Seismic Vulnerability and Parametric Study on a Bare Frame Building in Nepal

A diverse range of masonry infill walls is frequently used for low and medium rise reinforced concrete residential and office buildings. Exterior and interior partitioning walls are usually regarded as non-structural elements, even though masonry infill panels alter the seismic behaviour of buildings. Under earthquake loadings, the influence of infill panels may significantly increase stresses developed in some structural elements of the building. Residential and office buildings that have ground floor commercial or parking spaces develop a particularly dangerous pattern, where soft storey mechanisms might lead to premature failures. This paper examines the structural behaviour of masonry infilled RC frames under in-plane loading. A numerical modelling approach is adopted. Infill masonry walls are modelled as equivalent single diagonal struts. This model depicts the general behaviour of a building adequately enough, even if it cannot accurately reproduce local effects resulting from the interaction between frames and infill panels. Nonlinear push-over analyses are carried out for a range of alternative configurations of an outer wall of a building. Bare frame and masonry infilled frame behaviour are compared and the influence of masonry types is assessed. Subsequently, the influence that the ground floor infill walls absence exerts on the failure pattern is analysed. Conclusions reflect the influence that masonry infills have on the behaviour of RC frames for in-plane lateral loads.

Concrete block infill walls, due to their high strength and stiffness, can significantly influence the seismic behavior of the frames. The infill walls can increase the overall lateral frame strength and can also induce local failures in the surrounding frames. In general, if local failure can be avoided, the presence of the infill walls can provide additional reserved strength that can be beneficial to the frames. For this reason, a new RC frame with infill walls could be designed as a bare frame without considering the increase in strength, but measures must be taken to prevent local failures due to the infill wall-frame interaction. However, this infill wall-frame interaction is very complex, and clear design strategies to prevent local failures are not normally given in design codes. For this reason, two full-scale intermediate RC moment-resisting frame specimens with infill concrete block walls were tested under a horizontal cyclic load to study the infill wall-frame interaction. Finite element analysis was carried out to evaluate the response particularly on the infill-frame interactions. Based on the results, a design strategy to eliminate local failure in the surrounding frame is suggested. The proposed method is based on local plastic mechanism analysis of the column considering the variation in the column shear demand and column shear capacity at different states of the response as the frame deforms. The shear demand depends on the magnitude and direction of the bearing force from the infill wall. The column is considered as a captive or slender column depending on the restraint from the infill wall, thereby affecting the shear capacity of the column. The proposed approach can be readily applied without radically changing common design practices and design codes.

Experimental tests on strengthening strategies for masonry infill walls: A literature review

Experimental study on progressive collapse of reinforced concrete frames under a corner column removal scenario

Experimental study on separating reinforced concrete infill walls from steel moment frames

Improperly designed and constructed reinforced concrete (RC) buildings with moment-resisting frame (MRF) systems have proven to perform poorly in earthquakes. During recent earthquakes, particularly during the Marmara (1999), Bingol (2003), and Van (2011) earthquakes, large number of RC MRF buildings either sustained severe damage or collapsed. In most of these buildings, masonry infill walls were installed in the structural frames. These so-called non-structural infill walls can interfere with the structural system and may cause premature failure of the latter especially during stronger ground shaking. If infill walls are used to improve strength, stiffness and the overall performance of a structural system, they need to be designed and constructed accordingly. Diagonal strut FRP/steel strip system is one of the preferred retrofit techniques with its mechanical properties, ease of application and low disturbance to inhabitants

The objective of this study is to use autoclaved aerated concrete (AAC) for infill walls in existing buildings that are unsafe for earthquakes to increase their stiffness. The study included two topics; the first topic introduced six models using AAC in buildings resistance to earthquakes and the effect of self-weight of the buildings comparing bare frame clay partition masonry model (1), bare frame AAC partition masonry model (2), reinforced concrete frames clay infill wall model (3), reinforcement concrete frames AAC infill wall model (4), reinforcement concrete frames AAC infill wall core model (5), reinforcement concrete frames AAC infill wall first and second floors model (6). ETABS software was used to investigate all frame models. Results of the study revealed that AAC infill wall decreases base moment, base shear and displacement. On the other hand, second topic presented five models of single reinforcement concrete frame under lateral loading, considering effect of anchored and unanchored AAC infill wall and clay infill wall. These models are bare frame model (a), RC frame with clay infill wall unanchored model (b), RC frame with AAC infill wall unanchored model (c), RC frame with clay infill wall with anchors model (d), RC frame with AAC infill wall with anchors model (e). Using finite element software (ANSYS WORKBENCH 18.2) failure load, displacement and ductility were presented for all five frames. The results showed that the ‘RC frame with AAC infill wall with anchors’ model gives the biggest failure load whereas displacement and ductility are the lowest.

