Influence of loading rate on bond shear strength of autoclaved aerated concrete masonry

This study aims to investigate the bond shear strength of autoclaved aerated concrete (AAC) masonry, focusing on the influence of pre-compression and load rates. Experimental results show that the bond shear strength of AAC masonry increases with increasing load rates as well as with increasing pre-compression stress. It is understood from the experimental studies that both loading rate and pre-compression stress significantly affect the failure mode and stress distribution of AAC masonry specimens under shear loading. To provide further insights, the paper aims to develop a nonlinear finite element modelling approach with Abaqus software employing detailed surface-based cohesive contact approaches, which can reliably capture the bond shear behaviour and failure modes of AAC masonry. Higher stress contours are seen at higher displacement rates due to the development of sudden dynamic and irregular loads compared to lower rates. The stress-strain characteristics and the deformed shape of the specimens obtained from the numerical analyses were found to be identical to those from the experimental studies. Instead of expensive and time-consuming experimental tests, the proposed numerical modelling approach can be an effective alternative to studying the bond shear behaviour of AAC masonry

A macro‐model for describing the in‐plane seismic response of masonry‐infilled frames with sliding/flexible joints

Masonry infill walls are among the most vulnerable components of reinforced concrete (RC) frame structures. Recently, some techniques for enhancing the performance of the infills have been proposed, aiming at improving both the global and the local behaviour of the infilled frame structure. Among the most promising ones, there are those that aim to decouple or reduce the infill-frame interaction by means of flexible or sliding joints, relying respectively on rubber or low-friction materials at the interface between horizontal subpanels or between the panels and the frame. Numerous models have been developed in the last decades for describing the seismic response of masonry-infilled RC frames, but these have focused mainly on the case of traditional infills. This study aims to fill this gap by proposing a two-dimensional macro-element model for describing the in-plane behaviour of RC infilled frames with flexible or sliding joints. The proposed modelling approach, implemented in OpenSees, is an extension of a discrete macro-element previously developed for the case of traditional infill panels. It is calibrated and validated in this study against quasi-static tests from the literature, carried out on masonry-infilled RC frames with sliding and rubber joints. The study results show the capabilities of the proposed modelling approach to evaluate the benefits of using flexible joints in terms of minimising the negative effects of the interaction between infill and RC frame and limiting the increase of global stiffness of the system with respect to the bare frame condition

Seismic Performance of Masonry-Infilled RC Frames and Its Implications in Design Approach: A Review

Predicting the seismic response of masonry-infilled (MI) RC frames holds immense importance due to the significant influence of masonry on the structural performance. Despite numerous studies delving into the seismic behavior of these frames, their complex interaction of masonry infills and RC frame presents ongoing challenges for researchers, designers, and standards committees. Although numerous studies have been conducted to investigate the seismic behavior of masonry-infilled reinforced concrete frames, its complex behavior poses a challenge to researchers, designers, and the specification-making committees. In recent years, several national codes have been revised to include the estimation of the stiffness of reinforced and nonreinforced masonry walls and have provided guidelines for the modeling and analysis of structures considering MI. This article aims to provide a comprehensive review of how infilled masonry walls impact the seismic performance of RC frames, drawing comparisons with codal provisions. The focus lies on scrutinizing experimental, numerical, and analytical studies that explore in-plane and out-of-plane behaviors. Factors like masonry strength, stiffness, area of openings, stiffness degradation, energy dissipation capacity, and damage patterns are thoroughly examined. Key findings with critical implications are highlighted, shedding light on potential future research directions in this crucial field

Safety assessment of gravity load–designed reinforced concrete–framed buildings

A large number of gravity load–designed (GLD) reinforced concrete (RC) buildings are found in many seismic-prone countries including India. Many of them were built before the advent of seismic codes or with the utilization of old and inadequate seismic design criteria. Engineers and decision makers need to have information on the seismic vulnerability of such buildings in a given region for mitigation planning. The present study aims to evaluate the relative seismic vulnerability of a GLD building subjected to seismic hazards in a practical load and resistance factor format corresponding to various seismic zones of India. The results of this study show that the relative vulnerability of the GLD building (with respect to a building designed for seismic forces) shows a multifold increase from lower to higher seismic zone. It also indicates that the GLD buildings existing in higher seismic zones of India (IV and V) should be immediately uninhabited as an urgent mitigation measure

Implications of importance factor on seismic design from 2000 SAC-FEMA perspective

The seismic design of buildings uses global ductility factor and occupancy importance factor (IF) as two major fixed parameters in defining the safety of the structure. The study of performance variation of the structure with global ductility factor is available but there is hardly any study that provides information regarding the increase in the level of safety achieved by increasing the IF values. Being a building categorical dependent parameter, IF is used by the international seismic design codes for increasing the design loads of the structure. The change in the level of safety achieved through the variation in the value of the IFs for reinforced concrete (RC)–framed buildings will perhaps be an important and useful representation of the stakeholders for the approximate damage cost estimation. This article performs the structural safety assessment against seismic load using a standard structural reliability method with second-order hazard approximation to evaluate the effect of the IF on the level of safety and the cost associated with the building. Results show that an overall reduction of 50%–60% in the damage index of the selected buildings can be achieved by increasing the IF from a value of 1.0–2.0 with a consequent increase in the cost of the building

