华北理工大学土木工程中英文1

学号：[1**********]5

HEBEI UNITED UNIVERSITY

毕业设计外文

GRADUATE DESIGN

设计题目：唐山市中山宾馆建筑结构设计

学生姓名：史知广

专业班级：08土木3班

学院：建筑工程学院

指导教师：韩建强副教授

2012年05月25日

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Prestressed Concrete

Concrete is strong in compression,but weak in tension:its tensile strength varies from 8 to 14 percent of its compressive strength. Due to such a love tensile capacity ,flexural cracks develop at early stages of loading .In order to reduce or prevent such cracks from developing, a concentric or eccentric force is imposed in the longitudinal direction of the structural element. This force prevents the cracks from developing by eliminating or considerably reducing the tensile stresses at the critical midspan and support sections at service load,thereby raising the bending,shear,and torsiona capacity of the concrete in compression can be efficiently utilized across the entire depth of the concrete sections when all loads act on the structure.

Such an imposed longitudinal force is called a prestressing force,i.e.,a compressive force that prestresses the sections along the span of the structural element prior to the application of the transverse gravity dead and live loads or transient horizontal live loads.The type of prestressesing force involved,together with its magnitude,are determined mainly on the basis of the type of system to be constructed and the span length and slenderness desired.Since the prestressing force is applied longitudinally along or parallel to the axis of the member, the prestressing principle involved is commonly known as linear prestressing.

Circular prestressing, used in liquid containment tanks, pipes, and pressure reactor vessels, essentially follows the same basic principles as does linear prestressing, The circumferential hoop, or”hugging” stress on the cylindrical or spherical structure, neutralizes the tensile stresses at the outer fibers of the curvilinear surface by the internal contained pressure.

It is plain that permanent stresses in the prestressed structural member are created before the full dead and live loads are applied in order to eliminate or considerably reduce the net tensile stresses caused by these loads. With reinforced concrete,it is because the tensile forces resulting from the bending moments are resisted by the bond created in the reinforcement process. Cracking and deflection are therefore essentially irrecoverable in reinforced concrete once the member has reached its limit state at service load.

The reinforcement in the reinforced concrete member does not exert any force of its own on the member, contrary to the action of prestressing steel. The steel required to produce the prestressing force in the prestressed member actively preloads the member , permitting a relatively high controlled recovery of cracking and deflection. Once the flexural tensile

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strength of the concrete is exceeded, the prestressed member starts to act like a reinforced concrete element.

Prestressed member are shallower in depth than their reinforced concrete counterparts for the same span and loading conditions. In general, the depth of a prestressed concrete member is usually about 65 to 80 percent of the depth of the equivalent reinforced concrete member. Hence, the prestressed member requires less concrete,and about 20 to 35 percent of the amount of reinforement. Unfortunately, this saving in material weight is balanced by the higher cost of the higher quality materials needed in prestressing. Also, regardless of the system used, prestressing operations themselves result in an added cost: formwork is more complex, since the geometry of presstressed sections is usually composed of flanged sections with thin webs.

In spite of the these additional costs, if a large enough number of precast units are manufactured, the difference between at least the initial costs of prestressed and reinforced concrete systems is usually not very large. And the indirect long-term savings are quite substantial, because less maintenance is needed, a longer working life is possible due to better quality control of the concrete, and lighter founations are achieved due to the smaller cumulative weight of the superstructure.

Once the beam span of reinforced concrete exceeds 70 to 90 feet (21.3 to 27.4m), the dead weight of the beam becomes excessives, resulting in heavier members and, consequently, greater long-term shrinkage and creep they undergo. Very large spans such assegmented bridges or cable-stayed bridges can only be constructed through the use of prestressing.

Prestressed concrete is not a new concept,dating back to 1872, when P.H.Jackson, an engineer from California, patented a prestressing system that used a tie rod to construct beams or arches from individual blocks. After a long lapse of time during which little progress was made because of the unavailability of high-strength steel of the shrinkage and creep (transverse material flow) of concrete on the loss of prestress. He subsequently developed the principles of circular prestressing. He hoop-stressed horiaontal reinforcement around walls of concrete tanks through the use of turnbuckles to prevent cracking due to internal liquid pressure, thereby achieveing watertightness. Thereafter, prestressing of tanks and pipes developed at an accelerated pace in the United States, with thousands of tanks for water, liquid, and gas storage built and much mileage of prestressed pressure pipe laid in the two to three decades that followed.

Linear prestressing continued to develop in Europe and in France, in particular through the ingenuity of Eugene Freyssined, who proposed in 1926~28 methods to overcome pretress

losses through the use of high-strength and high-ductility steels.In1940, he introduced the now well-known and well-accepted Freyssinet system.

P.W.Abeles of England introduced and developed the concept of partial prestressing between the 1930s and 1960s. F.Leonhardt of Germany,V.Mikhailov of Russia, and T.Y.Lin of the United States also contributed a great deal to the art and science of the design of prestressed concrete.Lin’s load-balancing method deserves particularl mention in this regard, as it considerably simplified the design process,particularly in continuous prestressing throughout the world, and in the United States in particular.

Today, prestressed concrete is used in buildings, undergroud structures, TV towers, floating storage and offshore structures, power stations, nuclear reactor vessels, and numerous types of bridge system including segmental and its all-encompassing application. The success in the development and construction of all these structures has been due in no small measures to the advances in the technology of materials, particularly prestressing stelel, and the accumulated knowledge in estimating the short-and long-term losses in the prestressing forces.

Structure of BuildingsConstruction Engineering

and Construction Engineering

A building is closely bound up with people, for it provides people with the necessary space to work and live in. As classified by their use, buildings are mainly of two types: industrial buildings and civil buildings. Industrial buildings are used by various factories or industrial production while civil buildings are those that are used by people for dwelling, employment, education and other social activities.

The construction of industrial buildings is the same as that of civil buildings. However, industrial and civil buildings differ in the materials used, and in the structural forms or systems they are used.

Considering only the engineering essentials, the structure of a building can be defined as the assemblage of those parts which exist for the purpose of maintaining shape and stability. Its primary purpose is to resist any loads applied to the building and to transmit those to the ground.

In terms of architecture, the structure of a building is and does much more than that. It is an inseparable part of the building form and to varying degrees is a generator of that form. Used skillfully, the building structure can establish or reinforce orders and rhythms among the architectural volumes and planes. It can be visually dominant or recessive. It can develop

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harmonies or conflicts. It can be both confining and emancipating. And, unfortunately in some cases, it cannot be ignored. It is physical.

The structure must also be engineered to maintain the architectural form. The principles and tools of physics and mathematics provide the basis for differentiating between rational and irrational forms in terms of construction. Artists can sometimes generate shapes that obviate any consideration of science, but architects cannot.

There are at least three items that must be present in the structure of a building: stability, strength and stiffness, economy.

Taking the first of the three requirements, it is obvious that stability IS needed to maintain shape. An unstable building structure implies unbalanced forces or a lack of equilibrium and a consequent acceleration of the structure or its pieces.

The requirement of strength means that the materials selected to resist the stresses generated by the loads and shapes of the structure(s) must be adequate. Indeed, a "factor of safety" is usually provided so that under the anticipated loads, a given material is not stressed to a level even close to its rupture point. The material property called stiffness is considered with the requirement of strength. Stiffness is different from strength in that it directly involves how much a structure strains or deflects under load. A material that is very strong but lacking in stiffness will deform too much to be of value in resisting the forces applied.

Economy of a building structure refers to more than just the cost of the materials used. Construction economy is a complicated subject involving raw materials, fabrication, erection, and maintenance. Design and construction labor costs and the costs of energy consumption must be considered. Speed of construction and the cost of money (interest) are also factors. In most design situations, more than one structural material requires consideration. Completive alternatives almost always exist, and the choice is seldom obvious.

Apart from these three primary requirements, several other factors are worthy of emphasis. First, the structure or structural system must relate to the building's function. It should not be in conflict in terms of form. For example, a linear function demands a linear structure, and therefore it would be improper to roof a bowling alley with a dome. Similarly, a theater must have large , unobstructed spans but a fine restaurant probably should not. Stated simply, the structure must be appropriate to the function it is to shelter.

Second, the structure must be fire-resistant. It is obvious that the structural system must be able to maintain its integrity at least until the occupants are safely out. Building codes specify the number of hours for which certain parts of a building must resist the heat without collapse. The structural materials used' for those elements must be inherently fire-resistant or

be adequately protected by fireproofing materials. The degree of fire resistance to be provided will depend upon a number of items, including the use and occupancy load of the space, its dimensions, and the location of the building.

Third, the structure should integrate well with the building's circulation systems. It should not be in conflict with the piping systems for water and waste, the ducting systems for air, or the movement of people. It is obvious that the various building systems must be coordinated as the design progresses. One can design in a sequential step-by-step manner within anyone system, but the design of all of them should move in a parallel manner toward completion. Spatially, all the various parts of a building are interdependent.

Fourth, the structure must be psychologically safe as well as physically safe. A high-rise frame that sways considerably in the wind might not actually be dangerous but may make the building uninhabitable just the same. Lightweight floor systems that are too "bouncy" can make the users very uncomfortable. Large glass windows, uninterrupted by dividing motions, can be quite safe but will appear very insecure to the occupant standing next to on 40 floors above the street.

