Radical Re-examination of Stiffened Raft Footing Technology

A radical re-examination of fundamental principles of analysis and design of stiffened raft footings is presented. A major flaw is exposed in existing theory of two-dimensional linearly elastic beams supported on linearly elastic foundation material, in respect of the treatment of interactive soil/structure response to foundation movements induced by moisture changes in reactive clay soils. Correct two-dimensional linearly elastic theory is presented. Results for a typical practical example indicate that residential stiffened raft beam design solutions published in Australian Standard AS-2870, and routinely applied in Australian practice, fail to satisfy traditionally accepted performance criteria. Ultimate strength analysis is presented as an introduction to two-dimensional non-linear theory. A three-dimensional ultimate strength design model based on the conventional yield line method is presented and recommended to obviate the mandatory design and construction selection process currently practised in Australia.