Shear behavior of adobe and rammed earth walls of heritage structures

In Colombia and other South American countries, most structures in the colonial period were built with adobe and/or rammed earth masonry. During past earthquakes, some of these structures collapsed even with moderate magnitude earthquakes resulting not only in significant loss of human lives, but also in large economic, cultural and heritage losses. The assessment of the seismic vulnerability of these historic buildings requires knowledge of the in-plane and out-of-plane capacity of the shear walls that constitute the structural system of the construction. In this investigation, the in-plane shear capacity is addressed by conducting cyclic tests on six 2.50 m × 1.80 m × 0.40 m solid walls and two 7.00 m × 3.45 m × 0.60 m walls with openings built with adobes obtained from a mid-nineteenth century construction and rammed earth with properties similar to those heritage buildings of Colombia. The experimental program involves variations in the vertical load and the construction material of the specimens. The effect of windows and doors openings in the shear capacity of the specimens is also evaluated. The experimental results show that: (a) failure mechanisms of earthen walls are dominated by the presence of diagonal cracks that divide the walls into large segments that eventually will fall off leading to loss of shear capacity; (b) shear capacity is controlled by the wall axial load and aspect ratio; (c) lower bounds of local drift capacity at initial cracking and peak shear strength of the walls and piers are 0.08% and 0.80%, respectively. Finally, based on the experimental results of this investigation and others available in the literature, a simplified expression is proposed to estimate shear capacity of earthen walls considering their axial load and aspect ratio.