Failure Criteria and Constitutive Relationship of Lightweight Aggregate Concrete under Triaxial Compression

This paper investigates the compression behavior and failure criteria of lightweight aggregate concrete (LAC) under triaxial loading. A total of 156 specimens were tested for three parameters: concrete strength, lateral confining pressure and aggregate immersion time, and their effects on the failure mode of LAC and the triaxial stress-strain relationship of LAC is studied. The research indicated that, as the lateral constraint of the specimen increases, the failure patterns change from vertical splitting failure to oblique shearing failure and then to indistinct traces of damage. The stress-strain curve of LAC specimens has an obvious stress plateau, and the curve no longer appears downward when the confining pressure exceeds 12 MPa. According to the experimental phenomenon and test data, the failure criterion was examined on the Mohr–Coulomb theory, octahedral shear stress theory and Rendulic plane stress theory, which well reflects the behavior of LAC under triaxial compression. For the convenience of analysis and application, the stress-strain constitutive models of LAC under triaxial compression are recommended, and these models correlate well with the test results.

Introduction: Infrastructural stigma and urban vulnerability

In this introduction to the Special Issue ‘Infrastructural Stigma and Urban Vulnerability’, we outline the need to join up debates on infrastructural exclusion on the one hand and urban stigma on the other. We argue that doing so will allow us to develop a better understanding of the co-constitutive relationship between the material and the symbolic structures of the city shaping urban exclusion and vulnerability. Positing that stigma is not merely a symbolic force but has significant material effects, we show how urban dwellers often experience it in deeply embodied ways, including through impacts on their physical health. Furthermore, stigma is not only imposed on the built environment through discourse, it also emanates from the materiality of the city; this agentic role of the city is often disregarded in sociologically-informed approaches to urban stigma. When infrastructures become sites of contestation about urban inclusion, stigma can be utilised by stigmatised residents to demand connection to public networks, and the wider symbolic inclusion this entails. Through examining the issue of infrastructural stigma in cities and urban territories across the Global North and Global South, as well as the places in between, the nine articles in this Special Issue pay attention to the global relationalities of infrastructural stigma. Ultimately, our focus on the infrastructural origins of stigma draws attention to the structural causes of urban inequality – a reality which is often occluded by both stigma itself and by prevalent academic approaches to understanding it.

Evolution of Hydraulic Conductivity of Unsaturated Compacted Na-Bentonite under Confined Condition—Including the Microstructure Effects

Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping the gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect.

Simulation Research on Risks of Entrepreneurship Platform Organization Complex Network

The risks of entrepreneurship platform are considered one of the most significant factors that affect regional economic development. However, the complexity of the constitutive relationship and the dynamics of the research process have made it difficult for studies to analyse the evolution and risks from the quantitative perspective. According to the analysis perspective of complex networks, this study determined the coupling relationship between the entrepreneurship platform network structure and complex network model. With the results studied and described in the paper, this study had constructed a platform structure model portraying the evolution process of the platform structure under two types of risks by using the simulation method. Three main conclusions are being drawn from the study: Firstly, endogenous and exogenous risks showed substantial results in affecting the changes in microentities and network relationship of enterprises within the platform, causing the robustness of platform to risk to differ significantly. Secondly, based on exogenous risks, the robustness distribution scaling from highest to lowest among three types of platforms studied is hub-and-spoke > mixed > market. Lastly, based on endogenous risk, the robustness distribution scaling from highest to lowest among the three types of platform studies is market > mixed > hub-and-spoke.

Analysis of the bond-slip performance of steel bars and steel fiber recycled concrete based on the constitutive relationship model

In order to promote the application of steel fiber recycled concrete in projects such as roads and bridges, 25 groups of steel fiber recycled concrete with different mix proportions were designed, taking the replacement rate of recycled aggregate and the volume fraction of steel fibers as experimental parameters, and 77 steel bars and steel fiber recycled concrete bonded specimens were made and pasted with strain gauges for the pull-out test. The research results showed that the greater the replacement rate of recycled aggregates was, the lower the bond strength between steel bars and steel fiber recycled concrete was; in the range of 0~1.2%, the higher the mixing amount of steel fibers was, the greater the bond strength of the specimen was; in the range of 0~1.6%, the higher the mixing amount of steel fibers was, the greater the slip value of the specimen under the peak load was; the addition of steel fibers improved the failure behavior of the recycled concrete pull-out specimens; the test specimens mainly had pull-out failure when the mixing amount of steel fibers was 1.2% and 1.6%. Finally, this study modified the bond-slip constitutive relationship model of steel and steel fiber recycled concrete, analyzed the influence of the replacement rate of recycled aggregate and the mix proportion of steel fibers on its bonding performance, and compared the results with the test results. The results demonstrate that the test curve is in good agreement with the fitted curve, which can provide theoretical support for engineering applications.

