University of Cambridge > > Engineering Department Structures Research Seminars > ELASTIC-BRITTLE FRACTION MODEL FOR CONCRETE AND MASONRY STRUCTURES


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  • UserProf Jan G. Rots (Delft University of Technology) and Prof Max A.N. Hendriks (Delft University of Technology and Norwegian University of Science and Technology)
  • ClockFriday 25 April 2014, 15:00-16:00
  • HouseCambridge University Engineering Department, LR5.

If you have a question about this talk, please contact Lorna Everett.

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A model is presented that splits the material cross section into a number of fractions each of them having a different elastic-perfectly brittle characteristic. The idea is that the summation of all parallel fractions provides an approximation of the overall continuum softening curve. Softening is interpreted as a gradual reduction of the cross-sectional area, which it actually is from a physical point of view. Disorder and heterogeneity are introduced by assigning the fractions i different values of area Ai, Young’s modulus Ei and strength fi such that the overall fracture energy is consumed properly. At global level, a scaled sequentially linear solution procedure is adopted that traces structural failure via successive snapping/cracking of critical fractions. Preliminary results were presented at Euro-C 2014 [1].

The prime advantage of the model compared to other smeared crack models is that all fractions can have their own crack direction. Consequently, the gradual shift in orientation from micro-damages to the eventual position of the macro-crack emerges automatically. This bypasses current difficulties of smeared crack models such as over-rotation of rotating smeared cracks in the vicinity of reinforcements leading to premature failure, or over-stiff response of fixed smeared cracks due to shear retention. The model is not a micro-plane model, neither is it a fixed multi-directional crack model. The differences with these approaches will be discussed. For the uni-axial case, the elastic-brittle fraction model will be shown to degenerate to the saw-tooth softening approach presented earlier [2]. For general rotating multi-axial stress states, the model will be shown to perform significantly better. The advantages of the sequentially linear scheme or event-by-event method [2] are preserved. Snap-backs automatically appear and bifurcations are avoided as not the increment of load, displacement or arc-length is prescribed, but rather the damage in single consecutive events drives the process.

The model will be verified for elementary tension-shear problems where softening proceeds while the principal stress rotates. The model will be verified 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 settlement, (b) brittle shear failure in a RC structure, (c)multiple cracking, localization and crack spacing in a RC bending structure. For these applications, the model was extended to include non-proportional loading. A double-load multiplier method was developed which scales the current load, while maintaining the existing initial load [3]. In all cases, failure emerged as a chain of mesh-objective elastic-brittle events.

This talk is part of the Engineering Department Structures Research Seminars series.

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