建筑材料
钢的最严重缺点是它容易被氧化而需要被油漆或一些其他的适当涂料保护。当钢被用于可能发生火灾环境时, 钢应该包围在一些耐火的材料中, 例如石料或混凝土。通常，钢的组合结构不易被压碎除非是在冶金成分不好，低温的不利组合, 或空间压力存在的情况下。
建筑用铝仍然不广泛被在土木工程结构中用,虽然它的使用正在稳定地增加。藉着铝合金作为一个适当的选择和对其进行热处理,可获得各式各样的强度特性。一些合金所展现的抗压强度特性相似于钢, 除线形弹性模量大约是7,000,000 牛/平方厘米，相当于刚的三分之一。质量轻和耐氧化是铝的两个主要优点。因为它的特性对热处理是非常敏感的,当铆接或焊接铝的时候，一定要小心仔细。一些技术已为制造预制铝组合配件及形成若干的美丽的设计良好的外型结构的铝制结构而发展起来。组合房屋配件制造的一般程序藉由螺栓连接，这似乎是利用建筑用铝的最有前途的方法。
加强和预应力混凝土是主要的建筑材料。天然的水泥混凝土已经被使用长达数世纪之久。现代的混凝土建筑兴起于十九世纪中叶,尽管人造水泥被 Aspidin ，一个英国人于1825年申请了专利.虽然一些建筑者和工程师在十九世纪后期用钢筋混凝土作实验, 但作为一种建筑材料它占统治地位是在二十世纪初期。后五十年钢筋混凝土结构设计和建筑得到迅速发展, 早期在法国的 Freyinet 和比利时的 Magnel被大量使用。
素混凝土作为建筑材料有一个非常严重的缺点：就是它的抗拉强度非常有限, 只是它的抗压强度的十分之一。素混凝土不仅受拉破坏是脆性破坏，而且受压破坏也是在没有多大变形预兆的情况下发生的准脆性破坏。(当然,在钢筋混凝土建筑中,可以得到适当的延性)。只有进行适当的养护和合理的选择并且掺加适当的混合天加剂,否则 霜冻破坏能严重的损害混凝土。在长期荷载作用下混凝土在选择设计受压情况方面要仔细考虑。在硬化的时候和它的早期养护下,混凝土收缩占主要地位, 因此需要添加适当地比例的添加剂而且用适当的建筑技术来控制。
藉由所有的这些可能的严重缺点，工程师已经试着为各种实际结构设计建立美丽的，持久的，和经济的钢筋混凝土结构。这是藉着设计尺寸和钢筋排列安排的谨慎选择，和适当的水泥的发展已经趋于同步, 适当添加剂混合比例, 混合配置, 而且养护技术和建筑方法，仪器的快速发展。
混凝土具有多种用途，其组成材料广泛可取，并且能非常方便地浇制成满足强度及功能要求的形状，同时，随着新型预应力混凝土、预制混凝土以及普通混凝土施工方法令人兴奋的进一步改善和发展的潜力，这些因素综合起来使得混凝土在绝大多数结构中有着比其他材料更大的竞争力。
在现代,藉由钢和加强钢筋的使用量在建筑结构中的增加,木材在建筑期间主要地已经被撤离到附属的、暂时的和次要的结构中使用,成为建筑材料的次要成员。然而, 现代的技术在最后六十年中已经有使木材作为建筑材料恢复生气的迹象,藉由大量的改良了木材的加工方法,各种不同的处理方法增加了木材的耐久性, 而且叠片木材连同使用黏结技术的革命使得木材的性能有了更好的保证。各向同性的胶合板是最广泛使用的压层胶合板，随着技术的发展，压层胶合板已经发展成为特定的结构材料并对混凝土和钢造成了强大的竞争力。
将来可能发展的材料是工程塑料和稀有金属及他们的合金,如铍，钨，钽，钛，钼，铬，钒和铌。有许多不同的塑料可以用，而且这些材料所展现的力学性能在很大的范围内改变。在如此许多的特性中我比较设计方案选择适当的可能的塑料材料是可能的。对塑料的使用受经验的限制。一般而言，塑料一定要与空气隔离。设计的这一个方面要求主要是对塑料结构元素在使用中的考虑。 塑料被应用的最有希望的潜能之一是嵌板和贝壳型结构。叠片或夹心嵌板已经被用于此种结构以鼓励未来建筑大量应用这一个类型材料。
另一种引起注意的材料由纤维或像粒子的胶结加筋的微粒组成的合成物材料正在开发。虽然一种由玻璃或塑料胶结材料组成的玻璃纤维加筋合成物已经被用长达数年之久, 但是他们很可能退落为次要的结构材料。加筋混凝土是另一个积极地被学习而且发展的混合料。一些实验正在工作情况下进行。实验主要内容为钢和玻璃纤维，但是大部份的使用经验在钢纤维方面比较先进。
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Building materials The most serious disadvantage of steel is that it oxidizes easily and must be protected by paint or some other suitable coating.When steel is used in an enclosure where a fire could occur, the steel members must be encased in a suitable fire-resistant enclosure such as masonry, concrete.Normally, steel members will not fail in a brittle manner unle an unfortunate combination of metallurgical composition, low temperature, and bi-or triaxial stre exists.
