Abstract:
In recent years, there has been increased interest in studying the strengthening of
concrete structures using different methods. Improvement of strength and ductility is often demanded in the existing structure with deficient design. Various studies have shown that structural concrete members such as square reinforced concrete (RC) columns can experience a significant increase in the ultimate load-carrying capacity and ductility when strengthened by a concrete jacket. Despite a large number of experimental studies on the strength improvement of jacketed columns, no method exists for assessing the strength of jacketed concrete sections. With an aim to assess the axial strength of jacketed concrete column analytically, this study investigates the interface behavior of fresh concrete used for retrofitting and existing concrete with various grades of concrete.
The study included modeling of the RC columns using ABAQUS (2013) and verifying the analyzed results with experimental findings from published papers to check the reliability of the model. One set of the column has been analyzed following the same cross-section and material properties done by Bassam et al. (2019). The core column section was 100X100 mm and two jacket thicknesses of 25 and 35 mm concrete to achieve the overall cross-section of 150X150 and 170X170 mm respectively. The two groups of the column have been modeled in this study. In group-1, normal strength concrete has been used for jacketing, and in Group-2, ultra-high-strength concrete has been used as a jacket to strengthen the column. The surfaces of all column cores have been prepared for a better bond between the new and old concretes by two methods; roughening by mechanical wire brushing, scarification, and using shear studs.
Another set of the column has been modeled using cross-section and material properties of the experimental study by Billimoria et al. (2019). The core column section was 150X150 mm and that column was jacketed by 70 mm concrete achieving an overall cross-section of 290X290 mm. In this study, the same concrete strength of the core column section has been used for preparing the jacketed column section.
Another numerical work has been done to the experimental work done by Islam et al. (2017). In that case, a retrofitted column has been prepared with a cross-section of 250X250 mm from a 150X150 mm core column section. The predicted results matched closely with the experimental result for all cases.
Based on the study of various retrofitted schemes presented in the thesis an attempt has been made to devise a formula to predict the axial strength of a jacketed column. A factor α, defined as the ratio of the retrofitted minus core column strength of the jacketed column has been introduced to analytically predict the ultimate strength of a jacketed column.
