Afterthoughts of a Founding Structural Control Theorist

This paper reflects back on the author’s research in structural control, originating in the early 1970’s. Upon reflection, in the early 1970’s and even as far as into the 1990’s, it constituted near heresy to suggest that large civil engineering structures could be candidates for control. The previous techniques of the 1930’s of building structures with masonry and stone were then being phased out, being replaced with lighter and more cost-effective steel-framed structures. The newer designs then emerging in the late 1960’s and early 1970’s were steel-framed structures that functioned as cantilevered tubes. The characteristic designs emerging included an absence of stone or masonry especially around the steel pillars, glass or similar non-load bearing cladding. Additionally, interior walls were non-load bearing affording more spacious rooms as well as affording the occupants the ability to reposition interior walls as desired. Moreover, the newly emerging steel-framed structures with increased compliance properties were increasingly prone to wind excitations as compared to the prior generation of structures. As a consequence, a number of these newer structures exhibited increased sway and other related dynamic behaviors. My mechanical engineering servomechanisms background included groundings in observability, controllability, as well as control of spatially distributed systems. Therefore, I felt confident then that control systems theoretic methods held promise to produce favorable and cost-effective results if properly applied to problematic civil engineering structures. That confidence still remains. I also realized the critical importance of being able to design structures in advance to be controlled, as opposed to the less desirable situation of dealing with an after-the-fact retrofit of an existing problematic structure. This paper affords an opportunity for the author to provide his anecdotal recollections and afterthoughts. Because the story to be told is of personal recollections, it is presented in first person.