Macromodeling of in- and out-of-plane behavior of unreinforced masonry infill walls

Surveys on damaged and collapsed reinforced concrete (RC) buildings following recent earthquakes indicated that poor performance is associated with the influence of unreinforced masonry (URM) infill walls. In the event of an earthquake, a typical URM infill wall is subjected to a three-dimensional acceleration field and undergoes simultaneous in-plane (IP) and out-of-plane (OoP) loading. Depending on the direction of the seismic action, the observed damage mechanisms for URM infill walls may be classified as IP and OoP performance failures or a combination of both. Since the turn of the millennium, there have been a number of distinct experimental studies in the field of infilled frames, addressing the OoP response of URM infill walls. This has led to a number of numerical macro models able to represent the OoP behavior of the URM infill wall. The main limitation of the proposed models is the difficulty in using them as practical models, since all the proposed models were implemented in software tools without a graphical user interface (GUI), such as OpenSees. In this paper, one of the recently presented models is utilized and a methodology presented for a more practical and user-friendly implementation. The model previously validated using OpenSees is recalibrated and revalidated using the computer software SAP2000, which has a powerful GUI utilizing the material models and numerical elements available in the program library. The model considers the IP and OoP response as well as their interaction. For the determination of failure patterns, respective local damage grades for primary (frame) and secondary (infill wall) elements are defined. Finally, a four-story RC frame structure with URM infill walls, which was tested in the European Laboratory for Structural Assessment considering the IP response only, is used to assess the combined failure mechanism of URM infill walls through the concept of interaction curves.