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Infilled frames are generally formed by the composite interaction between the frame and the infilled wall used for functional purposes. The composite interaction increases the in-plane lateral stiffness of the frame, which is considered an advantage. However, the interaction also alters the ductile mode of failure to the brittle mode along with the increased base shear owing to its higher stiffness compared with the bare frame. A detailed and comprehensive study of the literature revealed that many of research works have been done on rectangular and square frames, and studies on trapezoidal infilled frames are scarce. In this article, we studied different configurations of reinforced concrete frame structures known as trapezoidal frames, which have higher stiffness than rectangular frames. A trapezoidal frame is used for industrial buildings, and its behavior under a lateral load has already been established for a bare frame. However, the interaction and behavior of the infilled frame were investigated in this research. The behavior of a trapezoidal single-story frame was examined under both lateral loading and various interface materials. One of the most frequently suggested methods for infilled-frame analysis is the equivalent diagonal strut. Effective strut width design recommendations are available for rectangular and square frames but not for trapezoidal frames for macro modeling. Hence, to make the design easier, an effective diagonal width was developed for different interface materials with respect to the relative stiffness of various frame cross-sections, and further validation was conducted with a framework of ideology from biomimicry using the nature of a one-sixth scale model. The effective strut width for the trapezoidal infilled frame varied between d/8 and d/9 for the cement mortar and cork interfaces, where d is the diagonal length of the frame. [ABSTRACT FROM AUTHOR]

Infilled frames are generally formed by the composite interaction between the frame and the infilled wall used for functional purposes. The composite interaction increases the in-plane lateral stiffness of the frame, which is considered an advantage. However, the interaction also alters the ductile mode of failure to the brittle mode along with the increased base shear owing to its higher stiffness compared with the bare frame. A detailed and comprehensive study of the literature revealed that many of research works have been done on rectangular and square frames, and studies on trapezoidal infilled frames are scarce. In this article, we studied different configurations of reinforced concrete frame structures known as trapezoidal frames, which have higher stiffness than rectangular frames. A trapezoidal frame is used for industrial buildings, and its behavior under a lateral load has already been established for a bare frame. However, the interaction and behavior of the infilled frame were investigated in this research. The behavior of a trapezoidal single-story frame was examined under both lateral loading and various interface materials. One of the most frequently suggested methods for infilled-frame analysis is the equivalent diagonal strut. Effective strut width design recommendations are available for rectangular and square frames but not for trapezoidal frames for macro modeling. Hence, to make the design easier, an effective diagonal width was developed for different interface materials with respect to the relative stiffness of various frame cross-sections, and further validation was conducted with a framework of ideology from biomimicry using the nature of a one-sixth scale model. The effective strut width for the trapezoidal infilled frame varied between d/8 and d/9 for the cement mortar and cork interfaces, where d is the diagonal length of the frame.

The model updating procedures employed in vibration-based health monitoring need to be reliable and computationally efficient. The computational time is a fundamental task if the results are used to evaluate, in quasi-real-time, the safe or the unsafe state of strategic and relevant structures. The paper presents an efficient two-step procedure for the identification of the mechanical parameters and for the assessment of the corresponding uncertainty in model updating problems. The first step solves a least squares problem, providing a first estimate of the unknown parameters. The second (iterative) step produces a refinement of the solution. Moreover, by exploiting the error propagation theory, this article presents a direct (non-iterative) procedure to assess the uncertainty affecting the unknown parameters starting from the experimental data covariance matrix. To test the reliability of the procedure as well as to prove its applicability to structural problems, the methodology has been applied to two test-bed case studies. Finally, the procedure has been used for the damage assessment in an existing building. The results provided in this article indicate that the procedure can accurately identify the unknown parameters and properly localize and quantify the damage.

The non-linear behavior of infilled frames is very complex. The behavior of this structure may be studied by experimental and numerical approaches. An experimental test can provide a more realistic output but has the disadvantages of high costs, relatively long time and specific room usage. A numerical analysis can be an alternative to analyze the behavior of infilled frames. One of the most powerful numerical approaches is meso-modeling. This approach has the advantage of being able to capture local damage to the panel. For this reason, the progressive damage identified in the meso-model can be used as a basis for determining damage state criteria. The grouping of damage states is proposed based on the initial identification in the form of local damage linked to global damage, i.e., IDR. This study's proposed level of infilled frame damage is DS1 = 0.17%, DS2 = 0.52%, DS3 = 0.79% and DS4 = 1.99%. However, the quantification results of the structural damage level cannot be generalized because many complex factors influence the behavior of infilled frames. Subsequently, a parametric study was carried out to determine the contribution of the mechanical properties of the infilled frame material to the degree of structural damage. [ABSTRACT FROM AUTHOR]

