NUMERICAL STUDY OF THE IN-PLANE BEHAVIOUR OF CONCRETE MASONRY INFILLS BOUNDED BY STEEL FRAMES

Abstract

A finite element study was conducted to investigate the in-plane behaviour and strength of masonry infills bounded by steel frames with the focus on the effect of several influential parameters. In this study, two finite element models were developed using commercial software ANSYS adopting the simplified micro-modelling approach. The main difference of two models resided in the modeling technique used for simulating the mortar effect. The first model adopted a user-defined linkage element for mortar effect simulation whereas this was modelled by cohesive zone interface contact pairs in the second model. Both models were validated against experimental results available in the literature. Following the validation, the models were used in a series of studies to investigate the effect of several parameters on the stiffness and strength of infilled steel frames. For the infill opening study, it was found that the presence of openings decreased the in-plane stiffness and strength of the infill, and the degree of this reduction was associated with the location of the opening. For the vertical loading study, it was found that when applied as a uniformly distributed load on the frame beam, the vertical load had an optimal load level and within this level, the vertical load was found to be beneficial to the lateral stiffness and strength of the infilled frame. When applied as point loads on columns, the vertical load was shown to reduce the lateral strength of the infilled frame. For the interfacial gap study, it was found that the top beam-infill gap was more detrimental to the stiffness and strength of infill than the side column-infill gaps. Gap(s) had less effect on infills bounded by weak frames than strong frames. In most cases, the reduction factor for the gap effect specified in the American masonry standard (MSJC 2013) produced conservative estimates for both the stiffness and strength. For the material and geometric property study, it was found that while grouting was beneficial to both the stiffness and strength of the infill, the loaded corner cells need to be grouted to achieve the maximum benefit. In terms of increasing stiffness and strength of the infills, the joint reinforcement showed a noticeable effect while the vertical reinforcement had almost negligible effect. Frame column stiffness had a greater effect on the behaviour of infilled system than the frame beam stiffness. However, the net strength of infill was less affected by either column or beam stiffness. Compared with the finite element results, the American masonry standard (MSJC 2013) generally underestimated the stiffness and strength of infills while the Canadian masonry standard (CSA S304-14) achieved a much better agreement. Simplified analytical equations to account for the effect of the size and location of window openings; the uniformly distributed vertical load; and the size and location of gaps have been proposed respectively based on the regression analysis on finite element results. The proposed methods were shown to provide good agreement with both experimental and finite element results.