Search Results (41)

The 2020 southern Puerto Rico earthquake sequence highlighted the severe seismic vulnerability of informally constructed two-story reinforced concrete (RC) houses. This study examines the failure mechanisms of these structures and assesses the effectiveness of first-floor RC shear-wall retrofitting. Nonlinear pushover and dynamic time–history analyses were performed using fiber-based distributed plasticity models for RC frames and nonlinear macro-elements for second-floor masonry infills, which introduced a significant inter-story stiffness imbalance. A bi-directional seismic input was applied using spectrally matched, near-fault pulse-like ground motions. The findings for the as-built structures showed that stiffness mismatches between stories, along with substantial strength and stiffness differences between orthogonal axes, resulted in concentrated plastic deformations and displacement-driven failures in the first story—consistent with damage observed during the 2020 earthquakes. Retrofitting the first floor with RC shear walls notably improved the performance, doubling the lateral load capacity and enhancing the overall stiffness. However, the retrofitted structures still exhibited a concentration of inelastic action—albeit with lower demands—shifted to the second floor, indicating potential for further optimization. Full article

For the past few decades, during each disastrous earthquake, severe damage and poor seismic performance of masonry infilled RC frames, including many newly designed ones, have been reported extensively. Inherent problems related to analysis and design methods for tight-fit infilled frame structures have not yet been solved and are recognized as being far from satisfactory in terms of completeness and reliability. The primary objective of this research was to propose and test an innovative method that can effectively mitigate undesirable interaction damage to masonry infilled RC frame structures. This proposed technical solution consists of connection of the infill panel to the bounding columns with steel reinforcement connections deployed in mortar layers and anchored to the columns. This is practical, cheap and easy to implement without any specific technology, which is especially important for developing countries. A three story, two bay RC building model with the proposed connection implemented on the infill walls was designed and tested on the shake table at IZIIS in Skopje, N. Macedonia. The test results and design guidelines/recommendations from the proposed research are also expected to benefit the infrastructural development in other countries threatened by earthquakes, preferably in the Balkan and the Mediterranean region. Full article

Given the significant damage caused by earthquakes over the years, accurate prediction and assessment of the extent of structural damage is critical to ensure safety and guide post-disaster recovery efforts. This study examines the effectiveness and reliability of various damage indexes for reinforced concrete buildings, particularly in the context of seismic events. It highlights the potential of these indexes for future use in digital twin applications or for direct analysis of sensor data recorded during an earthquake, with the ultimate goal of improving real-time damage assessment and decision making. A comprehensive literature review was carried out looking at the damage indexes developed over the last decades. These indexes were applied to a case study involving an RC building with three different structural configurations: a pre-code moment-resisting frame, a code-compliant moment-resisting frame, and a code-compliant shear wall system, both bare and infilled with masonry. The seismic performance of these configurations was evaluated using Multi-Stripe Analyses (MSA) to account for the variability of the seismic input. The results of applying the damage indexes highlight the versatility of these indexes in detecting damage, although some limitations were noted, particularly with cycle-related indicators and their application to infilled structures. The study emphasizes the importance of refining these tools to improve their accuracy and reliability in different structural contexts, ultimately contributing to more accurate seismic damage assessment and damage prediction for specific seismic scenarios. Full article

The substantial influences of masonry infills used as partition walls on the seismic behavior of multistory reinforced concrete (RC) structures have long been recognized. Thereupon, in this study, considering open-ground floors due to a lack of infills (pilotis configuration), the structural pounding phenomenon between adjoining RC buildings with unequal story levels and unequal total heights is investigated. Emphasis is placed on the impact of the external columns of the higher structure, which suffer from the slabs of adjoining shorter buildings. The developing maximum shear forces of the columns due to the impact are discussed and compared with the available shear strength. Furthermore, it is stressed that the structures are partially in contact, as is the case in most real adjacent structures; therefore, the torsional vibrations brought about due to the pounding phenomenon are examined by performing 3D nonlinear dynamic analyses (asymmetric pounding). In this study, an eight-story RC frame structure that is considered to be fully infilled or has an open-ground floor interacts with shorter buildings with n_s stories, where n_s = 6, 3, and 1. Two natural seismic excitations are used, with each one applied twice—once in the positive direction and once in the negative direction—to investigate the influence of seismic directionality on the asymmetric pounding effect. Finally, from the results of this study, it is concluded that the open-ground story significantly increases the shear capacity demands of the columns that suffer the impact and the inelastic rotation demands of the structure, whereas these demands further increase as the stories of the adjoining shorter building increase. Full article

