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Generation of statically indeterminate strut-and-tie models for structural concrete by topology optimization methods
The strut-and-tie method is an efficient method for the design of discontinuity regions in concrete structures. Such regions are poorly represented by the building codes and this has led some collapses. The first step of the strut-and-tie method is to identify the discontinuity regions by applying simple rules. The second, and most crucial, step is the creation of a truss framework that represents the flow of stresses inside the structure. The principal compressive stresses are assumed to be taken by concrete struts and the principal tensile stresses must be taken by the reinforcement. Without extensive experience, the creation of the truss model is very difficult for general structures. However, in recent years researchers has suggested that the truss framework can be generated by topology optimization computer software. The result is that also inexperienced structural engineers quickly can generate the truss framework and use the strut-and-tie method to dimension complex concrete structures.
This project is a continuation of a previous MSc thesis, where the use of topology optimization methods for the generation of strut-and-tie models was evaluated for several two- and three-dimensional structures. Also, attempts were made to generate the strut-and-tie model for the massive pile cap for the new Årsta railway bridge in Stockholm. The conclusions from this work are: (i) that the software ANSYS can be used to generate three-dimensional strut-and-tie models if it is modified by a more efficient algorithm and (ii) the condition that the truss should be statically determinate prevents the method to be used for complex structures, since it is very difficult and tedious to create such a truss.
The aims of the proposed project are thus to critically evaluate the static determinacy condition for strut-and-tie models and also incorporate the modified optimization algorithm using ANSYS and MATLAB.
Good knowledge in mechanics, solid mechanics and finite elements. Experience in MATLAB programming and ANSYS is preferred.
This is a joint project between the divisions of concrete structures and theoretical and applied mechanics at KTH.
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