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无论是预制或现浇的钢筋混凝土构件,其保护层的厚度都有适宜的数值。一般常用的厚度有:梁保护层厚为25mm;板厚大于100mm者,保护层厚15mm;板厚小于100mm者,保护层厚10mm。保护层厚度的增大或减小都会给构件造成不良影响。保护层厚度的减小,会使钢筋受有害气体的侵蚀,发生锈蚀,缩短钢筋的使用寿命。保护层厚度的增加,减少了截面的有效高度,如:h_0=h-a_g,而a=c+(d/2),这里d为钢筋直径,是一个固定值(对某一构件而言),c为保护层厚度,是一个变值,c值增大,a_g值随之增大,相应h_0值小。由矩形截面梁受压区高度x的适用条件x≤0.55h_0可知,x值减小,构件的承载能力就会相应降低,现举例如下:已知某矩形梁原设计截面尺寸为20 ×40cm,配置Ⅰ级钢筋3φ20,钢筋净保护层厚度为2.5cm,混凝土标号为200号,现因施工不慎,超过了施工规范所允许的误差,实际截面尺寸变成20×39cm,实际钢筋净保护层厚度为3.4cm,。
Regardless of prefabricated or cast-in-place reinforced concrete structures, the thickness of the protective layer has a suitable value. Commonly used thicknesses are: beam protective layer thickness 25mm; plate thickness greater than 100mm, protective layer thickness 15mm; plate thickness less than 100mm, protective layer thickness 10mm. The increase or decrease in the thickness of the protective layer will have an adverse effect on the components. The reduction of the thickness of the protective layer will cause the steel bar to be eroded by harmful gases, cause corrosion, and shorten the service life of the steel bars. The increase in the thickness of the protective layer reduces the effective height of the section, such as: h_0 = h-a_g, and a = c + (d/2), where d is the diameter of the bar and is a fixed value (for a component), c is the thickness of the protective layer, it is a variable value, c value increases, a_g value increases, the corresponding h_0 value is small. According to the applicable condition x≤0.55h_0 of the height x of the compression area of a rectangular section beam, the value of x decreases, and the bearing capacity of the component will decrease accordingly. The following example is as follows: The original design section size of a certain rectangular beam is known as 20 × 40cm. The grade I steel bar 3φ20 is installed, the thickness of the net protective layer of the steel bar is 2.5cm, and the concrete number is 200. It is due to careless construction and exceeds the error allowed by the construction specification. The actual section size becomes 20×39cm, and the actual reinforcing steel net protection layer The thickness is 3.4cm.