PSI - Issue 78

Christoph Butenweg et al. / Procedia Structural Integrity 78 (2026) 1689–1696

1690

1. Introduction Reinforced concrete (RC) frames with masonry infills are used worldwide. Although infills are typically considered as non-structural elements due to their lack of vertical load-bearing capacity, they significantly influence the structural behavior of frame structures under earthquake loading. Under seismic actions, infills in full contact with RC frames are loaded in-plane due to frame deformations and are also subjected to out-of-plane forces, either independently or in combination, depending on the seismic action. Despite decades of research on frame-infill interaction, most experimental studies focus on in-plane behaviour. Key parameters affecting in-plane response include brick type (Mehrabi et al. 1994; Mohgaddam 2004; Cavaleri et al. 2014), frame strength (Mehrabi et al. 1996; Flanagan and Bennett 1999a), aspect ratio (Mehrabi et al. 1996; Stylianidis 2012), presence of openings (Stavridis 2009; Kakaletsis and Karayannis 2008; Milijaš et al. 2023), and vertical loading on the frame (Mehrabi et al. 1994; Stylianidis 2012; Emami and Mohammadi 2016). These parameter influence both the failure mode and overall seismic performance. However, their complexity makes a general design approach difficult, leading to infills being often neglected in seismic design, which is an unsafe assumption, as they greatly affect the dynamic building characteristics. The neglection of masonry infills can have serios implications. To improve seismic resistance, the most promising approach seeks to decouple infills from frames. Gaps filled with soft materials (Tsantilis and Triantafillou 2018a) delay in-plane activation but require supplementary measures to ensure out-of-plane stability. The INODIS system (Marinković and Butenweg 2019) integrates elastomeric and plastic profiles to provide decoupling in in-plane direction and out-of-plane stability. This system performed well across all loading scenarios and was validated through cyclic connection tests, wall-level experiments, and shaking table tests on a masonry infilled structure. The paper introduces the design and fundamental concept of the advanced INODIS (Innovative Decoupling System) system. 2. System INODIS Fig. 1 depicts the latest version of the decoupling system INODIS (REGUPOL 2025). The system comprises three elastomeric strips: a central strip bonded to the RC frame, and two outer strips adhered to the masonry infill with thin-layer mortar. A distinction is made between vertical and horizontal elastomeric strips, with the vertical strips fabricated from a softer elastomeric material, and the horizontal strips constructed from a stiffer elastomeric material exhibiting higher compressive and shear stiffness. In addition, thin plastic sliding profiles are integrated at the top and bottom interfaces. Depending on the design value of the interstorey drift, the thickness and stiffness of the vertical elastomeric strips can be easily designed and modified to preserve masonry infill from in-plane damage. The proposed concept can be applied to all types of masonry and masonry infills with openings within the standard brick-up process, as no additional measures are necessary.

Fig. 1. Decoupling System INODIS (REGUPOL, 2025).

Fig. 2 shows the construction of masonry infills with the decoupling system. In the first step middle strips are glued to columns and beams of the surrounding frame. In the second step, outer strips are placed on the bottom beam and first pieces of outer strips are placed on the columns. After application of thin layer mortar to the bottom outer strips, first row of bricks is laid. Afterwards, bricklaying continues in a usual manner where outer strips are further placed on columns and thin layer mortar is applied to them. After the last row of bricks is constructed, thin layer mortar is applied to outer strips in the fourth step. Finally, outer strips are inserted and attached with mortar to the bricks of the uppermost row. The description of installation steps shows that bricking of infills with INODIS is