Masonry Infilled Reinforced Concrete Research Articles

Solving the Problem of Short Column Effects in Masonry Infilled RC Frames: Numerical Investigations

In this study, the common issue related to the masonry infilled reinforced concrete (RC) frames under earthquake loading has been investigated. Namely, infilled RC frames are used in construction sector all over the world since they are easy and fast to construct. However, every medium to strong earthquake showed that this system is highly vulnerable to the seismic effects. Significant damage of infill walls, but also of the load carrying frame system demonstrates that stiff mortar connection between brittle masonry and highly deformable RC frames is not adequate. Damage of infilled RC frames lead to the high amounts of losses after earthquakes. Therefore, there is need to improve this behavior. Several problems caused by the infill/frame interaction have been investigated for decades and different approaches for modelling and improvement have been proposed. However, still there is no consensus on the modelling approach for infilled frames, as well none of the proposed solutions has not been accepted in practice. The most promising solution is to decouple infills from the frames and in this way diminishes negative effects of infill/frame interaction. This paper focuses on the short column effects, where infill walls increase shear forces in the columns, thus causing their damage. The numerical investigation of the short column effects on the traditional and decoupled infill has been presented. The analysis shows that the proposed decoupling system significantly improves the behavior of infilled RC frames. Infills are not activated by the frame deflection under earthquake loading and infills are not causing increase of forces in the surrounding frame. Results confirm that decoupled infills behave much better than traditional infills where contact between frame and infill has been achieved via mortar. Much higher in-plane drifts can be reached by using the decoupling INODIS system.

Effect of masonry infill on the response of reinforced concrete frames subject to in-plane blast loading

This paper presents a numerical study investigating the effect of masonry infill on the response of reinforced concrete (RC) frames subject to in-plane blast loading. Three-dimensional single-bay single-story masonry infilled reinforced concrete (MIRC) frames were modeled, in which a simplified micro-modeling approach was adopted for the masonry infill. The surface-based cohesive model was employed between the expanded brick units by adopting the traction-separation law. A non-integral modeling approach was considered with an appropriate contact algorithm between the infill wall and bounding RC frame. The dynamic material models with explicit dependency on strain rate were incorporated in the finite element (FE) models and validated against the experimental test data. The developed FE models of bare RC and MIRC frames were subjected to surface blasts with variable scaled distances representing the far-field, near-field, and close-in blasts. The effect of masonry infill on the response of RC frames subject to in-plane blast loading was investigated using the general-purpose FE software ABAQUS without employing user-defined subroutines. The blast response was characterized using displacements, energy dissipation, strain localization and accumulation, stiffness degradation, and damage modes. Results highlight the beneficial influence of masonry infill in reducing the local deformation and altering the failure modes of RC frames subject to in-plane blasts. However, results suggest that the effects of infill on the overall structural response, including axial, flexural, and shear demands, must be considered during the design of bounding RC frames. Furthermore, parametric studies were carried out based on varying masonry bonding patterns and wall thickness, number of bays and stories, and masonry infill heights, and provided conclusive remarks.

Quantification of Equivalent Strut Modeling Uncertainty and Its Effects on the Seismic Performance of Masonry Infilled Reinforced Concrete Frames

ABSTRACT Quantifying aleatory and epistemic uncertainty in nonlinear structural response simulation is key to robust performance-based seismic assessments. This paper focuses on the modeling parameters that are used to describe the nonlinear force-deformation response of the equivalent infill struts used in models of reinforced concrete frames with infills. The variability in several parameters is characterized by developing empirical and theoretical multivariate probability distributions based on the deduced-to-predicted ratios derived using data from 113 physical experiments. The effect of the uncertainty in the infill strut modeling parameters on maximum story drift ratios and associated limit state fragility functions is investigated for a 3-story reinforced concrete frame building with infills. Multiple stripe analysis is performed using hazard-consistent ground motions. Relative to when only record-to-record variability is considered, modeling parameter uncertainty has a non-negligible effect on the dispersion of the maximum story drift ratios, and affects both the median and dispersion of the limit state fragilities.

