First of all, the location of the centroid of the given section is determined. The the given section is splitted into rectangles or triangles. The moment of inertia of the rectangles is determined about its centroid. Then this moment of inertia is transferred about the axis passing through the centroid of the given section, using theorem of parallel axis.
Problem 4.14. Fig. 4.31 shows a T-section of dimensions 10 × 10 × 2 cm. Determine the moment of inertia of the section about the horizontal and vertical axes, passing through the centre of gravity of the section.