外文文献翻译
Reinforced Concrete
Concrete and reinforced concrete are ud as building materials in every country。 In many, including the United States and Canada， reinforced concrete is a dominant structural material in engineered construction. The universal nature of reinforced concrete construction stems from the wide availability of reinforcing bars and the constituents of concrete, gravel, sand, and cement， the relatively simple skills required in concrete construction， and the economy of reinforced concrete compared to other forms of construction. Concrete and reinforced concrete are ud in bridges, buildings of all sorts underground structures， water tanks， television towers, offshore oil exploration and production structures， dams， and even in ships.心中的家
Reinforced concrete structures may be cast-in-place concrete， constructed in their final location， or they may be precast concrete produced in a factory and erected at the construction site. Concrete structures may be vere and functional in design， or the shap
e and layout and be whimsical and artistic。 Few other building materials off the architect and engineer such versatility and scope。
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Concrete is strong in compression but weak in tension. As a result, cracks develop whenever loads， or restrained shrinkage of temperature changes, give ri to tensile stress in excess of the tensile strength of the concrete。 In a plain concrete beam， the moments about the neutral axis due to applied loads are resisted by an internal tension-compression couple involving tension in the concrete. Such a beam fails very suddenly and completely when the first crack forms. In a reinforced concrete beam， steel bars are embedded in the concrete in such a way that the tension forces needed for moment equilibrium after the concrete cracks can be developed in the bars.
The construction of a reinforced concrete member involves building a from of mold in the shape of the member being built. The form must be strong enough to support both the weight and hydrostatic pressure of the wet concrete, and any forces applied to it by workers， concrete buggies， wind, and so on. The reinforcement is placed in this form a
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nd held in place during the concreting operation。 After the concrete has hardened， the forms are removed。 As the forms are removed, props of shores are installed to support the weight of the concrete until it has reached sufficient strength to support the loads by itlf。
The designer must proportion a concrete member for adequate strength to resist the loads and adequate stiffness to prevent excessive deflections. In beam must be proportioned so that it can be constructed. For example， the reinforcement must be detailed so that it can be asmbled in the field， and since the concrete is placed in the form after the reinforcement is in place, the concrete must be able to flow around， between, and past the reinforcement to fill all parts of the form completely。
The choice of whether a structure should be built of concrete, steel， masonry， or timber depends on the availability of materials and on a number of value decisions. The choice of structural system is made by the architect of engineer early in the design, bad on the following considerations:
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1。 Economy。 Frequently, the foremost consideration is the overall const of the structure。 This is， of cour， a function of the costs of the materials and the labor necessary to erect them. Frequently， however, the overall cost is affected as much or more by the overall construction time since the contractor and owner must borrow or otherwi allocate money to carry out the construction and will not receive a return on this investment until the building is ready for occupancy。 In a typical large apartment of commercial project， the cost of construction financing will be a significant fraction of the total cost。 As a result， financial savings due to rapid construction may more than offt incread material costs. For this reason, any measures the designer can take to standardize the design and forming will generally pay off in reduced overall costs。
In many cas the long-term economy of the structure may be more important than the first cost。 As a result, maintenance and durability are important consideration。
2。 Suitability of material for architectural and structural function. A reinforced concrete system frequently allows the designer to combine the architectural and structura
l functions。 Concrete has the advantage that it is placed in a plastic condition and is given the desired shape and texture by means of the forms and the finishing techniques。 This allows such elements ad flat plates or other types of slabs to rve as load—bearing elements while providing the finished floor and / or ceiling surfaces. Similarly, reinforced concrete walls can provide architecturally attractive surfaces in addition to having the ability to resist gravity, wind， or ismic loads. Finally， the choice of size of shape is governed by the designer and not by the availability of standard manufactured members.
3。 Fire resistance. The structure in a building must withstand the effects of a fire and remain standing while the building is evacuated and the fire is extinguished。 A concrete building inherently has a 1— to 3-hour fire rating without special fireproofing or other details. Structural steel or timber buildings must be fireproofed to attain similar fire ratings.
4. Low maintenance。 Concrete members inherently require less maintenance than do
structural steel or timber members。 This is particularly true if den, air—entrained concrete has been ud for surfaces expod to the atmosphere, and if care has been taken in the design to provide adequate drainage off and away from the structure. Special precautions must be taken for concrete expod to salts such as deicing chemicals.
5。 Availability of materials.宜昌小吃 Sand, gravel, cement, and concrete mixing facilities are very widely available, and reinforcing steel can be transported to most job sites more easily than can structural steel。 As a result, reinforced concrete is frequently ud in remote areas.