This paper studies the performance of infilled frame of Multi-Ribbed Composite Wall (MRCW) after fire, using a combined experimental and Finite-Element (FE) analysis method. To this end, 14 infilled frame specimens were tested under fire, where different fire conditions, including both single-side and double-side fire, were considered. After fire, they were tested under diagonal loads to evaluate their residual bearing capacities. Based on the test results, the residual capacities of the specimens subjected to 60 min single-side fire, 60 min double-side fire, and 120 min single-side fire were about 3/4, 1/2, and 2/3, respectively, of those at room temperature. For specimens subjected to 120 min double-side fire, the bearing capacity was completely lost. Corresponding to the two types of tests, two types of FE analyses were conducted, including temperature and mechanical loading analyses. A temperature-related reduction factor of the elastic modulus was adopted to account for the cracks in the Autoclaved Aerated Concrete (AAC) blocks after fire, due to the restraining effect of the ribbed beams and columns. Good correlations were obtained between FE and test results. The FE model was further used to conduct a parametric study to evaluate different factors on the infilled frames' residual capacities after fire. It was found that, compared with concrete strength and the height of the ribbed beams and columns, the grade of AAC had the most significant effect on the infilled frames' residual capacities. The residual capacities of the infilled frames with the same size decreased significantly with the increase of fire time. Under the same fire time, the increase rate of the bearing capacity was higher when the height of the ribbed beams and columns was in the range of 70–90 mm. [ABSTRACT FROM AUTHOR]

Fundamental period of vibration is one of the most critical parameters to evaluate in the seismic design of new buildings, considering its role in the seismic forces estimation. The challenge of this research is to define a new approach for predicting the fundamental period of vibration for reinforced concrete buildings, designed according to the new generation seismic codes. The proposed formulations in this paper represent useful tools in the pre-design phase and they are based on some global parameters including mass and stiffness properties. To this scope, a set of 40 new buildings have been collected and modelled, considering bare and infilled frame configurations. Through regression analysis procedures two new formulations have been firstly proposed, compared with other existing formulations and finally validated through some case studies proposed in the recent scientific literature. The results show a good agreement with some of the existing formulations and a nearly perfect prediction of the fundamental period of vibration for the selected case study buildings. [ABSTRACT FROM AUTHOR]

Seismic assessment of structures is often performed using their force–displacement capacity or pushover curve computed via non‐linear static analysis. However, these analyses' reliability depends on the numerical model's detail and its ability to capture salient failure mechanisms. Simplified analysis methods offer effective means of identifying structural deficiencies and provide analysts with a sound understanding of key structural characteristics, such as the strength hierarchy, status of the structural damage in terms of limit state exceedance or the progression of the inelastic mechanism, in addition to providing a method with which to check numerical analysis results. This work builds upon the existing literature for simplified analysis of moment frame structures and describes a simplified pushover‐based analysis procedure for infilled frame structures. Individual storey responses are obtained by combining the flexural resistance of the frame and accounting for the axial resistance of the infill (modelled as an equivalent axial strut) and the boundary frame members, assuming both systems work in parallel. Then, the displaced shape of the structure is iteratively calculated for a given base shear, which can be repeated until a pushover curve is obtained with relative ease. The proposed procedure is tested and evaluated versus other available methods by analysing several infilled reinforced concrete frames. It is shown that the method can perform simplified pushover analysis with a high degree of fidelity while improving over the other similar methods currently available. [ABSTRACT FROM AUTHOR]

The results of an experimental study of four infilled frames with brick masonry walls subject to reversal cyclic lateral load are presented. The variables studied were the height to length aspect ratio of the wall and the use of joint reinforcement. The investigation was motivated by the fact that the Mexican code establishes the same specifications about the use of joint reinforcement for infill walls as for confined walls, because there is not enough experimental evidence on joint reinforced infill walls. To investigate the possible interaction of the study variables in the seismic performance of the walls, two pairs of specimens, scaled 1:2, with different aspect ratios (H/L = 0.75, 0.41) were tested. The specimens in each pair were identical except that one of them included steel bars into the bed-joints as reinforcement leading to amount   p h f y h = 0.6   MPa . The infill walls with H/L = 0.41 were included from a previous study. The behavior of the specimens was defined in terms of lateral strength, ductility, displacement capacity, deformation of the joint reinforcement and crack pattern. The results indicate that joint reinforcement increases the strength of the system; however, the increase was more pronounced in longer walls. Ductility was reduced with horizontal reinforcement and this behavior was more important for longer walls. As occurred in confined walls, the joint reinforcement generates a more distributed cracking and reduces the width of the cracks. The experiments are described and this and other results are discussed in detail. [ABSTRACT FROM AUTHOR]

The use of lightweight autoclaved aerated concrete (AAC) block masonry is gaining popularity in earthquake-resistant infilled reinforced concrete (RC) frame buildings due to its various benefits. Therefore, appropriate knowledge of the strength properties of AAC block masonry is necessary for a reasonable evaluation of the seismic behavior of such buildings. In the present study, the uncertainties related to the two most critical parameters that control the resistance capacity of infilled masonry are investigated through laboratory experiments, and the best-fitted probability density functions are recommended. Furthermore, the in-plane seismic performances of typical RC frame buildings infilled with AAC block masonry are evaluated in a probabilistic framework considering the recommended probability density functions showing the ineffectiveness of an assumed normal distribution for this purpose. Although lightweight AAC block masonry slightly increases the seismic risk of the building compared to traditional brick masonry due to its lower strength properties, it can be safely used as an infill material in areas with high seismicity, as it achieves the codeprescribed reliability index. [ABSTRACT FROM AUTHOR]

