Strengthening reinforced concrete T connections by steel straps

Abstract

The aim of this paper is to present results of testing a full scale reinforced concrete T connection by static loading. The connection is a T connection representing a beam-column connection. The beam and column had a square cross section with a 300 mm dimension. The height of the column was 2.9 m and the clear beam length was 1.4 m. The connection was initially tested to failure. Galvanised steel straps were used to strengthen the connection. Epoxy resin was used to fix the steel straps to the concrete surface. The connection was tested after the rehabilitation. Results of testing the rehabilitated connection show that the yield and ultimate loads were 65 kN and 95 kN, respectively, compared with the original test results of 75 kN and 84 kN, respectively. joint if the shear area of the connection remained constant and the increase in column longitudinal reinforcement did not result in the increase in shear strength. Scott (1992) investigated the behaviour of reinforced concrete beam-column connections due to the different detailing methods of reinforcement. This research made detailed measurements occurring inside the connection specimen by using internally strain-gauged reinforcement. This was done to obtain detailed distributions of strain along the column and beam reinforcement bars. As such, the intrinsic mechanisms of the connection behaviour could be comprehended. Scott (1992) used three detailing arrangements for the reinforcement and three beam tension steel percentages in this research. They were: bending beam tension bars down into the column, bending beam tension bars up into the column and ‘U’ bars, in which the lower legs formed the bottom beam reinforcement. The beam tension steel percentage depended on the size of the steel bar used. This comprised of 1.0% and 1.9% respectively in a 12 mm or 16 mm diameter steel bar for shallow beam specimens and 1.3% in a 16 mm diameter steel bar for deep beam specimens. Several specimens were developed and tested in a purpose built testing rig. A full column load of 50 kN or 275 kN was used in increments of 25 kN. The load was held as the beam was loaded downwards in 1kN increments till failure. Strain measurements of the steel reinforcement bars were measured together with the concrete surface strains. Scott (1992) found that specimens with 1.0% beam tension reinforcement bent down into the column or bent into the ‘U’ bar failed due to development of a plastic hinge on the beam at the face of the column when a column load of 275 kN was used. Gross yield of the reinforcement beam bars resulted in high reinforcement strains. However, when a column load of 50 kN was used on similar specimens, failure due to extensive joint cracking and strains was recorded. Other specimens failed due to extensive joint cracking and the strains were lower occasionally in the elastic range. The load transfer in the three beam details was mainly due to the development of bond stresses at the bend up to the point of cracking. Upon cracking, the loss of bond in bars bent down and the ‘U’ bars was provided for by bond development stresses over their length. This enabled a large load increment between joint cracking and failure. In contrast, the bars bent up detail failed to account for the loss of bond and resulted in a brittle failure. Scott (1992) concluded that the bars bent down and the ‘U’ bar details performed better than the bars bent up detail and recommended the use of the bars bent down detail if ductility was of main importance. 3 TESTING THE INITIAL CONNECTION In 2006, a helically reinforced T connection was tested to failure. The dimensions for the beamcolumn connection and the testing geometry are shown in Table 1 and Figure 1, respectively. Table 1. Dimensions of the structural elements. Structural Element Dimension (mm)