FRP Confinement of Square Masonry Columns

The problem of masonry columns subjected to structural deficiency under axial load was studied and reported in this paper. The results of an extensive experimental campaign are presented in order to show the behavior of columns built with clay or with calcareous blocks, commonly found in southern Italy, especially in historical buildings. Rectangular masonry columns were tested for a total of 33 specimens; uniaxial compression tests were conducted on columns taking into account the influence of several variables: different strengthening schemes (internal and/or external confinement), curvature radius of the corners, amount of fiber-reinforced polymer (FRP) reinforcement, cross-section aspect ratio, and material of masonry blocks. Materials characterization was preliminarily carried out including a mechanical test on plain masonry. For all cases the experimental results evidenced a significant increase in load carrying capacity and ductility after FRP strengthening, which identified the columns as ductile elements despite the brittle nature of the unconfined masonry. Differences in mechanical behavior, due to the geometry of the columns, to the nature of different materials, to different strengthening schemes, and to the amount of reinforcement, are presented and discussed in the paper. The calibration of design equations recently developed by Italian National Research Council, CNR was conducted to compare analytical prediction and experimental results. The same procedure was applied to calibrate an analytical model recently published, in which the existing coefficients are related only to clay. Here the model is applied to limestone for the first time. Thus, new important information is furnished to researchers and practitioners involved in structural assessment and strengthening of compressed elements in historical buildings.