Framework to assess the seismic performance of non-engineered masonry infilled RC frame buildings accounting for material uncertainty

Non-engineered construction accounts for more than half of the building stock in low and middle-income countries. A significant portion of these buildings is constructed using masonry infilled reinforced concrete (RC) frames with inadequate seismic detailing. This type of construction is prone to high levels of variability in the material properties, posing a significant challenge in their seismic performance evaluation. This research proposes a framework to assess the seismic performance of non-engineered constructed masonry infilled RC frame buildings, which considers the material uncertainty. A four-stage procedure based on Monte Carlo simulations is introduced, wherein engineering demand parameters and seismic performance are expressed in terms of probability distributions. The framework is demonstrated using a non-engineered housing archetype located in Sincelejo, Colombia. The results showed that the framework allows capturing the uncertainty in the materials construction variability of non-engineered houses. The results also showed that mean values of material properties may lead to significant errors in the seismic performance assessment of non-engineered constructed masonry infilled RC frames. The differences between the predicted minimum and maximum exceedance probabilities of a damage state can be greater than 80%.

In-plane/out-of-plane seismic performance of masonry infilled RC frame structure made of nano-SiO2 reinforced mortar: Experimental study

Due to the seismic vulnerability of conventional masonry infill wall Reinforced Concrete (RC) frame buildings, which caused the infill wall structure to break and collapse, resulting in serious casualties and property damage. It was necessary to fully understand the action mechanism and seismic strengthening of the infill wall structure. Considering that few researches had paid attention to the effect of mortar performance on the seismic behaviors of infill wall structure, this study was the first to use a nano-SiO2 (NS) reinforced mortar to construct masonry infill wall RC frame structure. The pure out-of-plane (OOP) and in-plane and out-of-plane (IPOOP) loading tests were conducted to validate the structure's seismic performance. The experimental results of comparison with ordinary mortar specimen were shown. Due to the mitigation of the cracking of wall in pure OOP test, the initial stiffness, load-bearing capacity and ultimate displacement of new mortar specimen were increased by 65.88%, 23.57% and 11.12%, respectively. However, both infill wall specimens exhibited the similar cracking characteristics and load-displacement response, those indicated that the improvement in mortar performance was not sufficient to change the failure mode. In the in-plane (IP) tests, the infill walls constructed with new mortar provided a better diagonal bracing mechanism, resulting in a 13.32% and 12.67% increase in the IP load-bearing and energy dissipation capacity. The less side shear cracking of infill wall caused stiffness degrades more slowly. In the IPOOP tests, at approximately the same previous IP damage level, the slower propagation of crack resulted in a slower reduction in the load-bearing capacity and an increase in the deformability during subsequent OOP loading. Therefore, the application of the new mortar improved the shear and bond strength of the members, which mitigated IP damage and improved the stability of the wall, while slowed down the OOP cracking of the wall and reduced the risk of collapse.

Numerical Modeling Technique of Damage Behavior of MaSonry-Infilled RC Frames

The damage pattern of masonry-infilled reinforced concrete (RC) frame structures in earthquake events is complicated, and understanding the detailed failure behavior of these structures and modeling it accurately has been a challenging task. In this paper, the extended finite element method (XFEM) is introduced to reproduce arbitrary cracks initiating and propagating in concrete frame and masonry units, combined with interface elements to model various behaviors of masonry-infilled RC frames. Within the finite element analysis program FEAP, a user element subroutine is adopted for the incorporation of XFEM and two types of extended finite elements with and without crack tip enrichments are built to simulate the behavior of concrete material for frame members and masonry blocks for the infill panel, respectively. In addition, a macro command is created to check the crack-propagation criterion and update crack and enrichment information. Furthermore, numerical examples are performed with existing test data, which reveal the efficiency of the implementation procedure. A comparison of the analytical and experimental results show that the proposed modeling can be used to predict the crack and failure process and the load-bearing capacity curves of the structures and reflect accurately the interaction of masonry infill and RC frames.

