Dynamic amplification factors of girder and cables of extradosed bridges during sudden cable failure

The rupture of a cable in cable-supported bridges is an accidental condition that should be considered during the design phase due the impact that this situation could have on the structural safety of the bridge and users. For that reason, design guidelines suggest carrying out a pseudo-static analysis where the failing cable is replaced by a load of the same magnitude as the pre-rupture tension but applied in the opposite direction and multiplied by a dynamic amplification factor (DAF) between 1.5 and 2.0. Previous studies in cable-stayed bridges have shown that the pseudo-static approach may not be suitable. Due to the wide use of extradosed bridges in infrastructure projects around the world, a computational analysis was performed in this investigation to estimate the dynamic amplification factors of extradosed bridge girders and cables when sudden failure of an extradosed cable occurs. The main goal of the study is to determine whether the pseudo-static approach suggested in the guidelines is acceptable. Linear response history analyses were performed by using computational models of extradosed bridges in which the girder stiffness and the suspension (lateral or central) and cable layout (fan or harp) of the cables were modified. From the analysis, the DAFs were calculated and compared to those recommended in the design guidelines. The calculated DAFs for the axial forces and bending moment in the girder of the bridges and for the axial forces in the extradosed cables were smaller than 2.0. However, in some cases the DAF for shear forces were higher than 2.0, especially when the girder stiffness was relatively low. The results indicate that the recommendations of the design guidelines are adequate for extradosed bridges, which is a result of the relatively high stiffness of the girder and low inclination of extradosed cables. Despite this, response history analyses like the one performed in this study are recommended to assess the response of the bridge under cable breakage.

Metamorphoses of Portrait Genre in Russian Art at the Turn of the 18th–19th Centuries

The article is dedicated to the research of changes in the development of portrait painting in Russian art at the turn of the 18th–19th centuries. A more common approach in the academic literature is a study of typological variants for the portrait image within the stable system, formed under the influence of classicism, or the review of a new concept in portrait painting, embodied by the artists of Romantic period. In that regard the transitional stage, related to the fundamental revision of portrait’s nature as a specific genre, lacks the close attention of researchers. The crisis of Enlightenment’s ideals at the end of the 18th century causes a rethinking of the relationship between a person and the outside world. This tendency directly influences the art of portraiture, which is now distinguished by more expressed dynamism of image. This is particularly important to the national tradition of portrait painting in the 18th century, which before showed the static approach for the representation of model and the moderation of portrait characteristic. Meanwhile, the fluidity becomes not only a method of artistic expression in a single work, but also a guiding principle for the modification of portrait painting at the system level. In other words, there is a new understanding of the fundamental categories inherent in the portrait genre: the popularity of more compact forms of portrait art, the ratio of ceremonial and chamber trends, new relationships between the master and the model, the active interaction of the individual and the surrounding nature. The interest in English culture also plays an important role in these processes. Despite the transitional nature of the era and external influences, Russian portrait painting at the turn of the 18th–19th centuries remains one of the main national features of genre — the prevalence of semi-ceremonial variants of image.

Mathematical simulation of the processes of two-beam laser controlled thermal-splitting of quartz glass

The paper presents the results of modeling the processes of controlled thermal cracking of quartz glass under the parallel action of two infrared laser beams of different geometries on the material: with maximum intensity in the center and with zero intensity in the center (annular section). To calculate the temperature distribution in the material, the method of Green's functions was used, which allows us to obtain a well-interpreted solution for almost any type of function of surface heat sources. Further, taking into account the quasi-static approach, using the methods of the classical theory of thermoelasticity, thermoelastic microstresses were calculated, both on the surface and in the depth of the material. It is established that the simultaneous use of these two types of laser exposure makes it possible to control the temperature field more efficiently, and create prerequisites for the most stable formation of a microcrack. The simulation results show that with a bi-beam effect, the micromechanical stresses necessary for the formation of a microcrack are realized in shorter time intervals, both on the surface and in the depth of the material, which allows increasing the processing speed by up to 30 %. Strengthening control over the process of controlled thermal cracking can significantly reduce the percentage of defects and improve the quality of the resulting microeletronics products.

Should biogenic carbon be analysed separately in the calculation of the GWP indicator?

The life cycle assessment method is widely accepted for calculating the environmental impacts of buildings. However, the approaches used to translate greenhouse gas emissions to a global warming potential score are largely criticised. By following a static approach (known as 0/0) and a time-dependent approach (known as dynamic) in this paper, we assessed the environmental impacts of two buildings with structures made of reinforced concrete and wood, respectively. The relative difference between the results calculated with the 0/0 approach and the time-dependent approach were larger for the building with the wooden structure. A more detailed analysis identified biogenic carbon as the source that was most responsible for this difference in results. For this reason, biogenic carbon should be treated separately and must be calculated with the time-dependent approach. Meanwhile, the impacts from fossil energy sources should be calculated with the 0/0 approach.

