Saint-Venant's Principle 생 베낭(상브난) 의 원리

If the forces acting on a small portion of the surface of an elastic body are replaced by another statically equivalent system of forces acting on the same portion of the surface, this redistribution of loading produces substantial changes in the stresses locally but has a negligible effect on the stresses at distances which are large in comparison with the linear dimensions of the surface on which the forces are changed.

즉, 상브난의 원리는 한점에 P 힘이 주어질때 그 주어진 곳에서 멀어질수록 stress(응력)이 그 단면에는 거의 균일한 값을 가진다.

 이 한점을 두점으로 나누어 각각 P/2 씩 주더라도 그 단면에는 역시 일정한 stress 값을 가진다. 

이때 우리는 P의 작용점 부터 충분히 멀리 떨어져있다고 표현할수 있다.

 "This principle is not a rigorous law of mechanics but is a common-sense observation based upon theoretical and practical experience."

이것은 실험적인 관찰로 얻어진 사실이다. 

Saint-Venant's principle states that 

we can use a more practical loading technique that is statically equivalent to the theoretical loading and obtain similar results at distances greater than the largest cross-sectional dimension from the load.

즉, 우리는 이 사실을 바탕으로 만약 하중에 단면이 충분히 떨어져있다면,

복잡한 stress distribution 을 계산에서 피할수 있다.

It should be noted, however, that this rule does not apply to every type of member and loading case.

For example, members made from thin-walled elements, and subjected to loadings that cause large deflections, may create localized stresses and deformations that have an influence a considerable distance away from the point of application of loading.

하지만, 만약 재료가 얇고 loading 이 large deflection 을 만들어낸다면, 멀리 떨어져있더라도 이 효과를 이어가긴 어렵다.

출저:

http://classes.mst.edu/civeng120/lessons/flexure/elastic/saint_venant/index.html