Compared with concrete, steel is a high strength material. The useful strength of ordinary reinforcing steels in tension as well as compression, i. e., the yield strength, is about 15 times the compressive strength of common structural concrete, and well over 100 times its tensile strength. On the other hand, steel is a high-cost material compared with concrete. It follows that the two materials are best used in combination if the concrete is made to resist the compressive stresses and the steel tensile stresses. Thus in reinforced concrete beams, the concrete resists the compressive?force,?longitudinal steel reinforcing bars are located close to the tension face to resist the tension force, and usually additional steel bars are so disposed that they resist the inclined tension stresses that are caused by the shear force in the beams. However, reinforcement is also used for resisting compressive forces primarily where it is desired to reduce the cross-sectional dimensions of compression members, as in the lower-floor columns of multistory buildings. Even if no such necessity exists, a minimum amount of reinforcement is placed in all compression members to safeguard them against the effects of small accidental bending moments that might crack and even fail an unreinforced member.

與混凝土相比，鋼是一種高強度材料。普通鋼筋在抗拉和抗壓時可以利用的強度，即屈服強度，約為普通的結構混凝土抗壓強度的15倍，而且超過其抗拉強度的100倍。另一方面，與混凝土相比，鋼材的成本要高很多。所以，兩種材料最好的結合使用是，混凝土用于抵抗壓應力，鋼材用來抵抗拉應力。因此，在鋼筋混凝土梁內，混凝土抵抗壓應力，縱向鋼筋配置在靠近受拉面處以抵抗拉應力，通常還附加配有一些鋼筋，抵抗梁內剪力所引起的斜向拉應力。然而，鋼材也可以用于抵抗壓力，主要是為了減小受壓構件的截面尺寸，例如用于多層建筑的下部樓層柱。即使不存在這種必要性，所有受壓構件也要配置最少數(shù)量的鋼筋，以保證這些構件在偶然出現(xiàn)的小彎矩作用下的安全性，在這種情況下，不加鋼筋的混凝土構件可能會開裂，甚至破壞。

For most effective reinforcing action, it is essential that steel and concrete deform together, i.e., that there be a sufficiently strong bond between the two materials to ensure that no relative movements of the steel bars and the surrounding concrete occur. This bond is provided by the relatively large chemical adhesion which develops at the steel-concrete interface, by the natural roughness of the mill scale of hot-rolled reinforcing bars, and by the closely spaced rib-shaped surface deformations with which reinforcing bars are furnished in order to provide a high degree of interlocking of the two materials.

Additional features which make for the satisfactory joint performance of steel and concrete are the following:

(1) The thermal expansion coefficients of the two materials, about 1. 2×?/°C for steel vs. an average of 1. 25 × /°C for concrete, are sufficiently close to forestall cracking and other undesirable effects of differential thermal deformations.

(2) While the corrosion resistance of bare steel is poor, the concrete which surrounds the steel reinforcement provides excellent corrosion protection, minimizing corrosion problems and corresponding maintenance costs.

(3) The fire resistance of unprotected steel is impaired by its high thermal conductivity and by the fact that its strength decreases sizably at high temperatures. Conversely, the thermal conductivity of concrete is relatively low. Thus, damage caused by even prolonged fire exposure, if any, is generally limited to the outer layer of concrete, and a moderate amount of concrete cover provides sufficient thermal insulation for the embedded reinforcement.

使配筋最有效地發(fā)揮作用的基本條件是鋼筋和混凝土的變形要一致，即這兩種材料間要有足夠強的粘結力，以確保鋼筋和其周圍混凝土不發(fā)生相對移動。這種粘結力是由鋼筋－混凝土結合面上較強的化學黏合作用、熱軋鋼筋表面層的固有粗糙度，以及間距較小的肋形表面變形等所構成的。鋼筋的表面變形為兩種材料間提供了很高的咬合作用。

使鋼筋和混凝土能夠很好地共同工作的其他特性有：

(1)兩種材料的熱膨胩系數(shù)，鋼筋大約為1.2×/°C，而混凝土的平均值為1.25×/°C。這兩個數(shù)值相當接近，足以避免熱變形差值引起的混凝土開裂和其他不利影響。

(2）裸露的鋼筋的抗腐住性很差，鋼筋周圍的混凝土為其提供了優(yōu)良的防腐蝕保護層，使腐蝕問題及相關的維護費用降至最低。

(3)鋼材的熱傳導系數(shù)高，而且在高溫時其強度會大幅度下降，因而無防護層鋼筋的抗火性能較差。相反，混凝土的熱傳導系數(shù)相對較低。因此，即使長期暴露在火焰下，如果發(fā)生損壞的話，也僅僅限于混凝土的外層。厚度適當?shù)幕炷帘Ｗo層，可以為埋置在其內的鋼筋提供充分的溫度絕緣。

Steel is used in two different ways in concrete structures: as reinforcing steel and as prestressing steel. Reinforcing steel is placed in the forms prior to casting of the concrete. Stresses in the steel, as in the hardened concrete, are caused only by the loads on the structure, except for possible parasitic stresses from shrinkage or similar causes. In contrast, in prestressed concrete structures large tension forces are applied to the reinforcement prior to letting it act jointly with the concrete in resisting external loads.

