Moment-curvature relationships for RC chimney sections

The 3rd revision of IS: 4998 i.e. 2015 edition adopted a limit state method of design for RC chimney and gave a new model of stress-strain relationship for concrete and steel. RC chimneys are tall cantilever columns having thin-walled hollow circular sections and subjected to axial compression resulting from self-weight and bending moment resulting from lateral forces. It has been seen that there are many disparities between the stress-strain relationship of these materials adopted by IS: 4998 – 2015 and other well-established design standards. This paper compares and discusses these disparities in terms of strength, ductility factor and energy absorption with the help of plotted moment-curvature charts. For the comparison, design recommendations of IS: 4998 – 2015, CICIND 2011, ACI: 307 – 08 are used. Moment-curvature curves are plotted using the major two conditions of the section i.e. yielding of tension reinforcement and crushing of concrete in compression. It is obtained from the study that CICIND 2011 gives higher results for all parameters, namely strength, ductility factor and energy absorption.