Chapter 20 – Influence Lines

Publisher Summary The effects of loads that occupy different positions on a structure can be examined by means of influence lines. Influence lines give the value at a particular point in a structure of functions such as shear force, bending moment, and displacement for all positions of a traveling unit load. They may also be constructed to show the variation of support reaction with the unit load position. The value of a function from these influence lines at a point can be calculated for a system of loads traversing the structure. The principle of superposition can be used to ensure that the structural systems considered must be linearly elastic. This chapter investigates the construction of influence lines for support reactions and for shear force and bending moment at a section of a beam when the traveling load is in continuous contact with the beam. A simple and convenient method of constructing influence lines is to employ the Mueller–Breslau principle, which gives the shape of an influence line without the values of its ordinates.