Sometimes the architect must make deliberate attempts to increase the apparent strength or solidness of the structure. This apparent safety may be more important than honestly expressing the building's structure, because the untrained viewer cannot distinguish between real and perceived safety.

The building designer needs to understand the behavior of physical structures under load. An ability to intuit or "feel" structural behavior is possessed by those having much experience involving structural analysis, both qualitative and quantitative. The consequent knowledge of how forces, stresses, and deformations build up in different materials and shapes is vital to the development of this "sense".

Structural analysis is the process of determining the forces and deformations in structures due to specified loads so that the structure can be designed rationally, and so that the state of safety of existing structures can be checked.

In the design of structures, it is necessary to start with a concept leading to a configuration which can then be analyzed. This is done so members can be sized and the needed reinforcing determined, in order to: a) carry the design loads without distress or excessive deformations (serviceability or working condition); and b) to prevent collapse before a specified overload has been placed on the structure (safety or ultimate condition).

Since normally elastic conditions will prevail under working loads, a structural theory based on the assumptions of elastic behavior is appropriate for determining serviceability

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conditions. Collapse of a structure will usually occur only long after the elastic range of the materials has been exceeded at critical points, so that an ultimate strength theory based on the inelastic behavior of the materials is necessary for a rational determination of the safety of a structure against collapse. Nevertheless, an elastic theory can be used to determine a safe approximation to the strength of ductile structures (the lower bound approach of plasticity), and this approach is customarily followed in reinforced concrete practice. For this reason only the elastic theory of structures is pursued in this chapter.

Looked at critically, all structures are assemblies of three-dimensional elements, the exact analysis of which is a forbidding task even under ideal conditions and impossible to contemplate under conditions of professional practice. For this reason, an important part of the analyst's work is the simplification of the actual structure and loading conditions to a model which is susceptible to rational analysis.

Thus, a structural framing system is decomposed into a slab and floor beams which in turn frame into girders carried by columns which transmit the loads to the foundations. Since traditional structural analysis has been unable to cope with the action of the slab, this has often been idealized into a system of strips acting as beams. Also, long-hand methods have been unable to cope with three-dimensional framing systems, so that the entire structure has been modeled by a system of planar subassemblies, to be analyzed one at a time. The modem matrix-computer methods have revolutionized structural analysis by making it possible to analyze entire systems, thus leading to more reliable predictions about the behavior of structures under loads.

Actual loading conditions are also both difficult to determine and to express realistically, and must be simplified for purposes of analysis. Thus, traffic loads on a bridge structure, which are essentially both of dynamic and random nature, are usually idealized into statically moving standard trucks, or distributed loads, intended to simulate the most severe loading conditions occurring in practice.

Similarly, continuous beams are sometimes reduced to simple beams, rigid joints to pin-joints, filler-walls are neglected, shear walls are considered as beams; in deciding how to model a structure so as to make it reasonably realistic but at the same time reasonably simple, the analyst must remember that each such idealization will make the solution more suspect. The more realistic the analysis, the greater will be the confidence which it inspires, and the smaller may be the safety factor (or factor of ignorance). Thus, unless code 'provisions control, the engineer must evaluate the extra expense of a thorough analysis as compared to possible savings in the structure.

The most important use of structural analysis is as a tool in structural design. A such, it will usually be a part of a trial-and-error procedure, in which an assumed configuration with assumed dead loads is analyzed, and the members designed in accordance with the results of the analysis. This phase is called the preliminary design; since this design is still subject to change, usually a crude, fast analysis method is adequate. At this stage, the cost of the structure is estimated, loads and member properties are revised, and the design is checked for possible improvements, The changes are now incorporated in .the structure, a more refined analysis is performed, and the member design is revised, This project is carried to convergence, the rapidity of which will depend on the capability of the designer, It is clear that a variety of analysis methods, ranging from "quick and dirty to exact", is needed for design purposes.

An efficient analyst must thus be in command of the rigorous methods of analysis, must be able to reduce these to shortcut methods by appropriate assumptions, and must be aware of available design and analysis aids, as well as simplifications permitted by applicable building codes. An up-to-date analyst must likewise be versed in the bases of matrix structural analysis and its use in digital computers as well as in the use of available analysis programs or software.

Construction Engineering

Construction engineering is a specialized branch of civil engineering concerned with the planning, execution, and control of construction operations for such projects as highways, buildings, dams, airports, and utility lines.

Planning consists of scheduling the work to be done and selecting the most suitable construction methods and equipment for the project. Execution requires the timely mobilization of all drawings, layouts, and materials on the job to prevent delays to the work. Control consists of analyzing progress and cost to ensure that the project will be done on schedule and within the estimated cost.

Planning The planning phase starts with a detailed study of construction plans and specifications. From this study a list of all items of work is prepared, and related items are then grouped together for listing on a master schedule. A sequence of construction and the time to be allotted for each item is then indicated. The method of operation and the equipment to be used for the individual work items are selected to satisfy the schedule and the character of the project at the lowest possible cost.

The amount of time allotted for a certain operation and the selection of methods of operation and equipment that is readily available to the contractor. After the master or general

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construction schedule has been drawn up, subsidiary detailed schedules or forecasts are prepared from the master schedule. These include individual schedules for procurement of material, equipment, and labor, as well as forecasts of cost and income.

Execution The speedy execution of the project requires the ready supply of all materials, equipment, and labor when needed. The construction engineer is generally responsible for initiating the purchase of most construction materials and expediting their delivery to the project. Some materials, such as structural steel and mechanical equipment, require partial or complete fabrication by a supplier. For these fabricated materials the engineer must prepare or check all fabrication drawings for accuracy and case of assembly and often inspect the supplier's fabrication.

Other construction engineering duties are the layout of the work by surveying methods, the preparation of detail drawings to clarify the design engineer's drawings for the construction crews, and the inspection of the work to ensure that it complies with plans and specifications.

On most large projects it is necessary to design and prepare construction drawings for temporary construction facilities, such as drainage structures, access roads, office and storage buildings, formwork, and cofferdams. Other problems are the selection of electrical and mechanical equipment and the design of structural features for concrete material processing and mixing plants and for compressed air, water, and electrical distribution systems.

Control Progress control is obtained by comparing actual performance on the work against the desired performance set up on the master or detailed schedules. Since delay on one feature of the project could easily affect the entire job, it is often necessary to add equipment or crews to speed up the work.

Cost control is obtained by comparing actual unit costs for individual work items against estimated or budgeted unit costs, which are set up at the beginning of the work. A unit cost is obtained by dividing the total cost of an operation by the number of units in that operation.

Typical units are cubic yards for excavation or concrete work and tons for structural steel. The actual unit, cost for any item at any time is obtained by dividing the accumulated costs charged to that item by the accumulated units of work performed.

Individual work item costs are obtained by periodically distributing job costs, such as payroll and invoices to the various work item accounts. Payroll and equipment rental charges are distributed with the aid of time cards prepared by crew foremen. The cards indicate the time spent by the job crews and equipment on the different elements of the work. The allocation of material costs IS based on the quantity of each type of material used for each

specific item.

When the comparison of actual and estimated unit costs indicates an overrun; an analysis is made to pinpoint the cause. If the overrun is in equipment costs, it may be that the equipment has insufficient capacity or that it is not working properly. If the overrun is in labor costs, it may be that the crews have too many men, lack of proper supervision, or are being delayed for lack of materials or layout. In such cases time studies are invaluable in analyzing productivity.

Construction operations are generally classified according to specialized fields. These include preparation of the project site, earthmoving, foundation treatment, steel erection, concrete placement, asphalt paving, and electrical and mechanical installations. Procedures for each of these fields are generally the same, even when applied to different projects, such as buildings, dams, or airports. However, the relative importance of each field is not the same in all cases.

Preparation of site This consists of the removal and clearing of all surface structures and growth from the site of the proposed structure. A bulldozer is used for small structures and trees. Larger structures must be dismantled.

Earthmoving This includes excavation and the placement of earth fill. Excavation follows preparation of the site, and is performed when the existing grade must be brought down to a new elevation. Excavation generally starts with the separate stripping of the organic topsoil, which is later reused for landscaping around the new structure. This also prevents contamination of the nonorganic material which is below the topsoil and which may be required for fill. Excavation may be done by any of several excavators, such as shovels, draglines, clamshells, cranes, and scrapers.

Efficient excavation on land requires a dry excavation area, because many soils are unstable when wet and cannot support excavating and hauling equipment. Dewatering becomes a major operation when the excavation lies below the natural water table and intercepts the groundwater flow. When this occurs, dewatering and stabilizing of the soil may be accomplished by trenches, which conduct seepage to a sump from which the water is pumped out. Dewatering and stabilizing of the soil may in other cases be accomplished by well points and electroosmosis.

Some materials, such as rock, cemented gravels, and hard clays, require blasting to loosen. Blast holes are drilled in the material j explosives are then placed in the blast holes and detonated. The quantity of explosives and the blast-hole spacing are dependent upon the type and structure of the rock and the diameter and depth of the blast holes.

