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Masonry infills are a common solution for inner and outer partitions in RC frame structures. However, uncontrolled and heavy damage to masonry infills in recent earthquake events often caused by the interaction of masonry infills with RC frames showed the high seismic vulnerability. Severe damage to masonry infills results in high economic losses and presents a threat to human safety. The bad seismic performance of masonry infills is a strong motivation for finding solutions that can prevent or reduce the damage to masonry infills. This paper presents the principles of an innovative system for decoupling of masonry infills from the surrounding frame. The decoupling is achieved by inserting recycled rubber strips between masonry infills and RC frame. The installed decoupling system postpones the activation of masonry infills under in-plane seismic loads and provides support under out-of-plane seismic loads. Experimental results on RC frames with rigidly connected infills and RC frames with decoupled infills are presented and compared for infills with and without openings. Results of the study show the highly improved seismic performance of masonry infills with the innovative decoupling system.

Tehnologija izgradnje zidova sa AB serklažima u zidanim konstrukcijama pruža ubedljivo rešenje za izgradnju stambenih zidanih zgrada u regionima podložnim seizmičkoj opasnosti sa umerenim do visokim seizmičkim rizikom. Svrha ovog rada je da se ispita seizmička otpornost novorazvijene tehnologije modernih zidova sa AB serklažima građenih od glinenih blokova sa velikim šupljinama za termoizolaciju, koji se lepe poliuretanskim lepkom umesto malterom. Na osnovu rezultata dva eksperimentalna ciklična testa smicanja razvijen je detaljan numerički model zasnovan na metodi konačnih elemenata u softveru Abaqus. Razvijeni 3D mikro model je bio uspešan jer je bio sposoban da precizno predvidi globalni odgovor zidova u smislu krive sila-pomeranje (pushover krive), uzorka oštećenja u zidu i AB serklažima, kao i lokalnog efekta „odsecanja“ isturenog dela zida.

This article presents an investigation into seismic resistance of modern confined masonry built from hollow clay blocks with large holes for thermal insulation, which is glued by polyurethane glue instead of mortar. Based on the results of two experimental tests from cyclic shear tests a detailed micro numerical model based on the finite element method was developed in the Abaqus software. The developed model was able to accurately predict the global response of the walls in terms of a force-displacement pushover curve as well as the damage evolution and pattern in the masonry and in the tie-columns. Because the tie-columns were thinner than the masonry, special type of damage occurred at the contact between these two elements. This effect was also successfully reproduced by the model.

Masonry structures are widely used in construction of residential buildings throughout the Balkans, but especially in Slovenia, Serbia and Croatia, confined masonry (CM) is typically used because of seismic risk. The reinforced concrete (RC) tie-columns in such construction are crucial for preventing brittle response and increasing the structure's ductility and stability. Although tie-columns' effect on seismic response is known, tie-columns remain a nonengineered element for which the stresses and internal forces are neither calculated nor checked. Recently, two confined masonry walls were tested in shear compression tests. The masonry was constructed from modern hollow clay blocks with large vertical perforations and polyurethane (PU) glue. The walls were 38 cm thick, and the tie-columns were 25 by 25 cm. Tests showed that the part of the masonry, which was protruding from tie-columns sheared off. This prompted a numerical investigation into the tie-column – masonry panel interaction through the use of numeric parametric analyses. The numerical model was first validated against the experiments and then used in a parametric study of tie-columns' effect on seismic response. Several parameters are considered, such as wall aspect ratio, the vertical load on the wall, the size of tie-column cross-section and the amount of longitudinal and transversal reinforcement. The results are evaluated in terms of lateral resistance, damage propagation, strains and stresses, and displacement capacity, and clearly show that tie-columns have a large effect on response of CM walls.

