土木工程专业英语 陈瑛 4.3. Bond, Anchorage, and Development Length新.pptVIP

4.3 Bond, Anchorage, and Development Length 粘结、锚固、基本锚固长度 无粘结梁Beam with unbonded interface between reinforcement and concrete If the reinforced concrete beam of Figure 4.17(a) was constructed using round reinforcing bars, and, furthermore, if those bars were greased or lubricated before the concrete were cast, the beam would be only little stronger than if it were built of plain concrete, without reinforcement. If a load were applied, as shown in Figure 4.17(b), the bars would tend to maintain their original length as the beam deflects. The bars would slip longitudinally with respect to the adjacent concrete, which would experience tensile strain due to flexure. For reinforced concrete, it is essential that bond forces be developed on the interface 界面between concrete and steel, such as to prevent significant slip from occurring at that interface. Figure 4.17(c) shows the bond forces that act on the concrete at the interface as a result of bending, while Figure 4.17 (d) shows the equal and opposite bond forces acting on the reinforcement. It is through the action of these interface bond forces that the slip indicated in Figure 4.17 (b) is prevented. Some years ago, when plain bars without surface deformations were used, initial bond strength was provided only by the relatively weak chemical adhesion and mechanical friction between steel and concrete Once adhesion and static friction were overcome at larger loads, small amount of slip led to interlocking of the natural roughness of the bar with the concrete. However, the natural bond strength is so low that in beams reinforced with plain bars, the bond between steel and concrete was frequently broken. 端布有锚固的无粘结梁Beam with unbonded interface between reinforcement with end anchorage and concrete To prevent this, end anchorage was provided, chiefly in the form of hooks. If the anchorage is adequate, such a beam will not collapse, even if the bond is broken over the entire length between anchorages. This is so bec