Structural aluminum is still not widely used in civil engineering structures, though its use is steadily increasing.By a proper selection of the aluminum alloy and its heat treatment, a wide variety of strength characteristics may be obtained.Some of the alloys exhibit stre-strain characteristics similar those of structural steel, except that the modulus of elasticity for the initial linearly elastic portion is about 10,000,000 psi (700,000 kgf/cm*cm) or about one-third that of steel.Lightne and resistance to oxidation are, of course, two of the major advantages of aluminum.Because its properties are very sensitive to its heat treatment, care must be used when riveting or welding aluminum.Several techniques have been developed for prefabricating aluminum subaemblies that can be readily erected and bolted together in the field to form a number of beautiful and well-designed shell structures.This general procedure of prefabrication and held aembly by bolting seems to be the most promising way of utilizing structural aluminum.
Reinforced and prestees concrete share with structural material.Natural cement concretes have been used for centuries.Modern concrete construction dates from the middle of the nineteenth century, though artificial Portland cement was patented by Aspidin, an Englishman, about 1825.Although several builders and engineers experimented with the use of steel-reinforced concrete in the last half of the nineteenth century, its dominant use as a building material dates from the early decades of the twentieth century.The last fifty years have seen the rapid and vigorous development of prestreed concrete design and construction, founded largely on early work by Freyinet in France and Magnel in Belgium.
Plain (unreinforced) concrete not only is a heterogeneous material but also has one very serious defect as a structural material, namely, its very limited tensile strength, which is only of the order of one-tenth its compreive strength.Not only is tensile failure in concrete of a brittle type, but likewise compreion failure occurs in a relatively brittle fashion without being preceded by the forewarning of large deformations.(Of course, in reinforced-concrete construction, ductile behavior can be obtained by proper selection and arrangement of the reinforcement.) Unle proper care is used in the selection of aggregates and in the mixing and placing of concrete, frost action can cause serious damage to concrete masonry.Concrete creeps under long-term loading to a degree that must be considered carefully in selecting the design stre conditions.During the curing proce and its early life, concrete shrinks a significant amount, which to a degree can be controlled by properly proportioning the mix and utilizing suitable construction techniques.
With all these potentially serious disadvantages, engineers have learned to design and build beautiful, durable, and economical reinforced-concrete structures for practically all kinds of structural requirements.This has been accomplished by careful selection of the design dimensions and the arrangement of the steel reinforcement, development of proper cements, selection of proper aggregates and mix proportions, careful control of mixing, placing, and curing techniques and imaginative development of construction methods, equipment and procedures.
The versatility of concrete, the wide availability of its component materials, the unique ease of shaping its form to meet strength and functional requirements, together with the exciting potential of further improvements and development of not only the newer prestreed and precast concrete
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2 construction but also the conventional reinforced concrete construction, combine to make concrete a strong competitor of other materials in a very large fraction of structures.
In modern times, with the increased use of steel and reinforced-concrete construction, wood has been relegated largely to acceory use during construction, to use in temporary and secondary structures, and to use for secondary members of permanent construction.Modern technology in the last sixty years has revitalized wood as a structural material, however, by developing vastly improved timber connectors, various treatments to increase the durability of wood, and laminated wood made of thin layers bonded together with synthetic glues using revolutionary gluing techniques.Plywood with eentially nondirectional strength properties is
the most widely used laminated wood, but techniques have also been developed for building
large laminated wood members that for certain structures are competitive with concrete and steel.
Materials with future poibilities are the engineering plastics and the exotic metals and their alloys, such as beryllium, tungsten, tantalum, titanium, molybdenum, chromium, vanadium, and niobium.There are many different plastics available, and the mechanical
properties exhibited by this group of materials vary over a wide range that encompaes the range of properties available among the more commonly used structural materials.Thus in many specific design applications it is poible to select a suitable plastic material for an alternative design.Experience with the use of plastics outdoors is limited.Generally speaking, however, plastics must be protected from the weather.This aspect of design is therefore a major consideration in the use of plastics for primary structural elements.One of the most promising potential used of plastics is for panel and shell-type structures.Laminated or sandwich panels have been used in such structures with encouraging results that indicate an increased use in this type of construction in the future.
Another materials development with interesting poibilities is that of composites consisting of a matrix reinforced by fibers or fiber like particles.Although gla-fiber-reinforced composites with a gla or plastic matrix have been used for years, they appear to have much broader poibilities for a large variety of secondary structural components.Fiber-reinforced concrete is another composite being actively studied and developed.Several experimental applications are being observed under service conditions.Experiments have been conducted with both steel and gla fibers, but most of the service experience has been with steel fibers.
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