Effect of In-Plane Damage on Out-of-Plane Response of FRCM Strengthened Masonry Infilled RC Frames

The out-of-plane (OP) strength of masonry infills is reduced when damaged under the action of the in-plane (IP) forces. A strengthening approach using a fabric-reinforced cementitious matrix (FRCM) was proposed for improving the OP strength of damaged infill walls. A finite-element (FE) model of a reinforced concrete (RC) frame, infilled with FRCM-strengthened masonry, was developed and validated using experimental results and analytical predictions. Interaction curves representing the interplay between in-plane damage and out-of-plane response were generated for unstrengthened (ordinary) and FRCM-strengthened infill walls using FE analysis. Results of the FE analysis showed that FRCM-strengthened infills had greater OP strength in the undamaged state and suffered less strength degradation at high-damage states compared to unstrengthened infills. Anchoring of the fabric proved effective in utilizing the strength and ductility of the FRCM reinforcement. The fabric with ±45° orientation contributed more in resisting the diagonal tension under in-plane shear but was not as effective as 0°–90° orientation in resisting the OP flexural stresses corresponding to in-plane damage at 2.2% drift level. A novel definition of damage state was introduced for fragility analysis that can consider the effect of in-plane damage and out-of-plane strength using interaction curves. A four-bay, five-story masonry infilled RC frame was analyzed using the capacity spectrum method, and fragility curves were developed for unstrengthened and FRCM-strengthened infills. The effect of variation in out-of-plane demand and in-plane damage on each floor was included in the analysis. The RC frame using FRCM strengthened infills exhibited a smaller probability of exceedance of the performance limit than the unstrengthened infills. The proposed methodology helped identify critical infills that require strengthening.

Infill Variability and Modelling Uncertainty Implications on the Seismic Loss Assessment of an Existing RC Italian School Building

Past earthquake evidence has shown the high vulnerability of Italian school buildings, given by the extensive damage observed to structural and non-structural elements. Such vulnerability demonstrates the need to undertake a seismic risk assessment and reduction strategies for critical facilities and allocation of national funds for retrofit interventions to those regions where seismic risk is higher. To do so, Expected Annual Losses (EAL) are evermore considered one of the main seismic risk metrics, which can, however, be largely affected by the epistemic uncertainty that typically characterizes the material and geometrical properties of existing buildings, particularly masonry-infilled reinforced concrete (RC) ones. This paper investigates the implications of accounting for a thorough identification of sources and characterization of uncertainty in seismic loss estimates on the risk assessment of a typical Italian masonry-infilled RC school building. The variability in masonry infill properties and modeling assumptions, as well as the subsequent epistemic uncertainty, are explicitly considered in the loss estimation of the RC school building. Specifically, the impact on the expected annual loss ratio is quantified in terms of both structural and non-structural components, depending on the engineering demand parameter to which they are sensitive. The results show that, when considering the uncertainty related to the variability in masonry infills, higher loss ratios of up to 30% are obtained with respect to the available literature estimates.

Earthquake Retrofitting of “Soft-Story” RC Frame Structures with RC Infills

Multi-story, old reinforced concrete (RC) structures with a “soft-story” on the ground floor, sustain considerable damage to the soft story during earthquakes due to the presence of masonry infills in the upper stories. Aspects of such masonry infill–RC frame interaction are briefly discussed and a particular retrofitting scheme for the soft story is studied. It consists of RC infills, added within the bays of the ground floor frames and combined with RC jacketing of the surrounding frame, aiming to avert such soft-story deficiency. The impact of such a retrofit is studied through the measured response of 1/3 scaled single-story, one-bay frames subjected to cyclic seismic-type horizontal loads. It is shown that this retrofit results in a considerable beneficial increase in stiffness, strength, and plastic energy consumption. The importance of the presence of effective steel ties connecting this RC infill with the surrounding frame is also demonstrated. In order to achieve these desired beneficial effects to such vulnerable buildings, additional design objectives are established with the aim of avoiding premature failure of the RC infill panel and/or fracture of the steel ties and to protect the surrounding RC frame from undesired local damage. A numerical methodology, which is validated by using the obtained experimental results, is shown to be capable of predicting reasonably well these important response mechanisms and can therefore be utilized for design purposes.

Masonry-Infilled RC Frames Exposed to Blast Loads: A Review on Numerical Modeling and Response

The spurt in terrorist activities worldwide has drawn the attention of engineers and researchers to the vulnerability of building structures to blast loads. Response of masonry-infilled reinforced concrete (RC) frames subjected to blast loads is a widely researched area that still poses considerable complexity and challenges. Most of the works are based on finite element (FE) methodology to simulate the blast-induced behavior of the masonry-infilled RC structures considering the material constitutive and interaction aspects. Many literature studies have focused on FE codes for numerical modeling of masonry-infilled RC frames and interpretation of their response to various blast load scenarios (far-field, near, and contact blasts). The review presented herein addresses the aspects to include: Estimation of the blast load parameters, including the code provision and its simulation in the analysis module; updated knowledge on geometric and material modeling; effect of strain rate on constitutive parameters while modeling the materials; macro, micro, and simplified micro approaches to model masonry infill walls and their response under blast loading; modeling of interaction between RC frame and masonry infills and the performance of the integral and nonintegral system under blast loading. It is envisaged that such studies, in turn, would facilitate evolving the rational design methodologies for the blast-resistant design of framed structures. At the end of this paper, some parametric studies of field interest that are carried out in the literature are reported to understand the behavior of masonry-infilled RC frames against blast loads and derived some valuable conclusions. The review presented in this study provides a thematic analysis of the available literature aimed to assist the analyst in selecting a suitable tool for investigating masonry-infilled RC frames exposed to blast loads.

Seismic Retrofitting of Masonry Infilled Reinforced Concrete Frames with an Open Ground Story Using Inverted-Y Steel Bracing System

ABSTRACT This paper presents results from numerical investigation into the seismic retrofit of masonry infilled reinforced concrete (RC) frame structures with soft ground story using inverted-Y steel bracing system. The dynamic response of the retrofitted four-story RC frame with an open ground story is evaluated and compared with the response of the original frame. Comparisons are carried out with the variation of the mechanical characteristics of infills in order to investigate the way in which the soft story mechanism occurs. Results from nonlinear dynamic analyses indicate that this type of bracing can effectively eliminate the formation of a soft-story collapse mechanism.

Numerical analysis of the in-plane behaviour of decoupled masonry infilled RC frames

Damage of reinforced concrete (RC) frames with masonry infill walls has been observed after many earthquakes. Brittle behaviour of the masonry infills in combination with the ductile behaviour of the RC frames makes infill walls prone to damage during earthquakes. Interstory deformations lead to an interaction between the infill and the RC frame, which affects the structural response. The result of this interaction is significant damage to the infill wall and sometimes to the surrounding structural system too. In most design codes, infill walls are considered as non-structural elements and neglected in the design process, because taking into account the infills and considering the interaction between frame and infill in software packages can be complicated and impractical. A good way to avoid negative aspects arising from this behavior is to ensure no or low-interaction of the frame and infill wall, for instance by decoupling the infill from the frame. This paper presents the numerical study performed to investigate new connection system called INODIS (Innovative Decoupled Infill System) for decoupling infill walls from surrounding frame with the aim to postpone infill activation to high interstory drifts thus reducing infill/frame interaction and minimizing damage to both infills and frames. The experimental results are first used for calibration and validation of the numerical model, which is then employed for investigating the influence of the material parameters as well as infill’s and frame’s geometry on the in-plane behaviour of the infilled frames with the INODIS system. For all the investigated situations, simulation results show significant improvements in behaviour for decoupled infilled RC frames in comparison to the traditionally infilled frames.

