Test on seismic strengthening of RC columns using wire rope and T-plate units

Abstract

There has been a growing interest in the unbonded-type strengthening technique to enhance the seismic performance of reinforced concrete (RC) columns. The present paper reports the significance and limitation of the strengthening procedure using unbonded wire rope and T-shaped steel plate units, based on flexural tests of RC columns. Five strengthened columns and one unstrengthened column were tested to failure under constant axial load and cyclic lateral loads. The main variables considered were the presence of mortar cover for strengthening steel element and the anchorage method for the T-shaped steel plate. The flexural capacity of the column specimens tested is compared with predictions obtained by using (a) an extended version of the section laminate method and (b) an equivalent stress block specified in ACI 318-05. The displacement ductility ratio of tested columns is also compared with those of conventionally tied columns and of columns strengthened with carbon fibre reinforced polymer (CFRP) sheets. Test results clearly showed that the subsequent strengthening procedure significantly improves the cyclic behaviour of the column specimens. T-shaped steel plates with a proper anchorage contribute to the transfer of applied moment as well as the enhancement of ductility of RC columns. On the other hand, when a T-shaped steel plate is not anchored fully into the column base, it is seldom able to transfer the externally applied moment, although it does significantly improve the ductility of the column. While the presence of mortar cover for strengthening steel elements is significantly effective in enhancing the initial stiffness and flexural capacity of the strengthened columns, it has an adverse effect on enhancing the ductility. The strengthened columns tested showed a much higher displacement ductility ratio than the tied columns and the columns strengthened with CFRP sheets.The flexural capacity of the tested columns can be reasonably predicted using the extended version of the section laminae method, provided that the effect of the presence of mortar cover on the slippage of the T-shaped steel plate is properly considered.

Equivalent stress block for normal-strength concrete incorporating strain gradient effect

“…18%). The cross-sections of the test specimens were those commonly adopted by other researchers (Choi et al, 2009;Han et al, 2010;Sim et al, 2009). Table 3 summarises the section properties of all the specimens.…”

Strain gradient effects on flexural strength design of normal‐strength concrete beams

“…The height of the column was 1400 mm, and the length of the beam was 1500 mm. These cross‐section dimensions of the test specimens were commonly adopted by other researchers (Sim et al , 2009; Choi et al , 2009; Kim et al , 2009; Han et al , 2010; Ho, 2010). Figure 2 shows the steel reinforcement details of the specimens.…”