建筑结构外文文献翻译.doc

Architecture Structure
We have and the architects must deal with the spatial aspect of activity, physical, a needs in such a way that overall performance integrity is assured. Hence, he or she well think of evolving a building environment as a total system of interacting and space forming subsystems. Is represents a complex challenge, and to meet it the architect will need a h design process that provides at least three levels of feedback thinking: schematic, preli final.
Such a hierarchy is necessary if he or she is to avoid being confused , at conceptua design thinking ,by the myriad detail issues that can distract attention from more basic considerations .In fact , we can say that an archity to distinguish the more basic form the ect’s abili more detailed issues is essential to his success as a designer .
The object of the schematic feed back level is to generate and evaluate overall site-plan, activity-interaction, and building-configuration options .To do so the architect must be a
on the interaction of the basic attributes of the site context, the spatial organization, and the symbolism as determinants of physical form. This means that ,in schematic terms ,the archi first conceive and model a building design as an organizational abstraction of essential performance-space in teractions.Then he or she may explore the overall space-form implica the abstraction. As an actual building configuration option begins to emerge, it will be include consideration for basic site conditions.
At the schematic stage, it would also be helpful if the designer could visualize his or her options for achieving overall structural integrity and consider the constructive feasibility and economic of his or her scheme .But this will require that the architect and/or a consultan conceptualize total-system structural options in terms of elemental detail .Such overall t be easily fed back to improve the space-form scheme.
At the preliminary level, the architect’s emphasis will shift to the elaboration of his or her more promising schematic design options .Here the architect’s structural needs will shift to approximate design of specific subsystem options. At this stage the total structural scheme is developed to a middle level of specificity by focusing on identification and design of major subsystems to the extent that their key geometric, component, and interactive properties are established .Basic subsystem interaction and design conflicts can thus be identified and the context of total-system objectives. Consultants can play a significant part in this effort; these preliminary-level decisions may also result in feedback that calls for refinement or even major change in schematic concepts.
When the designer and the client are satisfied with the feasibility of a design prop preliminary level, it means that the basic problems of overall design are solved and det likely to produce major change .The focus shifts again ,and the design process moves into level .At this stage the emphasis will be on the detailed development of all subsystem
Here the role of specialists from various fields, including structural engineering, is much larger, since all detail of the preliminary design must be worked out. Decisions made at this level may produce feedback into Level II that will result in changes. However, if Levels I and II a with insight, the relationship between the overall decisions, made at the schematic and p levels, and the specifics of the final level should be such that gross redesign is not in question, Rather, the entire process should be one of moving in an evolutionary fashion fcreation and om refinement (or modification) of the more general properties of a total-system design conc fleshing out of requisite elements and details.
To summarize: At Level I, the architect must first establish, in conceptual terms, t space-form feasibility of basic schematic options. At this stage, collaboration with speci helpful, but only if in the form of overall thinking. At Level II, the architect must be a
the major subsystem requirements implied by the scheme and substantial their interactive f by approximating key component properties .That is, the properties of major subsystems n worked out only in sufficient depth to very the inherent compatibility of their basic fo behavioral interaction . This will mean a somewhat more specific form of collaboration with specialists then that in level I .At level III ,the architect and the specific form of co specialists then that providing for all of the elemental design specifics required to prod construction documents .
Of course this success comes from the development of the Structural Material.
1.Reinforced Concrete
Plain concrete is formed from a hardened mixture of cement ,water ,fine aggregate, coarse aggregate (crushed stone or gravel),air, and often other admixtures. The plastic mix is consolidated in the formwork, then cured to facilitate the acceleration of the chemical hydration reaction lf the cement/water mix, resulting in hardened concrete. The finished product has high compressive strength, and low resistance to tension, such that its tensile strength is a one tenth lf its compressive strength. Consequently, tensile and shear reinforcement in regions of sections has to be provided to compensate for the weak tension regions in the concrete element.
It is this deviation in the composition of a reinforces concrete section from the homo standard wood or steel sections that requires a modified approach to the basic principles of structural design. The two components of the heterogeneous reinforced concrete section are arranged and proportioned that optimal use is made of the materials involved. This is possible
because concrete can easily be given any desired shape by placing and compacting the wet of the constituent ingredients are properly proportioned, the finished product becomes strong, durable, and, in combination with the reinforcing bars, adaptable for use as main member structural system.
The techniques necessary for placing concrete depend on the type of member to be cas
whether it is a column, a bean, a wall, a slab, a foundation. a mass columns, or an extension of previously placed and hardened concrete. For beams columns, and walls, the forms should oiled after cleaning them, and the reinforcement should be cleared of rust and other harmful materials. In foundations, the earth should be compacted and thoroughly moistened to about depth to avoid absorption of the moisture present in the wet concrete. Concrete should a placed in horizontal layers which are compacted by means of high frequency power-driven vibrators of either the immersion or external type, as the case requires, unless it is placed by pumping. It must be kept in mind, however, that over vibration can be harmful since it co segregation of the aggregate and bleeding of the concrete.
Hydration of the cement takes place in the presence of moisture at temperatures above F. It is necessary to maintain such a condition in order that the chemical hydration reaction can take place. If drying is too rapid, surface cracking takes place. This would result in reductio strength due to cracking as well as the failure to attain full chemical hydration.
It is clear that a large number of parameters have to be dealt with in proportioning a concrete element, such as geometrical width, depth, area of reinforcement, steel strain, concrete strain, steel stress, and so on. Consequently, trial and adjustment is necessary in the choice of concrete sections, with assumptions based on conditions at site, availabilityof the constituent materials, particular demands of the owners, architectural and headroom requirements, the applicable codes, and environmental reinforced concrete is often a site-constructed composite, in contrast to the standard mill-fabricated beam and column sections in steel structures.
