In the shown structure obtain the natural periods in both x and y directions, assuming the mass of the roof to be 800 kg/m, modulus of elasticity of the materials to be 2,100,000 kgf/cm, moment of inertia of each of the four columns to be 900 cm in both x and y directions, and the cross-sectional area of each of the cable bracing elements to be 2.5 cm. Neglect the weight of columns and cables comparing to the weight of the roof. 4m