Infilled RC Frames Research Articles

Post-earthquake damage identification of an RC school building in Nepal using ambient vibration and point cloud data

This paper presents a damage identification and performance assessment study of a four-story masonry-infilled reinforced concrete building in Sankhu, Nepal, using ambient vibration and point cloud data measurements. The building was severely damaged during the 2015 Gorkha earthquake. A set of accelerometers was used to record the ambient response of the building in order to extract its modal parameters, and a series of lidar scans were collected to estimate the surface defects of certain structural components. An initial model of the structure is created using a recently proposed strut model for masonry infills and a novel modeling approach for infilled RC frames. Dimensions are extracted from lidar-derived point cloud data in the absence of as-built drawings. The FE model updating is first performed through a deterministic formulation where optimal model parameters are estimated through a least squares optimization, and then through a Bayesian inference formulation where the joint posterior probability distribution of the updating parameters are estimated based on the prior knowledge of updating parameters and likelihood of measured data. The error functions for both formulations are defined as the difference between identified and model-predicted modal parameters. Two cases of model updating are performed using different parameterizations and different prior information about the damage. In the first case, updating parameters include walls and columns along the four stories of the building and exclude structural components observed to be severely damaged. The prior knowledge about structural component stiffness values is based on the expected material properties. In the second case of model updating, updating parameters include walls and columns of only the first story, and the prior stiffness values are estimated from the point-cloud measurements. The prior values are then updated using the vibration measurements. The damage identification results are in good agreement with visual observations and point cloud damage quantifications. The most probable model parameters in the Bayesian approach are also found to be in good agreement with the optimal results obtained in the deterministic formulation. Finally, it is shown that the probabilistic natural frequency predictions provide more realistic confidence bounds when both modeling errors and parameter uncertainties are accounted for in the prediction process.

Effect of prior in-plane damage on the out-of-plane behavior of masonry infill walls

Out-of-plane collapse is one of the most important failure modes for masonry infill walls in frame structures during earthquakes and may result in significant economic loss, blocked evacuation pathways and even injuries and fatalities. To investigate the effect of prior in-plane damage on the out-of-plane behavior of masonry infill walls, a series of full-scale masonry infilled RC frame specimens that conform to the Chinese practice were subjected to sequential in-plane and out-of-plane quasi-static loading. The results show that the out-of-plane strength of the masonry infill walls was reduced by 22% and 47% at 1/500 and 1/200 prior in-plane drift ratios, respectively, whereas the out-of-plane stiffness was not significantly affected by the prior in-plane damage. Based on the test results of the present experiment and the collected data available in the literature, an empirical equation was derived to relate the out-of-plane strength reduction factor with both the prior in-plane drift ratio and the slenderness of the wall panel. According to the equation, the out-of-plane strength starts to degrade when the in-plane drift ratio reaches approximately 0.1% to 0.3% depending on the wall slenderness. Both the rate and extent of the strength degradation are greater for slenderer wall panels. Through a numerical example, we demonstrate that neglecting such an in-plane-out-of-plane interaction may lead to substantial underestimation of the loss by seismic damage of masonry infill walls in buildings.

Architectural and engineering design criteria for earthquake resistant masonry infilled RC frames containing openings

In earthquake resistant design of RC frame structures, the definition of masonry infilled frame is often split between reinforced concrete and the masonry structures. However, it is known that the frame elements and the masonry wall work as a coupled system. Additionally, a dedicate chapter for the definitions of openings size, quantity and position is missing. The definition of a full, partial or non-masonry infilled frame with opening is not establish in engineering and architectural codes; rather, recommendations are given. A competent masonry infilled frame with openings would mean to correlate the architectural and engineering concepts as to define an engineered or non-engineered infilled wall. Likewise, certain boundaries should be established using both the architectural and engineering concepts to relate the importance of illumination and air ventilation product of the openings and masonry infilled frame failure patterns.

