Limit equilibrium analysis of masonry buttresses and towers under lateral and gravity loads

This paper revisits the fracturing of masonry buttresses and towers when subjected either to a concentrated oblique force at their head or to lateral inertial loading due to ground shaking and presents the corresponding failure criteria in elongation and shear. The loading configurations examined result either from the thrust that an elevated arch exerts on its supporting buttresses or from earthquake shaking on solitary masonry towers. At their limit state, tall, slender masonry buttresses and towers collapse by pivoting about their base corner, whereas less slender masonry structures may collapse by developing a shear failure. Because of the unilateral behavior of masonry, at the initiation of collapse of a slender buttress, the compression-free region separates from the rest of the buttress and reduces the stabilizing moment. As the ratio, base/height or the gravity load, increases, masonry buttresses and towers may fail in shear; therefore, the paper presents envelopes of their limit lateral capacity depending on the aspect ratio, the mechanical properties of masonry and the level of vertical loading. The equivalent static analysis adopted in this paper concludes that in most cases under lateral inertial loading, elongation failure is the lower failure mechanism of a tall masonry tower; nevertheless, a subsequent initiation of rocking that engages the large rotational inertia of the detached portion of the tower attracts additional inertia forces that may induce a follower shear failure.