Abstract This study analytically investigated the behavior of reinforced concrete frames with masonry infills. For the analysis, VecTor2, a nonlinear finite element analysis program that implements the Modified Compression Field Theory and Disturbed Stress Field Model, was used. To account for the slip behavior at the mortar joints in the masonry element, the hyperbolic Mohr–Coulomb yield criterion, defined as a function of cohesion and friction angle, was used. The analysis results showed that the lateral resistance and failure mode of the infilled frames were significantly affected by the thickness of the masonry infill, cohesion on the mortar joint–brick interface, and poor mortar filling (or gap) on the masonry boundary under the beam. Diagonal strut actions developed along two or three load paths on the mortar infill, including the backstay actions near the tension column and push-down actions near the compression columns. Such backstay and push-down actions increased the axial and shear forces of columns, and ultimately affect the strength, ductility, and failure mode of the infilled frames.

In the last few decades, important attention was given to infill masonry panels due to their worldwide uses. Many experimental and numerical studies were conducted to study their effect on the behavior of RC frames. In general, three modeling strategies are widely applied to model infill masonry, namely, micro-models, meso-models, and macro-models. This study investigates the accuracy of the width models to predict the behavior of masonry infills using the meso-modeling technique. To this aim, the masonry infills are modeled as an equivalent homogenized diagonal element in order to represent the diagonal action of masonry infills. The width models used to determine the width of the diagonal strut are used in meso-modeling. In addition, the study contains comparisons between different modeling techniques to predict the global behavior of the infilled frames. Experimental tests conducted on two infilled frames from the literature are considered to calibrate the numerical simulations. The results indicate that the micro-modeling approach gives a good agreement with the experimental tests in terms of lateral force and deformation shapes, the related errors varying between 0.12 and 2.8%. Using single strut models, the differences between numerical and experimental results vary from 1.1 to 20%. On the other hand, the errors obtained from multiple strut models are varying between 9 and 40%.

During major earthquakes, existing buildings have collapsed or suffered serious damage, resulting in number of losses, severe injuries, and deaths. Based on literature, the influence of this work reviewed the effects of interface with different materials and also to find how infilled frames behave in framed structure. This study's primary goal is to strengthen RC-framed structures and increase the ductility of infilled frames by using interface materials. The research offers a full range and points relevant to ductile parameters for more results in the field of infilled frames using interface materials. In parametric investigation the interface material with interface thickness and the combination of interface material with a particular frame, from that optimum value to be identified. This research benefits researchers, professionals, and specialists the behaviour of various structural systems, as well as innovative mitigation techniques that have been used in the literature to build progressive collapse resistance experimentally.

The non-linear behavior of infilled frames is very complex. The behavior of this structure may be studied by experimental and numerical approaches. An experimental test can provide a more realistic output but has the disadvantages of high costs, relatively long time and specific room usage. A numerical analysis can be an alternative to analyze the behavior of infilled frames. One of the most powerful numerical approaches is meso-modeling. This approach has the advantage of being able to capture local damage to the panel. For this reason, the progressive damage identified in the meso-model can be used as a basis for determining damage state criteria. The grouping of damage states is proposed based on the initial identification in the form of local damage linked to global damage, i.e., IDR. This study’s proposed level of infilled frame damage is DS1 = 0.17%, DS2 = 0.52%, DS3 = 0.79% and DS4 = 1.99%. However, the quantification results of the structural damage level cannot be generalized because many complex factors influence the behavior of infilled frames. Subsequently, a parametric study was carried out to determine the contribution of the mechanical properties of the infilled frame material to the degree of structural damage.

Previous studies and observations of the earthquake have shown that frame filled with concrete 3d panel wall, can have adverse effects on the seismic behavior of structures. On the other hand, yielding dampers that used with steel braces, have a high capacity to absorb and depreciating energy from the earthquake. In this paper, targets are reducing damage to the infills and moment frame in during of the earthquake, reduce the horizontal and vertical irregularities in structure. To rech these targets, Three experimentally models with half scale were constructed and tested on the shaking table under 7 scale accelerated. Also, for investigate the Effective of parameters in the seismic behavior of moment frames, using Abaqus software, finite element analysis was performed after verification of model behavior with experimentally results. Experimentally results showed that use the yielding connection between wall and frame, reduces the lateral displacement and plastic strain in the structure. Numerical analyzes showed that by adding the yielding connection to the frame and infill wall, The frame has linear behavior In high intensity earthquake, and not be created plastic hinges in the members of the frame. The input energy is amortized only in the connections. So the number and geometric specification of these connections can affect the lateral hardness and lateral strength of the structure.

