Enhanced 3D strut-and-tie method for design of discontinuity regions - Validation of the method through a case study
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Chaudhry, Nemir
Bohman, David
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
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.
Beskrivning
Ämne/nyckelord
strut-and-tie, strut, tie, D-region, 3D, Rhinoceros 3D, Grasshopper, , parametric, optimisation, corbel