Lectures are grouped into two parts: a) nonlinear theory of elasticity, and b) nonlinear analysis of girders. Within the nonlinear theory of elasticity, vectors and tensors are considered (the basic and reciprocal basic vectors, the contravariant and covariance components of the vector, the curvilinear coordinates, the derivatives of the base vectors, the covariant derivative, the Christoffel symbols), deformations, stresses, equilibrium conditions, constituent equation and the linear theory of elasticity. Idealization within nonlinear statics of girders. Exact theory of displacement geometry and equilibrium equations on a deformed rod. Material nonlinearity. Idealizations within material nonlinearity. Relations of internal and external forces in geometric nonlinearity. Physical nonlinearity, basic concepts. Approximation of physically nonlinear problems. Plastic hinges and plastic analysis. Iterative methods of calculating load capacity and deformations of planar girders. Application of computers in the solution of nonlinear problems of girders.