对影响线正负号问题的探讨

Discussion on the positive and negative sign for influence line

对力学中影响线正负号的规定进行了研究 ,通过对几个例子的分析 ,指出了规定中的局限性所在 ,并得出了新的结论 :( 1 )影响线的正负号仅表示实际的内力 (或反力 )与假设的方向是否一致 ;( 2 )为避免静力法和机动法作图有时可能出现的矛盾 ,提出作影响线时需再建立一个 y坐标 ,并以与 P=1指向相反的方向作为 y轴的正向 .最后 ,用算例全面验证了结论的正确性 .

In view of the limitations in the stipulations to the positive and negative sign for the influence line,the problem by some examples is analyzed and some new conclusions are drawn:(1)the positive and negative sign for the influence line simply indicates if the direction of the actual internal force is consistent with the hypothesis;(2)a y axial coordinate which directs the negative direction of the unit load was needed to avoid the occasional contradictions result obtained by the static method and kinematic method.Finally,an example was given to verify the correctness of the conclusions all round.