PERFORMANCE COMPARISON BETWEEN MODIFIED NSM OVER EMBEDDED METHOD OF STRENGTHENING OF RC BEAMS
NSM technique forms a versatile method of retrofitting RC members subjected to flexure, particularly beams. The configuration of NSM technique is such that the embedment of reinforcement is only in the cover concrete but the strength gain is phenomenal compared to other methods. The main drawback of the NSM technique is the residual strength of deteriorated concrete between the grooves sometimes, limiting the performance of strengthened material. Hence an investigation was attempted to study the effectiveness of strengthened material by embedment of CFRP laminates inside a single large groove both bottom and on the side face regarded as modified NSM technique. Beams were casted, they were pre-loaded up to the service load to inculcate control damage to simulate practical situations. Further beams were strengthened by adopting two schemes, only at the bottom and bottom with side faces and they were tested adopting uniform procedure for all the specimens. Observations were recorded over the flexural parameters such as first crack, load response, ductility etc. It was observed in both the schemes that indicated an increase in the first crack load proportionally however, bottom and side face embedment specimens showed substantial increase in ultimate load compared to control specimens. Regarding the deflections, the values increased at cracking load level and decreased at ultimate load level further deflection ductility values were comparable. Based on the promising results, modified NSM method of strengthening i.e. embedment at bottom and side face may be adopted under situations wherein it is not possible to provide multiple grooves in the cover concrete. However, further research results are needed in this topic to enhance the performance strengthened materials to utilise their full capacity.
NSM Strengthening, Embedded NSM, RC Beam Strengthening, Retrofitting, Preloading