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SUMMARY:ELASTIC-BRITTLE FRACTION MODEL FOR CONCRETE AND MASONRY STRUCTURES
  - Prof Jan G. Rots (Delft University of Technology) and Prof Max A.N. Hen
 driks (Delft University of Technology and Norwegian University of Science 
 and Technology)
DTSTART:20140425T140000Z
DTEND:20140425T150000Z
UID:TALK52098@talks.cam.ac.uk
CONTACT:Lorna Everett
DESCRIPTION:A model is presented that splits the material cross section in
 to a number of fractions each of them having a\ndifferent elastic-perfectl
 y brittle characteristic. The idea is that the summation of all parallel f
 ractions\nprovides an approximation of the overall continuum softening cur
 ve. Softening is interpreted as a gradual\nreduction of the cross-sectiona
 l area\, which it actually is from a physical point of view. Disorder and\
 nheterogeneity are introduced by assigning the fractions i different value
 s of area Ai\, Young’s modulus Ei\nand strength fi such that the overall
  fracture energy is consumed properly. At global level\, a scaled\nsequent
 ially linear solution procedure is adopted that traces structural failure 
 via successive\nsnapping/cracking of critical fractions. Preliminary resul
 ts were presented at Euro-C 2014 [1].\n\nThe prime advantage of the model 
 compared to other smeared crack models is that all fractions can have\nthe
 ir own crack direction. Consequently\, the gradual shift in orientation fr
 om micro-damages to the\neventual position of the macro-crack emerges auto
 matically. This bypasses current difficulties of smeared crack models such
  as over-rotation of rotating smeared cracks in the vicinity of reinforcem
 ents leading to premature failure\, or over-stiff response of fixed smeare
 d cracks due to shear retention. The model is not a micro-plane model\, ne
 ither is it a fixed multi-directional crack model. The differences with th
 ese\napproaches will be discussed. For the uni-axial case\, the elastic-br
 ittle fraction model will be shown to\ndegenerate to the saw-tooth softeni
 ng approach presented earlier [2]. For general rotating multi-axial stress
 \nstates\, the model will be shown to perform significantly better. The ad
 vantages of the sequentially linear\nscheme or event-by-event method [2] a
 re preserved. Snap-backs automatically appear and bifurcations are\navoide
 d as not the increment of load\, displacement or arc-length is prescribed\
 , but rather the damage in\nsingle consecutive events drives the process.\
 n\nThe model will be verified for elementary tension-shear problems where 
 softening proceeds while the principal stress rotates. The model will be v
 erified and evaluated at structural level too. Three applications will be 
 discussed and compared with previous approaches: (a) cracking in the Delft
  Central Station masonry façade subjected to tunnelling induced settlemen
 t\, (b) brittle shear failure in a RC structure\, (c)multiple cracking\, l
 ocalization and crack spacing in a RC bending structure. For these applica
 tions\, the model was extended to include non-proportional loading. A doub
 le-load multiplier method was developed which scales the current load\, wh
 ile maintaining the existing initial load [3]. In all cases\, failure emer
 ged as a chain of mesh-objective elastic-brittle events.
LOCATION:Cambridge University Engineering Department\, LR5
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