Computation of Natural Frequencies of Masonry Infilled RC Frames Validated with Modal Assurance Criterion

Contribution of infill walls to in-plane structural response of reinforced concrete (RC) frame is an important aspect that many researchers have studied using experimental and numerical methods. This paper presents the modeling of 3D RC unreinforced masonry infill (MI) frames using multiple nodes to one node constraint (MTOCO) with the independent node at the center of gravity of infill with mass and inertial properties of infill. This method of modeling is then compared with other macro and micro modeling methods. A macro model with equivalent diagonal strut using 1D element and two micro models, both with 8-noded brick elements with the interface between infill and RC frame modeled using node to surface tied interface in one and small sliding contact in another. All these four models are solved using a Virtual Performance Solution (VPS) implicit FE solver. Natural frequencies of the structure from these four numerical solutions are then compared with available experimental shake table [25] results. To assess the degree of consistency between the four numerical methods, Modal Assurance Criterion (MAC) [29] is used. The Modal Assurance Criterion is a statistical indicator that is most sensitive to large differences and relatively insensitive to small differences in the mode shapes. This yields a good statistical indicator and a degree of consistency between mode shapes. From a functional point of view, the openings in the infills are a significant parameter to consider because they influence the lateral stiffness and strength. Having established its validity as explained above, this new methodology is then extended to RC frames with openings and partial fillings. A comparison of the results of both micro and macro methods shows a very good correlation.

Experimental investigation of strengthening of masonry-infilled RC frames using prefabricated engineered cementitious composite panels

Cement-based composite materials such as engineered cementitious composites (ECCs) are appropriate for retrofitting buildings because of their high tensile strength and strain. This research evaluated the lateral behavior of strengthened masonry-infilled reinforced concrete (RC) frames reinforced with prefabricated engineered cementitious composite (PECC) panels. The goals of the proposed technique were to increase the energy absorption capacity and the lateral capacity of infilled RC frames and protect the stability of the masonry infills after cracking and brittle failure in the out-of-plane direction, which can contribute to the seismic vulnerability of a structure. The mechanical characteristics of the ECC materials, such as the tensile strength and strain and multiple cracks, were first determined. Then, nine diagonal compression tests were done on masonry panels strengthened with PECC panels. In these tests, two types of connection were compared and the best one was selected. Next, an existing one-story RC moment frame with one bay was scaled down for testing under lateral cyclic loading. The results indicated that the strength, deformation, stiffness, and energy absorption of the RC frames increased considerably. Additionally, the effects of the precast panel thickness, performance of the connections, and type of damage sustained were compared between the different types of tests. Overall, the PECC panels connected to the infill wall with the proposed connections improved the lateral behavior of the system in the in-plane direction and markedly mitigated the risk of collapse by confining the masonry infill wall.

Experimental testing of decoupled masonry infills with steel anchors for out-of-plane support under combined in-plane and out-of-plane seismic loading

Because of simple construction process, high energy efficiency, significant fire resistance and excellent sound isolation, masonry infilled reinforced concrete (RC) frame structures are very popular in most of the countries in the world, as well as in seismic active areas. However, many RC frame structures with masonry infills were seriously damaged during earthquake events, as the traditional infills are generally constructed with direct contact to the RC frame which brings undesirable infill/frame interaction. This interaction leads to the activation of the equivalent diagonal strut in the infill panel, due to the RC frame deformation, and combined with seismically induced loads perpendicular to the infill panel often causes total collapses of the masonry infills and heavy damages to the RC frames. This fact was the motivation for developing different approaches for improving the behaviour of masonry infills, where infill isolation (decoupling) from the frame has been more intensively studied in the last decade. In-plane isolation of the infill wall reduces infill activation, but causes the need for additional measures to restrain out-of-plane movements. This can be provided by installing steel anchors, as proposed by some researchers. Within the framework of European research project INSYSME (Innovative Systems for Earthquake Resistant Masonry Enclosures in Reinforced Concrete Buildings) the system based on a use of elastomers for in-plane decoupling and steel anchors for out-of-plane restrain was tested. This constructive solution was tested and deeply investigated during the experimental campaign where traditional and decoupled masonry infilled RC frames with anchors were subjected to separate and combined in-plane ‬and out-of-plane loading. Based on a detailed evaluation and comparison of the test results, the performance and effectiveness of the developed system are illustrated.

