###### Abstract  
On 16 April 2016, an earthquake of Mw 7.8 shook the coast of Ecuador, causing the destruction of buildings and a significant number of casualties. Following a visit by the authors to the city of Portoviego during the debris removal and recovery stage, it was noted that several reinforced concrete buildings located on corners had collapsed in the central part of the city. These buildings were characterized by the presence of masonry at the edges of the buildings but not between the two mostly open-plan facades on the corner for practical reasons. This article reviews the effect of masonry infill panels on the seismic response of reinforced concrete structures. For this, a model that contains the geometric and mechanical characteristics typical of collapsed buildings was generated and subjected to nonlinear analysis, with both static and dynamic increments. The results show the clear influence of the masonry infill panels on the structural response through the torsional behavior that is reflected in the evolution of the floor rotations. Finally, dynamic incremental analysis is used to obtain the collapse fragility curve of the building, and a new damage measure based on floor rotations is proposed. m 1 <  
This acceptable performance contrasts with the precarious performance of other informal construction typologies that include unreinforced masonry or adobe buildings, which have presented much more severe damage or even collapse [8]. Following the Wenchuan earthquake [9], various problems associated with the damage and even collapse of confined masonry buildings were detected, including floor diaphragm failure, excessive floor deformation failure, and local failure by debonding in beams and columns as a result of cyclical loads. The authors of this work have previously highlighted the adequate behavior of buildings designed in accordance with modern codes, without achieving a notable improvement in the global ductility. Similarly, based on observations of buildings damaged during the Jaya (Indonesia) earthquake, the following types of failures in confined masonry buildings were identified: loss of anchor, failure due to in-plane shear, failure due to out-of-plane action, and differential settlement [10]. In another post-earthquake building survey campaign, this time in Sumatra, the team identified the causes of failure of confined masonry structures to be shear column failure, longitudinal reinforcement buckling, and premature masonry collapse [11]. Likewise, the earthquake that affected Ludian Province in 2014 [12] provided an opportunity for the authors to corroborate that the confined masonry buildings designed, according to current standards demonstrated adequate performance, especially those with a uniform distribution of masonry. However, the beneficial effect of masonry on the seismic response of a reinforced concrete structure can produce a detrimental effect if the contribution of its stiffness and resistance is not taken into consideration [6]. In the event that the distribution of the masonry in the structure does not follow the uniformity and symmetry criteria in both plan and elevation, it can produce an irregular structure, whose dynamic response is completely different from the dynamic response of the concrete structures analyzed alone, causing torsional effects that mainly affect the columns of the outer frames [13]. Additionally, an inadequate distribution of masonry can produce harmful effects, such as changes in the dissipated energy and the generation of local failure mechanisms, such as the effects of a short column [6]. This detrimental effect of masonry can be described by taking the Ecuador earthquake of 16 April 2016, as an example [14]. In the city of Portoviejo, several buildings collapsed, among which it was possible to identify buildings with reinforced concrete frames in which the presence of masonry presumably caused an irregularity in the plan, producing a predominant torsional seismic response, and consequently the collapse of buildings located on corners.