Machine learning and nonlinear models for the estimation of fundamental period of vibration of masonry infilled RC frame structures

In this work, the estimation of the fundamental period of vibration of masonry infilled RC frame structures is achieved using both Machine Learning techniques and concise nonlinear formulas. The data used are extracted from a recently published extensive database that associates the period with relevant information, such as the height of the structure, the span length between columns, the wall opening ratio, and the masonry wall stiffness. It is shown that, as compared to the utilized data, the proposed methods produce excellent results at the cost of various levels of complexity.

Post-yield Damping Ratio Estimation Studies for Masonry-Infilled Reinforced Concrete Frames

Damping ratio is an important and central parameter for the dynamic analysis of structures. The present study focuses on the estimation of the equivalent damping ratio in a post-yield region for RC frames, both with and without infills. One-story one-bay RC frames casted non-integrally with fly ash (FA) bricks and autoclaved aerated concrete (AAC) blocks infills are considered and are tested under monotonic lateral half-cycle loading. Post-yield behavior parameters, displacement ductility and maximum drift ratio, are used to estimate the equivalent damping ratio at each cycle of lateral loading, and empirical relationships are established. Secant stiffness and stiffness degradation for RC frames are also extracted to determine the contribution and effectiveness of type of infills. Free vibration tests on RC frame specimens are conducted subsequent to each cycle of monotonic lateral loading, and the damping ratio is evaluated. It is found that the equivalent damping ratio substantially increases for RC frames with the onset of damage in the post-yield region. The major advantage of the infilled RC frame is a drastic reduction in the maximum drift ratio. However, types of infill are found to yield equivalent damping ratio at par, suggesting similar energy dissipation capabilities. RC frame infilled with AAC block is recommended due to its higher initial as well as secant stiffness vis- $$\grave{a}$$ -vis FA brick-infilled RC frames and higher stiffness degradation that allows it to behave similar to RC frame without infill.

Seismic performance of brick masonry infilled frame structures with bed joint reinforcements

This paper presents the evaluation of the seismic performance of brick infilled RC frame structures with bed joint reinforcements based on reversed cyclic lateral load tests. Three specimens of the structural model of 1/4 scale-down single-story single-bay brick infilled RC frame was prepared, which were brick infilled RC frames with and without bed joint reinforcements. Two specimens of brick infills with bed joint reinforcements were different in the spacing of bed joint rebars. The specimens were tested by applying a reversed cyclic lateral loading in-plane direction. During the tests, the crack propagation was observed at the peak and residual drifts of each loading cycle to recognize the failure mechanisms of the specimens. As the results, although the use of the bed joint reinforcements ineffective to increase the lateral strength of the overall infilled frame structure. The rebars in mortar bed joints role to sustain the lateral strength in plastic deformation, and provide the whole structure with high ductility. It seemed that the rebars in mortar bed joints confined the brick infills. Therefore, the infilled RC frames can survive in large deformation without failure of the infills in out of the plane direction.

Earthquake-proof system for masonry infills in RC frame structures

The use of masonry infill walls in RC frame structures is common in many countries, even in seismically active areas, where the observations made after strong earthquakes have shown that masonry infills significantly modify the dynamic behaviour of the structure, thus causing total collapses of buildings and loss of human lives. The innovative system called Innovative Decoupled Infill System (INODIS) was developed with the aim to improve the behaviour of infilled RC frames by decoupling the frame and the masonry infill. Description of the system with the installation steps is given with the experimental tests showing that INODIS system highly reduces the activation of infills, thus enables reaching high in-plane drifts without having any damage and at the same time provides stable and reliable connection in out-of-plane direction. Also, the micro model showed that INODIS system improves the behaviour of AAC masonry infills by reducing the level of damage in the walls and postponing infill activation to higher drift levels.