Experimental in-plane seismic strengthening of masonry infilled reinforced concrete frames by engineered cementitious composites (ECC)

The present study aimed to evaluate the performance of engineered cementitious composites (ECC) retrofit technique for unreinforced hollow clay brick masonry infill wall in non-ductile reinforced concrete (RC) frames subjected to in-plane cyclic loading (quasi-static loading). To this aim, the mechanical properties of ECC and masonry elements were tested. Then, four 1/3-scale, one-story, single-bay RC frames were fabricated. Among these specimens, one frame was tested without infill wall (BF), one frame with unretrofitted infill wall (IF-E0), and specimens IF-SF-E20 and IF-DF-E20-2 were retrofitted by using an overlay ECC on the masonry infill wall on one side and both sides, respectively. The retrofitted specimens provided higher lateral load capacity, stiffness, and energy dissipation capacity up to 215%, 32%, and 102%, respectively, compared to the unretrofitted specimen. Further, the proposed strengthening technique prevented brittle premature failure in the masonry infill walls and partially maintained the integrity of unreinforced infill walls. Also, the obtained backbone curves of specimens were idealized. Based on the results, the displacement ductility factor of the retrofitted specimens decreased up to 50%, but also the force reduction factor and the overstrength factor of them increased up to 19 and 68%, respectively. At the end of the paper, a simplified analytical method is proposed to calculate the peak strength of retrofitted masonry infilled RC frames. The results obtained from this method were close to the experimental results.

Blast Vulnerability of Multi-Storey Masonry Infill Reinforced Concrete Frames

The prototype or experimental study of blast effect on structures is not always possible due to high risk of life and environmental wellbeing. However, advancement in computational science had made it possible to solve such complex and risky problems. Researchers in the past few decades have presented ample computational and numerical studies on blast effect on masonry structure using deterministic approach. The studies have neglected the effect of various uncertainties that may perhaps occur during an actual blast scenario. Therefore, in present study probabilistic Finite Element (FE) analysis was performed on three statistically stable masonry infill RC (Reinforced Concrete) frames having single (G+0), two (G+1) and three (G+2) storey levels respectively to arrive at the blast fragility curves. The probability of failure was computed based on the inelastic tension damage curves developed for the masonry. The effect of scaled distance and different storey levels on blast vulnerability of masonry infill RC frame walls are investigated through these fragility curves. The results indicate a noteworthy effect of scaled distance and storey levels on the blast resistance of the structure. Frame G+0 is found to be comparatively more vulnerable against the blast load effect than other multi-storey frames. The critical value of scaled distance (Z_critical) corresponding to PF 90% in panel P1 was found as 6.67m/kg^1/3, 4.81m/kg^1/3 and 4.66m/kg^1/3 respectively of frames G+0, G+1 and G+2; in panel P2 was found as 4.3m/kg^1/3 and 4.6m/kg^1/3 respectively of frames G+2 and G+3 and; in panel P3 was found as 4.32 m/kg^1/3 of frame G+3. It is also observed that RC frame is negligibly affected with respect to the masonry panel in terms of blast load mitigation.

Nonlinear static characterisation of masonry-infilled RC building portfolios accounting for variability of infill properties

