已经显示作用在一根预应力梁上的外部荷载的变化会导致梁在弹性阶段时其压力线位置的变化。这是预应力结构的基本规律。在一根普通的预应力梁中，随着外力的增加，其压力线位置以一个相对均匀的速度不断移动直至受拉纤维形成开裂的位置。在已经超过开裂荷载后，随着附加荷载的施加，压力线移动的速度便会降低，且使预应力钢筋束中的应力和合成的混凝土力开始发生显著的增加。内部弯矩的作用不断变化直到所有压力线的移动都停止。其后施加的荷载引起的弯矩完全通过相应的、且按比例的内力变化来抵消，正如在钢筋混凝土的结构中。这个事实，即弹性阶段和塑性阶段的力由基本不同的作用来传送是非常重要的，且使强度计算变得对所有的设计都是必要的，以确保存在足够的安全系数。这是正确的，即使弹性阶段的应力可能符合公认的弹性设计准则。
             It should be noted that the load deflection curve is close to（接近于）a straight line up to the cracking load and that the curve becomes progressively（逐渐）more curved as the load is increased above the cracking load. The curvature（弯曲）of the load-deflection curve for loads over the cracking load is due to（由于..所造成的）the change in the basic internal resisting moment action that counteracts（抵消）the applied loads, as described above, as well as to plastic strains that begin to take place in the steel and the concrete when stressed to high levels（受到很大压力）.
            应该注意到荷载挠度曲线在开裂荷载以内是接近直线的，且在超过开裂荷载后，该曲线随着荷载的增加逐渐变得更弯曲。正如上面所描述的，当超过开裂荷载时，其荷载-挠度曲线的弯曲是由于抵消施加荷载的基本内部抵抗弯矩作用的变化以及当受到很大压力时钢筋和混凝土中开始发生的塑性应变所造成的。
             In some structures it may be essential that the flexural members remain crack free（保持构件不开裂）even under significant（明显的）overloads. This may be due to the structures’ being exposed to exceptionally corrosive（特别腐蚀）atmospheres during their useful life（有效寿命）. In designing prestressed members to be used in special structures of this type, it may be necessary to compute the load that causes cracking of the tensile flange（受拉翼缘）, in order to ensure that adequate safety against cracking is provided by the design. The computation of the moment that will cause cracking is also necessary to ensure compliance with（符合）some design criteria（criterion的复数形式，标准）.
            在一些结构中，保持受弯构件不开裂可能是必要的，甚至在明显的超载下。这可能是由于结构在它们的有效寿命期间被暴露在特别腐蚀的空气中的原因。当设计预应力构件用于这种类型的特殊结构时，可能有必要计算引起受拉翼缘开裂的荷载，以确保该设计提供足够抵抗开裂的安全性。也有必要计算会导致开裂的弯矩，以确保符合一些设计标准。
            Many tests have demonstrated（证明）that the load-deflection curves of prestressed beams are approximately linear（近似直线的）up to and slightly in excess of（稍微超过）the load that causes the first cracks in the tensile flange. (The linearity（直线性）is a function of the rate at which the load is applied.) For this reason, normal elastic-design relationships（关系式）can be used in computing the cracking load by simply determining the load that results in a net（净）tensile stress in the tensile flange (prestress minus the effects of the applied loads) that is equal to the tensile strength of the concrete. It is customary to assume that the flexural tensile strength of the concrete is equal to the modulus of rupture（断裂模量）of the concrete when computing the cracking load.
            很多试验证明，在引起受拉翼缘最初开裂的荷载以内或稍微超过时，预应力梁的荷载-挠度曲线是近似直线的。（直线性是荷载施加速度的函数。）因此，通过简单地确定导致受拉翼缘中产生一个净的受拉应力的荷载（预应力减去施加荷载的效应 ），普通的弹性设计关系式能用来计算开裂荷载，其值等于混凝土的抗拉强度。当计算开裂荷载时，习惯上假定混凝土的受弯抗拉强度等于混凝土的断裂模量。
           In should be recognized that the performance（性能）of bonded（有粘结的）prestressed member is actually a function of the transformed section（换算截面）rather than the gross（毛）concrete section. If it is desirable（想要）to make a precise estimate of the cracking load, such as is required in some research work, this effect（影响）should be considered.
            应该承认有粘结的预应力构件的性能实际上是一个换算截面的函数，不是混凝土毛截面的函数。如果想要对开裂荷载作一精确估计，例如在一些研究工作中需要的，该影响应该被考虑。
Principles of Ultimate Moments Capacity for Bonded members 
有粘结的构件极限弯矩能力的规则
           When prestressed flexural members that are stronger in shear and bond than in bending are loaded to failure, they fail in one of the following modes（方式）: