Safety factors in sheet pile wall design: considerations by using traditional methods and FEM analysis

The purpose of the work is: define and calculate a factor of collapse related to traditional method to design sheet pile walls. Furthermore, we tried to find the parameters that most influence a finite element model representative of this problem. The text is structured in this way: from chapter 1 to 5, we analyzed a series of arguments which are usefull to understanding the problem, while the considerations mainly related to the purpose of the text are reported in the chapters from 6 to 10. In the first part of the document the following arguments are shown: what is a sheet pile wall, what are the codes to be followed for the design of these structures and what they say, how can be formulated a mathematical model of the soil, some fundamentals of finite element analysis, and finally, what are the traditional methods that support the design of sheet pile walls. In the chapter 6 we performed a parametric analysis, giving an answer to the second part of the purpose of the work. Comparing the results from a laboratory test for a cantilever sheet pile wall in a sandy soil, with those provided by a finite element model of the same problem, we concluded that:in modelling a sandy soil we should pay attention to the value of cohesion that we insert in the model (some programs, like Abaqus, don’t accept a null value for this parameter), friction angle and elastic modulus of the soil, they influence significantly the behavior of the system (structure-soil), others parameters, like the dilatancy angle or the Poisson’s ratio, they don’t seem influence it. The logical path that we followed in the second part of the text is reported here. We analyzed two different structures, the first is able to support an excavation of 4 m, while the second an excavation of 7 m. Both structures are first designed by using the traditional method, then these structures are implemented in a finite element program (Abaqus), and they are pushed to collapse by decreasing the friction angle of the soil. The factor of collapse is the ratio between tangents of the initial friction angle and of the friction angle at collapse. At the end, we performed a more detailed analysis of the first structure, observing that, the value of the factor of collapse is influenced by a wide range of parameters including: the value of the coefficients assumed in the traditional method and by the relative stiffness of the structure-soil system. In the majority of cases, we found that the value of the factor of collapse is between and 1.25 and 2. With some considerations, reported in the text, we can compare the values so far found, with the value of the safety factor proposed by the code (linked to the friction angle of the soil).

Structural verification of the ESEO spacecraft: from launch loads analysis to composite panels verification

The present thesis work was performed in the frame of ESEO (European Student Earth Orbiter) project. The activities that are described in this document were carried out in the Microsatellites and Space Micro systems Lab led by Professor Paolo Tortora and in ALMASpace company facilities. The thesis deals with ESEO structural analysis, at system and unit level, and verification: after determining the design limit loads to be applied to the spacecraft as an envelope of different launchers load profiles, a finite element structural analysis was performed on the model of the satellite in order to ensure the capability to withstand the loads encountered during the launch; all the analyses were performed according to ESA standards and using the software MSC NASTRAN SIMXPERT. Amplification factors were derived and used to determine loads to be considered at unit level. In particular structural analyses were carried out on the GPS unit, the payload developed for ESEO by students of University of Bologna and results were used in the preparation of GPS payload design definition file. As for the verification phase a study on the panels and inserts to be used in the spacecraft was performed: different designs were created exploiting methods to optimize weight and mechanical behavior. The configurations have been analyzed and results compared to select the final design.