UNIT3reinforcedconcrete.pptx

UNIT 3 Reinforced Concrete;Although concrete is used very extensive in the construction of buildings, bridges and many other engineering structures, its mechanical properties are far from ideal. For example, it is not a particularly strong material. 虽然混凝土已广泛应用于房屋建筑、桥梁和其他许多工程结构物中，但它的力学性能却很不理想。例如，它的强度不是很高。;?;The tensile strength of concrete is extremely low, about one-tenth of its compressive strength and this precludes the use of plain concrete for most structural members. 混凝土的抗拉强度非常低，大约是抗压强度的1/10，因此大多数结构构件不能用素混凝土制作。;The elastic modulus for concrete subjected to compressive stress of short duration is reasonably high, in the range of 20,000 to 30,000 Mpa (about one-tenth of the elastic modulus of steel); 混凝土短期受压时的弹性模量相当高，为20000～30000Mpa（大约是钢弹性模量的1/10）；;however, concrete undergoes large additional long-term deformations due to creep and shrinkage, so that the effective stiffness is much lower―perhaps a third to a quarter of the instantaneous stiffness. 然而由于徐变和收缩，混凝土在又会产生较大的长期变形，所以其有效刚度要低得多－可能只有瞬时刚度的1/3到1/4。 ;The widespread use of concrete in engineering construction stems from its cheapness compared with other structural materials currently available. 混凝土在工程建筑中能得到广泛应用，是因为它比目前常用的其他建筑材料便宜。;Its lack of tensile strength is overcome by including reinforcement, usually in the form of steel bars, to produce a composite material known as reinforced concrete. 其抗拉强度低的缺点则用加配钢筋以形成称为钢筋混凝土的复合材料来克服。;Although the steel reinforcement does not prevent cracking of the concrete in regions of tension, it does prevent the cracks from widening, and it provides an effective means for resisting the internal tensile forces. 虽然钢筋不能防止混凝土受拉区裂缝的产生，但是确实能限制裂缝的开展，因此提供了抵抗内拉力的有效手段。;The quantity of reinforcement need is usually quite small, relative to the volume of concrete, so that the total cost of reinforced concrete construction remains commercially very competitive. 所需钢筋的数量，与混凝土的体积相比往往是很小的，所以钢筋混凝土结构的总造价在市场上的竞争力仍很强。;The primary purpose of the steel reinforcement is to carry internal tensile force