Enhanced 3D strut-and-tie method for design of discontinuity regions - Validation of the method through a case study

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Examensarbete för masterexamen
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2021
Författare
Chaudhry, Nemir
Bohman, David
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For many years discontinuity regions in concrete has been calculated by using the strut-and-tie method, where the force flow in a structure is represented as a truss system. Strut-and-tie models can be set up in three dimensions, however in structural engineering practise today the models are simplified to two dimensions in the calculations. This often results in complicated and unnecessarily conservative calculations since the force flow in the structure is not two dimensional. A suggestion of an enhanced method to set up and calculate strut-and-tie models in three dimensions was proposed by Chantelot and Mathern (2010), and presents a way of designing nodal zones that can handle forces in all directions. A case study was performed in this thesis where the calculations for a bridge detail based on the conventional theory was compared with calculations based upon the enhanced method by Chantelot and Mathern (2010). The three dimensional model was constructed and calculated parametrically with the use of the software Grasshopper, a plugin to the modelling software Rhinoceros 3D. When comparing the models, it was shown that the model based upon the enhanced method gives a reduction of 8% in the concrete amount and 30% in the reinforcement amount. Furthermore the actual material reduction is larger as the surface reinforcement and formwork material was not included in the comparison. Besides using less materials, the structure is also easier to manufacture at site. The case study validates the enhanced method for usage in this type of structures. It results in more rational calculations in three dimensional situations compared to the the current standard of calculating. However, it has also been shown in this thesis that the formulation of the rules in the method put unnecessary strict limitations on the model and affects it´s flexibility. A reformulation of the rules through further research would lead to an even better performance.
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strut-and-tie, strut, tie, D-region, 3D, Rhinoceros 3D, Grasshopper,, parametric, optimisation, corbel
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