Feasibility of Using Simple Adaptive Control Strategy for Dynamic Bridge Response Under Stiffness Variation. Rachel W. Soares, Luciana R. Barroso, Omar A. S. Al-Fahdawi.   Zachry Department of Civil Engineering-Texas A&M University 3136 TAMU, 199 Spence Street, College Station, TX, 77843-3136, USA. E-mail: rachelwysard@tamu.edu Abstract Simple Adaptive Control Strategy effectiveness in reducing the response of a three-span continuous bridge subjected to a 25% reduction in stiffness in both piers is studied. The performance of this control scheme combined to MR dampers is compared to the LQR strategy combined with hydraulic actuators, and to linear dampers, before and after the bridge is subjected to two different suites of earthquakes. 1. Introduction Control strategies and devices are used to reduce structural dynamic response, and enhance their dynamic performance. Bridges, however, can have different parameters than those considered during design, which can affect the controller performance. Adaptive control strategies can circumvent this issue, since they have the ability to consider existing parameters when they determine control forces. 2. Simple Adaptive Control Strategy (SACS) SACS is a direct adaptive control based on the concepts of the Model Reference Adaptive Control. The method is appealing to be applied in large scale structures because it is of simple implementation, and is successful in tracking the behavior of a model reference. It allows model states to be of lower order that the plant, that is, it is not necessary to track all plant states and explicitly identifying plant parameters. 3. Preliminary Results and Conclusion The bridge controlled by SACS presents a similar response before and after the reduction in stiffness in introduced, and for both scenarios it is successful in reducing the response. It has a better performance than the active control and the passive for both scenarios and suites of earthquakes, and it is maintained when the stiffness reduction is applied. Acknowledgement This work was partially supported by CNPq and HCED. Fig. 1 Bridge controlled response with SACS Fig. 2 SACS Block Diagram Fig. 3 Controlled response- ideal structure Fig. 4 Controlled response- reduced stiffness Fig. 5 Bridge geometry (m) Fig. 6 Earthquake NF01 Fig. 7 Earthquake LS01A Proceedings of the 2018 ASEE Gulf-Southwest Section Annual Conference The University of Texas at Austin April 4-6, 2018