffness of steel buildings against horizontal forces?
6. What are the best locations for the belt trusses?
7. Why are hollow tubes more efficient than a cantilever with a solid section?
8. How can the inherent efficiency of tube action be exploited in high-rise buildings?
9. What prevents deformation of the cross-section of the building throughout its height?
Лексическое упражнение
В списке А даны некоторые слова и выражения, которые использованы в тексте для домашнего чтения. Найдите их перевод в списке В.
| А | B | А | B |
| throughout | сплошной | pinned connection | полое сечение |
| service run | шарнирное соединение | exploit | противостоять |
| lateral stability | эффективность | difficulty | дополнительный |
| round | площадь в плане | central | окружать |
| compensate | взаимодействовать | flange | ферма |
| belt truss | проход для коммуникаций | efficiency | везде |
| perimeter | решётка(фермы) | truss | система |
| plan shape | здание башенного типа | interact | компенсировать |
| hollow section | поперечная устойчивость | window | хотя |
| further | фланец | web | периметр |
| resist | трудность | enclose | вокруг |
| although | окно | tower | консоль |
| cantilever | использовать | plan area | профиль в плане |
| solid | центральный | pattern | ленточная ферма |
ЗНАКИ ФОНЕТИЧЕСКОЙ ТРАНСКРИПЦИИ
Произношение в упражнениях задания и словаре даётся по международной фонетической системе.
Ударение в фонетической транскрипции ставится перед ударным слогом. Второстепенное ударение ставится внизу перед ударным слогом.
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Гласные звуки
J – долгий и
I – краткий, открытый и
e – как э в словах этот, эти
· - очень открытый э, как ударный гласный в слове бяка
± - долгий, глубокий а, как ударный гласный в слове палка P - краткий, открытый о
L - долгий о
V – краткий у
H – долгий у
µ - краткий а, как в словах варить, мосты W – как долгое ё в словах Фёкла, свёкла
q – безударный гласный похожий на русский безударный гласный в словах нужен,
голос, карета
Двугласные звуки
eI - эй OI - ой
qV - эу Iq - иа
aI - ай eq - эа
aV - ау Vq - уа
Согласные звуки
p - п b – б m - м
w – звук образуется, когда губы, в положении как при свисте, резко раздвигаются. Напоминает звук у.
| f - ф | ||
| v - в | ||
| T - (без голоса) | оба звука образуются при помощи языка, | |
| D - (с голосом) | кончик которого помещается между | |
| s - с | передними зубами | |
z - з
t – т, но при произношении кончик языка касается дёсен, а не зубов
d – д ~ ~ ~ ~
| n – н | ~ | ~ | ~ | ~ |
| l – л | ~ | ~ | ~ | ~ |
r – нераскатистое, краткое, слабое р (кончик языка немного завёрнут назад) S - мягкое ш
Z - мягкое ж
C - ч
» - очень мягкое слитное дж k - к
g - г
N - произнесённый задней частью спинки языка звук н h – простой резкий выдох
j – слабый звук й
СЛОВАРНЫЙ МИНИМУМ СТРОИТЕЛЬНЫХ ТЕРМИНОВ I – II СЕМЕСТРОВ