鋼材以兩種不同的方式應用于混凝土結構中：普通鋼筋和預應力鋼筋。普通鋼筋在澆筑混凝土之前先置于模板內。鋼筋中的應力，與硬化混凝土中的應力一樣，除了由收縮或類似原因造成的附加應力外，僅僅是由結構上作用的荷載引起的。比較起來，在預應力混凝土結構中，在鋼筋與混凝土共同工作承受外部荷載之前，對鋼筋己施加了很大的拉力。

The most common type of reinforcing steel ( as distinct from?prestressing steel) is in the form of round bars, sometimes called bars, available in a large range of diameters, from 10 to 35 mm for ordinary applications and in two heavy bar sizes of 44 and 57 mm.?These bars are furnished with surface deformations for the purpose of increasing resistance to slip between steel and concrete. Minimum requirements for these deformations ( spacing, projection, etc.) have been developed in experimental research. Different bar producers use different patterns, all of which satisfy these requirements.

最常見的鋼筋（區(qū)別于預應力鋼筋）的形式為圓棒狀，有時被稱為“rebars”?，F(xiàn)在可以使用的鋼筋的直徑范圍很大，在一般的應用中從10mm至35mm，兩種大型鋼筋的尺寸為44mm和57mm。對這些鋼筋表面進行了變形處理，其目的是增加鋼筋與混凝土之間的抗滑能力。已經通過實驗研究對這些變形（間距、凸起等）的最低要求進行了確定。不同的鋼筋制造廠家采用不同的變形花紋，它們全部都能夠滿足這些要求。

Welding of rebars in making splices, or for convenience in fabricating reinforcing cages for placement in the forms, may result in metallurgical changes that reduce both strength and ductility, and special restrictions must be placed both on the type of steel used and the welding procedures.?The provisions of ASTM A706 relate?specifically to welding.

為了對鋼筋進行拼接，或者便于制作置于模板內的鋼筋骨架所進行的焊接，可能會引起金相組織的變化而降低材料的強度和延性，因此，必須對所用鋼材的類型和焊接規(guī)程加以特殊的限制。ASTM中A706的條款是專門適用于焊接的。

In reinforced concrete a long-time trend is evident toward the use of higher strength materials, both steel and concrete. Reinforcing bars with 40ksi (276MPa) yield stress, almost standard 20 years ago, have largely been replaced by bars with 60ksi (414MPa) yield stress, both because they are more economical and because their use tends to reduce congestion of steel in the forms.

長期以來，在鋼筋混凝土?領域明顯地趨向于使用高強度材料，包括鋼筋和混凝土。屈服強度為 40ksi(276MPa）的鋼筋，在20年前幾乎是標準的，目前大部分已由屈服強度為 60ksi(414MPa) 鋼筋所取代。因為后者更為經濟，而且使用它們可以減少模板內鋼筋的擁擠狀況。

The ACI Code permits reinforcing steels up to = 80ksi (552MPa). Such high strength steels usually yield gradually but have no yield plateau. In this situation the ACI Code requires that at the specified minimum yield strength the total strain should not exceed 0.0035. This is necessary to make current design methods, which were developed for sharp-yielding steels with a yield plateau, applicable to such higher strength steels. There is no ASTM specification for deformed bars with yield stress above 60ksi, but such bars may be used, according to the ACI Code, providing they meet the requirements stated. Under special circumstances steel in this higher?strength range has its place, e.g., in lower-story columns of high-rise buildings.

ACI 規(guī)范允許使用強度 =80ksi (552MPa)的鋼筋。這類高強鋼筋通常是逐漸屈服的，沒有屈服平臺。在這種情況下，ACI規(guī)范要求在規(guī)定的最小屈服強度時的總應變不超過 0.0035。這是將現(xiàn)行的設計方法應用于這類高強鋼筋時所必須遵守的?，F(xiàn)行的設計方法是按鋼材突然屈服，而且有屈服平臺的情況而制訂的。ASTM 規(guī)范中沒有關于屈服強度高于60ksi 的變形鋼筋的條款，但是在實際中可能使用這種鋼筋，根據ACI規(guī)范，它們可以在滿足上述要求的情況下使用。在特殊情況下，例如高層建筑的下部樓層的柱子，使用這一高強度范圍內的鋼筋就非常適合。

In order to minimize corrosion of reinforcement and consequent spalling of concrete under severe exposure conditions such as in bridge decks subjected to deicing chemicals, galvanized or epoxy-coated rebars may be specified.

在惡劣的環(huán)境條件下，例如受除冰化學劑侵蝕的橋面，要求使用鍍鋅或環(huán)氧樹脂涂層的鋼筋，以便使鋼筋的腐蝕和隨之發(fā)生的混凝土的剝落減至最小。