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After placement of the earth fill, it is almost always compacted to prevent subsequent settlement. Compaction is generally done with sheepfoot, grid, pneumatic-tired, and vibratory-type rollers, which are towed by tractors over the fill as it is being placed. Handheld, gasoline-driven rammers are used for compaction close to structures where there is no room for rollers to operate.

Foundation treatment When subsurface investigation reveals structural defects in the foundation area to be used for a structure, the foundation must be strengthened. Water passages, cavities, fissures, faults, and other defects are filled and strengthened by grouting. Grouting consists of injection of fluid mixtures under pressure. The fluids subsequently solidify in the voids of the strata. Most grouting is done with cement and water mixtures, but other mixture ingredients are asphalt, cement and clay, and precipitating chemicals.

Concrete construction Concrete construction consists of several operations: forming, concrete production, placement, and curing. Forming is required to contain and support the fluid concrete within its desired final outline until it solidifies and can support itself. The form is made of timber or steel sections or a combination of both and is held together during the concrete placing by external bracing or internal ties. The forms and ties are designed to withstand the temporary fluid pressure of the concrete.

The usual practice for vertical walls is to leave the forms in position for at least a day after the concrete is placed. They are removed when the concrete has solidified or set. Slipforming is a method where the form is constantly in motion, just ahead of the level of fresh concrete. The form is lifted upward by means of jacks which are mounted on vertical rods embedded in the concrete and are spaced along the perimeter of the structure. Slip forms are used for high structures such as silos, tanks, or chimneys.

Concrete may be obtained from commercial batch plants which deliver it in mix trucks if the job is close to such a plant, or it may be produced at the job site. Concrete

production at the job site requires the erection of a mixing plant, and of cement and aggregate receiving and handling plants. Aggregates are sometimes produced at or near the job site. This requires opening a quarry and erecting processing equipment such as crushers and screens.

Concrete is placed by chuting directly from the mix truck, where possible, or from buckets handled by means of cranes or cableways, or it can be pumped into place by special concrete pumps.

Curing of exposed surfaces is required to prevent evaporation of mix water or to replace moisture that does evaporate. The proper balance of water and cement is required to develop

full design strength.

Concrete paving for airports and highways is a fully mechanized operation. Batches of concrete are placed between the road forms from a mix truck or a movable paver, which is a combination mixer and placer. A series of specialized pieces of equipment, which ride on the forms, follow to spread and vibrate the concrete, smooth its surface, cut contraction joints, and apply a curing compound.

Build materials

Materials for building must have certain physical properties to be structurally usefull. primarily ,they must be able to carry a load , or weight , without changing shape permanently . when a load is applied to a structure member , it will deform ; that is , a wire will stretch or a beam will bend . however , when the load is removed ,the wire and the beam come back to the original position ,this material property is called elasticity ,if a material were not elastic and a deformation were present in structure after removal of the load , repeated loading and unloading eventually would increase the deformation to the point where the structure would become useless . all material used in architectural structure , such as stone and brick , wood , steel , aluminum , reinforced concrete ,and plastics , behave elastically within a certain defined range of loading . if the loading is increased above the range , two type of behavior can occur ; brittle and plastic . in the former , the , material will break suddenly . in the latter , the material begins to flow at a certain load (yield strength) , ultimately leading to fracture . as example , steel exhibits plastic behavior , and stone is brittle . the ultimate strength of a material is measured by the stress at which failure (fracture) occurs .

A second important property of a building is its stiffness . this property is defined by the elastic modulus ,which is the ratio of the stress (force per unit area) , to the strain (deformation per unit length) . the elastic modulus , therefore , is a measure of the resistance of a material to deformation under load . for two material to equal area under the same load , the one with the higher elastic modulus has the smaller deformation .structural steel , which has an elastic modulus of 30 million pounds per square inch (psi) , or 2100000 kilograms per square centimeter , is 3 time as stiff as aluminum , 10 times as stiff as concrete , and 15 times as stiff as wood .

Masonry masonry consists of natural materials , such as stone , or manufactured products , such as brick and concrete block . masonry has been used since ancient times ; mud brick were used in the city of Babylon for secular buildings , and stone was used for the great temples of the Nile Valley . the great pyramid in Egypt . standing 481 feet (147 meters) high , is the most spectacular masonry construction . masonry units originally were stacked without

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using any bonding agent , but all modern construction uses a cement mortar as a bonding material . modern structural materials include stone , brick of burnt clay or slate , and concrete blocks .

Masonry is essentially a compressive material ; it cannot withstand a tensile force , that is , a pull. The ultimate compressive strength of bonded masonry depends on the strength of the masonry until and the mortar. The ultimate strength will vary form 1000 to 4000 psi (70 to 280 kg/sq cm), depending on the particular combination of masonry unit and mortar used.

Timber timber is one of the earliest construction materials and one of the few natural materials with good tensile properties. Hundreds of different species of wood are found throughout the world , and each species exhibits different physical characteristics. Only a few species are used structurally as framing members in building construction. In the untied states, for instance, out of more than 600 species of wood, only 20 species are used structurally. These are generally the conifers, or softwoods, both because of their abundance and because of the ease with which their wood can be shaped. The species of their more commonly used in the untied states for construction are Douglas fir, southern pine, spruce, and redwood. The ultimate tensile strength of these species varies form 5000 to 8000 psi (350 to 560 kg/sq cm). Hardwood are used primarily for cabinetwork and for interior finishes such as floors.

Because of the cellular of wood, it is stronger along the grain than across the grain. Wood id particularly strong in tension and compression parallel to the grain. And it has great bending strength. These properties make it ideally suited for columns and beams in structures. Wood is not effectively used as a tensile member in a truss, however, because the tensile strength of a truss member depends upon connections between members. It is difficult to devise connections which do not depend on the shear or tearing strength along the grain, although numerous metal connectors have been produced to utilize the tensile strength of timbers.

Steel steel is an outstanding structural material. It has a high strength on a pound-for-pound basis when compared to other materials, even thought its volume-for-volume weight is more than times that of wood. It has a high elastic modulus, which results in small deformations under load. It can be formed by rolling into various structural shapes such as I-beams, plates, and sheets; it also can be cast into complex shapes; and it is also produced in the form of wire strands and ropes for use as cables in suspension bridges and suspended roofs, as elevator rope, and as wire for prestressing concrete. Steel

element can be joined together by various means, such as bolting, riveting, or welding. Carbon steels are subject to corrosion through oxidation and must be protected form contact with the atmosphere by painting them or embedding them in concrete. Above temperatures of about 700F(371℃), steel rapidly loses its strength, and therefore it must be covered in a jacket of a fireproof material(usually concrete) to increase its fire resistance.

The addition of alloying elements, such as silicon or manganese, results in higher strength steels with tensile strengths up to 250000 psi(17500kg/sq cm). These steels are used where the size of a structural member become critical, as in the case of columns in a skyscraper.

Alnminum alnminum is especially useful as a building when lightweight, strength, and corrosion are all important factors. Because pure aluminum is extremely soft and ductile, alloying elements, such as magnesium, silicon, zinc, and copper, must be added to it to impart the strength required for structural use. Structural aluminum alloys behave elastically. They have an elastic modulus one third as great as steel and therefore deform there times as much as steel under the same load. The unit weight of an aluminum alloy is one third that of steel, and therefore an aluminum member will be lighter than a steel member of comparable strength. The ultimate tensile strength of aluminum alloys ranges form 20000 to 60000 psi (1400 to 4200kg/sq cm).

Aluminum can be formed into a variety of shapes; it can be extruded to form I-beams, drawn to form wire and rode, and rolled to form foil and plates. Aluminum members can be put together in the same way as steel by riveting, bolting, and (to a lesser extent) by welding. Apart form its use for framing members in buildings and prefabricated housing, aluminum also finds extensive use for window frames and for skin of the building in curtain-wall construction.

Concrete concrete is a mixture of water, sand and gravel, and Portland cement. Crushed stone, manufactured lightweight stone, and seashells are often use in lieu of natural gravel. Portland cement, which is a mixture of materials containing calcium and clay, is heated in a kiln and then pulverized. Concrete derives its strength form the fact that pulverized Portland cement, when mixed with water, hardens by a process called hydration. In an ideal mixture, concrete consists of about three fourths sand gravel (aggregate) by volume and one cement paste. The physical properties of concrete are highly sensitive to variations in the mixture of the components, so a particular combination of these ingredients must be custom-designed to achieve specified results in terms of strength or shrinkage. When concrete is poured into a mold or form, it contains free water, not required for hydration,

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which evaporate. As the concrete hardens, it releases this excess water over a period of time and shrinks. As a result of this shrinkage, fine cracks often develop. In order to minimize these shrinkage cracks, concrete must be hardened by keeping it moist for at least 5 days. The strength of concrete in time because the hydration process continues for years; as a practical matter, the strength at 28 days is considered standard.

Concrete deform under load in an elastic manner. Although its elastic modulus is one tenth that of steel, similar deformations will result since its also about one tenth that of steel. Concrete is basically a compressive material and has negligible tensile strength.

