Abstract
Steel jacketing is an efficient way to retrofit reinforced concrete columns. Previous studies focused on the performance improvement without considering the preloads on the original columns. The preloads might inevitably affect the structural performance of the retrofitted columns. Comprehensive experimental and numerical studies on the behaviour of steel-jacket retrofitted RC columns with preload effects are presented in this paper. Twenty-nine steel jacketing columns with different steel tube thicknesses, axial preloading levels and load eccentricities are tested under concentrically or eccentrically compressive loading.
The experimental results are discussed and illustrate that the effects of preloading levels on the axial compression strength of the retrofitted columns are negligible while increasing the preloads could decrease the eccentric compressive strength. A fibre element model is developed to predict the behaviour of the retrofitted columns. The material non-linear behaviour of all the components considering the steel tube and stirrup confining effects on the concrete as well as the preloading action are taken into account in the model. The model is validated by comparing its results with the experimental results. Extensive parametric studies are undertaken by using the proposed numerical model to elucidate the effects of axial and moment preloading and the effects of preloads with various other parameters on the performance of the retrofitted columns.
6. Conclusions
Experimental and numerical studies on the behaviour of steeljacket retrofitted RC columns with preload effects were performed. Twenty-nine columns retrofitted by steel jackets were tested under concentrically or eccentrically compressive loading. The experimental results manifested that the effects of axial preloading on the axial compressive strength of retrofitted columns are negligible. The observation is in consistent with the previous research finding of Takeuti et al. [12] on concrete jacketed columns. The eccentric compressive strength of the columns decreased after preloading, but the influence reduced as the thickness of steel tube increased. A fibre element model is developed to predict the behaviour of the retrofitted columns. The geometric and material non-linear behaviour of all the components, the steel tube and stirrup confining effects on the concretes and the preloading actions are taken into account in the model.
