This paper experiments on each of two control algorithms which are adapted into a unified control algorithm, in order to decide which is better for semi-active control of civil structures using a squeeze mode smart damper. These algorithms are Lyapunov algorithm and a clipped optimal algorithm, both of which are superior in efficiency and reliability to any existing semi-active control algorithms. Such adaptation makes it easier to develop a control algorithm because it accommodates both continuous and discrete time signals at the same time, and to analyze the control characteristics in the case of broadly distributed natural frequency by securing enlarged stable regions. In order to prove its validity, we performed vibration control tests using a prototype steel plate girder bridge. Since the model is a reduced one, we also scaled EI Centro earthquake wave to the same scale as the reduced model bridge. Various performance indexes have been used to see which algorithm is most effective in control. Also, other experiments were performed to define the control characteristics which would enable us to see how all control conditions--displacement control, force control, and acceleration control--work with each control algorithm. Those experiments showed that each control algorithm works differently according to each different control condition. It is found that Lyapunov algorithm of the two is more effective for semi-active control in the unified control system. Therefore, it is necessary to design a control system according to structural conditions and circumstances.