Reinforced concrete Reinforced concrete has steel bars that are placed in a concrete member to carry tensile force. These Reinforced bars, which range in diameter form 0.25 inch(0.64cm) to 2.25 inches (5.7cm), have wrinkles on the surfaces to ensure a bond with the concrete. Although reinforced concrete was developed in many countries, its discovery usually is attributed to Joseph Monnier, a French gardener, who used a wire network to reinforce concrete tuber in 1868. this process is workable because steel and concrete expand and contract equally when temperature change. If this were not the case, the bond between the steel and concrete would be broken by a change in temperature since the two materials would respond differently. Reinforced concrete can be molded into innumerable shapes, such as beams, columns, slabs, and arches, and is therefore easily adapted to a particular form of building. Reinforced concrete with ultimate tensile strengths in excess of 10000 psi (700 kg/sq cm) is possible, although most commercial concrete is produced with strengths under 6000 psi (420 kg/sq cm).

Plastic plastics are rapidly becoming important construction materials because of the great variety, strength, durability, and lightness. A plastic is a synthetic material or resin which can be molded into any desired shape and which uses an organic substance as a binder. Organic plastic are divided into two general groups; thermosetting and thermoplastic. The thermosetting group becomes rigid though a chemical change that occurs when heat is applied; once set, these plastics cannot be remolded. The thermoplastic group remains soft at high temperatures and must be cooled before becoming rigid; this group is not used generally as a structural material. The ultimate strength of most plastic materials is form 7000 to 12000 psi (490 to 840 kg/sq cm), although nylon has a tensile strength up to 60900 psi (4200 kg/sq cm).

Urban Design

The Domain of Urban Design

We can start identifying the elements of urban design by defining the domain of urban design. Urban design is that part of the planning process that deals with the physical quality of the environment. That is to say, it is the physical and spatial design of the environment. However, it should be quite clear to us that in designing the environment, planners and designers cannot design all elements and components; they cannot in every instance design entire buildings. It might be possible to do this in new towns or planned residential communities, but in an existing community, such complete design is quite difficult.

In addition, the domain of urban design extends from the exterior of individual buildings outward, with consideration of positive and negative effects of individual buildings on each other's interiors. "Designing cities without designing buildings" we may, therefore, say that the spaces between the buildings are the domain of urban design. But how do we design these spaces?

Using the nomenclature of the Urban Design Plan of San Francisco, we can distinguish among the purposes of four interrelated groups of spaces: (1) internal pattern and image ;(2) external form and image;

(3) circulation and parking, and (4) quality of environment. Internal pattern and image describe the purpose of spaces between urban structures at the micro level, that is, key physical features of the city's organization-focal points, viewpoints, landmarks and movement patterns. External form and image focus on the city's skyline and its overall image and identity. Circulation and parking look at street and road characteristics quality of maintenance, spaciousness, order, monotony, clarity of route) orientation to destination, safety and ease of movement, and parking requirements and locations. Finally, quality of environment includes nine factors: compatibility of uses, presence of natural elements, distance to open space, visual interest of the street facade, quality of view, and quality of maintenance, noise, and microclimate.

The domain of urban design as just set forth does not pinpoint very specific physical elements (plaza, mall, seating areas, trees, lamp posts), but it is a reasonable way of grouping them and gives direction to study and identification of the more specific' elements that are unique or important to a community. Since every community has different physical characteristics, the range of specific elements may vary extensively from one community to another, from one downtown to another, from one city to another.

In the past, most planners and designers have emphasized the first two groups of elements-internal pattern and image and external form and image-probably because these two groups are strongly oriented toward the form-making aspects of urban design. Yet when we also consider these elements from the standpoint of function and environmental quality, the spaces created for people (both those who are walking in the streets and those who are living inside the buildings) are potentially more pleasant.

For example, we might observe a beautifully designed plaza that very few people use, simply because it does not have any direct sunlight or it is windswept. On the other hand, there are plazas that have been designed only tolerably well, and crowds of people use them. It is undoubtedly true that there might be a

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number of factors involved (location , support for activity, and so on) , but such environmental considerations as wind, noise, sun, view, and natural elements always contribute significantly to successful urban design.

Having thus identified the framework for analysis of urban design-that is, the domain of urban design-we now shall attempt to identify a method of presenting this information in the form of policies, plans, guidelines, and programs. Variations in analysis of the elements of urban design (or lack of any analysis at all) have created variety in the form and range of policies, plan, guidelines, and programs in different cities. Even close examination of the urban design of various cities does not make one certain that planners have used a framework of analysis or have identified a specific element as the most important one to zero in on. Perhaps a lack of comprehensiveness in their framework has caused concentration on a few physical items.

However, we can now move from the four groups of analysis just outlined to a third categorization of the elements of urban design:

1. Land use

2. Building form and massing

3. Circulation and parking

4. Open space

5. Pedestrian ways

6. Activity support

7. Signage

8. Preservation

The categories we are using are of course interrelated. Urban design strategies for special urban areas or cities will necessarily have to group, or distinguish among, the physical elements identified here according to the problems and opportunities of the area under study.

The Future of Tall Building

Zoning effects on the density of tall buildings and solar design may raise ethical questions. Energy limitations will continue to be a unique design challenge. A combined project of old and new buildings may bring back human scale to our cities. Owners and conceptual designers will be challenged in the 1980s to produce economically sound, people oriented buildings.

In 1980 the Lever House, designed by Skidmore, Owings and Merrill (SOM) received the 25-year award from the American Institute of Architects "in recognition of architectural design of enduring significance”. This award is given once a year for a building between 25 and 35 years old. Lewis Mumford described the Lever House as "the first office building in which modem materials, modem construction, modem functions have been combined with a modem plan". At the time, this daring concept could only be

achieved by visionary men like Gordon Bunshaft, the designer, and Charles Luckman, the owner and then-president of Lever Brothers. The project also included a few "firsts": (1) it was the first sealed glass tower ever built; (2) it was the first office building designed by SOM j and (3) it was the first office building on Park Avenue to omit retail space on the first floor. Today, after hundreds of look-alikes and variations on the grid design, we have reached what may be the epitome of tall building design: the nondescript building. Except for a few recently completed buildings that seem to be people-oriented in their lower floors, most tall buildings seem to be a repetition of the dull, graph-paper-like monoliths in many of our cities. Can this be the end of the design-line for tall buildings? Probably not. There are definite signs that are most encouraging. Architects and owners have recently begun to discuss the design problem publicly. Perhaps we are at the threshold of a new era. The 1980s may bring forth some new visionaries like Bunshaft and Luckman. If so, what kinds of restrictions or challenges do they face?

Zoning Indications are strong that cities may restrict the density of tall buildings, that IS, reduce the number of tall buildings per square mile. In 1980 the term grid-lock was used for the first time publicly in New York City. It caused a terror-like sensation in the pit of one's stomach. The term refers to a situation in which traffic comes to a standstill for many city blocks in all directions. The jam-up may even reach to the tunnels and bridges. Strangely enough, such an event happened in New York in a year of fuel shortages and high gasoline prices. If we are to avoid similar occurrences, it is obvious that the density of people, places, and vehicles must be drastically reduced. Zoning may be the only long-term solution.

Solar zoning may become more and more popular as city residents are blocked from the sun by tall buildings. Regardless of how effectively a tall building is designed to conserve energy, it may at the same time deprive a resident or neighbor of solar access. In the 1980s the right to see the sun may become a most interesting ethical question that may revolutionize the architectural fabric of the city. Mixed-use zoning which became a financially viable alternative during the 1970s, may become commonplace during the 1980s, especially if it is combined with solar zoning to provide access to the sun for all occupants.

Renovation Emery Roth and Sons designed the Palace Hotel in New York as an addition to a renovated historic Villard house on Madison Avenue. It is- a striking example of what can be done with salvageable and beautifully detailed old buildings. Recycling both large and small buildings may become the way in which humanism and warmth will be returned to buildings during the 80’s. If we must continue to design with glass and aluminum in stark grid patterns, for whatever reason, we may find that a combination of new and old will become the great humane design trend of the future.

Conceptual design It has been suggested in architectural magazines that the Bank of America office building in San Francisco is too large for the city's scale. It has also been suggested that the John Hancock Center in Boston is not only out of scale but also out of character with the city. Similar statements and opinions have been made about other significant tall buildings in cities throughout the world. These

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comments raise some basic questions about the design process and who really makes the design decisions on important structures-and about who will make these decisions in the 1980s.

Will the forthcoming visionaries-architects and owners-return to more humane designs?

Will the sociologist or psychologist play a more important role in the years ahead to help convince these visionaries that a new, radically different, human-scaled architecture is long overdue? If these are valid questions, could it be that our" best" architectural designers of the 60' sand 70' s will become the worst designers of the 80' sand 90' s? Or will they learn and respond to a valuable lesson they should have learned in their "History of Architecture" course III college that "architecture usually reflects the success or failure of a civilized society"? Only time will tell.

