09-10-2014, 04:09 PM
Seismic analysis of tall chimneys has been carried out by finite element analysis. The analysis includes shear deformation and rotatory inertia in addition to bending deformations. Four degrees of freedom displacement y, slope y', flexural slope f flexural curvature have been considered for each node. Ten chimneys with height ranging from 107.5 to 336.2 m have been analysed by response spectra method. IS Code recommendations for time period, base shear, base moment and ACI Code provision for time period have been compared with the results of finite element analysis. IS an ACI Codes-distribution of shear force and bending moment with height have also been compared with distribution obtained by finite element analysis. IS Code overestimates fundamental time period by up to 13% base shear by 45 to 70% and base moments in the range of 2 to 13%. IS and ACI distribution of shear along height are satisfactory. ACI distribution of bending moment with height is better than that of IS Code. IS Code tends to be overly conservative in moment distribution near the top of a chimney.