Structural Analysis: Moving Loads

Study Notes

Moving loads can cause bending moments and shear forces in beams
Maximum moment under a particular load occurs when the center of the beam is midway between that load and the resultant of all the loads on the span

Compute the maximum moment under each load
Use the largest of these moments for the design
Usually, the largest moment occurs under the largest load
Maximum shear occurs at the reaction where the resultant load is nearest
Sometimes, it is necessary to check the condition when the larger loads are on the span and the rest of the smaller loads are outside

Sample Problem #1: A truck with axle loads of 40KN and 60KN on a wheel base of 5m rolls across a 10m span. Maximum bending moment and maximum shearing force are calculated as 160KNm and 80KN, respectively.
Sample Problem #2: A tractor weighing 3,000lb, with a wheel base of 9ft, carries 1,800lb of its load on the rear wheels, crosses a 14ft span. Maximum moment and maximum shear are calculated as 6,380lb-ft and 2,318.5lb, respectively.
Sample Problem #3: Three wheel loads roll as a unit across a 44ft span, maximum moment and maximum shear are calculated as 12,736lb-ft and 12,881lb, respectively.

Maximum moment occurs when the load is at the mid-span
Maximum shear occurs when the load is very near the support (usually assumed to lie over the support)