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Dr Nicholas Alexander

Google Scholar Citations,

http://www.researchgate.net/profile/Nicholas_Alexander/?ev=prf_highl

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The current projects that I am working on are

  • Behaviour of nonlinear moment resisting frames under seismic excitation - how do you develop robust low order models for complex nonlinear dynamical systems that are subjected to uncertain loading histories? Are nonlinear response spectra and performance based approaches the way forwards?
  • Pre-stressed frames with opening joints that allow structures to soften but remain undamaged after earthquakes. - can we design structures with morphing geometry that remains undamaged after earthquakes?
  • Nonlinear tuned mass dampers - can we improve on a linear tuned mass damper? What advantages are gained by the nonlinearity? Are smart semi-active devices the way forwards?
  • All analysis in earthquake engineering is predicated on the accurate processing of ground motion timehistories. We use state of the art signal processing ideas such as wavelet decomposition and denoising, Wigner-ville methods, Bispectra, Volterra Kernels, adaptive total least squares etc. - can we determine robust and accurate measure of displacement timehistories from recorded accelerations? (thought to be impossible because of influence of low frequency noise)
  • Analysis of long structures that are subjected to differential seismic excitation both in acceleration and displacement; i.e. the multi-support excitation of bridges - How should be analyse these structures to take into account all the true complexity of spatial-temporal variation in ground motion?
  • Human-Structure interaction - dynamic feedback between structures and people that can produce complex and unexpected resonances - can we model human beings responses to moving structures and hence the feedback into structures?
  • Understanding the dynamics of piled structures, using a nonlinear dynamics perspective - can we model these systems to understand both short terms and long term behaviour?
  • Vulnerability of cities; structure-soil-structure interaction - do buildings near to one another interact dynamically? Does the assessment of vulnerability of such systems require a detail knowledge of such dynamic, nonlinear interactions?
 

Research keywords

  • Pre-stressed frames
  • non-linear moment resisting frames
  • mass dampers
  • signal processing
  • differential seismic excitation