Cyclic response of I-shaped bridge columns with substandard transverse reinforcement

Abstract

The cyclic response of a typical bridge column with I-shaped cross-section and substandard transverse reinforcement was investigated by means of experimental and analytical research. The amount of transverse reinforcement was sufficient to ensure adequate shear strength, but other requirements of the Eurocode 8/2 standard related to the confinement and buckling of the longitudinal bars were not fulfilled. Failure was brittle due to the buckling and rupture of the longitudinal bars, which caused a progressive reduction of strength. The results of the experiment showed that the requirements of Eurocode 8/2 (which are quite stringent) related to the minimum volumetric ratio and the maximum centre-to-centre distance of the stirrups along the column, as well as the maximum distance between the engaged longitudinal bars, are justified in the investigated case. It was demonstrated that improperly designed stirrup hooks can cause a significant reduction in the ductility capacity of the column.An attempt was made to strengthen the column using CFRP sheets. The strengthening was not straightforward. Two types of anchoring were investigated. The most efficient method of anchoring was based on the use of bolted steel plates. Due to the unfavorable dimension ratio of the column cross-section, the efficiency of the strengthening was limited.The results of the experiment were used in order to identify the most suitable numerical models. Two engineering numerical macro models were analysed: a fibre based beam with hinges model, and a Giberson’s model. In both cases agreement with the results of the experiment was fairly good, as long as the buckling of the flexural reinforcement was not pronounced, and substantial in-cycle strength degradation was consequently obtained. Some of the parameters (e.g. the ultimate deformation of the concrete in non-strengthened column) were calibrated according to the experiment, since the available models, reported in the literature, did not suit the investigated case. These parameters require further investigation.The methods included in Eurocode 8/3, which are used to estimate the properties of the strengthened column, were compared. The procedures for estimation of the ultimate deformation capacity were also compared with some methods proposed in the literature. In the investigated case the best simulation of the experiment was obtained when the Lam and Teng’s model of confined concrete was taken into account, together with a standard theoretical procedure for the estimation of the maximum chord rotation.