The present study illustrates the main results of an extensive campaign of numerical simulations aimed at quantifying the seismic reliability of reinforced concrete (RC) bare and masonry-infilled frames compliant with the current Italian Building Code. For this purpose, a set of different residential-use archetype structures are considered, and a prototype seismic design-assessment tool is created to quantify their performance with respect to the relevant limit states, deriving fragility curves via the execution of several non-linear time-history analyses (NLTHAs). The fragilities are subsequently combined with the hazard curves derived for each of the over 8000 Italian municipalities based on the national seismic hazard model currently in force to obtain the respective seismic mean failure rates across Italy. The seismic reliability maps obtained for the investigated code-compliant designs highlight how the current Italian Building Code fails to provide uniform seismic safety across Italy, showing—on the contrary—a strong hazard-dependency. The results are finally used to calibrate regression laws able to correlate the seismic mean failure rates with an intensity measure representative of the seismic hazard. Full article

This paper studies the impact of half-height infilled walls on the failure modes of frame columns through quasi-static tests of both frame models and half-height infilled wall frame models. Based on the experimental results, a seismic analysis model of reinforced concrete (RC) frame structures is established, and parametric studies are carried out to analyze the effects of masonry materials and masonry heights on the seismic performance of structures. The results show that the load-bearing capacity and stiffness of the structure are improved, while the ductility of the structure is reduced because of the existence of infilled walls. As the height of infilled walls increases, there is a notable decrease in the free height of frame columns. At a wall-to-column height ratio of 0.2, the masonry walls exert a negligible effect on the frame structure’s seismic performance. In contrast, at a ratio of 0.6, there is a transition in column failure modes from bending to shearing. When evaluated at consistent masonry heights, aerated concrete block-infilled walls demonstrate the least impact on the seismic performance of RC frame structures. Thus, in the absence of additional structural enhancements, the use of aerated concrete blocks is recommended to mitigate the negative implications of infilled walls on the seismic integrity of RC frames. Full article

Reinforced Concrete (RC) buildings often rely on masonry walls to increase their rigidity and strength, distinguishing them from bare frames. Consequently, the lateral capacity of the RC frames is significantly impacted by the presence or absence of these walls. Numerical models are fundamental to understanding this behavior interaction, but the development of robust simplified models is still scarce. Based on this motivation, the reliability of a simplified numerical modelling approach was examined in this study and compared to several experimental tests. An optimized approach was implemented to determine the strut parameters, rather than relying on existing empirical formulae. The reliability of the initial stiffness, maximum strength, and energy dissipation was studied. From the results, the accuracy of the considered modelling strategy can be observed in different types of masonry elements (strong and weak units) with and without openings. The validated simulation approach reveals that the adopted macro-modelling procedure can accurately represent the behavior of infilled masonry frames. The maximum deviation of the prediction of the initial stiffness and maximum strength was found to be around 23% and 14%, respectively. These findings illustrate that the strut model effectively replicates real behavior with a satisfactory level of accuracy. However, using a consistent formula to define the strut can result in significant errors, particularly in strut width. Full article

Masonry has been widely used for the construction of residential buildings in Serbia and the majority of European countries. Confined masonry (CM) is a contemporary masonry technology that consists of load-bearing masonry walls enclosed in lightly reinforced horizontal and vertical reinforced concrete (RC) confining elements. CM has been widely used for the construction of low-rise and mid-rise residential buildings in Serbia and the region (Yugoslavia) since the 1960s. The design case study of a typical multi-family residential building located in Niš, Serbia (the third-largest urban center in the country), is discussed in this paper. This building was initially designed as a five-story CM structure in accordance with the 1981 Yugoslav seismic design code PTN-S, which was enforced in Serbia until 2019, when the Eurocode was adopted for official seismic design codes. Due to architectural constraints, the original design solution involving the CM system was not compliant with the code; hence, an alternative design using an RC-frame system with masonry infills was adopted. A comparison of two different design solutions provides insight into the different requirements of seismic design codes that have been used in the region. It is important to observe that seismic forces for RC structures determined in accordance with the PTN-S code are considerably lower compared to the ones determined according to EC 8-1, with the ratio ranging from 0.37 to 0.69. The seismic shear force according to Eurocode 8 is 1.46 times higher than the force that was used for seismic design according to the PTN-S code in the case of RC-frame structures. The results of an analysis of CM structures show that the seismic shear force in accordance with Eurocode 8 is almost 2.6 times higher than the force that was used for seismic design in accordance with the PTN-S code. The findings of this study are believed to be useful for understanding the difference in seismic design solutions for previous seismic design codes (which were used in the region for more than 40 years) and the present codes (Eurocodes). Full article