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预应力混凝土

混凝土抗压但不抗拉，其抗拉强度是其抗压强度的8%~14%。由于混凝土的抗拉能力如此低，在荷载作用早期，混凝土内部即出现弯曲裂缝。为减缓或裂缝发展，可沿结构构件纵向施加轴心力或偏心力。这种力通过消除或尽可能地减少使用荷载作用下跨中临界截面的拉应力，以防止裂缝发展，从而增大了截面抵抗弯曲、剪切和扭转的能力。当全部荷载作用在结构上时，混凝土截面表现出弹性，混凝土的极限抗压能力几乎在混凝土全截面高度得到有效利用。

这种沿纵向施加在混凝土构件上的力，称为预应力，也就是在横向的自重恒载、活载或瞬间的水平活载作用之前，对构件跨度方向的截面预加了压应力。所施加的预应力类型及其大小，主要取决于建筑体系的类型、跨度和设计长细比。由于预应力沿着或平行于构件轴线方向施加在构件上，这种预加应力的原理一般称为线性预加应力法。

用于盛装流体的箱罐、管道、压力反应堆容器的环形预应力，基本上遵循线性预应力的基本原理。作用在圆形或球形结构上的环形箍筋或环抱应力克服了由内部的压力所引起的曲面外层纤维的拉应力。

很明显，为了消除或尽可能减少有全部静荷载和活荷载所引起的纯粹的拉应力，在这些荷载作用之前，预应力结构构件中已经产生了持久的压应力。对于钢筋混凝土，一般设想混凝土中的抗拉强度可以忽略不计。这是因为弯矩引起的拉力由钢筋与混凝土之间产生的粘结力抵抗。因而一旦构件达到其使用荷载作用下的极限状态，钢筋混凝土中的开裂和变形不可恢复。

与预应力钢筋作用不同的是，钢筋混凝土构件中的钢筋没有在构件上施加任何力。为了在预应力构件中产生预应力，预应力筋预先对构件中主动施加荷载，使得裂缝和变形可相对易于控制恢复。一旦超过混凝土的弯曲抗拉强度，预应力构件开始像钢筋混凝土构件一样工作。在相同跨度和荷载条件下，预应力构件比钢筋混凝土构件截面的65%~80%。因此，预应力构件所用混凝土较少，大约是钢筋混凝土中混凝土用量的20%~35%。然而，不幸的是，预应力构件在材料用量上虽然节约了，但其需要高质量材料的代价较高，可以说在造价上与钢筋混凝土持平。另外，不管采用哪种体系，预应力操作本身也会引起费用的增加；由于预应力构件截面通常由翼缘和薄壁腹板组成，所以支模较复杂。

尽管有额外增加的费用，如果生产很多的预制构件，至少预应力体系和钢筋混凝土体系之间初始费用的差别不是很大。而且由于预应力构件需要的维护费用较少，因混凝土质量控制较好使其可能具有更长的使用寿命，以及上层建筑的累积重量较小

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使其具用更轻型的基础，因而其间接的长期费用减少是相当可观。

一旦钢筋混凝土梁跨超过70~90in（1.3~27.4m），梁自重变得过大，使构件粗大，从而使构件长期变形和裂缝增大。对于大跨度的情况，建造拱形结构的费用昂贵，且因存在较大的长期收缩和徐变使其性能不理想。因此，大跨度结构，如分段拼装式桥或斜拉桥只能采用预应力结构来建造。

预应力混凝土不是一个新概念，这一概念可以追溯到1872年，当时加州的一名工程师P.H.Jackson申请了预应力系统的专利，其预应力系统采用了拉杆和砌块来建造梁或拱。从那以后相当时间里，预应力的发展进程缓慢，这是由于当时没有能够克服预应力和损失的高强钢材。直到内布拉斯加州的R.E.Dill亚历山大认识到混凝土的收缩和徐变（横向的材料流动）引起预应力损失，随后发展了一种观念，提出对无粘结预应力筋实施逐级张拉可以补偿钢筋与时间相关的应力损失，这种应力损失由徐变和收缩使构件长度缩短而引起。在20世纪20年代早期，明尼阿波利斯市的W.H.Hewett提出了环形预应力理论，通过应用螺旋扣，在混凝土箱壁四周环绕水平钢筋施加环向应力，以防止由容器内部流体压力所引起的开裂，从而获得水密效果。其后，箱罐和管的预加应力在美国获得加速发展，在后来的20~30年时间里，人们建造了成千上万个用作用水、液体或气体容器的箱罐，铺设了数英里长的预应力管道。

线性预应力在欧洲和法国继续发展，尤其通过Eugene Freyssinet 富有独创性的工作，他在1926~1928年提出通过使用高强度和高延性的钢材来克服预应力损失的方法。在1940年，他提出了现在被广泛接受的著名的弗式（预应力）体系。

20世纪30~60年代，英国的P.W.Abeless提出和发展了部分预应力的概念。德国的F.Leonhardt、俄罗斯的V.Mikhailov和美国的T.Y.Lindui对预应力混凝土的技术和科学的设计做出了贡献。在这点上，T.Y.Lin的荷载平衡方法特别值得一提，因为它大大地简化了设计过程，尤其是在连续结构中。这些20世纪预应力的发展使得预应力在全世界尤其是在美国得到了广泛的应用。

今天，预应力混凝土被应用于建筑物、地下结构、电视塔、流体容器、海上结构、发电站、核反应堆容器，以及包括分段拼装式桥梁和斜拉桥在内的无数类型的桥梁体系。他们展示了预应力概念的多面性和应用的广泛性。所有这些结构的发展和建造的成功很大程度上归功于材料科学的进步，尤其是预应力钢筋的发展，一级估计预应力短期和长期损失的知识积累。

建筑结构与建筑工程

建筑结构

建筑物与人类有着密切的关系，它能为人们在其中工作和生活提供必要的空

间。根据其功能不同，建筑物主要有两大类：工业建筑和民用建筑。工业建筑有各种工厂或制造厂，而民用建筑指的是那些人们用以居住、工作、教育或其他社会活动的场所。

工业建筑的建造与民用建筑相同，但两者在选用的材料、结构形式或体系方面是有差别的。

就工程的实质而言，建筑结构可定义为：以保持形状和稳定为目的的各个基本构件的组合体。其基本目的是抵抗作用在建筑物上的各种荷载并把它传到地基上。

从建筑学的角度来讲，建筑结构并非仅仅如此。它与建筑风格是不可分割的，在不同程度上是一种建筑风格的体现。如能巧妙地设计建筑结构，则可建立或加强建筑空间与建筑平面之间的格调与节奏。它在直观上可以是显性的或隐性的。它能产生和谐体或对照体。它可能既局限又开放。不幸的是，在一些情况下，它不能被忽视。它是实际存在的。

结构设计还必须与建筑风格相吻合。物理学和数学的原理及工具为区分在结构上的合理和不合理的形式提供了依据。艺术家有时可以不必考虑科学就能画出图形，但建筑师却不行。在建筑结构中至少应包括三项内容：稳定性，强度和刚度，经济性。

在上述三项要求中，首先是稳定性。它在保持建筑物形状上是必不可少的。一座不稳定的建筑结构意味着有不平衡的力或失去平衡状态，并且由此导致结构整体或构件产生加速度。

强度的要求意味着所选择的结构材料足以承受由荷载产生的应力并且结构形状必须适当。实际上，通常都提供一个安全系数以便在预计的荷载作用下，所使用材料的应力不会接近破坏应力。被称为刚度的材料的特性，需与强度要求一起考虑。刚度不同于强度，因为它涉及荷载作用下结构应变的大小和变形的程度。具有很高强度，但刚度较低的材料，在外力作用下会因变形过大而失去其使用价值。

建筑结构的经济性指的不仅仅是所用材料的费用。建筑经济是一个复杂的问题，其中包括原材料、制作、安装和维修。必须考虑设计和施工中人工费及能源消耗的费用。施工的速度和资金成本(利息)也是需要考虑的因素。对大多数设计情况，不能仅仅考虑一种建筑材料，经常存在一些有竞争性的其他选择，而具体应选择哪种并不明显。

除了这三种最基本要求之外，其他几种因素也值得重视。

首先，结构或结构体系必须和建筑物的功能相吻合而不应该与建筑形式相矛盾。例如，线性功能要求线性结构，所以把保龄球场的顶部盖成圆形是不合适的。同样剧院必须是大跨度、中间没有障碍的结构，而高档饭店也许不是这样。简而言之，结构形式必须与所围护空间的功能相适应。

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第二，结构必须防火。很显然，至少一直到内部人员安全撤离为止，结构体系必须能保持完整。建筑规范详细规定了建筑物的某些构件抵抗热量而不倒塌的时间。用于那些构件的结构材料自身必须具有防火性或者用耐火材料加以适当保护。所规定的防火等级将取决于一系列因素，它包括建筑空间的占有量和使用情况、建筑物的尺寸及建筑物的位置。

第三，结构应与建筑物的循环系统很好地结合。它不应与给排水管道、通风系统或人的活动空间相矛盾。很显然，各种建筑系统在设计时必须相互协调。对任何单个系统的设计，可以有顺序地一步一步地进行，而对所有系统的设计则采用并行方式来完成。从空间上来讲，在一座建筑物中所有的构件之间都是相互依存的。

第四，结构在心理上及外观上必须给人一种安全感。在风载作用下晃动剧烈的高层框架虽然没有危害，但仍然不适宜居住。弹性太大的轻质楼盖系统可能给居住者很不舒适的感觉。没有窗板的巨大玻璃窗户尽管是相当安全的，但对居住在楼房里的人来说，特别是当他站在临街40层高楼的大玻璃窗前时，总会感到极不安全。

