Zagadnienie Dynamiczne w Obliczeniach Statycznych Budowli
Sec. II contains approximate calculation of free vibration. A method based on successive approximations and on the method of secondary moments is used. Vibrations of 1, 2, 3 and 4 degrees of freedom are discussed as well as transversal and longitudinal vibrations of elastic bodies. The frequencies of vibrations of first and second order as well as first and second approximations of those frequencies are calculated. Sec. III is devoted to the dynamic interpretation of the equation d(V-T) = 0, which constitutes the basis of the method of approximate determination of deformations. V denotes here the elastic energy of the element and T the work of external forces, assumed in the form of a sum of products of forces P and the corresponding displacements of their attachment point. The dynamic interpretation of the equation d(V - T) = 0 consists in that the forces P are considered to be attached in a sudden manner which provokes damped vibration of the structure. It follows therefore that this equation expresses the condition for a minimum of the function U = V - T, corresponding to the state of equilibrium of the structure in other words - to its static deformation.