A refined design procedure for the seismic retrofit of warehouses or, more generally, single-storey RC frames bounded by “drift-sensitive” masonry infills and glazed curtain walls, is proposed in this paper by means of hysteretic braces. The calculation method is based on displacement-based design (DBD) procedures in which both the as-built frame and the dissipative braces are modelled through simple linear equivalent SDOF systems arranged in parallel. In this regard, with respect to the provisions of the Italian Building Code, two refinements are introduced: (1) the definition of two performance targets tailored to the protection of glazed curtain walls (among most expensive non-structural components) and to ensure an acceptable level of damage level for masonry infills; and (2) the adoption of a more accurate formulation for the estimation of the equivalent viscous damping developed both by the main frame and the dissipative braces. The refined design method is applied to a case-study building and the achievement of the performance targets is verified through NLTH analyses. Full article

The interfaces between masonry infill and reinforced concrete (MI-RC) frames are identified as the weakest regions under lateral loads. Hence, the behavior of such frames under lateral loads can be understood mainly through experimental investigations. The deformation demands induced by horizontal loads on RC frames with infill masonry walls change due to contact losses between the infill masonry and the RC frames. This can be controlled by providing proper reinforcements at the interfaces. In the present experimental investigation, three half-scaled models subjected to reversed cyclic lateral in-plane loads were tested. In detail, the specimens considered are the MI-RC frame model, an MI-RC frame with geo-fabric reinforcement at the interface and an MI-RC frame with geo-fabric reinforcement at interfaces with an open ground story. The models were subjected to reversed cyclic lateral in-plane loads, and the post-yield responses of the models with respect to stiffness degradation, drift, energy dissipation, ductility and failure mode have been discussed. Full article

Structural pounding between adjoining multistory buildings with different total heights and different story levels has been repeatedly identified as a frequent cause of severe damage during seismic excitations. This phenomenon is very intense when upper floor slabs of short buildings hit the columns of taller and more flexible structures within their deformable length. On the other hand, it is well accepted that infill masonry panels strongly affect the seismic response and overall behavior of multistory reinforced concrete (RC) frames and especially in the common case of an open first story (pilotis). Thereupon, the interaction between a multistory frame with an open first floor and shorter and stiffer adjacent buildings was studied and the influence of the open first story on pounding investigated with inelastic dynamic step-by-step analyses. The results of the pounding cases of an 8-story RC frame with a single story and 4-story buildings were examined. Three cases of short structures were considered as follows: a frame structure, a stiff structure and a very stiff non-self-vibrating one. All studied interaction cases included type A (floor-to-floor) pounding cases and type B (floor-to-column) pounding cases. This study focused on the influence of an open first story (pilotis) on the pounding phenomenon. Therefore, all examined two-building poundings were studied considering two cases: the first case involving a fully infilled 8-story frame and second case involving an infilled 8-story structure with an open first story (pilotis). Moreover, as expected due to the asymmetry of the examined two-structured pounding pairs, the directions (plus and minus) of the seismic excitation proved to be important for the evaluation of the developing capacity demands. In the present study for the first time, it is stressed that pounding cases between structures with different geometries (asymmetric) have to be examined in both directions (plus and minus) of each seismic excitation. From the results, it can be deduced that the developing shear forces on the columns that suffer a hit in the case of type B pounding exceed the shear strength of the column even if detailing for critical regions according to Eurocode 8 is applied. Further, it is inferred that pilotis configuration increases the developing pounding forces and consequently increases the capacity demands mainly in terms of the ductility of the column that suffers the hit. Full article