Masonry infills are among the most vulnerable components of building frames, often undergoing severe damage even under minor or moderate seismic shaking. In recent years, flexible joints have emerged as a promising technique for protecting the infills from damage. To fully demonstrate the effectiveness of this technique, it is necessary to carry out full-scale tests on a structural prototype under realistic loading conditions, which can be simulated with shaking table testing. There is also a need to assess whether the joints can provide enough energy dissipation capabilities to enable a resilient-based design of infilled frames. The ERIES-FLEJOI project aims to address these gaps by investigating the performance of two promising systems based on flexible joints, one aimed at increasing the compliance of the infills, the other aimed at decoupling them from the frame. These systems, installed in two identical reinforced concrete (RC) frame prototypes, will be tested at the Dynamic Testing Laboratory of IZIIS (Skopje, N. Macedonia). This paper illustrates the two systems, the preliminary investigations, and the numerical analyses carried out to design the joint systems in order to meet the performance objectives and constraints posed by the shaking table capacity. The analyses involve two recently developed alternative modelling strategies, one based on a meso-scale description of the infill walls and the other on an equivalent discrete macro-element.

RC frames with masonry infills are a widespread construction form in seismically active regions. Under seismic loading, masonry infills are activated in in-plane direction due to the frame deformation. This leads to the complex frame-infill interaction which can cause the failure of masonry infills or whole RC frame structures. Therefore, the in-plane behaviour of in-filled RC frames was a subject of many research projects that aim to predict the seismic performance of infilled frame structures or prevent the damage in masonry infills. Among many parameters that affect seismic response of infilled frames, openings are recognized to play the most significant role as they can affect the stress fields and thus alter the failure mechanism of masonry infills. This paper presents results of the investigation of in-plane behaviour of masonry infilled RC frames with and without openings. In the study, experimental results are firstly presented, and they are afterwards used for validation of numerical model. Further, influence of different opening arrangements on in-plane response of infilled frames is studied in numerical simulations. Results of the study show that openings cause the extensive damage on masonry infills and thus lead to deterioration in in-plane behaviour of infilled RC frames. Additionally, the study reveals that even large openings affect the seismic response of infilled RC frames and that they cannot be easily neglected in design process, which makes the reliable prediction of the seismic response of infilled RC frames complicated. The study points at the urgency of development of innovative solutions that will be able to prevent the damage in masonry infills and simplify their seismic design.

Masonry structures are commonly used for building residential buildings throughout the Balkans and worldwide, in urban and rural areas and areas with seismic risk. For masonry construction in regions with seismic risk, confined masonry (CM) construction offers an appealing alternative to unreinforced masonry (URM) due to its better seismic performance. The numerical simulation of CM is often based on the Equivalent Strut Model (ESM). Such a model provides a very reasonable compromise between accuracy and efficiency and is simple enough for use in design. The purpose of this paper is to compare the results of an experimental shear compression test on a modern CM wall with different ESM models. Five ESM models proposed by various authors are compared. The numerical pushover analyses were performed in the SAP2000 software, and the reference points of the model that gave the best alignment with experimental results were estimated using regression analyses. The results show that the simple modelling of CM walls with an equivalent diagonal strut, which carries load only in compression, can accurately simulate the global seismic response and is suitable for practical applications.

Confined masonry (CM) is one of the most popular and affordable earthquake-resistant con-struction technology for masonry structures. The reinforced concrete (RC) tie-columns in such construction play a crucial role in improving seismic response. However, their interaction with the masonry warrants a review due to recent changes in masonry construction, which are typical for Southeastern Europe. The modern masonry walls built from clay units are thick to achieve thermal efficiency. The tie-columns size has also increased, but they are narrower than the masonry. A part of masonry thus protrudes from the area confined by tie columns, which can lead to stress concentrations and early onset of damage of the protruding masonry, as was observed in recent tests on such masonry. This paper numerically analyzes this problem using a detailed three-dimensional (3D) finite element (FE) model that can capture this effect. The numerical model was developed in ABAQUS, and uses Concrete Damage Plasticity (CDP) material model to model the brittle response of clay blocks. All input data for the numerical model were obtained by dedicated tests. The results are compared to tests of walls in terms of damage propagation, strength and deformation response and show that damage to the protruding masonry can be successfully modelled. The results show a good alignment with the experiments and can be used for detailed modelling of seismic response of CM masonry structures and further research.