SIMULATION AND ANALYSIS OF SOILSTRUCTURE INTERACTION FOR TURBINE FOUNDATION UNDER DYNAMIC LOAD

Abstract

ABSTRACT In fact, the turbine-generator foundations are considered as one of the most critical structures because they have very strict limits of vibration requirements specifically at the bearing locations. Finite element simulation and the dynamic analysis of the soil-structure interaction (SSI) phenomena for turbine-generator foundation have been considered in this study. Al-Mansuriya (728MW) Power Plant Station located in Diyala province/ Iraq has been taken as case study for this purpose. The foundation and the soil have been modeled by using Abaqus v.6.13 package. This model has been used to carry out all the analysis steps with the consideration of all variables (i.e static,harmonic and seismic loading steps). Mohr-Coulomb elasto-plastic model has been implemented for soil in additional to linear-elastic model for concrete body. The type of applied loads and the influence of the interaction between the soil and the foundation systems are considered as important aspects which have been studied to check their effects on such sensitive and massive foundations. This study tries to explore SSI on the performance (maximum displacements and stresses) of the foundation and the surrounding soil medium under various loading conditions. In static analysis, it is noted that the results obtained when using the elastoplatic model for soil gives larger values of response other than when using the elastic soil model because the soil has been allowed to move in elasto-plastic VII range. In addition, the results show that SSI effect produced significant increment for the displacements reach to 25.3%. In free vibration analysis, it can be showed that the fundamental mode is the vertical bending mode, while the effect of the torsional appeared for the second and third mode, Therefore, in this case it is important to take this modes of deformation into account when design such foundations. The soil-foundation system was analyzed under the operational case (i.e. the harmonic force excitation). The influence of the approaches between the `frequency of the foundation and the frequency of the machine has been observed. When the two frequencies coming near, the response also get increase. Additionally, when comparing the results obtained from analyzing the system with and without taking SSI effect under such loads, it showed that there is significant increase of the response when accounting SSI effect by 28.2%. The system performance under the effect of seismic excitation has also been analyzed. Two different ground motions (i.e. El-Centro and Ali Al Gharbi earthquakes) have been applied in two different directions. The analysis was performed once with SSI consideration and another without taking the SSI effect. The results showed that SSI effect should be taken into account, especially in the region with strong ground motions activities. For the strong ground motion, the displacement increased by 37% and the stress increased by 25%. Finally, the soil-structure system analyzed under the effect of earthquake during the operational conditions (i.e. coupled loading: harmonic and earthquake). Pronounce increase in the maximum displacements and the stresses for the soil-foundation system for the strong ground motion reaching (38.8%) and (31%) respectively when taking soil structure interaction effect.