A new energy approach to critical response of elastic-plasticstructures under impulsive or long-duration excitations: Semm Seminar

Seminar | September 11 | 12-1 p.m. | 502 Davis Hall

 Izuru Takewaki, Professor, Dept of Archi. and Architectural Eng., Kyoto University

 Civil and Environmental Engineering (CEE)

This talk is on the critical response of elastic-plastic structures under near-fault (1994 Northridge earthquake, 1995 Kobe earthquake) or long-duration (2011 Tohoku earthquake) ground motions. In the early stage of dynamic nonlinear structural response analysis (around 1960), simple hysteretic structural models, simple, often, sinusoidal earthquake ground motions and random vibration inputs were generally considered. The steady-state response was tackled by an equivalent linearization method or iterative methods. To draw the steady-state response curve and investigate resonance, two kinds of iterative proce-dures were introduced. In one, an initial guess of the steady-state response amplitude is made to construc-tion an equivalent linear model, which is refined in subsequent iterations. The other involves sweeping over a range of forced input frequencies. Both processes are quite tedious.
To overcome this difficulty, a new approach was proposed by Kojima and Takewaki (2015). They demonstrated that the elastic-plastic response under impulse input can be derived in a closed form by a sophisticated energy approach without solving directly the equations of motion. Using double, triple or multiple impulses enable us to describe directly the critical timing of impulses leading to resonance, which is not easy for the sinusoidal and other inputs without an iterative procedure. The proposed approach is an epoch-making accomplishment to open the door for simpler and deeper understanding of structural relia-bility of built environments in the elastic-plastic range.
The applications of the proposed method to soil-structure interaction problems, MDOF problems, elas-tic-plastic dynamic stability problems, and rocking response problems involving rigid blocks are presented.