BOLTED CONNECTIONS FOR EASILY REPAIRABLE SEISMIC RESISTANT STEEL STRUCTURES

Recent years have brought significant advances in the design capabilities and construction practices of steel structures. These were partially caused by technological development and a direct effect of the research community efforts towards the mitigation of the earthquake induced damage. Making the traditional structural systems more resilient is one of the directions taken but, more and more, solutions with reduced post-earthquake repair costs are preferred. Steel structures are particularly malleable in the modern spirit of integrating devices which render the structure as “low-damage” or “easily repairable”. The recent earthquakes of Japan and New Zealand have demonstrated the feasibility and the advantages of such structural typologies. The current work presents an investigation on two steel structural solutions, including thus both moment resisting and braced frames, which have the potential of being easily used in practice, with minimal alteration of the design and erection procedures and improved post-earthquake economic benefits. The thesis focuses on (i) bolted connections of detachable short links for eccentrically braced frame and second, and (ii) on bolted friction connections for moment resisting frames. The main objective is to facilitate the application of these structural solutions in practice by enhancing the knowledge of their relevant bolted connection design and behavior

Toma de decisiones compartidas: barreras y limitaciones de las mujeres embarazadas ante la vacunación

INTRODUCCIÓN: las tasas de vacunación en el grupo de las embarazadas siguen siendo subóptimas. Uno de los principales motivos propuestos es la vacilación ante la vacunación, aspecto que ha podido tener un mayor impacto después de la pandemia COVID-19. El grupo SAGE (Strategic Advisory Group of Experts on Immunization) de la OMS considera la comunicación en el entorno clínico entre médico y paciente como una herramienta que contribuye positivamente en la aceptación de las vacunas. La toma de decisiones compartida proveyendo información acerca de los beneficios y riesgos de la vacunación constituiría una de las intervenciones más eficaces. OBJETIVOS: el objetivo principal del presente trabajo es recabar la evidencia disponible acerca de las barreras y limitaciones que surgen en la toma de decisiones compartidas en la vacunación de mujeres embarazadas después de la pandemia COVID-19. MÉTODOS: Se llevó a cabo una búsqueda bibliográfica en tres bases de datos del ámbito de ciencias de la salud (MEDLINE a través de PubMed, Scopus y Embase) sobre artículos originales sobre las barreras y limitaciones de la toma de decisiones compartida ante la vacunación en embarazadas. La revisión y la extracción de las variables de los artículos se llevó a cabo por dos evaluadoras independientes siguiendo las recomendaciones PRISMA. La calidad de los artículos se evaluó a través de las guías STROBE, GUIDED y SRQR, de acuerdo al diseño del estudio. RESULTADOS: se obtuvieron un total de 1021 artículos, seleccionando finalmente 15 para la revisión: 2 eran estudios cuantitativos transversales, 11 estudios cualitativos y 2 de métodos mixtos. Las barreras encontradas para profesionales sanitarios incluyeron la falta de tiempo, el fuerte deseo de respetar la autonomía de las embarazadas en relación a la vacunación y la falta de conocimiento acerca de los beneficios y riesgos de las vacunas. Para las mujeres embarazadas, las barreras halladas fueron: la falta de conocimiento, la percepción a la susceptibilidad frente a las enfermedades, el miedo a los efectos secundarios, barreras organizativas en la accesibilidad a la vacunación y creencias. CONCLUSIONES: la presente revisión recopila las principales barreras presentes en la toma de decisiones frente a la vacunación en embarazadas, por parte de los profesionales sanitarios y las mujeres embarazadas. Se mencionan varias barreras modificables, cuyo abordaje podría contribuir a la implementación de la toma de decisiones compartidas también en el ámbito de la vacunación materna. Asimismo, se describen por primera vez nuevas barreras surgidas a partir de la pandemia del COVID-19.INTRODUCTION: vaccination uptake in pregnant women is still suboptimal. One of the proposed reasons is the vaccination hesitancy. The SAGE group belonging to the OMS considers communication in clinical settings between doctor and patient to be a tool that contributes positively to the acceptance of vaccination. Shared-decision making, providing information about the benefits and risks of vaccinations would constitute one of the most effective interventions. OBJECTIVES: the main objective of this work is to review the available evidence about the barriers and limitations for shared decision-making in maternal vaccination after the COVID-19 pandemic. METHODS:a bibliographic search was conducted in three health science databases (MEDLINE via PubMed, Scopus, and Embase) on original articles about the barriers and limitations of shared decision-making regarding vaccination in pregnant women. The review and extraction of variables from the articles were conducted by two independent evaluators following PRISMA recommendations. The quality of the articles was assessed using STROBE, GUIDED, and SRQR guidelines, according to the study design RESULTS: A total of 1021 articles were obtained, finally selecting 15 for review: 2 were cross-sectional quantitative studies, 11 were qualitative studies, and 2 were mixed-methods studies. The barriers found for healthcare professionals included lack of time, a strong desire to respect pregnant women's autonomy regarding vaccination, and lack of knowledge about the benefits and risks of vaccines. For pregnant women, the barriers found were lack of knowledge, perception of susceptibility to diseases, fear of side effects, organizational barriers in accessing vaccination, and beliefs. CONCLUSIONS: This review gathers the main barriers present in decision-making regarding vaccination in pregnant women, from the perspective of healthcare professionals and pregnant women themselves. Several modifiable barriers are mentioned, the addressing of which could contribute to the implementation of shared decision-making in the field of maternal vaccination. Additionally, new barriers arising from the COVID-19 pandemic are described for the first time