The Stick‐IT model (Stick for Infilled frames Typologies), that is a MDOF system consisting of a series of lumped masses connected by nonlinear shear link elements, was introduced to predict the response, in terms of interstory drift ratio (IDR) and peak floor acceleration (PFA), for infilled RC building typologies. Stick model parameters can be defined starting from low level building geometrical features, easily retrievable at the large scale, such as in plan dimensions, number of stories or the percentage of infills openings and considering the infills consistency. This paper investigates the applicability of Stick‐IT to predict the performance and direct economic losses for existing RC infilled frame type buildings. In the framework of a performance‐based assessment, the comparison of seismic‐loss outcomes provided by using either a detailed finite element model (FEM) (L1) or simplified Stick‐IT structural models (L2) are illustrated and discussed. The potential of Stick‐IT model is investigated referring to a real building damaged and repaired after the 2009 L'Aquila earthquake and adopting as earthquake input records registered in the proximity of the building. Story‐level building damage simulated by L1 and L2 models is compared to real damage, showing satisfactory prediction. The comparison of the real repair costs with those evaluated using L1 and L2 models provides encouraging validation. The application suggests that simplified models such as Stick‐IT, despite the low level of information required for its application, can be usefully applied to perform damage and loss scenarios at the large scale. Matlab code to generate the Stick‐IT, as well as the example code for the present study, are openly shared through the repository https://github.com/marcogaetanidaragona/Stick-IT. [ABSTRACT FROM AUTHOR]

Openings in the walls of infilled frame structural systems are very common. Reinforcement around the wall openings confines and strengthens the wall, making an infilled frame with a confined opening (IFcO) a reliable structural system for seismically active regions. To encourage the application of IFcO, an analysis method is proposed by introducing a simple equivalent diagonal strut formula with reduced width due to the wall opening. Finite element models using shell elements were used as reference to develop strut width formula for IFcO with varying opening ratios (r) and diagonal angles (?). The formula was verified against previous test results and then applied for the design of 3 and 5-story buildings, consisting of IFcOs with r of 30, 60 and 80% to represent medium, large and very large openings. The seismic responses of the strut models were then compared to those of the shell and the bare frame models. The effect of the opening on internal forces, frame reinforcement, wall stresses and soft story mechanisms were also investigated.

Abstract In the last decades, several studies have been developed regarding structures composed by frames infilled with masonry walls, proving the increase of lateral stiffness by the infill. In this work, an analysis was carried out, based on design codes which adopt the equivalent diagonal strut method, to compare theoretical results with experimental ones of tests performed on steel frames infilled with concrete block masonry. Two of the three assessed codes specify lateral stiffness smaller than that measured from experimental testing, as safety measures for design. Regarding the masonry ultimate loads, the two specifications analyzed yielded similar values of critical force, although they pointed out different failure modes. The equivalent diagonal strut method has been proved to be a simple and useful tool for considering masonry walls and it should be used in case of reduced horizontal loads, prior to initial cracks of the infill wall.

Despite numerous studies on seismic performance of masonry infilled reinforced concrete frames have been conducted, experimental study on effect of type of lateral load on masonry infilled reinforced concrete frames is sparse. This paper investigates the seismic performance of masonry infilled reinforced concrete frames with different aspect ratios subjected to monotonic and cyclic loadings. Six half-scale, single-storey, single-bay frame specimens designed according to code provisions commonly adopted in Malaysia were tested. Behaviours of frames were assessed based on observed failure modes, strength, stiffness, ductility and energy dissipation capacity. Experimental result reveals that typical infilled frame in Malaysia has high tendency to fail under shear on columns. Type of loading does not affect strength of both bare frames and infilled frames. However, the drift to reach peak strength drops about 40–52% for infilled frames subjected to cyclic loading as compared to monotonic loading. Initial stiffness of infilled frames is found elevated with slower stiffness degradation under the influence of cyclic loading. Ductility of infilled frames subjected to cyclic loading is 48% higher than those subjected to monotonic loading, regardless of aspect ratio. A total of 84% increase in energy dissipation is observed with 60% of increment in bay length. [ABSTRACT FROM AUTHOR]

This study analytically investigated the behavior of reinforced concrete frames with masonry infills. For the analysis, VecTor2, a nonlinear finite element analysis program that implements the Modified Compression Field Theory and Disturbed Stress Field Model, was used. To account for the slip behavior at the mortar joints in the masonry element, the hyperbolic Mohr–Coulomb yield criterion, defined as a function of cohesion and friction angle, was used. The analysis results showed that the lateral resistance and failure mode of the infilled frames were significantly affected by the thickness of the masonry infill, cohesion on the mortar joint–brick interface, and poor mortar filling (or gap) on the masonry boundary under the beam. Diagonal strut actions developed along two or three load paths on the mortar infill, including the backstay actions near the tension column and push-down actions near the compression columns. Such backstay and push-down actions increased the axial and shear forces of columns, and ultimately affect the strength, ductility, and failure mode of the infilled frames. [ABSTRACT FROM AUTHOR]

The results of an experimental study of four infilled frames with brick masonry walls subject to reversal cyclic lateral load are presented. The variables studied were the height to length aspect ratio of the wall and the use of joint reinforcement. The investigation was motivated by the fact that the Mexican code establishes the same specifications about the use of joint reinforcement for infill walls as for confined walls, because there is not enough experimental evidence on joint reinforced infill walls. To investigate the possible interaction of the study variables in the seismic performance of the walls, two pairs of specimens, scaled 1:2, with different aspect ratios (H/L = 0.75, 0.41) were tested. The specimens in each pair were identical except that one of them included steel bars into the bed-joints as reinforcement leading to amount phfyh=0.6 MPa. The infill walls with H/L = 0.41 were included from a previous study. The behavior of the specimens was defined in terms of lateral strength, ductility, displacement capacity, deformation of the joint reinforcement and crack pattern. The results indicate that joint reinforcement increases the strength of the system; however, the increase was more pronounced in longer walls. Ductility was reduced with horizontal reinforcement and this behavior was more important for longer walls. As occurred in confined walls, the joint reinforcement generates a more distributed cracking and reduces the width of the cracks. The experiments are described and this and other results are discussed in detail.

