Strength of cracked masonry buttresses under horizontal loads

The masonry buttresses are structural elements mainly used in Gothic Cathedrals, with the static function to withstand the horizontal thrusts of arches and vaults. dynamic actions, due to wind or seismic loads, are also added to these static actions. The horizontal actions, together with the vertical gravity loads, determine a combined compressive and bending stress in the masonry element that causes the cracking of the structure. This phenomenon is worth of interest because of the need to properly individuate the weight of the element that contributes to counteract the overturning actions. The paper analyses the collapse load of masonry buttresses in the framework of the macro-block modelling, accounting for either an overturning or a sliding failure condition. The possibility to consider an associative or a non-associative flow rule is also discussed together with the implications on the assessment of the collapse load multiplier. Eventually an application to a case study related to the estimation of the collapse load of a masonry portal frame is presented.