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

In the composite walls stiffness system of reinforced concrete walls with composite boundary members, boundary members resist most of the moment due to seismic loading. In contrast, the reinforced concrete (RC) wall provides shear resistance. The SRCW system comprises partially restrained steel frames with reinforced concrete infill walls. The steel columns and beams act as boundary members to resist gravity loads and most of the overturning moment due to seismic loading, while the reinforced concrete (RC) infill wall acts as shear-resisting web. The RC infills increase the lateral stiffness dramatically compared to a bare steel frame, thus avoiding excessive drift and reducing the seismic demands on the steel frames. In that way, why not use just steel shear frames instead of partially restrained steel frames with reinforced concrete infill walls? This paper presents a numerical study of the behavior of a composite structural system consisting of steel shear frames with reinforced concrete infill walls (SFRCW). The composite interaction is achieved using welded bolts as shear connectors along the steel frame–infill interfaces. Welded bolts were used as shear connectors because they are frequently used in Colombia due to their ease of installation. The SFRCW system may be particularly appropriate for low-to-moderate-height structures. In addition, the steel shear frame will support gravity loads at the construction stage, allowing progress in height. The system can also be used to strengthen existing steel buildings. The relatively light steel frame constructed using shear connections maximizes the system's economy.This study compared the behavior of the SFRCW with columns acting in their weak and strong axes and with different numbers of shear connectors. It also compared the behavior of the bare steel moment frame, bare steel shear frame, and reinforced concrete wall. The numerical models show interesting results.

The progressive collapse resistance of reinforced concrete (RC) frames in which a middle column has been removed has been investigated by many researchers. However, previous experimental and computational studies have focused mainly on the catenary action provided by longitudinal reinforcement in the beams spanning the missing column. This study investigated the contribution of infill walls. Finite-element analysis was used after calibrating a reference model using test results reported by other researchers. Models were developed for a RC frame with and without infill walls. An equivalent strut was used in the infill walls to allow the removed column load to be transferred through the struts instead of developing catenary action in the beams. A simplified model of the progressive collapse resistance of frames with infill walls was then derived to estimate the peak strength provided by the infill wall under the scenario of middle-column removal.

A probabilistic simplified Seismic Model from Ambient Vibrations (SMAV) of existing reinforced concrete buildings

Progressive collapse mechanisms of post-tensioned reinforced concrete frames considering effect of infill walls

Seismic performance of mid-rise reinforced concrete buildings in Izmir Bayrakli after the 2020 Samos earthquake

In open ground storey buildings, along the building height, sudden change of stiffness takes place. Therefore, the storey is more flexible than adjacent storey. As a result, beams and column in these storey get heavily stressed. The behaviour of building gets changed due to infill walls under lateral loads. However, in industry, while analysing the framed building, the stiffness of infill wall is ignored. To compensate for stiffness, discontinuity IS1893:2002 allows analysis of open ground storey building with a multiplication factor of 2.5 without considering infill walls. According to design office, for low-rise building, the multiplication factor of 2.5 is not real. This gives a call for review and assessment of code recommendation on multiplication factor for low-rise buildings with open ground storey. The present study deals with the modelling of the reinforced concrete structure with infill walls in the software. The results shall be studied for the fully infill wall, partially infill walls and without infill wall.KeywordsInfill wallStorey stiffnessLateral displacementTime periodStorey shearStorey drift

The influence of masonry infill walls on the progressive collapse performance of reinforced concrete (RC) frame structures was investigated in this paper, using a nonlinear dynamic analysis approach. Based on ANSYS/LS-DYNA finite element software, two finite element models of RC frame structures with and without masonry infilled walls were established. Then, the collapse modes of the two RC frame structure models were analyzed for different scaled distance blast loads, different locations of column damage, and different span numbers. The results show that with the increase of explosive amount, the collapse degree of the structure is more serious in the same time. Under the condition of destroying the outermost central column, the degree of progressive collapse of the RC frame model with infilled walls in the same time is lower than that of the RC frame model without infilled walls. The RC frame model with infilled walls is more resistant to collapse when the outermost side columns are damaged. With the increase of span number, the structure is more likely to be damaged and collapsed.