Brittle failure in RC masonry infilled frames: The role of infill overstrength

Abstract

The interaction between an infill panel and a reinforced concrete (RC) column can lead to the brittle failure of the structural element. A novel combination of cutting-edge analytical modelling approaches for masonry infills and RC elements is employed to simulate five experimental tests (three infilled and two bare) characterized by brittle failure modes. The infill is modelled with a multi-strut idealisation, and the RC column is modelled using the recently developed PinchingLimitStateMaterial in OpenSees. The effects of the infill type (solid or hollow) and ductility characteristics of the RC elements on the optimal modelling parameters are investigated. The focus of this study is on the assumption of the overstrength ratio between the maximum and cracking strengths of the panel when brittle failure occurs. The preliminary assumption for this parameter is the widely accepted value of 1.3 suggested in the formulation by Panagiotakos and Fardis. This value is found to influence the shear failure simulation. To more accurately predict brittle failure, higher overstrength values of the infill are used in the numerical model to improve the matching between the numerical and experimental tests. These values are then compared with the approximate estimation of the overstrength ratio from a database of 98 experimental tests. The suggested estimation of the overstrength ratio is systematically greater than 1.3 and dependent on the infill type (i.e., 1.44 for hollow and 1.55 for solid infills). The proposed values can have a high impact on future code-compliant recommendations aimed at verifying the likelihood of the occurrence of brittle failure in columns due to their interaction with infill panels. KEYWORDS: masonry infilled reinforced concrete frame; experimental tests; equivalent strut model; shear failure; infill overstrength. * Corresponding author Numerous studies were conducted on different types of infilled frames to provide simplified analytical models to evaluate the forces transferred to the frames, depending on the failure mode of the infill (e.g., Mehrabi et al. 1996;Colangelo 2005;Cavaleri and Di Trapani 2014;Noh et al. 2017). At the onset of damage in the panel, a strut mechanism occurs due to the migration of the stresses to the diagonal zone, and stresses at the interface between the corners of the panel and the frame members increase. Experimental studies on the local interaction between frames and masonry panels showed that, in the case of poor transverse reinforcement of the columns, early shear failure can occur due to the presence of the infill Basha and Kaushik 2016;Verderame et al. 2016). Based on the experimental observations, different analytical models were derived in the literature to consider the effect of the infill panel on the response of RC frames under lateral loads. Many numerical analyses aimed at simulating the local interaction phenomena through micro-and macro-modelling approaches (e.g., Stavridis and Shing 2010;Jeon et al. 2015;Ning et al. 2017). The equivalent truss macro-model...

MID 1.1: Database for Characterization of the Lateral Behavior of Infilled Frames

“…In numerical and analytical studies, the equivalent strut formulation is a widely adopted method to assess the influence of the infill walls on the seismic response of RC buildings, both at global and local level. Referring to local interaction studies, complex modelling approaches have been recently adopted (Blasi et al 2018a;Jeon et al 2015;Redmond et al 2018), to assess the reliability of existing analytical formulation in predicting the influence of the infill walls on the failure mode of the frames. An accurate estimation of the lateral response of the infill is indeed fundamental for the local interaction assessment.…”

“…Based on the piece-wise linear curves obtained in this work, the lateral force-displacement behaviour of the infill-alone was derived according to the approach by Blasi et al (2018a). Firstly, the lateral response of the RC frame was defined, considering a bilinear hardening model, with yielding strength Vy = 4My/hc and ultimate strength Vu = 4Mu/hc, where My, Mu and hc are the yielding moment, the ultimate resisting moment and the height of the column, respectively.…”

“…Therefore, an accurate characterization of the loaddisplacement response of the structural system is required. In the case of infilled frames, the correct evaluation of the lateral response of the masonry wall is fundamental for the prediction of brittle failure modes in the frame members caused by the local interaction with the infill (Blasi et al 2018a;Jeon et al 2015).…”

“…Recent studies evidenced the main shortcomings of the most used formulations for the lateral response of infilled frames, which might fail in predicting the actual collapse mechanism of the frame (Blasi et al 2018a) or neglect the failure mode of the infill wall in defining its lateral strength (Di Trapani et al 2018). The development of data-driven approaches based on experimental results is a useful mean to identify the parameters influencing the behaviour of infilled frames and to improve analytical formulations for employment in the engineering practice.…”

Experimental and Analytical Study of Masonry Subjected to Uniaxial Cyclic Compression

“…Furthermore, within the Reinforced Concrete (RC) framed structures, masonry is used as infill walls and internal partitioning system. These infill walls are considered as non-structural elements, nonetheless they certainly contribute to the lateral load resisting mechanism through diagonal compressive strut-and-tie action to the RC frame [ 1 , 2 , 3 , 4 ]. Therefore, understanding the compressive strength characteristics of masonry is an important aspect in the assessment and design of masonry structures.…”