Identity and help in calls to Victim Support

<p>The link between identity and action is a fundamental topic across the social sciences. A key site to investigate this relationship is social interaction, where identities and social relations are built and used to accomplish action. In this thesis, I used discursive psychology to analyse the relationship between identity and the action of help in recorded calls to a victim support helpline. Victim is a contentious identity, with feminists and other critical scholars pointing to the politics involved when certain people are categorised as victims and others are overlooked. The name of the organisation that was the setting for my research, ‘Victim Support,’ explicitly links a victim identity with rights to access the help the service offers. Drawing on concepts in discursive psychology and using conversation analysis and membership categorisation analysis, I examined how participants oriented to the contentious questions of who victims are and how they should be helped. Drawing on contemporary interactional research which theorises the epistemic, deontic, and affective basis of human social relations, I examined how participants used self-other relations as a resource to build and interpret actions as help. The findings provide evidence for the mutually constitutive relationship between identity and action. Counter-intuitively, most callers did not explicitly categorise themselves as victims when asking for help. My analyses show how call-takers understood callers’ identities as victims even when they did not say so directly. The act of asking for help from Victim Support constituted callers’ identities as victims; and their identities rendered their requests accountable. Call-takers on the victim helpline act as gate-keepers, determining callers’ eligibility before providing help. I analysed how call-takers denied callers’ requests by implicitly or explicitly disavowing their identities as victims. Conversely, I showed that offers of help constituted callers as legitimate victims. Yet even once participants had accomplished joint understanding of callers as victims, they negotiated their respective epistemic and deontic rights to determine what help was needed and how it should be provided. The negotiation of how victims should be helped was particularly salient when callers sought help on behalf of others. Participants negotiated whether the moral obligation to help victims was associated with friends and family members, or institutions. The emotional support and practical advice offered by Victim Support is delivered by volunteer support workers, reflecting a common-sense assumption that these forms of help are normatively available to any competent person. My analyses attend to the dilemmas involved when callers sought help for others rather than providing it themselves. The findings contribute to three main areas of research: conversation analytic study of help as social action; membership categorisation analysis research on categorically organised rights and obligations; and the re-specification of psychological phenomenon as interactional objects within discursive psychology. The mutually constitutive link between identity and help is consequential, as the provision or withholding support can have material effects when callers are highly distressed or in fear for their lives. Thus, studying real-life interaction demonstrates the practical ways identity matters for seeking help.</p>

Identity and help in calls to Victim Support

<p>The link between identity and action is a fundamental topic across the social sciences. A key site to investigate this relationship is social interaction, where identities and social relations are built and used to accomplish action. In this thesis, I used discursive psychology to analyse the relationship between identity and the action of help in recorded calls to a victim support helpline. Victim is a contentious identity, with feminists and other critical scholars pointing to the politics involved when certain people are categorised as victims and others are overlooked. The name of the organisation that was the setting for my research, ‘Victim Support,’ explicitly links a victim identity with rights to access the help the service offers. Drawing on concepts in discursive psychology and using conversation analysis and membership categorisation analysis, I examined how participants oriented to the contentious questions of who victims are and how they should be helped. Drawing on contemporary interactional research which theorises the epistemic, deontic, and affective basis of human social relations, I examined how participants used self-other relations as a resource to build and interpret actions as help. The findings provide evidence for the mutually constitutive relationship between identity and action. Counter-intuitively, most callers did not explicitly categorise themselves as victims when asking for help. My analyses show how call-takers understood callers’ identities as victims even when they did not say so directly. The act of asking for help from Victim Support constituted callers’ identities as victims; and their identities rendered their requests accountable. Call-takers on the victim helpline act as gate-keepers, determining callers’ eligibility before providing help. I analysed how call-takers denied callers’ requests by implicitly or explicitly disavowing their identities as victims. Conversely, I showed that offers of help constituted callers as legitimate victims. Yet even once participants had accomplished joint understanding of callers as victims, they negotiated their respective epistemic and deontic rights to determine what help was needed and how it should be provided. The negotiation of how victims should be helped was particularly salient when callers sought help on behalf of others. Participants negotiated whether the moral obligation to help victims was associated with friends and family members, or institutions. The emotional support and practical advice offered by Victim Support is delivered by volunteer support workers, reflecting a common-sense assumption that these forms of help are normatively available to any competent person. My analyses attend to the dilemmas involved when callers sought help for others rather than providing it themselves. The findings contribute to three main areas of research: conversation analytic study of help as social action; membership categorisation analysis research on categorically organised rights and obligations; and the re-specification of psychological phenomenon as interactional objects within discursive psychology. The mutually constitutive link between identity and help is consequential, as the provision or withholding support can have material effects when callers are highly distressed or in fear for their lives. Thus, studying real-life interaction demonstrates the practical ways identity matters for seeking help.</p>