Seismic Behavior of Rectangular Reinforced Concrete Walls Prone to Out-of-Plane Shear-Axial Failure under Bidirectional Loading

Unexpected failure modes were observed in RC walls in the 2010 Chile and 2011 New Zealand earthquakes. A peculiar failure mode, not previously reported in the structural engineering literature, was the brittle collapse of one of the structural walls of the 28-story Grand Chancellor Hotel in Christchurch, New Zealand. As one of the first steps toward the understanding of this failure mode, three rectangular RC walls were tested under bidirectional quasi-static cyclic loading. The only parameter varied among the three specimens was the structural detailing associated to various level of ductility design of the wall cross section. It was found that whereas the wall with nominal ductility section detailing ($\mu =1.25$) experienced an out-of-plane shear-axial failure, those with higher ductility section detailing ($1.25<\mu <3$ and $\mu >3$) performed reasonably well. However, a relatively abrupt axial crushing failure was observed in the ductile walls at higher drift levels that needs further investigation. The bidirectional loading, rarely adopted in experimental tests or in numerical simulation due to its inherent complexity, was found to be one of the key factors in the development of out-of-plane shear-axial failure. Moreover, it was observed that walls with $0.3A_g{f}_c^{\prime }$ axial load, which is the maximum limit of the current New Zealand standard for concrete structures, and designed according to nominal ductile detailing might be prone to out-of-plane shear-axial failure.