Non-linear analysis of reinforced concrete frames

Abstract

The work presented in this thesis constitutes an investigation into the use of computer mehods for the non·linear analysis ot reinforced concrete frames. Two computer methods are proposed, both of which use a concept of gradually reducing flexural rigidity of a section up to collapse. The change in stiffness and properties along a frame are accounted for by dividing it into smaller submembers of constant stiffness. The first method uses an incremental technique to account for the non-linearity of the material. A series of linear analyses are performed for each increment of proportional loads applied to a frame up to collapse, the stiffuesses of all submernbers are modified at every increment accord­ing to their induced curvatures. In this method, the instantaneous flexural rigidity-curvature diagram of the material is used. For the second method, the smooth non -linear moment-curvature relationship of reinforced concrete is assumed to consist of a series of straight lines. The points joining these lines are termed critical points, An iterative technique is adopted to predict load factors at which these critical points are attained for each submember up to collapse, To verify the accuracy ot these analyses, a set of twelve pin-ended reinforced concrete frames were tested subject to proportional loading upto collapse. The moment-curvature relationships of each section used in the frames are obtained from tests performed on beams of identical section. A method is also presented whereby these relationships can be found from the properties of a section and its constituent materials. The effect of axial load on these relationships is also examined. Comparison of the results shows that the non-linear behaviour of reinforced concrete frames can be predicted successfully by computer analysis