A Straightforward Procedure for Deriving the Biaxial Interaction Diagrams of RC Sections in Fire

Based on the lower bound static approach of the yield design (or limit analysis) theory, this contribution presents a straightforward computational procedure for establishing the biaxial interaction diagrams of RC sections in fire conditions, taking into account the experimentally-based relationships linking the degradation of material strength properties to the temperature increase. In the present approach, material characteristics are introduced in two steps: (i) a preliminary heat transfer analysis for evaluating the temperature distribution on the RC section and (ii) the introduction of reduced factors as functions of temperature into both the concrete and steel strength properties. For illustrative purpose, calculations will be conducted on a typical RC section subjected to different fire exposures. Finally, the theoretical predictions will be compared to those obtained from numerical simulations using a finite element software.

Seismic Analysis of a Limestone Rock Slope Through Numerical Modelling: Pseudo-Static vs. Non-Linear Dynamic Approach

In the present work, a seismic analysis was performed in advance on a limestone rock slope (height = 150 m) outcropping along the Tagliamento River valley, in the Friuli Venezia Giulia Region, north-eastern Italy. The analysed slope is characterised by strong rock mass damage, thus resulting in a critical stability condition (unstable volume = 110,000–200,000 m3). The seismic analysis was performed adopting the 2D finite difference method (FDM) and employing both a pseudo-static approach and a non-linear dynamic approach. Model outcomes demonstrate that the seismic motion induces internal, localised ruptures within the rock mass. Some important differences in the mechanical behaviour of the rock slope were highlighted, depending on the specific modelling approach assumed. When adopting a pseudo-static approach, the slope failure occurs for PGA values ranging between 0.056 g and 0.124 g, depending on the different initial static stability condition assumed for the slope (Strength Reduction Factor SRF = 1.00–1.15). According to the non-linear dynamic approach, the slope failure is achieved for PGA values varying between 0.056 g and 0.213 g. Pre-collapse slope displacements calculated with the pseudo-static approach (12–15 cm) are much more greater than those obtained through the non-linear dynamic approach (0.5–3 mm). The modelling results obtained through the non-linear dynamic analysis also testify that the seismic topographic amplification is 1.5 times the target acceleration at the slope face and 2.5 times the target acceleration at the slope toe.

Transient gas pipeline flow: analytical examples, numerical simulation and a comparison to the quasi-static approach

The operation of gas pipeline flow with high pressure and small Mach numbers allows to model the flow by a semilinear hyperbolic system of partial differential equations. In this paper we present a number of transient and stationary analytical solutions of this model. They are used to discuss and clarify why a PDE model is necessary to handle certain dynamic situations in the operation of gas transportation networks. We show that adequate numerical discretizations can capture the dynamical behavior sufficiently accurate. We also present examples that show that in certain cases an optimization approach that is based on multi-period optimization of steady states does not lead to approximations that converge to the optimal state.

Comparison of Two Cutibacterium acnes Biofilm Models

The study of biofilms in vitro is complex and often limited by technical problems due to simplified models. Here, we compared C. acnes biofilm formation, from species involved in bone and prosthesis infection, in a static model with a dynamic model. Using similar parameters, the percentage of live bacteria within the biofilm was higher in dynamic than in static approach. In both models, bacterial internalization in osteoblast-like cells, playing the role of stress factor, affected this proportion but in opposite ways: increase of live bacteria proportion in the static model (×2.04 ± 0.53) and of dead bacteria proportion (×3.5 ± 1.03) in the dynamic model. This work highlights the huge importance in the selection of a relevant biofilm model in accordance with the environmental or clinical context to effectively improve the understanding of biofilms and the development of better antibiofilm strategies.

Seismic bearing capacity of shallow strip footing embedded in slope resting on two-layered soil

In this paper, the limit equilibrium method with the pseudo-static approach is developed in the evaluation of the influence of slope on the bearing capacity of a shallow foundation. Particle swarm optimisation (PSO) technique is applied to optimise the solution. Minimum bearing capacity coefficients of shallow foundation near slopes are presented in the form of a design table for practical use in geotechnical engineering. It has been shown that the seismic bearing capacity coefficients reduce considerably with an increase in seismic coefficient. Be sides, the magnitude of bearing capacity coefficients decreases further with an increase in slope inclination.