Experimental and numerical study on the T-Stub behaviour with preloaded bolts under large deformations

The bolts and their arrangement strongly influence stiffness, strength and ductility of T-Stub connections. Preloaded bolts are typically adopted to improve the stiffness and limit the opening of the connection under serviceability conditions. EN1993-1-8 allows using two types of high resistance preloaded bolts, namely the German HV (acronym of Hochfeste Bolzen mit Vorspannung, which is the German for High Resistance bolts for pretension and the British/French HR (acronym of High Resistance) without making any distinction. However, the tensile failure modes of these bolts are different (i.e. nut stripping for HV and shank necking for HR) and may affect the ultimate tensile response of the T-Stub connections with weak bolts (e.g. failure mode type 2 and 3). Furthermore, despite the effects of geometrical non-linearities at large deformations are not specifically addressed in current codes, the membrane action developing in the flange and the shear force and bending moment in the bolt may influence the reserve of ductility of the T-Stub that plays an important role in case of seismic and robustness scenarios. In addition, the presence of initial imperfections (e.g. the misalignment of the web as respect to the bolts and the flange bowing) can influence the non-linear behaviour of the connection. The influence of all these aspects on resistance and ductility of T-Stub connections are investigated by means of both experimental monotonic tests and parametric finite element analyses. On the basis of the obtained results, design rules are discussed with the aim to guarantee extra ductility of T-Stub connections

Texture and rheological evaluation of aerated confectionery

Confectionery industry represents a field that uses a large number of ingredients and techniques to develop unique sweet products. To produce aerated confectionery samples two different procedures were used to incorporate the ingredients in the beating vegetable or dairy cream. The objective of this research was to determine the texture parameters and the viscoelastic properties of aerated confections using compression stress-relaxation test and applying a modified Maxwell model. The highest fat content was presented by dairy cream aerated samples (20.04-20.25%), while the samples based on vegetable cream displayed a lower fat content. By applying the modified Maxwell mechanical model to the relaxation curves the equilibrium stress, σe, relaxation time, λrel, viscosity, η, and modulus of elasticity, G0, were determined. The aerated samples’ viscosity was greater than 137.96 kPa·s and less than 451.793 kPa·s; furthermore, Pearson correlation showed that density influences positively this rheological parameter (r = 0.955*). Fixing air into the product structure causes a decrease in density (0.388-0.788 g/cm3), leading to a lower equilibrium stress, a lower elasticity modulus and also a decrease of viscosity and relaxation time

