Behaviour of Ferrocement Encased RC Columns Under Concentric Loading

Abstract

Reinforced concrete structures show excellent performance in terms of structural behavior and durability except for those zones that are exposed to severe environmental influences and high mechanical loading. Reinforced concrete is a commonly used construction material. RCC as a construction material has come into use for the last one century. In India RCC has been used extensively in the last 50 to 60 years. As with time the codes are upgraded for different reasons, the structures which were constructed on the bases of old codes may have some deficiencies according to the new codes. Change in use or higher loads and performance demands require modifications and strengthening of structural elements. Replacement of damaged structural elements is difficult and cost intensive task and replacement of a particular structural element may lead to the integrity of the connecting members. Retrofitting of a damaged structural element is one of the best solutions instead of replacing it. Retrofitting may be carried out on a global basis by adding extra load resisting elements or it can be done on a local basis by retrofitting the existing structural elements. From all global and local retrofitting techniques, jacketing construction is most preferred method of retrofitting. There are various composite materials available for jacketing of structural elements. Among all of them jacketing with ferrocement confinement is the oldest, efficient and economical technique of retrofitting or re-strengthening of deteriorated and weak columns. Ferrocement is a form of thin wall reinforced concrete using wire mesh and high strength mortar. Small diameter of wires used as reinforcement, leads to a higher specific surface, providing homogeneity to the ferrocement. Closely spaced wires provide more ductility and energy absorption capacity. Column is a most important member in a framed structure and failure of this member may lead to the collapse of whole structure. The present study focused on the improvement in ferrocement jacketing technique in case of square columns and effect of different percentage of ferrocement jackets in case of circular columns. In case of square columns two different approaches are taken into account; i.e. (a) strengthen all the corners (b) reducing stress concentration at the corners. The stress concentration at the corners is reduced by making the corners rounded. Further these two iv approaches are used in two types of ferrocement jacketing; i.e. (i) three layer ferrocement jacketing and (ii) single layer ferrocement jacketing and two extra layer of wire mesh at all corners. In case of circular column different percentage of wire mesh is used for ferrocement jacketing. Circular columns are confined with single, double and three layers of GI wire mesh. In this study total 27 samples were casted out of them 15 were square and 12 were circular. The columns were confined using ferrocement after 7 days of curing and left for curing for further 28 days. After the completion of curing period all the specimens were tested under concentric compressive loading. From the results, it is observed that the load carrying capacity of square columns with rounded corners can be increased by 82.29% on confining the samples with three layer of ferrocement jacket. Similarly the load carrying capacity of square columns (sharp edges) confined with three layer of GI wire mesh, square column (sharp edges) confined with single layer of GI wire mesh and two extra layers of GI wire mesh at corners, square column (rounded corners) confined with single layer of GI wire mesh and two extra layers of GI wire mesh at corners, also increased by 68.01%, 53.13%, and 58.20% respectively. In case of circular samples the load carrying capacity of columns confined with one layer, two layers and three layers of GI wire mesh can be increased to 46.50%, 73.66%, and 132.51% respectively. The results showed that different techniques of retrofitting also enhance the ductility of column.