Simulation Framework for Infilled RC Frames Subjected to Seismic Loads

This paper proposes a computationally efficient approach to simulate the seismic behavior of masonry-infilled reinforced concrete frames. The proposed framework utilizes frame elements to represent the reinforced concrete members and diagonal struts to simulate the effect of the masonry panels. The struts are systematically calibrated once the backbone curve of the infilled frame is estimated based on the anticipated failure mechanism. The experimental results from the quasistatic test of a single-story, single-bay frame and the shake-table test of a two-bay, three-story frame are used to validate the proposed framework. The comparison with the experimental data indicates that the proposed framework is considerably more accurate than the widely used guidelines in ASCE/SEI 41-06 and can capture the basic features of the structural behavior.

Comparing seismic performances of pilotis and bare RC frame structures by shaking table tests

This study investigates the role of masonry infill walls in the responses and failure modes of RC frames subjected to earthquake, by applying shaking table tests on two three-story, two-bay, 1/4-scale RC frame structures. Two types of RC frame structures, an infilled RC frame without infill walls in the first story (pilotis frame) and a bare RC frame, are constructed according to the seismic design codes of China. The pilotis and bare frames are simultaneously deployed on a shaking table when I-ELC180 ground motion and Wolong ground motion excitations are used. The two specimens are subjected to a sequence of dynamic tests with increasing intensity. This paper mainly presents and compares the phenomena observed from the shaking table tests of the pilotis and bare frames, including the dynamic properties, acceleration and displacement responses, evolution of damage and final failure mechanisms. The tests indicate that, compared with the bare frame, the infill walls in the pilotis frame can significantly affect the failure mode and damage distribution. Plastic hinges first appear in the 1st story columns for the pilotis frame under seismic loading, while plastic hinges first appear at the beam ends in the 1st story for the bare frame; The damage to the pilotis frame is increasingly concentrated in the 1st story as the earthquake intensity increases, while the damage distribution along the height of the bare frame remains almost the same as the earthquake intensity increases. The maximum interstory drift ratio of the pilotis frame is up to 50% larger than that of the bare frame under the same earthquake intensity.

Influence of Clay Block Masonry Properties on the Out-of-Plane Behaviour of Infilled RC Frames

In order to determine the characteristics that govern the out-of-plane behaviour of masonry infills, two groups of wall specimens were built and tested in the laboratory. Specimens were assembled and tested as described in EN 1052-2 provisions and constitute of flexural strength for a plane of failure parallel and perpendicular to the bedjoints specimens. By obtaining data from experiments, numerical micromodels were developed to predict their mechanical behaviour. A calibration procedure undertaken and results obtained from the experimental campaign were found to be in agreement with those obtained from the numerical models. Additionally, former in-plane infilled frame numerical models were tested with acquired out-of-plane calibrated material model. No significant difference was found.

Openings in infills with horizontal sliding joints: a parametric study to support the design

In the present paper a numerical study is reported, aimed at investigating the role of openings in the in-plane response of infilled RC frames when masonry infills with sliding sub-panels are adopted. Such innovative infills are meant to reduce post-earthquake damage and infill-frame interaction, with respect to traditional solid masonry infills. Their study was carried out mainly on the fully infilled configuration, and limited information is available about its response in presence of an opening. In the paper focus is made on the interaction of the infill with both the surrounding frame and with the specific post placed at the opening side, which is essential to confine the infill and protect the opening fixtures. The adopted numerical model is calibrated on the experimental results of a test performed on a real scale infill wall with horizontal sliding joints and a full-height opening on a side. A parametric study is carried out to investigate the influence of different design parameters. In detail, the focus is placed on the stiffness of the post and on the geometry of the infill (in terms of position of the opening, infill length and sliding joint configurations). The obtained results show the beneficial effect of the post deformability in reducing the infill-frame interaction, with a significant reduction of the shear action exerted on the frame columns and on the post itself. Moreover, the obtained results allowed to define some preliminary recommendations for the design of the infill and of the post at the opening side.

