The Analysis about the unit-step function of the bending moment equation of girder

Today, the common expression of the bending moment equation is an expression of piecewise function, which causes heavy work in its theoretic research. The bending moment equation is often used when the bend of girder is being studied. Under the action of the concentrative loads, the expression of piecewise function of the equation of bending moment can be expressed with a monolithic equation by unit-step function, and then the calculative workload will be simplified when bend distortion is solved. And at the same time it also has a certain theoretic value.