A trial section has to be chosen for each critical location in a structural system. The trial section has to be analyzed to determine if its nominal resisting strength is adequate to carry the applied factored load. Since more than one trial is often necessary to arrive at the requ the first design input step generates into a series of trial-and-adjustment analyses.
The trial-and –adjustment procedures for the choice of a concrete section lead to the convergence of analysis and design. Hence every design is an analysis once a trial section The availability of handbooks, charts, and personal computers and programs supports this a as a more efficient, compact, and speedy instructional method compared with the traditional approach of treating the analysis of reinforced concrete separately from pure design.
2. Earthwork
Because earthmoving methods and costs change more quickly than those in any other br of civil engineering, this is a field where there are real opportunities for the enthusias of the methods now in use for carrying and excavating earth with rubber-tyred equipment exist. Most earth was moved by narrow rail track, now relatively rare, and the main methods of excavation, with face shovel, backacter, or dragline or grab, though they are still wide only a few of the many current methods. To keep his knowledge of earthmoving equipment u date an engineer must therefore spend tine studying modern machines. Generally the only r up-to-date information on excavators, loaders and transport is obtainable from the makers
Earthworks or earthmoving means cutting into ground where its surface is too high ( and dumping the earth in other places where the surface is too low ( fills). Toreduce e the volume of the fills should be equal to the volume of the cuts and wherever possible the cuts should be placednear to fills of equal volume so as to reduce transport and double handl This work of earthwork design falls on the engineer who lays out the road since it is th the earthwork more than anything else which decides its cheapness. From the available ma levels, the engineering must try to reach as many decisions as possible in the drawing office by drawing cross sections of the earthwork. On the site when further information becomes avai can make changes in jis sections and layout,but the drawing lffice work will not have be will have helped him to reach the best solution in the shortest time.
The cheapest way of moving earth is to take it directly out of the cut and drop it as same machine. This is not always possible, but when it canbe done it is ideal, being both cheap. Draglines, bulldozers and face shovels an do this. The largest radius is obtained with the dragline,and the largest tonnage of earth is moved by the bulldozer, though only over short distances.The disadvantages of the dragline are that it must dig below itself, it cannot d into compacted material, it cannot dig on steep slopws, and its dumping and digging are not accurate.
Face shovels are between bulldozers and draglines, having a larger radius of action than bulldozers but less than draglines. They are anle to dig into a vertical clifface in a way which would be dangerous tor a bulldozer operator and impossible for a dragline. Each piece of e should be level of their tracks and for deep digs in compact material a backacter is most its dumping radius is considerably less than that of the same escavator fitted with a fac
Rubber-tyred bowl scrapers are indispensable for fairly level digging where the distance of transport is too much tor a dragline or face shovel. They can dig the material deeply ( but only below themselves ) to a fairly flat surface, carry it hundreds of meters if need be, the level it roughly during the dumping. For hard digging it is often found economical to keep tractor ( wheeled or tracked ) on the digging site, to push each scraper as it returns to as the scraper is full,the pusher tractor returns to the beginning of the dig to heop to scraper.
Bowl scrapers are often extremely powerful machines;many makers build scrapers of 8 c meters struck capacity, which carry 10 m ³ heaped. The largest self-propelled scrapers are of 19 struck capacity ( 25 m ³ heaped )and they are driven by a tractor engine of 430 horse-powers.
Dumpers are probably the commonest rubber-tyred transport since they can also conveni be used for carrying concrete or other building materials. Dumpers have the earth containe front axle on large rubber-tyred wheels, and the container tips forwards on most types, articulated dumpers the direction of tip can be widely varied. The smallest dumpers have a of about 0.5 m ³, and the largest standard types are of about 4.5 m ³. Special types include the self-loading dumper of up to 4 m ³ and the articulated type of about 0.5 m ³. The distinction between dumpers and dump trucks must be remembered .dumpers tip forwards and the driver sits behin load. Dump trucks are heavy, strengthened tipping lorries, the driver travels in front lf the load is dumped behind him, so they are sometimes called rear-dump trucks.
3.Safety of Structures
The principal scope of specificationis to provide general principles and computational methods in order to verify safety of structures. The “ safety factor ”, which according to moder trends is independent of the nature and combination of the materials used, can usually be the ratio between the conditions. This ratio is also proportional to the inverse of the probability ( risk ) of failure of the structure.
Failure has to be considered not only as overall collapse of the structure but also as unserviceability or, according to a more precise. Common definition. As the reaching of state ” which causes the construction not to accomplish the task it was designedThere are two for.
categories of limit state :
(1)Ultimate limit sate, which corresponds to the highest value of the load-bearing capacity. Examples include local buckling or global instability of the structure; failure of some s subsequent transformation of the structure into a mechanism; failure by fatigue; elastic or plastic deformation or creep that cause a substantial change of the geometry of the structure; a of the structure to alternating loads, to fire and to explosions.
(2)Service limit states, which are functions of the use and durability of the structur include excessive deformations and displacements without instability; early or excessive cracks; large vibrations; and corrosion.
Computational methods used to verify structures with respect to the different safety c can be separated into:
(1)Deterministic methods, in which the main parameters are considered as nonrandom parameters.
(2)Probabilistic methods, in which the main parameters are considered as random parame
Alternatively, with respect to the different use of factors of safety, computational be separated into:
(1)Allowable stress method, in which the stresses computed under maximum loads are compared with the strengt