Masonry columns confined by composite materials: design formulae

The present paper is aimed at assessing analytical formulations and calibrating an accurate and reliable design formula for FRP-confined masonry columns. After a short introduction about the key issues regarding the confinement of masonry columns by means of composite wrapping, a wide experimental database is assembled in a second section of the paper. Such a database has been obtained by merging the test results presented by the authors in a companion paper with other ones available in the scientific literature. The content of the database, the nature of the specimens and the range of variation of the relevant parameters are reported in the paper. The most well-established analytical formulae for FRP-confined concrete members are summarised in the third section of the paper; their effectiveness when applied to confined masonry elements is investigated on the basis of the collected database. The very limited number of models currently available for masonry members are also reported and discussed; they generally result in inaccurate and non-conservative predictions, as they have been commonly calibrated on experimental results carried out on specific types of masonry. Finally, a general expression for a design-oriented formula is calibrated with respect to the above-mentioned experimental database. As a matter of principle, different levels of accuracy can be achieved in calibrating such an expression, depending on the number of parameters considered in its calibration: the higher the number of such parameters, the lower the expected residual error of the resulting formula. Thus, three different proposals of design formulae for FRP-confined masonry columns are reported and commented with the aim of describing their accuracy in terms of scatter, average error and distribution of the experimental-to-theoretical ratios.