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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Fig. 2. Construction stages of the numerical model in the structural software.

In the initial step, only the foundation mats are in action, while in the subsequent step the pillars and the substructures are modeled; then, the steel beam is setup and later the slab is cast, acting as a distributed load along the beam, since it has not yet provided stiffness to the structure. After the slab starts collaborating with the underlying beam, there is also a final phase simulating the complete evolution of rheological phenomena: concrete viscosity and shrinkage. The loads acting on the structure include self-weight, structural permanent loads, as well as the effects of wind, snow, and thermal loads. Additionally, traffic loads were considered in accordance with the chosen standards (NTC 2018), the vehicle type, and traffic lanes. Braking loads were also applied. 3. Soil-structure interaction Every stage in Midas Civil was subsequently transferred to the geotechnical software Flac 3D, a general-purpose software designed to address geotechnical issues of any complexity developed by the north American software house Itasca. The development of this application became possible due to two key factors: the ability of Midas products to describe the model using a numerically formatted file and the availability of the FISH programming language in all Itasca software. Part of the code was also optimized using Python, which is directly accessible from within Flac 3D. The procedure involves initially preparing a "geotechnical context" directly within Flac 3D where vertical stresses at the end of geostatic consolidation are obtained and its displacements are reset. This seemingly trivial aspect constitutes one of the main distinguishing features of geotechnical software compared to the structural ones. It is crucial to note that the starting point for a correct calculation of soil-structure interaction is the identification of the "zero" or geostatic state. This initial phase is characterized by soil consolidation over geological ages under its own weight. The ground on which the structure rests is characterized by a non-zero stress state and an absence of deformation. The ability to provide initial actions to volume elements representing the soil or to allow the model to settle under gravity, initializing the related displacements to zero, is a characteristic feature of geotechnical analysis products, typically absent in structural analysis software.