PSI - Issue 62

Adalgisa Zirpoli et al. / Procedia Structural Integrity 62 (2024) 492–498 Adalgisa Zirpoli/ Structural Integrity Procedia 00 (2019) 000 – 000

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Similarly, the presence of water, the need to simulate short-term construction effects, and the possibility of simulating long-term effects of viscosity in certain types of soils are typical features of algorithms developed for the geotechnical field. Another aspect that facilitated the interaction between the two programs is that Flac 3D is based on a "finite volume" algorithm, not a "finite element" one. One of the advantages of this approach is the freedom from ensuring node congruence in the mesh since there is neither a mesh nor nodes. The terms used are grid and grid points, where the solver algebraically resolves motion equations (it is effectively an explicit dynamic solver). Consequently, users have significant freedom in generating both the calculation model and the soil model. A Flac3D command instructs the analysis algorithm to maintain continuity between grids, even if the grid points are not coincident. Once the foundation soil was prepared, shell elements simulating the foundation mats were directly introduced into Flac 3D. They were transferred as Flac 3D liner elements with Mindlin formulation. Liners are 2D elements with interface, to which the elastic and strength properties of the supporting material, between concrete and soil, were assigned. The beam was translated as simple inertial properties because Flac 3D do not contemplate a database of structural sections, being an advanced calculation core for geotechnical problems. All types of loads were transferred: self-weight, loads on the deck (structural and non-structural permanent loads), loads distributed along the beam (traffic loads). Regarding the loads, each load combination to be transferred to Flac 3D must be considered as a basic load case. The interaction between these two environments is typically established in reference to specific combinations where it is essential to activate soil-structure interaction. For example, in this article, an SLE combination was considered, which included not only the primary vertical loads but also a specific configuration of mobile traffic loads. This choice was possible due to the Moving Load Tracer option in Midas Civil, which converts the effects of mobile loads into a static load case based on the parameter (displacement, internal action, etc.) that the user intends to maximize. Once the final configuration was placed within the geostatic context, a Mohr-Coulomb failure criterion was assigned to the soil, as it is advisable to conduct initial consolidation in a linear fashion. Analyses were run in Flac 3D for every stage and the displacements of all structural nodes in contact with the ground (the liner elements) were transferred to Midas Civil. These displacements were applied in the structural software as prescribed displacements, so that every subsequent stage in Midas Civil could take into account the soil structure interaction of the previous one.

Fig. 3. Construction stages in the geotechnical software.