The Effects of Amount and Location of Openings on Lateral Behavior of Masonry Infilled RC Frames

Many design codes didn’t consider masonry infills as structural elements inside moment resisting frames. Therefore, their presence is not assumed in analysis and design process. While, in real they could affect strength, energy dissipation, ductility, stiffness and many other features of moment frames. The presence of masonry infills could also change the reaction of frames exposed to lateral loads like earthquake and wind. This issue becomes more important if the built frame was placed in seismically active region. In current study, the effects of opening location by placing openings in 3 different places and its percentage was evaluated. To this purpose an experimental scaled model was constructed and subjected to cyclic loading. Thereafter, by using simplified micromodeling, numerical modeling performed for extending studies. Subsequently, sensitivity analyses were done to survey the effects of opening ratio on the lateral behavior of intermediate RC moment frames. Analytical results indicate that the openings which were lo20cated at upper corner of the masonry infills will loss more strength. In all of the numerical specimens by increase in opening percentage the lateral strength was decreased. The lateral strength was negligible for infills with greater than 40% openings.

A new macromodel for the assessment of the seismic response of infilled RC frames

SummaryNumerous research studies have proved that numerical models aiming at an accurate evaluation of the seismic response of RC framed buildings cannot ignore the inelastic behaviour of infills and the interaction between infill and frame elements. To limit the high computational burden of refined non‐linear finite element models, in the latest decades, many researchers have developed simplified infill models by means of single or multiple strut‐elements. These models are low time‐consuming and thus adequate for static and dynamic analyses of multi‐storey structures. However, their simulation of the seismic response is sometimes unsatisfying, particularly in the presence of infill walls with regular or (particularly) irregular distributions of openings. This paper presents a new 2D plane macro‐element, which provides a refined simulation of the non‐linear cyclic response of infilled framed structures at the expense of a limited computational cost. The macro‐element consists of an articulated quadrilateral panel, a single 1D diagonal link, and eight 2D links and is able to model the shear and flexural behaviour of the infill and the non‐linear flexural/sliding interaction between infill and surrounding frame. The proposed macro‐element has been implemented into the open source software OpenSees and used to simulate the response of single‐storey, single‐span RC infilled frame prototypes tested by other authors. The above prototypes are selected as made of different masonry units and characterised by full or open geometric configuration.

Usporedba i ocjena modela za simulaciju ponašanja AB okvira s ispunom pod bočnim opterećenjem

In the present study, the behaviour of infilled RC frames under earthquake loading is investigated numerically, and the influence of three different concrete material models on the in-plane behaviour of infilled RC frames is evaluated using the finite element analysis (FEA). For this reason, the efficiency of infilled walls is examined on full scale models. Finite element analysis results show that mathematical model of concrete may change behaviour of infilled RC frames. The post-peak behaviour is especially influenced.

Behaviour of Reinforced Concrete Frames with Central Opening Masonry Infill under Lateral Reversed Cyclic Loading.

This paper will describe the seismic behaviour of masonry infilled RC frame with a central opening structure under reversed cyclic lateral loading. To achieve the purpose of this study, four 1/4-scale single story and single bay RC frame specimens were tested, i.e. one bare frame, one clay brick masonry infilled RC frame without opening and two clay brick masonry infills with a central opening in infills. The ratios of opening size to panel area were 25% and 40%. Through reversed cyclic lateral loading tests, the seismic performance of RC frames with a central opening brick masonry infills was investigated. As the results, significant distinctions of failure mechanism, lateral strength, stiffness, and ductility were observed between these specimens. In the case of infills with a central opening, the cracks sprouted and developed at the corners of the opening. Although the presence of the opening in infill reduces the lateral strength and stiffness overall structure, the brick infilled frames with a central opening of 25% and 40% of panel area show better seismic performance as compared to the bare frame.

