This thesis studies the behavior of a pinned half-sine arch under static concentrated moments with a constraint plane. Equilibrium positions and the associated stability of the arch under different conditions are investigated thoroughly. First, we prove that the arch can only contact the constraint plane at discrete points. The constraint conditions at the contact points are then derived. The method of mode expansion is used to solve the governing equations together with the constraint equations for the equilibrium positions. Then the variation of the equilibrium positions with the applied load and the system parameters are examined in detail. A modified energy method is proposed to determine the stability of the equilibrium positions. According to this method, comprehensive bifurcation analysis are conducted. Finally, experimental apparatus is set up to validate the theoretical results.