The seismic assessment of existing masonry infilled reinforced concrete (RC) building portfolios is a highly relevant issue in Italy and other Mediterranean countries, particularly in regions where a large part of the built environment was not designed according to modern seismic codes. In the past, masonry infills were generally considered as non-structural elements and were not accounted for in the design process. However, the results of experimental tests and past earthquake evidence demonstrated the influence of masonry infills on the global and local behaviour of RC buildings. Furthermore, the acknowledgment of different construction practices points out the significant variability affecting the masonry infills in terms of material properties, thickness, presence of openings and manufacturing techniques. This paper deals with the large-scale performance analysis of existing masonry infilled RC building portfolios accounting for the uncertainty related to the variability in the mechanical properties and the modelling of masonry infills. To accomplish this goal, a fully integrated building stock, representative of masonry infilled RC buildings designed according to the Italian codes in force between 1960 and 1980, was developed, using a simulated design approach. Statistical data and results of experimental tests were used to identify the main masonry infill typologies adopted in the Italian context. Detailed numerical models, whose prediction capability was appraised through the results of cyclic quasi-static tests, were developed to estimate the lateral response of the analysed RC buildings. Different response parameters, which can be easily implemented in seismic risk assessment frameworks, were considered and quantified, at the portfolio level, to understand the uncertainty propagation and impact of the masonry infills’ variability on the expected performance of existing RC buildings. The results demonstrated that the variability related to the definition and modelling of the masonry infills induces significant dispersion, with respect to the mean, on the lateral response of different classes of buildings within a given portfolio. Moreover, the provided parameters for multi-linear idealised capacity curves can be used in simplified seismic fragility and risk models for existing buildings, including a proper estimate of the associated uncertainty, leading to a more accurate quantification of economic losses.

Natural period and vertical distribution of base shear in confined masonry buildings using ambient vibration test

In semi-urban setting where availability of land can afford construction of low-rise buildings, confined masonry may compete with other alternatives of seismic resilient system provided well-articulated design standards and construction guidelines are available. Most seismic standards do not make explicit recommendations on the natural period and vertical distribution of base shear for the design of confined masonry buildings. In such a case, one of the two alternatives, such as (1) reinforced concrete (RC) frame building with masonry infill walls and (2) RC frame building with structural walls, is tacitly extrapolated. This paper is first aimed to explore the possible recommendations from the ambient vibration testing of a class of confined masonry building stock. Nine (G + 3) confined masonry hostel buildings are considered for Ambient Vibration Testing (AVT). Recorded signatures are processed and modal characteristics (primarily restricted to the first triplet of fundamental modes) are extracted. Each building is modelled numerically and fine-tuned followed by a comparison of natural frequencies and mode shapes in numerical model and experimental results. The fine-tuned numerical models are analysed against a set of recorded ground motions. Possible design recommendations for natural period and distribution of base shear along the height are the key contributions. Empirical equation for natural periods is derived from the seismic code recommendation on that of reinforced concrete (RC) buildings but removing the bias contributed from the height shorter than one storey while using the experimental results. Distribution of the base shear along the height follows a parabolic profile with an exponent close to 0.4. Results of AVT indicate the inherent damping ratio on an average of about 5% which, however, may not be directly used for seismic excitation. The building stock used for AVT in this paper does not include considerable variations in height and different varieties of confined masonry constructions. Therefore, recommendations of this paper should be verified against a larger size of dispersed building stock.

Numerical Modelling and Validation of the Response of Masonry Infilled RC Frames Using Experimental Testing Results

Reinforced concrete (RC) frame buildings with masonry infills represent one of the most common structural typologies worldwide. Although, in the past, masonry infills were frequently considered as non-structural elements and their interaction with the structure was neglected, earthquakes occurring over the last decades have demonstrated the important role of these elements in the seismic response of all RC-infilled building typologies. In this regard, the selection of the most suitable numerical modelling approaches to reproduce the hysteretic response of the masonry infills—and their interaction with the RC frames—is still an open issue. To deal with this issue, in this study, a macro-classification based on different available databases of experimental tests on infilled RC frames, is firstly proposed to understand the variability in the infill properties and the corresponding numerical modelling uncertainties. Five masonry infill types are selected as representative for the typical existing configurations in Italy and other Mediterranean countries. Three of those masonry infill types are then selected to carry out a more detailed analysis, namely their numerical modelling validation using experimental testing results, considering and comparing the main formulations available in the literature for the definition of the hysteretic behaviour of infills. From such a comparison, the model that minimizes the prediction error, according to specific features of the selected masonry infill, is identified for each masonry infill type.