RC shear walls have been widely used as the main lateral-load resisting system in medium and high-rise buildings because of their inherent large lateral stiffness and load resistance. But, in general, the energy dissipating capacity of RC shear walls is not very good and it is found that using the bracing system gives good results. The main purpose of this paper is to study the effect of the different types of bracing on the lateral load capacity of the frame. Also, the research contains a comparison between the braced and infilled frames to decide the best system. The research scheme consists of four frames; the bare frame, two frames one was braced with concrete, the second was braced with steel bracing and the fourth frame was infilled with solid cement bricks. All the specimens were tested under cyclic loading. The results gave some important conclusions as; braced and infilled the bare frames increased the lateral strength of the bare frame depending on the type of bracing and infill. Also, the different types of bracing and the infill increased the initial stiffness of the bare frame by a reasonable value. The energy dissipation for the braced and infilled frames is always higher than that for the bare frame up to failure. Also, numerical modeling was carried out with the nonlinear software platform (IDARC). The numerical results obtained with the calibrated nonlinear model are presented and compared with the experimental results. Good agreement was achieved between the numerical simulation and the test results.

This paper presents the experimental results of squat mud infill walls with three different height aspect ratios in the timber frames of traditional Japanese residential houses. The deformation and failure characteristics, lateral load-carrying mechanism, and influence of the height aspect ratio on the lateral behavior of squat mud walls are investigated. We observed that when the height aspect ratio of the mud wall is less than 0.5, the initial failure is dominated by corner crushing rather than by shear failure. The lateral stiffness of the squat mud wall is positively correlated with the wall height, whereas the drift angle corresponding to the bearing capacity exhibits an inverse relationship with the wall height. For a height aspect ratio less than 0.3, the internal deformation of the squat mud wall is primarily driven by the deformation angle related to corner crushing and sliding. However, when the height aspect ratio increases to 0.5, the rotation angle increases significantly. The transformation of the deformation characteristics and internal force distribution of the squat mud wall depends on the interplay between the wall height aspect ratio and friction coefficient between the mud wall and timber frame. Drawing from comparative experiments and internal force analysis, the lateral resistance of the squat mud infill wall can be separated into two groups of elements: Q c and Q c ' , stemming from the corner compression between the mud wall and adjacent timber frame or internal timber laths, respectively, which exhibits a significant positive correlation with the wall height; Q f and Q g , attributed to the frictional force of the protruding ends of bamboo laths and the gravitational force of the squat mud wall, respectively, which exhibit a consistent behavior unaffected by alterations in the wall height. • Experimental clarification of lateral load-carrying mechanism of squat mud walls infilled in the timber frame. • Internal force and deformation analysis of the squat mud infill wall subjected to lateral force. • Impact of height aspect ratio on the lateral behavior of the squat mud infill wall. [ABSTRACT FROM AUTHOR]

This study aims to obtain exact natural frequencies and mode shapes of infilled multi-storey frames using single variable shear deformation theory (SVSDT) which considers parabolic transverse shear stress distribution across the cross-section. The effects of infill walls on free vibration characteristics are investigated for different frame models such as one storey infilled, soft storey and fully infilled. The infill walls are modeled using equivalent diagonal strut approach. Natural frequencies are calculated via dynamic stiffness formulations for different wall thickness values. The results of SVSDT are tabulated with Euler-Bernoulli beam theory (EBT) and Timoshenko beam theory (TBT) results. Additionally, finite element solutions are presented to verify the natural frequencies that obtained from dynamic stiffness formulations. The results show that SVSDT can be used effectively for free vibration analysis of infilled frame structures by using dynamic stiffness formulations. The numerical analyses show that the effects of shear deformation and rotation inertia become observable for higher modes of infilled frame structures. It is seen from the results that ignoring effects of infill walls may cause significant errors on calculation of natural frequencies of frames. [ABSTRACT FROM AUTHOR]

Openings in the walls of infilled frame structural systems are very common. Reinforcement around the wall openings confines and strengthens the wall, making an infilled frame with a confined opening (IFcO) a reliable structural system for seismically active regions. To encourage the application of IFcO, an analysis method is proposed by introducing a simple equivalent diagonal strut formula with reduced width due to the wall opening. Finite element models using shell elements were used as reference to develop strut width formula for IFcO with varying opening ratios (r) and diagonal angles (θ). The formula was verified against previous test results and then applied for the design of 3 and 5-story buildings, consisting of IFcOs with r of 30, 60 and 80% to represent medium, large and very large openings. The seismic responses of the strut models were then compared to those of the shell and the bare frame models. The effect of the opening on internal forces, frame reinforcement, wall stresses and soft story mechanisms were also investigated. [ABSTRACT FROM AUTHOR]

