Integrated modelling of structure-foundation systems

Abstract

A problem endemic in the development of the built environment is poor communication between structural and geotechnical specialists. Through better communication and considering the structure and foundation as an integrated system, new opportunities may arise for achieving superior performance. This thesis investigates the seismic performance of the integrated system through the development of integrated structure-foundation models using the Ruaumoko structural analysis program. A detailed representation of the structural and foundation systems was created using Ruaumoko, providing insight into the response of a range of integrated structure-foundation systems during seismic loading. In developing both shallow and deep foundation models, some modifications were made to Ruaumoko elements in order to improve the foundation model, but generally existing element configurations were used to represent foundations. Multiple structural and foundation designs were developed using a range of approaches. Use of a range of shallow foundation design methods identified the significant impact that moment loading had on foundation performance. Partial uplift of footings was identified as detrimental to footing performance as it shifted the rotational axes, increasing moment loads and reducing effective footing area. Pinned connections between the structure and shallow footings eliminated these effects at the expense of significant redistribution of actions in the structure and increased displacements. Variation of soil conditions showed that softer soil was most likely to reduce demands on the structure at the expense of foundation non-linearity. Reduced stiffness and increased radiation damping characteristics of raft foundations compared to footing foundation systems reduced the demands on three storey structures for all soil conditions. Increased structural demands were identified for the ten storey structure as a result of the reduced impact of foundation characteristics on the response of the integrated system. The level of rotational restraint at the head of pile foundations had a considerable effect on the structure and the foundation, with free-head piles developing the largest pile displacements and actions. Reduced rotational stiffness caused a substantial change in the distribution of structural actions, while increasing rotational restraint moved the characteristics closer to the response of fixed base models. Softer soil conditions greatly increased non-linearity in the foundation soil without any definitive improvement in structural performance.