In civil engineering and structural analysis Clapeyron's theorem of three moments is a relationship among the bending moments at three consecutive supports of a horizontal beam. Let A,B,C-D be the three consecutive points of support, and denote by- l the length of AB and the length of BC, by w and the weight per unit of length in these segments. Then the bending moments at the three points are related by: This equation can also be written as The second equation is more general as it does not require that the weight of each segment be distributed uniformly.