In this study, an analytical study was conducted using the ABAQUS software on the effect of masonry infilled frame and the effect of opening in the seismic behavior of mid-rise reinforced concrete frame building. After modeling the four-story building frame and defining the plastic range for its materials, the structure is placed under the dynamic load of the earthquake from accelerogram and the horizontal and vertical load of the earthquake entered it. After receiving the considered outputs, the infilled frame load is removed and the infilled frame itself is placed in the structure after the modeling by micro-model method. Also, by comparing the hysteresis diagram between the first and second models, the energy dissipated by the wall was very high up to the moment before its failure and had a positive effect on the loading capacity. In addition, bracing the frame components by the wall prevents over limit deformation of the structural gradation and delayed the instable deformations in the structure. So that the structural components with ten-time more elastic capacity, in the frame without infilled frame, have been deformed in the time less than the considered analysis and instability has been created. The results show that the existing opening reduces the stiffness and strength of the composite frame and increasing the size of the openings more than the amount recommended in the regulation causes a more severe decline in the strength of the structure. Also, the deformation of opening from window type (increasing the opening dimensions in the vertical direction) as well as the irregularity in their position causes a severe decline in the strength and stiffness of the structure. [ABSTRACT FROM AUTHOR]

This paper investigates on the effect of story lateral stiffness variation on the maximum elastic interstory drift ratio (IDRmax) for existing reinforced concrete (RC) buildings. Several classes of existing gravity load designed RC buildings are obtained via a simulated design approach. The presence of infills in the perimeter frames as well as different opening percentages along the height are considered. A simplified elastic analysis is performed, adopting an equivalent multistory cantilever system to represent the stiffness variation along the buildings height. IDRmax is significantly influenced by the ratio of the lateral stiffness at the second and upper stories over the lateral stiffness of the first story. Such a ratio has been found dependent on a number of geometric and configuration factors, including the variation of the opening percentage ratio. Two regression formulas are proposed to estimate, given the spectral displacement at the fundamental period T, the roof displacement and IDRmax as a function of the building height and the opening percentage at first and upper stories. Suitable modification of the formulas is also introduced to account for possible cracking of RC elements and infill panels even at very low levels of lateral drift. These expressions could be used for the simplified evaluation of the expected drift demands for buildings of existing RC typologies. Finally, the proposed formulations are applied to a number of permanently monitored buildings, comparing the calculated IDRmax with the one resulting from record processing, obtaining a fair good agreement. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study for the behavior and ductility of H.S.R.C frames with infill wall under the effect of cyclic load. The experimental program was conducted on four specimens (frames). The parameters are studied change panel of frame from non infill to infill, change thickness of infill wall and change type of bricks. The dimension of frames is selected to represent half scale frames and tested under cyclic loading. All specimens of experimental program are tested in the reinforcement concrete testing laboratory at the Housing and Building National Research Center – Cairo. From the representation and the analysis of the obtained results, the main conclusions are pointed out; the lateral load resistance for infilled frames F2, F3 and F4 with infill wall (red bricks) thickness 12, 6 cm and cement bricks 12 cm, respectively was greater than the bare frame (F1) by about 184%, 61% and 99%, respectively. The ductility factor for infilled frames F2, F3 and F4 was less than the bare frame (F1) by about 57%, 51% and 46%, respectively.

Cyclic loading tests were earned out on four full-scale infilled RC frames and one bare RC frame to investigate the effects of different infilled masonry on the seismic behavior of RC frame stmetures. The infilling masonry included hollow clay bricks, hollow concrete blocks, light aggregate concrete blocks and aerated concrete blocks. The failure modes, hysteretic loops, skeleton curves, energy-dissipation capacity, and degradation of bearing capacity and stiffness of the specimens were comprehensively analyzed. Experimental results show that, the infilling wall using aerated concrete block shows good integrity during the whole loading process, whilst the other three infilling walls appear spalling under 1/50 drift angle, and the damage degree becomes more serious with the increase of drift amplitude. The infilling masonry greatly enhances the initial stiffness, secant stiffness and bearing capacity of infilled frames. The displacement ductility coefficients of all the specimens are more than five, and the infilled frame using aerated concrete block shows better deformation performance than other infilled frames. Based on the test results and combining with the domestic and international leveling standards for the seismic performance of frames, the inter-story drift index limits for different seismic performance levels of masonry infilled frame are proposed. [ABSTRACT FROM AUTHOR]

The seismic response of older R/C frames can be particularly sensitive to interaction with masonry infills, poor section detailing and smooth reinforcing bars. These aspects are quite often neglected in design and assessment both with linear and nonlinear models due to the modelling complexity and inherent increase in computational effort. This work presents a review of practical nonlinear models available in literature and quantifies, at the system performance level, the influence of bond-slip in critical plastic hinge locations and interaction effects with infill panels and shear deficient columns. Bond-slip effects are directly incorporated into the nonlinear fiber section models through a simplified approach and nonlinear shear behavior of columns is aggregated at the element level in conjunction to the common diagonal infill strut scheme. Three different infilled frame configurations are analyzed: a) bare frame, b) partially infilled frame (pilotis frame) and c) uniformly infilled frame. Static pushover analyses and Incremental Dynamic Nonlinear Response History Analyses (IDA) are performed spanning a wide range of hazard levels. Comparative analysis with concurrent incorporation of infill-induced shear damage and bond-slip quantify the loss of strength for the uniformly infilled configuration and the increased deformations for the bare frame and partially infilled configurations in terms of seismic performance parameters. [ABSTRACT FROM AUTHOR]

