Investigation on Seismic Performance of Reinforced Concrete Columns Concealing Drainage Pipe

An investigation is carried out to evaluate under constant axial load and concomitant monotonic and reversed cyclic loading the structural behavior of reinforced concrete columns containing a service pipe within the column core. The study comprises an experimental part involving the design, construction and testing of nine specimens, including two control specimens and seven specimens with a pipe embedded in their cores. All columns have 200×200 mm cross-section and 1500 mm length. Among the ones with pipe, two are highly confined with closely spaced stirrups. The numerical study consists of the Finite Element (FE) modeling of response of the same columns as well as sectional analysis. The commercial software ABAQUS is utilized for the FE simulations. The results show good agreement between the experimental and the companion numerical responses, both revealing that the column ultimate load carrying capacity, stiffness and ductility are reduced by the presence of service pipes. The extent of reduction depends on the level of axial load, level of confinement and the location of the pipe exit. It is observed that the length of plastic hinge, lp is highly affected by the presence of pipe, and existing well known equations for calculating the plastic hinge length underestimate the value of lp. Finally a high degree of stress concentration in the vicinity of the pipe is noticed. The latter, causes local damage in the region around the location of the pipe exit. To mitigate the negative impact of pipe embedment on column strength and ductility, some tentative design recommendations are made, including the preferred location of the pipe exit and the details of extra confinement steel that must be provided in the exit region. Keywords: compressive strength, cracks, failure, Finite Element Analysis, concrete columns