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连接筋在楼板和路面中有许多重要用途,由于能把轮荷载从一块板传递给另一块板而防止缝处的开裂。遗憾的是,连接筋有时妨碍缝张开,这样就失去了留缝的作用并在缝之间引起板开裂。连接筋对缝移动的约束当混凝土胀缩时缝要能自由地张闭。为了能够移动,连接筋应是直而光滑的,这样就可以没有阻力地在混凝土中滑进、滑出。仅光滑还不能保证对缝的移动没有约束,连接筋还必须和板边、表面平行且连接筋要互相平行。如果连接筋互相不平行,则要弯曲才能使缝张开,这给混凝土增加了一个约束力并引起开裂(图1).
Joining ribs have many important uses in floors and roads, and can prevent cracks at the seams by transferring wheel loads from one plate to another. Unfortunately, the connecting ribs sometimes prevent the seams from opening, thus losing the effect of leaving seams and causing cracking of the panels between the seams. Constraints of Joining Ribs on Seam Movement When the concrete expands and shrinks, the seams can open freely. In order to be able to move, the connecting ribs should be straight and smooth so that they can slide in and out of the concrete without resistance. Smoothness alone does not guarantee that there is no constraint on the movement of the seam. The connecting ribs must also be parallel to the edges of the plate, the surface and the connecting ribs. If the connecting ribs are not parallel to each other, they must be bent to open the seam, which adds a binding force to the concrete and causes cracking (Figure 1).