Introduction to Structural Motion Control

For graduate-level courses in structural design and analysis.

In keeping with recent shifts in the structural design field, this text employs an emphasis on serviceability and motion rather than safety. Motion based structural design is an alternate design paradigm that takes as its primary objective the satisfaction of motion related design requirements such as restrictions on displacement and acceleration. This text seeks the optimal deployment of material stiffness and motion control devices to achieve these design targets as well as satisfy the constraints on strength.

Conventional structural design procedures are generally based on two requirements: safety and serviceability. Safety relates to extreme loads that have a very low probability of occurring. Serviceability pertains to medium to large loadings that may occur during, the structure's lifetime. Safety concerns are satisfied by requiring the resistance of the individual structural elements to be greater than the demand associated with the extreme loading. Once the structure is proportioned, the stiffness properties are derived and used to check the various serviceability constraints. This approach is referred to as strength-based design.

Applying a strength-based approach for preliminary design is appropriate when strength is the dominant requirement. In the past, most structural design problems have fallen into this category. However, several recent developments have limited the effectiveness of the strength-based approach. First, there is a trend toward more flexible structures, which results in more structural motion under service loads. Second, some new types of structures, such as micro-manufacturing facilities, have severe constraints on motion. Third, recent advances in materials science have resulted in significant increases in strength for traditional civil engineering materials without a corresponding increase in material stiffness. Fourth, experience with recent earthquakes has shown that the repair cost of damage due to inelastic deformation is significantly greater than anticipated, and has led to a shift toward controlling structural motion with other types of energy-dissipation mechanisms.

Motion-based structural design is an alternate design paradigm that addresses these issues. The approach takes as its primary objective the satisfaction of motion-related design requirements such as restrictions on displacements and accelerations, and seeks the optimal deployment of material stiffness and motion control devices. Structural motion control is the enabling technology for motion-based design.

This book provides a systematic treatment of the basic concepts and computational procedures for structural motion control. Examples illustrating the application of motion control to a wide spectrum of buildings are presented. Also, an extensive set of problems are included. Topics range from optimal stiffness distributions for building type structures, the role of damping in controlling motion, tuned mass dampers, base isolation systems ,quasi-static active control, and dynamic time-invariant feedback control. The targeted audiences are practicing structural engineers and graduate students.