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混凝土结构用钢筋,按照钢筋的机械性能和化学成分,分为Ⅰ、Ⅱ、Ⅲ、Ⅳ4个级别。经热轧成型并自然冷却的光圆钢筋为Ⅰ级钢筋,它的强度等级代号为 R235,其中字母 R为“热轧”的汉语拼音字头,数字表示Ⅰ级钢筋的屈服点不小于235牛/毫米~2。Ⅰ级钢筋的直径为8～20毫米,抗拉强度不小于370牛/毫米~2,伸长率δ_5不小于25%,冷弯180°,弯心直径同钢筋公称直径,受弯部位外表面不得产生裂纹。Ⅰ级钢筋的化学成分为:碳(C)为0.14%～0.22%,硅
Steel bars for concrete structures are classified into I, II, III, and IV grades according to their mechanical properties and chemical composition. The hot-rolled and naturally cooled light round steel bar is grade I steel, and its strength grade code is R235, in which the letter R is the “hot rolled” Chinese pinyin prefix, and the number indicates that the yield point of grade I steel is not less than 235 cattle. /mm~2. Grade I steel rods have a diameter of 8 to 20 mm, a tensile strength of not less than 370 N/mm2, an elongation of δ_5 of not less than 25%, a cold bending of 180°, a diameter of the bending core to the nominal diameter of the steel bar, and an outer surface of the bended portion. No cracks can occur. The chemical composition of grade I steel is: carbon (C) is 0.14% to 0.22%, silicon