ABSTRACT
Influence lines for an arch are constructed as the dependences of a response versus the horizontal coordinate x of the unit load acting upon an arch; the horizontal below the plot of an arch is taken as the basic line. Influence lines for forces exerted upon the cross-section of an arch are made up of three branches: left, right, and median. The median branch corresponds to the position of the load at the arch’s portion, i.e., between the section and the crown hinge. The nil point of the bending moment is located under point of the intersection of two straight lines, one of which runs from the support hinge of a haunch comprising the section to the centroid of the section while another runs from the opposite support hinge to the crown hinge. Transition to the substitute arch supplied with cantilevers is necessary when the median segment of the wanted influence line doesn’t reach the abscissa axis.