Seismic safety assessment of buildings with fly-ash concrete

Sustainable concrete construction has encouraged the utilization of industrial wastes [fly ash (FA), silica fume, ground granulated blast furnace slag, metakaolin, and so forth] as a composite cementitious material due to its high pozzolanic activity. Among them, fly-ash concrete is gaining high popularity in the construction industry due to its many benefits to concrete structures, including increased structural performance. To estimate the seismic performance of FA concrete buildings, a probabilistic study was performed to determine its mechanical parameters at various performance limit states. Weibull, normal, log-normal, and gamma distribution probability distribution models were considered for three goodness-of-fit tests: the Kolmogorov–Smirnov (KS), chi-square (CS), and log-likelihood (LK) tests. Among them, the lognormal distribution was found to be the closest distribution describing the variations in the mechanical properties of FA concrete compared with other distributions. It was observed that 20%–40% partial replacement of FA with cement improves the performance of structures with enhanced structural safety at economical cost

Variability of silica fume concrete and its effect on seismic safety of reinforced concrete buildings

Design of structures made using silica fume (SF) concrete to an acceptable level of safety requires the probabilistic evaluation of its mechanical properties. An extensive experimental program was carried out on compressive strength, flexural strength, and tensile splitting strength of SF concrete. Seven concrete mixes with different proportions of SF were designed to produce 490 concrete samples. The probabilistic models to describe the variability of the mechanical properties of SF concrete were proposed. Two-parameter probability models such as Weibull, normal, lognormal, and gamma distribution were considered for the representation of variability. The probability distribution models were selected based on goodness-of-fit tests such as the Kolmogorov-Sminrov (KS), chi-square (CS), and log-likelihood (LK) tests. The results obtained from the models are useful for description of the variability of selected mechanical properties of SF-incorporated concrete. This study proposes the lognormal distribution function as the distribution model that most closely describes the variations of different mechanical properties of SF concrete from a practical point of view. Further, the performance of typically selected buildings using SF concrete was evaluated through fragility curves and reliability indices incorporating the proposed probability distributions and variability of compressive strength property. It was found that 15%-25% of partial replacement of cement with SF may yield better performance of the frames

Influence of ground-granulated blast-furnace slag on the structural performance of self-compacting concrete

In the last decades, the utilization of industrial waste like ground-granulated blast-furnace slag (GGBFS) has proven itself a great asset in the modern construction industry. Aiming at promoting the green housing initiatives, the present study focused on the study of the influence of GGBFS on the structural performance of self-compacting concrete (SCC). In the initial phase of the extensive experimental program, concrete cubes were prepared with the partial replacements of GGBFS (10%, 15%, 20%, 25%, and 30% with cement) and tested against the control mix in order to investigate the associated mechanical properties (compressive strength, tensile splitting strength, and flexural strength). At 20% GGBFS replacement, the optimum compressive strength was noted, and further addition of GGBFS caused a gradual decrease in the mechanical strength properties. This study further investigated the structural properties like axial load-displacement behavior and failure pattern of RC columns and flexural performance of RC slabs with and without the addition of GGBFS. SCC with 20% GGBFS demonstrated relatively better structural performance, causing the formation of smaller crack width/depth/length compared with the control mix. An empirical relationship was also proposed based on the experimental test results (in relation to the mechanical properties) in line with US and Indian standards code of practice

Variability of mechanical properties of cellular lightweight concrete infill and its effect on seismic safety

Cellular lightweight concrete (CLC) block masonry has gained popularity in the masonry market with the growing demand in the modern construction industry due to its various advantages, including a positive impact on the environment. Subsequently, the detailed characterization of its vital engineering properties should be studied for the development of the mathematical model, analysis, evaluation, and design of structures made of CLC block masonry. The present study investigates the variability in two important strength properties of CLC block masonry and proposes the most appropriate models for their statistical distribution to support probability-based structural analysis and design. This study shows that the assumption of a normal distribution in the absence of an appropriate uncertainty model can result in an inaccurate estimate of the seismic risk of an RC frame building infilled with CLC block masonry. The paper further assesses the seismic safety of a typical RC framed building infilled with CLC block masonry in relation to traditional brick masonry, considering the proposed uncertainty model. Although CLC block masonry results in a higher seismic risk compared with traditional brick masonry, it can be used as an infill material in high seismic areas because it results in a probability of failure within the acceptable limit

Seismic Performance Assessment of RC Multi-Storeyed Gravity Load Designed Frames

A large number of gravity load designed (GLD) RC buildings are found in many seismic-prone countries including India. Many of them were built before the advent of seismic codes or with the utilization of old and inadequate seismic design criteria. Engineers and decision makers need to have information on the seismic vulnerability of such buildings in a given region for mitigation planning. The present study aims at evaluating the relative seismic vulnerability of GLD building subjected to seismic hazards corresponding to various seismic zones of India. The relative seismic vulnerability of GLD buildings for various site hazard conditions is estimated in a practical ‘load and resistance factor’ format as per the Cornell et al. (2002) guidelines. This simplified methodology is based on the nonlinear time history analysis of the building models considering maximum inter-storey drift as the damage parameter and peak ground acceleration as the intensity measure. Limit state capacities for RC frames are defined for the analysis of all the designed frames. The results of this study show that the relative vulnerability of the GLD building (with respect to a building designed for seismic forces) increases many folds from lower to higher seismic zone. It also indicates that the GLD buildings existing in higher seismic zones of India (IV and V) should be immediately uninhabited as an urgent mitigation measure