In this study, an external post-tensioning technique was employed to enhance the seismic performance of infilled RC frames through preventing premature failure of infill walls and increase in their engagement with RC frames. Totally, six 1/3-scale single-story single-bay RC frames were constructed and tested. The frames were divided into two groups based on their aspect ratios. Each group consisted of a bare frame, an infilled frame and a retrofitted infilled frame. All specimens were subjected to a similar quasi-static cyclic loading and their responses were measured through load cells, strain gauges and linear variable differential transformers. Results indicated that the retrofitted infilled frames had higher initial stiffness, ultimate lateral strength and ductility ratio when compared with the bare and un-retrofitted infilled frames. The retrofitted infilled frames also showed a prolonged failure mode and a lower stiffness degradation rate compared to other frames. It was also observed that, compared to other frames, the retrofitted frames had smaller strain values at their critical zones. [ABSTRACT FROM AUTHOR]

An RC frame structure with masonry infill walls ('framed-masonry') exposed to lateral loads acts as a composite structure. Numerical simulation of framed-masonry is difficult and generally unreliable due to many difficulties and uncertainties in its modelling. In this paper, we reviewed the usability of an advanced non-linear FEM computer program to accurately predict the behaviour of framed-masonry elements when exposed to cyclic lateral loading. Numerical results are validated against the test results of framed-masonry specimens, with and without openings. Initial simplified micromodels were calibrated by adjustment of the input parameters within the physically justifiable borders, in order to obtain the best correlation between the experimental and numerical results. It has been shown that the use of simplified micromodels for the investigation of composite masonry-infilled RC frames requires in-depth knowledge and engineering judgement in order to be used with confidence. Modelling problems were identified and explained in detail, which in turn offer an insight to practising engineers on how to deal with them. [ABSTRACT FROM AUTHOR]

A large number of research studies deal with the modeling and analysis of infilled reinforced concrete (RC) buildings under seismic actions, at the aim to understand the actual contribution given by masonry infills to the overall seismic resistance of a building. In this paper this aspect is investigated in the framework of pushover analyses, describing the theoretical and computational choices related to the involved parameters. Differently from the approaches available in literature and standards, the “double-strut model” is adopted to simulate the infill behavior, according to which an infill panel is represented by two equivalent non-parallel struts; the peculiarity is that the positions of the extremities of the two struts coincide with the points of application of the stress resultants on each side of the panel. The results show that, by adopting the double-strut model, it is possible to capture dangerous local shear failures which are usually neglected in pushover analysis and which can compromise the safety of the overall structure. By including in the analysis shear plastic hinges together with bending ones, it is evident how the additional shear forces, arising at the extremities of beams and columns, can substantially change the collapse mechanism of a structure under seismic action. The main features of the double-strut model are its low computational cost together with its accuracy, which make it particularly suitable for applications in the engineering practice. In fact it could be easily implemented in commercial calculation codes, representing a practical predictive tool able to enhance the safety level of infilled RC buildings. [ABSTRACT FROM AUTHOR]

In assessing the structural performance of infilled frames, in particular those with irregular and discontinuous infill panels, under bi-directional seismic excitation, the interaction effect of in-plane and out-of-plane lateral loads should be properly considered. This paper presents an investigation into the effect of bi-directional horizontal loading on the nonlinear static and dynamic behaviour of masonry-infilled reinforced concrete frames with openings in association with discrete-finite element modelling techniques. Out-of-plane loading and openings can significantly soften the bracing action provided by infill walls to the bounding frame. Under static load, the lateral strength of the infilled frames can reduce by 20-50 % when the applied out-of-plane load increase from 0.5 times to 2.0 times the unit weight of infills. The out-of-plane effects are intensified in dynamic loading cases. It is found that the peak base shears of the fully infilled frame under the bi-directional excitations are lower by 24.7 % under the Superstition Hill earthquake (PGA = 0.45 g) and 54.1 % under the Chi-Chi earthquake (PGA = 0.82 g) as compared with the uni-directional load cases. The displacement demands are also greater under bi-directional dynamic loading. For 2/3 height infilled frame, the displacement demands are significantly increased by 99.7 % under Kobe (PGA = 0.65 g) and 111.0 % under Chi-Chi earthquake (PGA = 0.82 g) respectively. For the fully infilled frame, the displacement demands are 84.1 % higher under Kobe and 53.1 % higher under Chi-Chi. Due to the incapability of developing continuous arching action, the infill panels with openings are particularly vulnerable to out-of-plane action and that often leads to progressive collapse of infill components. The worst scenario is that total collapse of infill panels takes place at the first storey, creating a soft-storey that jeopardise the overall structural stability. [ABSTRACT FROM AUTHOR]

