Experimental campaign on RC walls: evaluation of code changes after 2010 Chile earthquake

Abstract

Significant damage has been observed in reinforced concrete (RC) walls during large seismic events in the last decade. Particularly in 2010 Chile earthquake, damage was observed in RC walls typically concentrated in first story or basements, characterized by concrete crushing, bar buckling and global wall buckling in some cases. This was a bending-compression failure, associated to high axial load and poor confinement detailing. The buildings that showed this type of failure in Chile were characterized by being medium rise buildings, with high wall area relative to the floor plan area, constructed mainly after year 2000 and with thin walls without confinement detailing. These buildings were designed according to the Chilean seismic code NCh433, that at the moment of the earthquake was based on ACI318 but excluding the wall boundary confinement requirements. One of the main changes in the Chilean seismic code after 2010 earthquake was the inclusion of boundary confinement elements in RC walls. Thus, aimed to experimentally understand the behavior of RC walls under these new provisions, an experimental campaign is presented in this research.A total of 6 wall specimens are considered in this study, three of them with shear-dominated behavior and three of them with flexure-dominated behavior. The shear-dominated walls are subjected to lateral displacement protocol considering cyclic loading, and the flexure-dominated walls are subjected to lateral cyclic loading as well, but considering additionally constant vertical load, with axial load ratios ranging from 6 to 9%. The test matrix considers the same geometric configuration on both types of walls but varying the concrete compressive strength in the three specimens of each type.The results are analyzed in terms of yield drift, strength, deformation capacity, energy dissipation and failure mode. Results are compared with previous experimental campaigns developed on similar RC walls but with non-seismic detailing, i.e., before the changes in the seismic code. Results show that the changes in the code provision traduces in improvements in the failure mode, displacement capacity and energy dissipation in the flexure-dominated walls.