Civil Engineering Design最新文献

This paper summarizes the results of two research projects that were carried out between 2016 and 2022 at the VDZ (Verein Deutscher Zementwerke) in Düsseldorf. The objective of the projects was to examine the influence of the cement type as well as the physical and chemical properties of the hardened cement paste on the explosive spalling of concrete in the case of fire. A particular focus was set on studying the way in which the concrete's moisture content contributes to the spalling phenomenon. The findings obtained for the different concretes examined in the dedicated experimental program were evaluated to better explain the mechanisms causing the heat-induced explosive spalling of concrete.

A resource-efficient use of concrete as a construction material can be achieved by adapting the individual shape of a component under consideration to the stresses that occur and by arranging composite construction materials (e.g., reinforcing steel, prestressing steel, or structural steel) in suitable areas of the component. Due to the advancing digitalization in the construction industry, for example in the context of Building Information Modeling, computer-aided 3D modeling methods are increasingly being used in the planning of structures. These allow engineers to design components in free form. In reinforced concrete, prestressed concrete, and composite construction, the design of such components is currently still associated with great effort. In the context of the development of a practical method for the calculation of free-form concrete components, this paper presents a CAD-integrated method for the calculation of cross-section values. Cross-section values are required as an essential calculation basis when real, three-dimensional structural components are treated using simplified calculation theories, such as the beam theory. In this paper, the mathematical and numerical fundamentals of a method for the calculation of cross-section values of free-form concrete, reinforced concrete, prestressed concrete, and compound components are presented. The calculation method is based on flat geometric regions described by Non-uniform Rational B-Spline tensor product surfaces, which can be extracted from solid models, for example.

The consistent evolution of concrete has led to a variety of concrete types that enhance the material's versatility, cost-efficiency, and sustainability. Despite the rapid development and extensive research regarding steel fiber-reinforced concrete (SFRC) in the last decades, there are still knowledge gaps on the material's resistance against locally applied tension loads on anchor bolts, as well as the interaction of possible nonhomogeneous fiber orientations on the anchorage axisymmetric stress field. This aspect becomes particularly relevant since anchors are placed at the component boundaries, where fibers tend to align parallel to the external surface. Through an innovative experimental investigation on 64 single-bonded anchors using layer-casting concrete and a supporting set of nonlinear finite element simulations, this work aspires to exhibit the influence of controlled unidimensional fiber orientation on the load-bearing capacity and behavior of anchorages in SFRC.

In civil engineering, carbon is typically regarded as a modern material to serve as reinforcement in concrete structures. Compared to steel reinforcement, it features two substantial benefits: It is not sensitive to corrosion, and has an enormously increased tensile strength. In contrast, carbon reinforcement is sensitive to lateral pressure and lacks the property of strain hardening. As a first step of establishing carbon reinforced concrete as a new building composite material, carbon reinforcement has basically served to replace the state-of-the-art steel reinforcement. This target led to pioneering findings with respect to determining the material properties of the composite and developing advanced individual components. However, barely substituting steel by carbon does not allow to fully utilize the carbon's benefits while its disadvantageous properties reveal the limits of this approach. Instead, novel design principles are required to meet the material's nature aiming at appropriately using its beneficial properties. Currently, new construction principles are being researched for high-performance building material combinations such as textile and carbon reinforced concrete. This paper provides an overview of baselines in the preliminary stages of this research. The overview includes history, inspiration, concrete matrices, non-metallic reinforcement, structural elements, modeling, production, tomography, and sustainability. The objective of the study is to provide a baseline for the envisaged development of principles for future construction: radically new concepts for the design, modeling, construction, manufacturing, and use of sustainable, resource-efficient building elements made of mineral building materials with the aim of entirely benefiting from the materials' potential.

Due to climate changes and environmental considerations, the current transportation changes to modern vehicles with different vehicles models and engine types. Especially vehicles with alternative types of drive, such as electrical vehicles, are increasing. This raises the question of whether modern vehicles, such as electric vehicles, lead to an increased fire risk as well as an increased heat release rate (HRR). In this article, a new fire design approach for modern vehicles is presented to evaluate the fire risk of electric vehicles compared to vehicles with combustion engines with respect to the fire resistance of the structural elements in open car parks. For this purpose, HRRs of different vehicles are analyzed and an approximated approach for modern vehicles is derived. The methodology can be used for performance-based design, where the HRR plays a fundamental role. Furthermore, modeling approaches of the vehicle dimensions are presented, which are based on statistical data of the German Federal Motor Transport Authority. The vehicle dimensions are used to determine the fire spread time between vehicles using a parameter study. Based on the statistical data analyses and the parameter studies, this article provides a new fire design approach for modern vehicles in fire.

The new innovative composite material textile reinforced concrete (TRC) has been intensively investigated in Germany since the end 1990s. It has become increasingly important in the construction industry. Compared with conventional steel reinforcement, TRC has advantages such as higher load-bearing capacity, higher strength-to-weight ratio, better ductility, and non-corrosive behavior. This made them a subject of extensive research and diverse applications both nationally and internationally. In 2004, Xu et al. started research on bond properties of TRC in China in cooperation with Hans-Wolf Reinhardt et al. from the University of Stuttgart in Germany. Since then, there have been numerous researches on TRC in China. This article introduces a calculation method for the flexural capacity of reinforced concrete (RC) beams strengthened with TRC in China. For comparison, the dimensioning procedure in Germany is also presented. Subsequently, the two models are compared with each other in a case study. Both models in China and Germany have the same mathematical background and also provide similar results. However, they have some differences in definitions of material characteristics (e.g., design concrete compressive strength, strain, and stress distribution) and consideration of the damage resulting from the preloading stage.

In this study, the influence of different water saturation achieved by different storage conditions on the static and dynamic compressive strength of three different concretes were investigated. The specimens were first dried then water-saturated and tested both under static and impact loading. The impact tests were carried out in a split Hopkinson bar. Depending on the concrete strength class, increases in the compressive strength of 200%–300% at strain rates in the range of 90–160 1/s were observed. Compared to storage under ambient conditions, the compressive strength decreases as a result of drying due to microcrack formation. Furthermore, the concretes compressive strengths of water-saturated specimens decrease compared to dry specimens. This decrease was observed under both static and impact loading and is independent of the strain rate. The failure of the dry specimens was more explosive with an increased number of cracks compared to water-saturated specimens.

Polymer-modified bentonite has reached significant attention in recent years, as polymers have been found to increase the resistance of clay barriers to detrimental environmental conditions. Studies on polymer modification of clays for barriers, in most cases, address a specific bentonite with a specific means of modification based on a specific polymer product. The term polymer, however, generally describes a broad category of macromolecules able to create a wide range of possible properties of the modified clay. This article reviews the basics of polymer modification of clays for use in hydraulic barriers to provide a general basis for comparison and design of different modification products and methods. Basics of both primary material categories, that is, polymer and clay, are presented, followed by possible polymer–clay interactions related to polymer charge properties and structure. Possible enhancements associated with polymer modification, but also open questions are addressed.

Glass fiber reinforced concrete (GFRC) comprises of hydration products of cement or cement plus sand, and glass fibers which take part in the concrete as reinforcement characteristics. GFRC has been used for over 50 years in several construction elements, such as facade panels, decorative no recoverable formwork, and other products. However, various anchor elements and pad hooks are needed to attach large or small parts made of GFRC panels to the main structure of the buildings. The corrosion rate of embedded metal fasteners over time is related to the water impermeability properties of the GFRC elements. In this study, corrosion of an electro galvanized pad hook embedded in 10–20 mm of the GFRC panel was investigated as a result of the salt spray test performed in accordance with ASTM B 117 standards. At the end of the experiment, the embedded pad hook was taken from the GFRC and analyzed by scanning electron microscopy, energy-dispersive spectroscopy methods. The results showed that the embedded pad hook in the GFRC, which was examined in the test procedures comply with the TS EN 12467 standards, was not corroded by 120-h test carried out in accordance with ASTM B 117 standards.

When evaluating existing bridges, supporting structural monitoring is increasingly being used in order to obtain the stresses in the structure more realistically than purely mathematically and to calibrate the calculation model. The question of how the additional information obtained through measurements have to be taken into account within the recalculation, including its safety concept, is currently still normatively unclear. On the load side, this can be done through the modified definition of the target load level or, alternatively, through object-specific load models for load-bearing capacity and fatigue to map the actual traffic. Furthermore, on the basis of the measurement data, the necessary safety factors can be justified, also taking into account future traffic developments, while maintaining the normatively required level of reliability.