Seismic Analysis of Partial Concrete-Filled Steel Tubular Columns (CFST)

Steel tubular columns are used in bridge piers in Iraq when necessary and when site conditions limited the work using ordinary R. C. columns. Al- Tala'a overpass in Baghdad is one of these cases. Since local buckling will occur in the lower part of such columns, it will be necessary to strengthen it through filling by concrete. Thin-walled concrete partially filled steel tubular (CFST) columns may undergo local and global buckling when subjected to seismic loading. The local buckling effects of steel tube walls have not been widely considered in existing numerical models for CFST columns. This work presents a development of a numerical dimensional model for the nonlinear inelastic analysis of thin-walled circular CFST columns under earthquake incorporating the effects of local buckling, and concrete filling level. The numerical model using SAP 2000 V.17 is used to check and calculate the local buckling location and the value of first-buckling load and failure load for five cases of concrete filling (namely 0%, 25%, 30%, 50% and 100%) of column height used in columns bridge piers of Al- Tala'a overpass under the general loading of bridges with an actual earthquake loading took place in Iraq, Ali Al-Gharbee 2014. The strength and ductility of these columns are also calculated and discussed with the deformation associated with these local buckling cases. It is concluded that filling the tubular columns of Al- Tala'a overpass to 30% of its length will remove the local buckling taking place at 200mm height and increase columns capacity by (36%). A final outcome from this work, the concrete partially filled steel tubular columns with (30-50) % filling ratios can be used effectively in bridge piers under seismic loadings instead of the completely filled columns with the same efficiency and capacity.