EARTHQUAKE RESPONSE OF TALL CHIMNEYS

Abstract

his work.' covers the. °analysis of -tall reinforced concrete chimneys. subjected to dynamic loading in the . -form. of an earthquake ground ''motion This dissertation presents the elastic dynamic response of five chimneys-of-'heights. 110, 150, 180,215 and 335 metres, respectively The response is calculated - in the form of time periods of vibration -,` shear ,force ,bending moment and deflections distributed' along the height of the chimney', for:fixedrbase -a.nd flexible base conditions The results ha 'e been worked out for the beam method and the finite "element -method-- " and compared with ' the ' IS code method,. The - time periods-` have been' . calculated' by solving the equivalent eigen-value problem' ", while the mode-superposition method - is used to, work out, the dynamic response `: The SRSS technique has'been' -used to combine the modes The earthquake input has been taken in the form of the average 'acceleration response spectra -specified in the 'I.S-1893: 1984 , for working out the ..shear forces and the bending moments" along the -heights of the chimney , -wherever applicable The stiffness matrix method uses the beam model for the dynamic analysis In deriving the element stiffness matrices the translational and rotational degrees of freedom have been considered for the beam element taking into account -the;'effects of bending and shear '.4eformations-.The finite element•.axisymmetric analysis models the shell• of the chimney by six ' noded pars-linear - el'ements. For _ both cases the . height: of the element has 'been .taken as .'5 metres 'Separate analyses have been carried out considering the flexibility of the' soil and this has been _done by