Abstract

A review of the international codes, including the National Building Code of Canada (NBCC), the American Association of State Highway and Transportation Officials (AASHTO) and the American Concrete Institute (ACI), indicates that these codes do not corporate the forces induced in the super-structural elements due to differential settlement of foundation elements in the design of multi-story structures. In fact the current design procedure, stipulates that foundation and superstructure are designed separately; furthermore, individual foundation elements may settle up to a total of one inch and 0.75 inch in differential settlement between the elements. It is then assumed that the adopted factor of safety for the superstructure will compensate for these additional stresses. This procedure may leads to a conservative design in some cases or serious cracks and damage. This thesis presents a two-dimensional analytical model for multi-story structures subjected to differential settlement of the foundation elements. The objective of this research is create a dialogue between the superstructure and its foundation during the design stage, to allow designer to tradeoff between the additional stresses due to the differential settlements and the factor of safety of the superstructure. The results will leads to the choice of an allowable differential settlement and appropriate factor of safety of the superstructure, which will produce the most economical design for the building, without jeopardizing its safety. In this study, 7 and 10-storey structures were analyzed using linear and non-linear techniques, (geometric and material nonlinearity). In this investigation, the computer program STAAD and ADINA were used to perform this analysis. The rigidity of the structure was represented by the relative slenderness ratio between beams and columns. Empirical formulae were developed and validated with the available analytical models to predict the stresses induced on the elements of the superstructure due to differential settlement of its foundation. These formulae will assist designers to include differential settlement as external load on its superstructure and further to perform a tradeoff between the superstructure and substructure to achieve the most economical design for the building. Detailed design examples were presented to demonstrate the proposed design procedure. The results of the present study will impact on the safety and economy of our building. It should be noted herein that the differential settlements take place at the working load level, and accordingly, they are relatively small. Thus the only difference between linear and non-linear stress-strain (moment curvature) relationship is that the second accounts for the first crack which is insignificant. It is hoped that the results and conclusions of this thesis to be incorporated in the current design codes for multi-story buildings.