5.2.3 The equivalent rectangular block The actual distribution of the compressive stress in a section has the form of a rising parabola.It is time consuming to evaluate the volume of the compressive stress block if it has a parabolic shape.An equivalent rectangular stress block can be used with ease and without loss of accuracy to calculate the compressive force and hence the flexural moment strength of the section.5.2.3 The equivalent rectangular block • The actual distribution of the compressive stress in a section has the form of a rising parabola. It is time consuming to evaluate the volume of the compressive stress block if it has a parabolic shape. An equivalent rectangular stress block can be used with ease and without loss of accuracy to calculate the compressive force and hence the flexural moment strength of the section