Study of minimum requirements of confinement in concrete columns confined with WRG in moment resisting frames

Abstract

The national concrete standard SNI 2847:2013 which refers to the ACI 318M-11 has not accommodated the influences of the axial load and deformation parameters as performance requirement, where both parameters are very critical to affect the required confining steel of concrete columns. This study presents the test results of reinforced concrete columns confined with WRG which were designed according to ACI standards. The test results were analyzed using several codes such as SNI 2847:2013, ACI 318M-14, CSA A23.3-04, and NZS 3101-06 standards. Furthermore, the minimum confinement equation is proposed for the design of columns confined with WRG, then it is also compared with selected confinement provisions. The study results showed that the equation for confining reinforcement adopted in the SNI 2847:2013 or ACI 318-11 is very conservative compared to other codes when applied to low axial load levels (≤ 0.25 Agf’c), but relatively less conservative or unsafe if the axial load level is greater than 0.3. From result of evaluation show that CSA A23.3-04 provide most conservative result for confinement design. The additional confinement design equations at ACI 318M-14 has been improve confinement design of ACI Code. Compared with SNI requirements, which do not depend on the level of axial load on the column, the equations proposed here would allow reduced confining reinforcement for columns with higher axial load. Overall, the proposed equation presents the best correlation to actual drift capacity of columns, and in addition it can be used for columns reinforced with WRG-transverse reinforcement having a yield strength higher than 500 MPa. The study also provides the recommendation for further refinement of SNI 2847 in the future related to the requirement of WRG confinement in concrete columns of Special Moment Frames in highly seismic regions.