Finite Element Analysis of Composite Replaceable Short Links

Eccentrically braced frames (EBF) with detachable short links are an efficient solution for buildings in seismic areas owing to their high energy dissipation capacity and ductility and ease of repair in the earthquake aftermath. Past studies revealed that short links can develop shear overstrength (i.e. Vu/Vp, where Vu is the ultimate shear strength and Vp the corresponding plastic resistance) larger than the value recommended in EC8 (i.e. Vu/Vp =1.5). One of the factors causing the higher shear overstrength is the presence of axial restraints that leads to the development of tensile forces in the link at large levels of rotation. Another reason for higher shear overstrength is the composite slab that can resist the shear distortion together with the short link. Within the DUAREM project, full scale pseudo-dynamic experimental tests were carried out on 3D EBF allowing thus the investigation of replaceable links considering two arrangements: (i) steel solution – the link was uncoupled from the slab (ii) composite solution – the slab and link are connected. The aim of this paper is to present the results of finite element analyses (FEAs), based on calibrated models and the comparison between the obtained results and the experimental tests performed within DUAREM project. The numerical investigation carried out aims to evaluate the shear overstrength and the level of axial force in the link for both tested configuration

Finite element simulations on the ultimate response of extended stiffened end-plate joints

The design criteria and the corresponding performance levels characterize the response of extended stiffened end-plate beam-to-column joints. In order to guarantee a ductile behavior, hierarchy criteria should be adopted to enforce the plastic deformations in the ductile components of the joint. However, the effectiveness of thesecriteria can be impaired if the actual resistance of the end-plate material largely differs from the design value due to the potential activation of brittle failure modes of the bolt rows (e.g., occurrence of failure mode 3 in the place of mode 1 per bolt row). Also the number and the position of bolt rows directly affect the joint response. The presence of a bolt row in the center of the connection does not improve the strength of the joint under both gravity, wind and seismic loading, but it can modify the damage pattern of ductile connections, reducing the gap opening between the end-plate and the column face. On the other hand, the presence of a central bolt row can influence the capacity of the joint to resist the catenary actions developing under a column loss scenario, thus improving the joint robustness. Aiming at investigating the influence of these features on both the cyclic behavior and the response under column loss, a wide range of finite element analyses (FEAs) were performed and the main results are described and discussed in this paper

Finite element modelling of detachable short links

Eccentrically braced frames with replaceable links are viable seismic resisting systems that guarantee large dissipative capacity and quick and easy replacement of the damaged dissipative zones after seismic events, thus reducing the repair costs. Experimental tests carried out within DUAREM research project [12] demonstrated the high effectiveness of this system and highlighted the importance of the bolted connections of the shear links on the system response at both global and local level. In order to investigate the behaviour of the tested detachable links, finite element analyses have been carried out. The finite element (FE) models are calibrated on the basis of the experimental response curves in terms of the shear force and link rotation. Once calibrated the finite element models, several parameters have been investigated such as the type of pre-loadable bolts (i.e. HR and HV), the level of bolt clamping force, the boundary conditions, the presence of constructional tolerances (e.g. initial gap between end-plate at both link ends). The results from the parametric study enables the characterization of the shear and axial force interaction on the link end connections

Removable friction dampers for low-damage steel beam-to-column joints

Beam-to-column joints equipped with friction dampers are promising solutions to improve the performance of steel moment resisting frames due to the possibility to guarantee large dissipation capacity limiting the structural damage under severe seismic conditions. In this paper, the experimental tests and the numerical simulations of two types of joints are shown and discussed with the aim of developing pre-qualified configurations. The friction dampers are designed to be easily removable from both the lower beam flange and the column face by means of bolted connections. The devices are composed of a stack of steel plates conceived to assure symmetrical friction. The friction surface is set in vertical direction in first case and in horizontal direction in the second type. The experimental tests confirmed the effectiveness of both examined joints and the finite element analyses allowed characterizing their local response, thus providing additional insights to improve the design requirements

The fire behaviour of extended stiffened joints designed for seismic actions

The structural behaviour of steel moment resisting frames (MRFs) is strongly dependent on the beam-to-column joint behaviour. The role of the joints is crucial especially under accidental natural and human induced actions, as in the cases of earthquake and fire scenarios, which can occur subsequently after severe seismic events in urban areas. The study summarized in this paper aims at investigating the fire behaviour of seismically designed extended stiffened end-plate joint by means of finite element analyses (FEAs). The joint performance was investigated considering two scenarios: (i) in the first case the assemblies were subjected only to the fire action; (ii) in the second scenario the fire actions were applied to seismically damaged joints. The numerical results show that the fire action changes the restraining capacity of the joint, and local failure can also occur, especially when fire occurs after severe seismic damage