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预应力混凝土发展的初期,预加应力的目标是全部消除使用荷载作用下混凝土的拉应力。这个全新的概念,是把梁看成匀质材料的,直到预计最大荷载作用下,它将不产生裂缝,并处于弹性状态。在全部使用荷载作用下,限制混凝土的拉应力为零,这个设计思想即是通常熟知的全部预应力。而另外一种方法是在设计中允许全部使用荷载时,混凝土产生一定的拉应力。这就是所谓部分预应力。
In the early stages of the development of prestressed concrete, the goal of prestressing is to completely eliminate the tensile stress of concrete under service load. The new concept is to treat a beam as a homogeneous material and it will not crack and be elastic until the maximum expected load is applied. Under all loading conditions, the tensile stress of the concrete is limited to zero. This design concept is known as all prestressing. Another approach is to allow the concrete to have a certain tensile stress when fully loaded with the design. This is called partial prestress.