Nelinearna seizmička analiza AB okvirnih konstrukcija sa zidnom ispunom

Nelinearna seizmička analiza AB okvirnih konstrukcija sa zidnom ispunom

A novel macromodel for prediction of shear failure in columns of masonry infilled RC frames under earthquake loading

Columns of masonry infilled reinforced concrete frames are prone to shear failure due to the detrimental effect of infill under lateral earthquake loads. This effect is catastrophic in ground storey columns, where the shear force demand is very high. The primary objective of the study is to understand the applicability of the codal recommendations to estimate the shear demand on the columns realistically, and propose an alternative solution for prediction of shear failure of columns by improving the existing macro-modelling techniques. Half-scaled specimens of masonry infilled RC frames tested in an experimental study were considered to evaluate the proposed improvements. Applicability of the improved macromodel was also verified with the results obtained in other past experimental studies. The proposed simplified analytical modelling technique can be used for practical engineering purposes to assess the shear failure of columns and can be utilized for designing or strengthening the shear deficient columns in such frames.

Comparative study on the seismic performance assessment of existing buildings with and without retrofit strategies

A large number of infilled RC frame buildings have undergone moderate to extensive structural damages and even collapsed after the 2015 Gorkha earthquake. The repair and maintenance works are still being carried out in the existing RC buildings, many of them without any consultation with design engineers. Such practices are likely to create a benefit of doubt on the efficiency of the retrofitting works and repair/maintenance works. Therefore, the present study aims to evaluate the seismic performance of the existing non- and pre-engineered buildings, and later employed retrofit measures that are commonly practised in the region. The analytical results revealed that the selected buildings were seismically deficient and are most likely to undergo extensive damage to collapse states, at 0.3 g PGA. It was found that the retrofit measure significantly enhances the stiffness, maximum strength and ductility in the existing buildings. The pushover curves indicated that the steel bracing highly increased the stiffness, strength and ductility capacity in all case study buildings. The steel-braced building was recorded to have increased the maximum base shear capacity by almost ten times for the soft-storey MRT1 building. Similarly, the retrofit measures also eliminated the potential single storey drift concentration recorded in the original building, such that a uniform inter-storey drift profile can be attained throughout. The conditional probability of collapse for the case study buildings, at 0.3 g PGA, ranges from 13.5 to 42% and could be minimized below 4% in the worst case scenario for the shear wall. All the numerical results demonstrated that steel bracing was much more effective in enhancing the seismic performance of the existing buildings.

Evaluation of earthquake load resistance of masonry infilled RC frames using linear and non-linear dynamic analysis

The understanding of the dynamic behavior of structures is essential to design them to resist the lateral loads due to earthquakes. Recent past earthquakes have demonstrated the importance of proper designing of structural members to avoid damages in the buildings and loss of life. Generally the lateral load resistance of masonry infilled moment resisting frames is achieved by frame action and truss action. In this paper the seismic performance of a G + 9 storeyed masonry infilled RC framed building is evaluated by linear and non-linear dynamic analysis. The analysis is carried out using the finite element software-ETABS. The response spectrum and time history pertaining to the specifications as given in the Indian Seismic Code IS 1893:2016 is considered for the analysis. Three different frame models are studied namely, bare frame, fully infilled frame and soft storey frame to understand the lateral load resistance of the frames. The dynamic characteristics of the frames such as time period, frequency, mode shapes, storey displacements, inter-storey drift, over-turning moments and energy dissipation capacity are evaluated and compared. The fully infilled frame shows better seismic behavior than that of other two frames though it attracts more forces.

Effect of URM infills on inelastic floor response of RC frame buildings

The effect of unreinforced masonry infills on the floor acceleration response of inelastically responding mid-rise RC frame buildings is studied using incremental dynamic analyses. Two structural building configurations, uniformly infilled, and with open ground storey are analyzed by using the FEMA P695 far-field ground-motion suite. It is observed that the effect of structural nonlinearity is much more pronounced in case of infilled RC frame buildings than bare RC frame buildings. Sequential failure of infills results in a significant elongation of period of vibration resulting in the shifting of peaks in floor spectrum towards longer periods. Modified floor spectral amplification functions are presented for both uniformly infilled and open ground storey RC frame buildings. The proposed spectral amplification functions are validated using nonlinear analysis of typical buildings for recorded as well as spectrum-compatible ground-motions and can be used to estimate the floor response spectra directly from the code-based or site-specific design spectra.