In this paper, two types of seismic retrofitting methods for reinforced concrete frames were suggested and examined through the cyclic loading tests: one is to insert a steel frame to existing partially masonry infilled concrete frame of the building after removing masonry from the concrete frame and the other is to adhere waved steel panels to the existing masonry fully infilled concrete frame. In order to evaluate validity of the suggested methods in seismic performance, five specimens were manufactured and tested: a bare concrete frame, a partially masonry infilled concrete frame, a masonry infilled concrete frame, a steel frame inserted concrete frame, and a waved steel panel adhered concrete frame. Compared were crack pattern, failure mode, load-displacement relation, ductility, stiffness and energy dissipation capacity. The specimens retrofitted with the inserted steel frame showed a maximum load approximately twice that of the partially masonry infilled frame, and the specimen retrofitted with the adhered waved steel panel showed a maximum load approximately twice that of the masonry fully infilled frame. [ABSTRACT FROM AUTHOR]

Experimental studies have proven that clay brick infills, confined with carbon-fiber-reinforced polymers (CFRP) in reinforced concrete (RC) frames, have some advantages in terms of stiffness, strength, energy dissipation capability and damage intensity. Owing to these advantages, existing infill walls in RC frames may be retrofitted with CFRP strips, especially in low-rise buildings in earthquake-prone areas. There is a gap in the literature concerning their behavior model, for use in structural analysis. A piecewise linear capacity curve model called 'DUVAR' is proposed here, which estimates the envelope of force-vs.-displacement hysteresis, depending on the data compiled from the literature and the completed experimental studies. A nonlinear shear spring element is utilized in the model to represent the bare and retrofitted infills. The ultimate shear strength and the corresponding displacement, the ratio of cracking stiffness to initial stiffness, the ratio of ultimate strength to cracking strength, and the ductility ratio are the five key parameters of the model. The model is validated against the experimental results of two sovereign studies. Finally, the model is employed in the performance evaluation of an existing three-story RC building to exemplify its straightforward application. [ABSTRACT FROM AUTHOR]

To study the earthquake response of RC infilled frame structures with variable wall opening, 3-D computer models were made for 3, 4, and 5 storey typical hotel buildings consisting of six frames of 3 bays. In X-direction, the middle bay was open and the side bays were in-filled with full (solid) walls. In Y-direction, the interior walls consisted of door opening in the corner and the exterior walls consisted of window openings with variable ratios of 20%, 40%, 60%, 80%, and 100%. Prior to modeling the 3-D structure, 2-D validation models using diagonal strut and shell element were made based on test results of simple infilled frames with various openings. For the strut model, the wall with opening was modeled using diagonal strut of reduced width. For the shell element model the wall was modeled as is with gap element at the interface between the frames and the wall. Considering crack development and non linear stress-strain relationship of the materials, the lateral load-displacement diagrams of the shell element models fit the test result better than the strut ones. Models with lintels around the wall openings were also created for validation and the results show that lintels stiffen the frame and strengthen the wall around the openings. The shell element model was then used to create 3-D models of the hotel building with lintels around the wall openings. Analysis and design of the 3-D models show that the earthquake responses of RC frames infilled with walls of opening ratios 20% to 60% are significantly stiffer and stronger than that without infill wall. However, the contribution of infill walls with 80% opening in reducing storey drift and frame reinforcement was much smaller. Accordingly, the infill walls with opening ratios of less than 80% should be considered in the structural modeling to obtain a more accurate analysis and efficient design. [ABSTRACT FROM AUTHOR]

• Stick: Multi-Degree of Freedom shear model for Nonlinear Response History Analysis. • Stick model generated for infilled RC frames in as-built and retrofitted configuration. • Generation of interstory backbone curves via a simplified procedure. • Applicability of Stick model for speed performance assessment at the community-scale. The Stick model is a MDOF system composed of masses lumped at the story level, connected in series by nonlinear shear link elements suitably calibrated to simulate the interstory inelastic behavior. The model has been demonstrated to predict with sufficient accuracy the dynamic response of existing masonry-infilled RC structures in terms of damage concentration and evolution under specific ground motion records. Previous works proposed interstory backbones calibrated on the response of refined MDOF finite element models representative of gravity-load designed buildings. In this work, with the aim of extending the applicability of the Stick model to different building typologies, a simplified procedure is proposed to generate interstory backbones for the Stick model simulating the behavior of existing masonry-infilled RC structures in as-built and retrofitted configurations. The procedure allows generating Stick models accounting for different levels of design (gravity load, obsolete seismic codes), age of construction, number of storeys and in-plan shape and dimensions. Relevant features characterizing existing buildings are accounted for, explicitly simulating typical failure modes of non-conforming RC elements, brittle failures induced by local frame-infill interaction phenomena, and introducing typical building-level collapse modes for existing buildings. The proposed procedure is extended to account for the possible implementation of retrofit intervention at the building level to both increase the structural capacity and the stiffness of the building. The proposed procedure can be employed to generate typological Stick models to be adopted in large-scale loss assessment studies, also evidencing the beneficial effect of possible retrofit interventions. [ABSTRACT FROM AUTHOR]