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 Portoviejo 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.
Highlights
At present, design standards prescribe few or no recommendations aimed at considering the contribution of masonry to the response of a structure
The seismic action causes the collapse of the masonry infill panels, and without that contribution to the stiffness of the extreme frames, this change drastically reduces the torsional behavior of the building; all the rotations reduce to a minimum value corresponding to a spectral acceleration of approximately 0.17 g
The need to incorporate the contribution of masonry infill panels to the strength and stiffness of the structure in design is evident, since at present, seismic codes take into account the contribution of only the seismic weight of buildings
Summary
Design standards prescribe few or no recommendations aimed at considering the contribution of masonry to the response of a structure. Recent reports, produced after the inspection of areas affected by strong earthquakes, have concluded that informally constructed reinforced concrete buildings responded with a low level of damage or did not collapse due to the contribution of the masonry [6]. 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]. 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 the collapse of buildings located on corners. This article studies the influence of masonry on the response of a model that attempts to reproduce the typology and the mechanical and geometric characteristics of the corner buildings of Portoviejo, obtaining the nonlinear response through incremental push (pushover) analysis and incremental dynamic analysis (IDA), with some records corresponding to the Ecuador earthquake of 16 April 2016
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