在箱形梁挠曲分析基础上,提出一种判别箱形梁正负剪力滞方法,导出用截面几何特性和广义力矩表达的判别式,结合实例判别简支箱梁、悬臂箱梁、外伸箱梁和连续箱梁正负剪力滞.与通过比较弯矩和附加弯矩之间相互关系判别方法相比,所提出方法更适合于复杂型式箱梁正负剪力滞判别.研究结果表明:箱形梁发生正剪力滞还是负剪力滞,主要取决于其横截面尺寸及弯矩与剪力滞力矩之间相对大小；对于在竖向荷载作用下有正、负弯矩分布箱梁,在反弯点附近梁段内判别式参数有“跳跃”现象；在弯矩分布呈折角处,剪力滞力矩分布比较平滑.%On the basis of the flexural analysis of box girders, the method for distinguishing between the positive and negative shear lags of box girders is presented. The discriminant is derived, which is expressed by the geometry of cross-sections and generalized moments. The positive and negative shear lags of simple, cantilever, overhanging and continuous box girders are discriminated by illustration of examples. In comparison with discrimination accomplished by relationship between bending moments and additional bending moments, the present method is more adaptable to discrimination between the positive and negative shear lags of complex-type box girders. The research results show as follows: Whether positive or negative shear lags emerge in a box girder, it mainly depends on the size of the cross-section of the box girder and the relative magnitude of the bending moments and shear lag moments; for the box girders under the action of vertical loads and with positive and negative bending moments, the discriminant parameters demonstrate the jumping property for the segment near the point of contraflexure; the shear lag moments are distributed smoothly where the bending moments are distributed in a sharp turn.
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