有时建筑师必须有意采取积极措施来增加建筑结构外表的强度和坚固性。外观的安全性也许比真实表达建筑结构更重要，因为没有受过训练的人是不能分清真实的和感觉中的安全性的。

建筑设计师需要理解荷载作用下实际结构的性能。在结构定性和定量分析两方面有丰富经验的设计师拥有直觉或感受结构性能的能力。关于力、应力、变形在不同的材料和形状的结构中是如何建立起来的相关知识，对于发展上述判断力是至关重要的。

结构分析是确定在给定荷载下结构中产生的力和变形，以便使结构设计得合理或检查现有结构的安全状况。

在结构设计中，必须先从结构的概念开始拟定一种结构形式，然后再进行分析。这样做能确定构件的尺寸以及所需要的钢筋，以便a)承受设计荷载而不出现损坏或过大变形(在正常使用或工作状态) ； b)防止结构在荷载未达到规定的超载以前倒塌(安全性或极限状况)。

由于通常在使用荷载作用下，结构处于弹性状态，因此以弹性状态假定为基础的结构理论适用于正常使用状态。通常只有当危险截面的材料远远超过弹性范围之后，才可能发生结构倒塌，因而建立在材料非弹性状态基础上的极限强度理论是合理确定结构安全性，防止倒塌所必需的。不过弹性理论可用来确定延性结构强度的安全近似值(塑性下限逼近法) ，在钢筋混凝土设计中习惯采用这种方法。基于这种原因，在本章中仅采用结构的弹性理论。

严格地讲，所有结构都是三维构件的组合体，对其进行精确分析，即使在理想

状态下也是棘手的工作，而在实际工程条件下，更是难以想像。基于这种原因，分析人员工作的一个重要部分是将实际结构和荷载状态简化成一个易于合理分析的模型。

这样，框架结构体系可分解成平板和楼板梁，楼板梁又通过框架传递给立柱支承的大梁，立柱再将荷载传递到基础上。由于传统的结构分析方法不能分析平板的作用，所以经常理想化成类似于梁的条形结构。同样，普通的方法不能分析三维框架体系，因此将整个结构简化为平面框架体系模型，逐一加以分析。现代的矩阵——计算机法可以分析整个体系从而革新了结构分析，这样可对荷载作用下结构的性能作出更可靠的预测。

实际荷载状态也是很难确定和很难客观表达的，为了进行分析，必须进行简化。例如，桥梁结构上的交通荷载主要是动荷载且是随机的，通常理想化成静态行驶的标准卡车或分布荷载，以用来模拟实际产生的最不利的荷载状态。

类似的还有，连续梁有时简化为简支梁，刚性节点简化为铰接点，忽略填充墙，把剪力墙视为梁；在决定如何建立一个结构摸型使之既比较客观又适度简单时，分析人员必须记住每一个理想化假设都将使求得的解更加不可靠。分析的越客观，产生的信心就越大，而所取的安全系数(或忽略的因素)可能就越小。这样，除非规范条款控制，工程师必须估算出结构精确分析所需追加的费用与由此节省的结构中费用比值，是否合算。

结构分析最重要的用途是作为结构设计中的工具。按此定义，它通常是反复试算过程中的一个环节，在这种方法中，首先，在假定的恒载下对假定的结构体系进行分析，然后根据分析结果设计各构件。这个阶段称为初步设计，由于此时的设计常常会变化，通常采用粗略的快速分析方法就足够了。在此阶段，估计结构的成本，修正荷载及构件特性，并对设计进行检查以便改进。至此，将所作的更改纳入到结构中，再进行更精细的分析，并修改构件设计。这一过程反复进行直至收敛，收敛的速度取决于设计者的能力。很清楚，为了达到设计目的，需要从“迅速而粗略”到“精确”的各种分析方法。

因而，有能力的分析人员必须掌握严密的分析方法，必须能够通过适当的假设条件进行简化分析，必须了解可利用的标准设计和分析手段以及建筑规范中允许的简化方法。同时，现代的分析人员必须精通结构矩阵分析的基本原理及其在数字计算机中的应用并且会应用现有的分析程序及有关软件。

建筑工程

建筑工程是土术工程的一个分支，涉及如公路、建筑物、堤坝、机场、公用事业管线这类项目的计划、实施和施工控制。

计划包括安排项目工作进程，选择适当的施工方法和设备。实施则要求及时筹备

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所有的图纸、资金和施工原料以防工作延期。控制包括进度和成本分析，以保证项目能按计划进行,并控制成本消耗在预期范围。

计划编制计划编制阶段首先要对施工平面图和规范进行仔细研究。据此调研结果，准备所有施工项目列表(明细栏) ，将相关项目分组一起列于主要进度表，说明施工顺序和每项工序所需时间。选择施工方法和每个施工项目所用设备，以确保施工进度按计划进行,尽可能保证项目最低造价的实现。

每个工序所需时间量，施工方法和承包人易用设备的选择。在总的或综合的施工进度制定出之后，根据总进度表准备辅助的详细的进度表或预报，这些表格包括调用材料、设备和劳动力的各种计划表，以及成本和收益的预算。

实施项目的迅速实施要求所有材料、设备和劳动力都能得到及时供应。建筑工程师通常负责采购大部分施工材料并将其迅速运输到工地。一些原料设备像结构钢材、机械装置等，要求由厂家部分或全部加工制作。对于这些工厂预制的材料，工程师必须准备或审查全部加工图纸的准确性，检查装配样品并经常现场检查厂商的制作。

建筑工程的其他包括负责通过测量的方法作施工规划，为施工队准备大样图阐明设计师的意图，进行施工检查确保施工符合图纸和规范的要求。

在许多大型的项目中，有必要为临时施工设施进行设计并做出施工图，这些临时设施有排水、通道，办公用房和仓库，模板和沉井。另外还要选择电气和机械设备，设计混凝土成型工艺、搅拌站、压缩空气、水和配电系统。

控制通过将实际进度与总进度表或详细进度计划表所要求的进度对比来控制进度。由于某项工作的延误很容易影响整个项目，所以必须经常通过增加设备或人员来加快施工进度。

成本控制是通过每个工序的实际单价与其施工开始时所做的估计或预算单价的对比来实现。单价可通过将施工总造价除以施工中的单位总数量而得到。

典型的单位对于土方工程或混凝土工程而言用的是立方码，对于钢材而言则是吨。任一工序在任一时刻的实际单价可通过将该工序累计的成本除以其总的施工工程量而求得。

每个工序成本可通过定期发放的现场消耗如薪水册、各施工工序应支付的账目清单来确定。薪水册和设备租金借助于工头准备的时间表定期发放。这些表显示了施工

队和设备在各施工单元上所消耗的时间。材料成本的分摊要根据每一具体项目所使用的各类材料的数量而定。

当实际单价与预算单价比较显示出超支时，需要分析查明原因。如果是设备消耗的超支，可能是由于设备的生产效力不够或其工作不正常造成。如果是劳动力消耗的超支，原因可能是施工队人员过多，缺乏正常的监督，或材料或施工图供应不及时导致施工队延期等。在这种情况下，工时研究对于分析生产率是极为重要的。

施工程序通常根据工种不同来分类，包括现场准备、挖运土方、地基处理、钢结构安装、混凝土浇注、沥青铺路以及电气和机械安装。每一工种施工的程序基本相同，即使对于不同项目如建筑物、堤坝或机场等也是如此。但是，每个工种的相对重要性在各种情况下并不总是相同的。

现场准备包括移走和清理拟建场地地表上所有的建筑和生长物。对于小型建筑和树木采用推土机即可，大型建筑必须拆除。

土方包括挖土和土方回填。挖土在现场准备之后进行，必须使现有地面标高降至一新的高度。挖土通常从清除表层有机土开始，这些表层土可以在后来新建筑物周围景观美化时再次利用。这也可防止表层土下面用作填方的无机物质受到污染。土方可以采用多种挖掘设备，如铁铲、索斗铲、蛤壳式挖泥机、起重机和铲土机等。

陆地上有效的土方开挖需要干燥的开挖范围，因为很多土体在潮湿状态下不稳定，不能支撑开挖和拖运设备。当在正常地下水位线以下开挖或截取地下水时，降排水就成为主要作业。此时，降水和土壤稳定可能要靠掘沟来完成，用这种沟将渗流导至水坑，然后将其用水泵排出。另外，降水和土壤稳定也可通过井点法和电渗法来实现。

一些物质，如岩石、胶结卵石、硬粘土，需要爆破松动。在这些物质中钻孔，将炸药放进钻孔中引爆。炸药量和钻孔间距取决于岩石的类型和构造、钻孔的直径和深度。

土方回填后，几乎总要将其压实以防后来的沉降。压实通常采用羊足压路机、方格铁板压路机、充气轮胎压路机、振动式压路机。土方回填时，拖拉机牵引着这些压路机压在回填土上。子动撞锤、汽油驱动撞锤用于没有压路机作业空间的建筑物附近回填土的压实。

地基处理当地质勘察揭示建筑物地基范围内地基土有结构缺陷时，必须进行地基加强处理。将水流、洞穴、裂缝、断层以及其他缺陷通过灌浆填塞、加固。灌浆就是在压力作用下注入流态混合物。随后这种灌入的浆体在地层空隙中凝固。大多数灌浆采

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用的是水泥和水的混合物，但有些采用的是沥青、水泥和粘土以及化学沉淀剂的混合物。

混凝土施工混凝土施工包括的几项操作有支模板，混凝土生产，浇注和养护。成型要求按照所需的最终外形包容和支撑流动的混凝土直至混凝土拌合物凝固并能够支撑自身的重量。模板由木材或型钢或两者结合制成，在混凝土浇注时模板通过外部支撑或内部联结组合在一起。模板与联结要设计得能够承受混凝土临时的流动压力。

垂直墙体成型的通常做法是在混凝土浇注后至少一天内使模板处于固定位置。当混凝土凝固或硬化后拆除模板。滑模施工法是模板在新浇混凝土高度上不断向前移动的方法。模板靠千斤顶向上升起，千斤顶安装在埋入混凝土中的垂直钢筋上，在建筑物周围间隔布置。滑模施工法用于像筒仓、贮罐、烟囱类的高层建筑。

如果工地距离商品混凝土搅拌厂很近，混凝土可以用运输混凝土拌合物的搅拌运输车从商品混凝土搅拌厂得到，否则可以在工地生产。现场制备混凝土要求安装搅拌设备、水泥和骨料的受料和加工设备。有时骨料在现场或工地附近生产，这就要求开辟采石场、安装像破碎机、筛子类的加工设备。

混凝土浇注采用斜槽溜浇的方式，可能的话直接从搅拌车上下料，或者从起重机或空中索道悬吊的铲斗中下料，也可通过特殊的混凝土泵采用泵送的方式进行浇注。

外露表面的养护需要防止搅拌用水的蒸发或需要补充蒸发的水分。水与水泥间的平衡应满足最终设计强度发展的需要。

机场和公路的混凝土路面施工完全是机械化的作业过程。混凝土从集搅拌机和灌注机综合功能为一身的搅拌车或移动的铺路机上浇注到路面模板里。跨在模板上的一系列专业设备接着铺展、振捣混凝土，平整混凝土表面，切割收缩缝，刷涂养护剂。

建筑材料

建筑材料必须具有对结构有用的某些物理性质。首先，建筑材料必须能够承受荷载或重量，而不会永久改变其原有的形状。当荷载施加到结构单元上时，材料将发生变形，也就是说，线材将伸长或梁将会弯曲。然后卸载后，线材和梁将恢复原状。材料的这种性质称为弹性。如果某种材料是非弹性的，在卸荷后结构将残留变形，重复加荷和卸荷，结构的变形将持续增加，直至最后结构失效。用于建筑结构的所有材料，诸如砖石、木材、钢材、铝材、钢筋混凝土的塑料等，在一定范围的荷载作用下均表现出弹性如果荷载增加超过这个范围，材料将表现出两种类型的性质：脆性和塑性。若为前者，材料将会突然断裂；若为后者，材料在达到某一荷载（屈服强度）开始塑性流动，最后破坏。例如，钢材表现出塑性，石材则是脆性的。材料的最终强度用材料破坏时的极限

应力来表示。

建筑材料第二个重要性质是刚度。这一性质用弹性模量来表示，弹性模量是应力（单位面积上的力）和应变（单位长度上的变形）的比值。因而弹性模量是衡量材料在荷载作用下抵抗变形能力的指标。对于相同荷载作用下相同面积的两种材料，弹性模量越高者变形越小。结构钢材，其弹性模量是3*108LB/IN2，或21000000kg/cm2，是铝材刚度的3倍、混凝土刚度的10倍、木材刚度的15倍。

砌体砌体包含天然材料，如石材、人造产品如混凝土砌块。砌体出现在远古时期。在古巴比轮城市，泥土砖用于建造非宗教性建筑物，而石材被广泛用语尼罗河流域雄伟的寺庙。高及481ft(147m)的埃及大金字塔是最为壮观的石工材料。最初，砌块的叠砌是不用胶粘剂的，但所有现代土砖或页岩砖以及混凝土砌块。

砌体材料基本上属于受压材料，不能承受张拉力，亦即拉力。砌体的极限抗压强度取决于砌体和砂浆。极限强度在1000到4000lb/in2(70~280 kg/cm2)之间变化，其值取决于所有块体和砂浆的具体结合。

木材木材是一种最古老的建筑材料，是少数具有抗拉性能的天然材料之一。全世界已经发现的木材种类有数百种，每一类都表现出不同的物理特性。只有少数木材在建筑中被用做结构构件。例如，在美国，600多中木材中仅有20种被用于结构。这些木材通常是一些针叶树或软木材，主要因为这两种木材资源丰富以及易于成型。在美国建筑中较为普遍使用的木材树种是花期松、南木松、云杉和红木。这些木材的极限抗拉强度变化范围为5000~8000 lb/in（350~560 kg/cm）。硬木材主要用于细木工或用于铺地板之类的室内装修。

由于木材本身有细胞状结构，其顺纹强度要大于其横纹强度，木材顺纹的抗拉强度和抗压强度尤其高，并且有很好的抗弯强度。这些性质使得木材成为建筑结构中柱和梁的理想材料。但是，由于桁架杆件中抗拉强度取决与各种杆件的连接，所以木材不能有效地在桁架中用作受拉构件。尽管为了利用木材的抗拉强度制造出许多金属节点，但很难设计出与顺纹剪切强度或抗裂强度关系不大的接头。

钢材钢材是一种优异的结构材料。与其他材料相比，钢材有高强度质量比（单位质量的强度），即在相同体积条件下其质量是木材的10倍以上。钢材具有较高的弹性模量，这就使得钢筋在荷载作用下变形较小。钢材可被轧制成各种不同的结构形状，如工字型梁、钢板和压型钢板，还能被铸造成复杂形状，也能用以生产出钢丝和钢绞线，用作悬索桥和旋索屋面的钢缆，电梯升运机缆索，或用作预应力混凝土的钢丝绞线。钢制构件可以用多种方法进行连接，如螺栓连接、铆接或焊接。碳素钢易遭氧化导致腐蚀，必须防止其与大气的接触，可采用在其上刷防锈或将其埋入混凝土的办法。当温度高于700F（371℃）时，钢材将迅速丧失其强度，因而必须在其外包裹上防火材料（通常为混凝土）对其加以保护。 22

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合金元素如硅或锰的加入使钢材强度变得更高，其抗拉强度可达250000lb/in2（17500kg/cm2）。当结构构件的尺寸变得重要时，如摩天大楼的柱子，就要使用这类合金钢。

铝材当轻质、强度和防腐蚀能力成为建筑考虑的重要因素时，铝材作为一种建筑材料就显得特别有用。因为纯铝极软，易延展，必须在其中加入锰、硅、锌和铜这些合金元素，使其获得结构所要求的强度。建筑用铝合金表现出弹性，其弹性模量是钢材的1/3，因而在相同荷载作用下，其变形为钢材的3倍。铝合金的密度为钢材的1/3，因而在相似强度条件下，铝合金构件比钢材构件轻。铝合金的极限抗拉强度范围在2000~6000lb/in2(1400~4200kg/cm2)。铝材能被加工成各种状态，可以被挤压成工字型梁，拔成线材和杆件，辊压成铝箔和板材。铝构件可以像钢材一样采用铆接、螺钉连接以及（较少地）焊接等方式进行连接。铝除了用作建筑和预制房屋的框架构件以外，还被广泛地用作窗框，以及幕墙建筑物的幕墙材料。

混凝土混凝土是水、砂石子和波特兰水泥和混合物。碎石、人造轻骨料、贝壳经常被用以代替天然石料。波特兰水泥，是将由钙质材料和黏土质材料形成的混合物在窑中进行煅烧然后进行粉磨而形成的。混凝土强度即源于磨细的水泥与水混合时经水化而硬化的过程。在理想的混合状态下，混凝土由占其体积大约3/4的砂、石子和占其体积1/4的水泥浆组成。混凝土的物理特性对其组成成分变化是极其敏感的，所以为了获得混凝土在强度和收缩等方面特定的效果，必须对这些组成材料的配料进行特定的设计。当往模具或模板中浇注时，混凝土中含有大量并非用于水化而是要蒸发掉的水。混凝土硬化时，经过一段时间将蒸发掉多余的水而产生收缩，这种收缩通常将导致细裂缝的发展。为了将这些裂缝减至最少，混凝土硬化时必须保持潮湿状态至少在5天以上。以为混凝土的水化过程能持续进行多年，故其强度能够持续增长。事实上，常把混凝土28天的强度视为标准强度。

混凝土在荷载作用下会发生弹性变形。尽管混凝土的弹性模量是钢材的1/10，但由于其强度也大约是钢材的1/10，所以它们有相似的变形。混凝土主要用作抗拉材料，其抗拉强度可不予考虑。

钢筋混凝土钢筋混凝土中配有钢筋，用以承受混凝土构件中的拉力。这些钢筋的直径范围在0.25in（0.64cm）~2.25in(5.7cm)，其表面带肋，以保证与混凝土的黏结。尽管钢筋混凝土在很多国家得到发展，但其发展一般归功于约瑟夫，一位法国园丁，他在1868年曾使用钢筋网片来加强混凝土管，因为温度变化时，钢材与混凝土胀缩系数相同，所以这种做法是可行的，如若不然，钢材与混凝土的黏结会因温度的变化导致两者变形不一致而破坏。钢筋混凝土可以浇注成各种形状，如梁、柱、板和拱，因而适用于特殊形态的建筑物。钢筋混凝土的极限强度抗拉强度可能会超过

10000lb/in2(700kg/cm2)，尽管产生的大部分商品混凝土的强度低于6000lb/in2(420kg/cm2)。

塑料塑料因其多样性、强度、耐久性和轻质而迅速成为一种重要的建筑材料。塑料是一种合成材料或树脂，能按要求塑造成各种形状，采用有机物作胶粘剂。有机的塑料分为两大类：热固性塑料和热塑性塑料。热固性塑料受热时发生化学变化而变硬，一旦成型，着类塑料不能在塑成型。热塑性塑料在高温时仍保持柔软，冷却后才变硬，这类塑料通常不能用作建筑材料。

城市设计

城市设计的范围

首先我们可以通过限定城市设计的范围来确定城市设计的要素。城市设计是指致力于提高环境形体质量的那部分规划程序，也就是说，是环境的形体与空间设计。然而，我们必须十分清醒地意识到，在环境设计的过程中，规划者和设计者不可能对所有的要素和组成部分进行设计，不可能在任何情况下都设计出完整的建筑物。这种完整的设计对于新建城镇和新规划的住宅区是可行的，但对现有社区难以实施。

另外，城市设计的范围可从建筑物的外部向外扩展延伸，同时，要考虑各个建筑物对彼此内部的积极和消极影响。城市设计的范围可以定义为“设计城市而不设计房屋”。因此，我们说，建筑物之间的空间就是城市设计的范围。但是, 我们该如何设计这些空间呢?

用旧金山城市设计规划的术语来表示，我们可以把相互联系的四组空间的意义区别开来:：(1)内部格局与意象；(2)外部形态与意象；(3)交通流线与停车场； (4)环境质量。内部格局和意象描述了城市结构之间的微级空间意义，即城市结构的主要形体特征，也就是焦点、视点、地标和运动模式。外部形态和意象的重点是城市的轮廓、总体意象和个性。交通流线及停车场是指街道与道路的特性，即道路的养护质量、宽敞度、秩序、单一性、流线清晰性、目的地的方向性、安全性、畅通性以及停车需求和停车场位置。最后，环境质量包括九个因素：共用性、自然环境的存在、与空地间的距离、街道立面的视觉效果、景观质量、环保质量、噪声和小气候。

上述城市设计的范围并未确认某些具体要素(广场、林荫道、休息场地、树木、路灯柱等) ，但这是对它们进行分类的合理方法并对某些更具体的要素的研究和确定具有指导作用，而这些要素正是社区所独有的，或是至关重要的。由于每个社区都有不同的形体特点,因而社区之间、市区之间以及城市之间的具体要素的范围变化很大。

过去，多数规划者和设计者注重的是前两类要素内部格局和意象以及外部形态和意象，这也许是因为这两类要素决定了城市设计的外形。然而，如果从功能和环境质量的角度去考虑这些要素，这些为人(无论是在街上行走的人还是呆在居室里的人)而创造

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的空间将会更加迷人。

例如，我们也许注意到一个设计很美的广场仅仅因为不见阳光或正当风口而空旷无人，而有些设计一般的广场却挤满了人。毫无疑问，这与某些因素有关(如地点、活动设施等) ，但是像风、噪声、阳光、景观和自然条件这类环境因素与成功的城市设计关系重大。

我们确定了城市设计的分析体制，即确定城市设计的范围之后，现在则想确定一下以政策、规划、指导方针和计划的形式表达这些信息的方法。对于城市设计要素的不同分析(或者根本不进行分析)在不同城市中产生了不同形式和不同范围的政策、规划、指导方针和计划。即使仔细观察不同城市的城市设计也无法使人肯定设计者是否使用了分析基准体系或者确定某个要素作为研究重点，也许是因为设计者对基准体系缺乏理解，从而导致了研究的重点集中在几个具体项目上。

但是，我们现在可以从上述城市设计的四组分析方法转到城市设计要素的第三种分类方法：

1.土地的使用

2.建筑形态及组合

3.交通流线与停车场

4.空地

5.人行道

6.活动设施

7.标志

8.保存

当然，我们所用的分类是相互联系的。用于特定市区或城市的城市设计战略必须根据所研究地区面临的问题和机会来组合或表现上述具体要素。

高层建筑展望

区域规划对高层建筑物的密度和对自然采光设计可能引起道德问题将产生影响。能源的有限性将继续成为建筑设计面临的独特挑战。新老建筑的结合将会给我们的城市带来人情味。要设计建造出经济实用，以人为本的建筑物，将会是业主和概念设计师在20世纪80年代面临的挑战。

1980年由斯柯摩尔、奥英斯和米瑞尔(SOM)设计的莱弗公寓获得了美国建筑师协会授予的25年奖“以奖励具有深远意义的优秀建筑设计”。这项奖每年授予一座房龄在25 ~ 35年之间的建筑物。用刘易斯·芒福德的话来说，莱弗公寓是 “第一座集现代材料、现代施工、现代功能与现代设计方案为一体的图书馆”。在当时，这样大胆的构思只有像设计师戈登·邦沙福特和业主一一莱弗兄弟公司当时的总裁查尔斯·卢克曼那

样富于幻想的人才能创造出来。而且，这项工程包含了几个“第一”：(1)是第一座全封闭的玻璃大厦；(2)SOM三人合作设计的第一栋图书馆； (3)是公园大街第一座一层楼不设零售商场的图书馆。今天,经过众多外观相似而柱网变化的设计，我们己难以对建筑物进行归类，这也许是高层建筑设计的缩影。除了最近竣工的几栋低层楼房似乎比较怡人外，在我们的许多城市中，多数高层建筑物看上去就像图表上的柱标，好似一块块单调而又拙笨的巨石。难道这就是高层建筑设计行业的终点吗?也许不是。有迹象表明其发展是非常令人鼓舞的。建筑师和业主最近己开始公开讨论设计问题。也许我们正处在一个新时代的开端，20世纪80年代也许会产生一些像邦沙福特和卢克曼那样的幻想家。要是如此，他们会面临什么样的限制或挑战呢?

区域规划很显然，城市可以限制高层建筑的密度，也就是减少每平方英里高层建筑的数量。1980年，“堵塞网”这个术语第一次在纽约市公开使用。它的出现在公众心中引起恐慌。这个词指的是城市中四面八方的街区同时出现的交通停滞不动的现象，堵塞甚至一直延伸到隧道里和高架桥上。奇怪的是，这种事情竟然发生在纽约燃料短缺、油价高涨的年份。很显然，要想避免类似情况的出现，就必须大幅度地降低人口、活动场所以及车辆的密度。区域规划也许是唯一长远的解决方法。

城市居民由于受到高层建筑的遮挡而见不到阳光，因此，阳光规划将越来越受欢迎。无论高层建筑设计得如何节能，它同时有可能剥夺居住者或邻居享受阳光的权力。20世纪80年代，享受阳光的权力会成为一个十分有趣的道德问题，这个问题会彻底改变城市的建筑布局。混合用途的分区规划在20世纪70年代还只是一种经济上可行的抉择，在20世纪80年代将会得到普及，特别是将混合功能分区规划与阳光分区规划相结合，让所有的住户都享受到阳光。

整修改造伊莫利·罗斯和桑斯两人合作设计的纽约王宫酒店是对麦迪逊大街上翻修后的古建筑维拉德公寓的补充和增色。这是一个如何对待可抢救的古建筑精品的突出实例。20世纪80年代对大小建筑物的重复利用将是人情味和温馨回到建筑物的途径。无论出于什么原因，如果我们必须继续使用玻璃和铝材进行那种呆板的方格式设计的话，我们会发现新老建筑的结合将成为未来富有人情味设计的大趋势。

概念设计有些建筑杂志认为位于旧金山的美洲银行办公大楼对于该城市来说规模过大，位于波士顿的约翰·汉考克中心不仅与该城市的规模不成比例，而且与其特点不符。对于世界各地主要高层建筑物的类似评论还有不少。这类评论提出了有关设计程序、谁是重点项目设计的决策者，以及上世纪80年代的建筑设计应由谁来决策等基本问题。

未来的幻想家，即建筑师和业主会回到更富人情味的设计吗?在今后的几年里社会学家和心理学家会发挥他们的重要作用使这些幻想家相信一种截然不同的、合乎人体尺寸的新型建筑设计早该付诸实施吗?如果这些问题的提出有其合理性的话，那么六七十

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年代被我们视为“最杰出的”建筑设计师到了八九十年代就变成最差的吗?他们在大学“建筑史”这门课程中应该了解到“建筑常常反映了文明社会的成功与失败”，他们会学到这有益的一课并对此做出反应吗?只有时间才会做出回答。