Verification of Design Bearing Capacity of Existing Reinforced Concrete Columns

Abstract

Most of the case studies reported in the literature on rebound hammer testing focus on the assessment of the compressive strength of concrete. The objective of this paper is to extend the use of rebound hammer data to assess the overall bearing capacity of existing reinforced concrete columns subject to combined compression and bending. This research concentrates on typical columns of two buildings under construction, with site-mixed concrete used for one building and ready-mixed concrete used for the other. Concrete specimens were taken from the construction sites for rebound hammer test and compression test whereby a correlation between the rebound index and concrete strength was developed. On-site rebound hammer tests were then performed on the columns to estimate the in-place concrete strength using the correlation established previously. In addition, the actual strength of reinforcement was determined via tensile testing of reinforcement specimens. Compared with the site-mixed concrete, the ready-mixed concrete exhibited an 18% lower coefficient of variation in strength. The in-place concrete strength was 24-31% greater than the standardized concrete strength. The moment-axial load interaction diagrams of the columns were calculated based on the determined strengths of concrete and steel reinforcement. It was found that the actual bearing capacity in combined compression and bending of the existing columns was 34-47% greater than the design bearing capacity. The proposed non-invasive procedure successfully verified the design strength of the surveyed columns. However, using only one non-destructive test method to estimate the concrete strength may somewhat limit the accuracy of the prediction.