This paper examines how the decision to include (or exclude) masonry infill walls in the modelling of non-seismically designed RC framed structures can affect the results of the EC8-3 seismic assessment process. A frequently used macro-modelling technique for the simulation of infill panels within bounding RC members is first reviewed. A case-study application follows in which the seismic assessment of a sample structure is carried out, with and without considering the effect of its infill walls, using nonlinear static and dynamic analysis models. The obtained results are then discussed according to the applicable limit states’ performance requirements, and conclusions are drawn regarding the overall outcome. The study indicates that, when low and medium seismic input motions constitute the base demand for the assessment of older-type RC framed buildings, the protection provided to the RC members by the confined masonry infill panels should not be neglected. Moreover, it shows that the identification of the most likely collapse mechanism might also be significantly influenced by the modelling decision in question. As such, the default recommendation is to include masonry infill walls in the modelling of such structures. Full article

For measuring the structural health of buildings, high-performance vibration detection devices are used in a structural health monitoring (SHM) system, which consists of a sensor and a data logger. Those devices are seismographs or devices with high-performance sensors which are expensive. Recently, smartphones are being used as seismographs to accumulate big data of earthquake wave detection because they have accelerometers of microelectromechanical systems. Since a smartphone has the functions of a detection sensor and a data logger, a low-cost SHM system can be developed by using a low-cost smartphone. In this paper, smartphones were used to confirm the possibility of the development of a low-cost SHM system. To evaluate the vibration detection performance from small displacement and large displacement, smartphones were installed in a specimen of a large shaking table test. The specimen is a scale model of a two-story non-reinforced masonry-filled reinforce concrete (RC) frame building. The natural period and interstory drift ratio were used as the evaluation criteria. The natural period estimated by the smartphone data agreed with that found by the piezoelectric accelerometer data. For estimating the building deformation, which is related to building stability, the measurement performance for large deformation using smartphones was evaluated. The smartphones have 90% or higher accuracies for the estimation of the maximum acceleration and displacement. Full article

Despite achieving consensus and having current knowledge on the behaviour and contribution of masonry infill walls, there remain unresolved issues regarding their nonlinear behaviour as a method for strengthening existing reinforced concrete (RC) frames with effective modifications, primarily infills and the interconnection of infills and frames. The challenge for safely and economically designing frames with competent walls is to utilise the stiffening benefits while ensuring that the increased lateral forces and reduced drift capacity do not hinder performance. This study aims to investigate the potential of using masonry infill to strengthen previously slightly damaged RC frames. Experimental tests were conducted on previously slightly damaged RC frame specimens infilled with vertically hollowed-clay and solid-clay masonry units, connected to the frame elements using traditional methods (i.e., avoiding the use of modern composite materials). These strengthened infilled frame structures were subjected to constant vertical and cyclic lateral loading, which revealed improved stiffness, strength, and damping characteristics, enhancing their overall behaviour. As the main novelties, the study found that when damaged RC frames were strengthened with masonry infill walls, their performance resembled that of undamaged infilled RC frames. The strengthened infilled frame structures exhibited enhanced stiffness, strength, and hysteretic damping. The increase in stiffness was observed regardless of the type of masonry units and the strengthening technique employed. However, the improvements in strength and hysteretic damping were influenced by the specific masonry units, particularly their robustness, and the chosen reinforcement method. Full article

To assess the health condition of structures and infrastructure during their service lives, continuous vibration-based monitoring represents a viable and cost-effective solution. Model updating and digital twins are increasingly adopted for damage detection. However, significant gaps and uncertainties in damage quantification still arise. This work presents original data from output-only modal identification tests on full-scale, two-storey reinforced concrete (RC) frames subjected to pseudo-dynamic loading to simulate seismic damage. The frames are tested with two masonry infill wall configurations with three-sided and four-sided boundary conditions, and the observed seismic damage is correlated to a damage scale. Output-only modal identification tests are performed before and after testing to catch variations in modal properties due to observed damage. Experimental data are used to build a refined finite element model able to reliably simulate the static and dynamic performance of the infilled RC frames before and after damage. The model allowed for the further assessment of the variation in natural frequencies of tested specimens at different earthquake intensities, the correlation of such variations to damage levels, and identification of the contribution of structural and non-structural components to the overall frequency variation. Full article