Modified moment distribution method for reinforced concrete equivalent frames

The purpose of this paper is to enhance and improve the moment distribution method used in solving reinforced concrete equivalent frame problems. In the analysis of a planar building frame which is a vertical cut from the building structure, the horizontal members are tee-sections (tee-beams) and vertical members are usually rectangular columns. When a moment is applied to the end of the tee-beam that creates compression stresses at the flange (top fibers), it can be observed that the tee-beam shows more flexural stiffness than applying the same magnitude of moment to create compression stress at the bottom fibers. In other words, its stiffness is different for applied clockwise and counterclockwise unit moments. In this study, the original moment distribution method (MDM) has been modified and the modified moment distribution method (MMDM) introduced and applied to the American Concrete Institute Equivalent Frame Method (ACI-EFM). The new technique applies different distribution factors for clockwise and counterclockwise moments at a joint and solves the problem accordingly. Several typical problems of reinforced concrete equivalent frame have been solved with the ACI-EFM, new MMDM, and also Portland Cement Association (PCA) computer software ‘Analysis and Design of Slab System’ (ADOSS). The results are found to be about 0–20% different. Considering the fact that the ACI-EFM is itself the approximate method, the results of the introduced method were observed to be close enough to use for preliminary analysis. It is also suitable for long-hand calculations.