In the beginning of 2010, several reinforced concrete structures collapsed due to floods in Sinai and Aswan, Egypt. Scour of soil beneath foundations lead to excessive differential settlements, failure of main structural members and finally complete structural collapse. A three-dimensional nonlinear dynamic analysis of a multi-storey reinforced concrete framed structure with induced soil scour under its foundation is carried out using the Applied Element Method. The analysis of the structure is followed until its complete collapse. The numerical analysis is then used to propose a safe design against collapse. Three different alternatives proposed for preventing progressive collapse are independently investigated; floor beams, tie beams connecting footings, and diagonal bracings.

Increasing the size of the floor beams was found not to have significant effect on mitigating progressive collapse, while the use of diagonal bracings in the ground floor or rigid tie beams connecting the structure’ footings was found to efficiently prevent progressive collapse. With diagonal bracings or rigid tie beams, the excessive differential settlements of the footings can be eliminated and the gravity loads can follow a safe alternative path preventing the structural collapse. The tie beam reinforcement was found to have a significant effect on the structural behavior during such an extreme loading case. Section analysis of the tie beam suggests that its ultimate strength should be based on rupture of main reinforcement, which is more economical and appropriate for such loading case.

Hamed, S. Computer-Aided Design of Framed Reinforced Concrete Structures Subjected to Flood Scouring. Journal of American Science 2011;7(10):191-200]. (ISSN: 1545-1003).