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SUMMARY:Stability and Plasticity in Structural Frame Behaviour Analysis an
 d Design: Seeking a Conceptual Framework for the Computer Age - Prof Micha
 el Rotter
DTSTART:20090313T143000Z
DTEND:20090313T153000Z
UID:TALK16122@talks.cam.ac.uk
CONTACT:Anita Clayson
DESCRIPTION:Concepts of stability in structural analysis and design are pr
 edominantly based on the behaviour of single members\, where the behaviour
  is often relatively simple.  However\, with both the advances in computat
 ional power and the wide dissemination of very powerful software for struc
 tural modelling\, it is important that the relationship between paradigms 
 for hand calculation and the outcomes of fully nonlinear computer calculat
 ions is clarified.  The different conceptual models used in hand calculati
 on and computer calculations of a structure require different criteria of 
 failure\, and the lack of attention to system analysis in standards for st
 ructural design has hidden the mismatches and incompatibilities between as
 sumptions about system behaviour and member behaviour.   \n\nThe key advan
 ces achieved in early studies of plastic collapse\, particularly in Cambri
 dge\, that recognised system behaviour as the critical concept\, have larg
 ely been forgotten in the early part of the computer age when linear elast
 ic analyses of complex structures became easy.  It is now high time to reg
 ain the lost ground and to find ways of interpreting complex computer anal
 yses within a conceptual framework that includes system behaviour\, plasti
 city and material nonlinearity in stability assessments into a methodology
  that can be used in design calculations. \n\nThis presentation briefly re
 views the historical roots of the current paradigms for structural calcula
 tion and finds that the conceptual framework being used in current design 
 really dates back to very early simplifications.  It presents some work th
 at extends the early Cambridge studies of steel column failure to a genera
 lised model of the collapse of columns of any material within a plasticall
 y collapsing frame.  This section of the talk argues that unless the compl
 ex interactions between members before collapse in a frame are understood 
 and treated algebraically\, it is unlikely that the output from sophistica
 ted computer analyses will be understood by the analysts.\n\nThe presentat
 ion further argues that it is the system strength that really matters in s
 tructural strength evaluations\, and that this strength can be relatively 
 easily determined by using fully nonlinear computer analyses of the struct
 ure.  The strength assessment should be referred to and characterised in t
 erms of the two well defined reference strengths: the results of linear bi
 furcation and plastic collapse analyses.  Using these\, the interactions b
 etween plasticity\, stability and imperfections can be characterised using
  a few simple parameters which can be applied to characterise all structur
 al systems.  Researchers are urged to develop a database of the values of 
 these key parameters to permit a better understanding of the roles that pl
 asticity\, stability\, geometric nonlinearit
LOCATION:Department of Engineering - LR6
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