梁纵截面单位长度法向内力计算公式

用纵截面把梁分成两部分，将梁横截面的内力分解到这两部分的横截面上，同时在纵截面上也得到对两部分的作用力，利用两的平衡条件和纵截面上的变形协调条件建立求解方程，推导出梁纵截面单位长度法向内力的计算公式。该公式经例题检验，在狭长矩形截面梁受均布力时，能得到纵截面正应力的精确解；在狭长矩形截面梁受正弦波型分布力时，当载荷集度变化不大或梁足够细长，也能得到足够精确的纵截面正应力。并对Ｎｏ．６３ｃ工字钢梁受

Formula for calculating internal normal force per unit length in longitudinal planes of beam

By dividing a beam into two parts with a longitudinal plane, resolving the internal forces on the cross section of the beam to the cross sections of the parts and obtaining the actions for the parts on the longitudinal plane, and using the conditions of equilibrium of each part and the compatible condition of deforms in the longitudinal faces, equations are established for the problem, then an expression is derived for calculating the internal normal force per unit length in the longitudinal planes of a beam. The expression verified by example problems can be used to obtain the correct solution of stresses on longitudinal planes in a narrow rectongular section beam under a uniform load, and the good accurate solution of stresses on longitudinal planes in a narrow rectangular section beam under a sine type of load when the variance of load along the beam is sufficient small or the beam is sufficient thin calculation is also made for Standard Shape Rolled-Steel beam No.63c(GB706-65)under a uniform load. The solution is that the variance of the internal normal force per unit length on the longitudinal planes depend upon the height in the web is similar to the variance in a narrow rectangular section beam and the strength of internal normal force per unit length on the middle longitudinal plane is half of the strength of load distributed on the upper face as a narrow rectangular section beam.