当外壳（混凝土）从螺旋箍筋柱上剥落时，柱子并没有立即失效，因为核心（混凝土）的强度由于螺旋箍筋的加强效应形成的三向应力而增强。因此，当螺旋箍筋屈服时柱子能经受大变形，最后达到另一个最大荷载，并最终倒塌。这样的失效更延性，并对即将发生的失效和可能的对其它构件的荷载重分布给予警告。但是应该注意到，这只有在非常大的应变时才能实现。例如，要达到第二个最大荷载，其应变必须相当于8英尺高的柱子缩短约1英寸。当螺旋箍筋柱受到偏心荷载时，第二个最大荷载可能小于初始的最大荷载，但失效时的变形仍然是大的，允许荷载重分布。
          When a symmetrical（对称的）column is subjected to a concentric（中心） axial load, longitudinal strains develop uniformly across（穿过）the section. Because the steel and concrete are bonded together, the strains in the concrete and steel are equal. For any given strains it is possible to compute the stresses in the concrete and steel using the stress-strain curves（应力-应变曲线）for the two materials.

            当一根对称的柱子承受中心轴向力时，则穿过截面均匀地形成纵向应变。由于钢筋与混凝土粘结在一起，混凝土的应变与钢筋的应变是相等的。对任何已知的应变，通过采用（混凝土与钢筋）两种材料的应力-应变曲线有可能计算出混凝土与钢筋的应力。
            Almost all compression members in concrete structure are subjected to moments in addition to axial loads. These may be due to the load not being centered（居中）on the column, or may result from the columns resisting a portion of the unbalanced moments at the ends of the beams supported by the columns. The distance e is referred to as the eccentricity（偏心距）of the load. These two cases are the same since the eccentricity load P can be replaced by a load P acting along the centroidal axis（形心轴）, plus a moment, M=Pe, about the centroid. The load P and moment M are calculated with respect to the geometric centroidal axis because the moments and forces obtained from structural analysis are referred to（关系到）this axis.
            在混凝土结构中，几乎所有的受压构件除了承受轴向力外，还承受弯矩。这可能是由于柱子上的荷载没有居中，或者可能是由柱子抵抗其支撑的梁端的部分不平衡弯矩而引起。距离e称为荷载的偏心距。因为有偏心距的荷载P可以替换成沿着形心轴作用的荷载P加上对形心的弯矩，即M等于Pe，因此这两种情况是相同的。荷载P和弯矩M是相对于几何形心轴来计算的，因为从结构分析得到的弯矩和力关系到该轴。
            Although it is possible to derive a family of（一族）equations to evaluate the strength of columns subjected to combined bending and axial loads, these equations are tedious（冗长）to use. For this reason, interaction diagrams for columns are generally computed by assuming a series of strain distributions, each corresponding to a particular point on the interaction diagram, and computing the corresponding values （对应值）of P and M. Once enough such points have been computed, the results are summarized（概括）in an interaction diagram.
            尽管有可能推导一族公式来估计承受弯曲与轴向力组合的柱子的强度，但是这些公式用起来很冗长。因此，柱子的相关图通常通过假定一系列的应变分布来计算，每一个（应变）相当于相关图上一个特定的点，并计算出对应的P和M的值。一旦这样的点已经计算得足够（多），其结果则被概括在一张相关图中。
             The maximum compressive strain（压应变）is set（设定）at 0.003, corresponding to failure of the section. The location of the neutral axis（中性轴）and the strain in each level of reinforcement（每层的钢筋）are computed from the strain distribution. This information is then used to compute the size of the compression stress block（区）and the stress in each layer of reinforcement. The forces in the concrete and the steel layers are computed by multiplying the stresses by the areas on which they act. Finally, the axial force Pn is computed by summing（求和）the individual（各个）forces in the concrete and steel, and the moment Mn is computed by summing the moments of these forces about the geometric centroid of the cross section. These values of Pn and Mn represent one point on the interaction diagram.
            最大的压应变设定在0.003，相当于该截面的失效。中性轴的位置和每层钢筋的应变通过应变的分布来计算。这个信息然后用以计算压应力区的大小和每层钢筋的应力。混凝土与钢筋层中的力通过应力乘以其作用的面积来计算。最后，轴向力Pn通过混凝土与钢筋中的各个力的求和得到，弯矩Mn通过这些力对横截面的几何形心的弯矩求和得到。这些Pn和Mn的值代表着相关图上的某一点。
           Generally, designers have access to（利用）published interaction diagrams or computer programs（程序）to compute interaction diagrams for use in design. Occasionally, this is not true, as for example, in the design of hollow bridge piers（墩）, elevator shafts, or unusual shaped members. In most cases it is adequate to represent（表示）the interaction diagram by a series of straight lines joining（加上）the load and moment values corresponding to the following（下列）five strain distributions: