Stability of steel columns with bolted strengthening under preload: An analytical model

The stability of steel columns strengthened using bolted components under a preload (the existing load during the strengthening process) is studied. An analytical model that considers the effects of the preload and bolting is proposed. The preload effect is expressed as the combined effect of equivalent initial deformation and stresses, based on which a preload-effect factor is derived. The adverse effect of bolt holes on the column stability is considered, and a bolting factor is derived based on interpolation and stress integral. A prediction formula, containing the preload-effect factor and bolting factor, for the ultimate load capacity of strengthened steel columns, is obtained. The proposed formula and the formulas in the current standards are evaluated against existing numerical and experimental results. The proposed formula is validated to be capable of providing accurate predictions, with a mean absolute percentage error of approximately 10%.