Professor Jerry Connor from the Civil and Environmental Engineering Department of MIT gave a lecture on "Structural Motion Control", a topic on which he has been working for the last few years. He is the author of a well known book published by WIT Press on this topic ("Introduction to Motion Based Design" by J Connor and B Klink, WIT Press, ISBN 1-85312-454-0, 1996).
Motion control is an important aspect in terms of structural requirements and comfort for the people using a building.
Active control is a way of generating forces to adjust the movements of a system such as a structure. The problem is basically an optimisation problem with a set of constraints involving maximum response measures such as displacement or acceleration by defining the optimal values for damping and stiffness (as in the case of passive control) plus an active control force.
Motion control concepts are particularly important in the case of seismic design where the control of the structural motion is an essential requirement. In this case, designs now include energy dissipation devices with either viscous or hysteretic damping. Another interesting application is control of wind induced motion for tall buildings located in regions of high wind intensity, such as ocean front sites.
The preferred way of controlling the structural response is by modifying the damping characteristics, as it is practically impossible to change mass and expansive to increase stiffness.
Jerry finished his lecture by showing some interesting applications of motion control concepts in actual buildings constructed in Japan and other locations.