Strength assessment of axially loaded RC column strengthened by steel cages

Abstract

In reinforced concrete buildings the columns are the main vertical elements, which sustain and carry the entire weight. Hence they should be capable to withstand the loads transferring from the beams and slabs without any failure. Any deficiency of the column may cause total collapse of the structure and it may lead to destruction of human life and also physical damages to other structures. But due to reasons such as change in use, design, number of floors, addition of other installations or deterioration, it is often necessary to strengthen RC columns in buildings during construction or post construction. Three main methods; concrete jacketing, steel jacketing and composite jacketing are used to strengthen RC columns. Concrete jacketing is popular in Sri Lanka but it is worth to implement steel jacketing in the construction industry due to the easiness of the usage. The composite jacketing cannot be implemented due to high cost. Hence the aim of the present study is to encourage the use of steel jacketing in Sri Lanka. To have economical use of steel, angles and strips can be used to strengthened RC columns. The objective of the present study is to check whether EUROCODE 4 (2004) or BS 5400-5 (1979) can be used to evaluate the load carrying capacity in compression for RC columns strengthened with steel angles and strips. The experimental results from foreign and local researches were gathered and compared with the calculated theoretical values. The ratio between gross capacity without safety factor and experimental value is ranging 0.95 to 1.05 based on EC4 and 0.96 to 1.06 based on BS 5400 5 in the experiment II of Ester G with five strips and it is 0.84 based on EC4 and 0.85 based on BS 5400 5 in the experiment I of Ester G. with seven strips. But, for the experiment of Kumaranjan A. the ratio between gross capacity without safety factor and experimental value is ranging 0.97 to 1.03 for seven and five strips. The ratios between theoretical ultimate values of BS 5400 5 and EC4 are varying from 0.87 to 0.88 in experiment done by Ester G. and 0.84 in the experiment done by Kumaranjan A. The experimental values are higher than the theoretical ultimate values and the safety factor of 1.1 to 1.6 is for EC 4 and 1.36 to 1.85 is for BS 5400 5. It is confirmed that the safety factor of the both codes have sufficient provisions for the capacity of strengthen RC columns using steel cages. Also, when using seven strips the capacity has increased but it is not quantified using the codes calculations. It is recommended to test the real size columns with several L angles sizes with load on it while strengthening to simulate a constructed column in a building. Also, an experimental study by varying the number of strips connected to the cage would lead to identify the limits of the enhancement of strength capacity.