Civil Engineering Design最新文献

The residual structural lifetime of concrete bridges is often limited by fatigue of the prestressing steel. In practice, numerical calculations of the structure are combined with Miner's rule—based on load frequencies and stress amplitudes—to estimate the damage. Thereby, various parameters must be accounted for whereof a few are actually relevant. Structural monitoring is valuable to increase the accuracy of lifetime predictions, but usually experts choose the right parameters on experience only. A more objective assessment can be reached by sensitivity analysis. A powerful method is provided by Sobol's variance-based indices. They quantify the influence of a single parameter's variance on the model's total variance and account for interactions in nonlinear models, too. Exemplified on a reference structure, sensitivity indices are determined. Meanwhile specific characteristics like the nonlinear behavior of concrete after cracking are considered. In this case, the key elements of lifetime prediction turn out to be the time-dependent losses of prestress and the traffic loads.

New materials allow new building designs and construction types. However, initial construction projects using the new materials show that traditional construction principles - in the case of carbon reinforced concrete those derived from steel reinforced concrete - are still being used. In other words, conventional materials are merely substituted. Only combined with intelligent construction strategies it is possible to exploit the full potential of innovative materials. Detached from established patterns of thought, the fundamentals for a new way of building with concrete are to be created in the frame of the Collaborative Research Centre Transregio (CRC/TRR) 280 project “Design Strategies for Material-Minimised Carbon Reinforced Concrete Structures–Principles of a New Approach to Construction” at Technische Universität Dresden (TUD) and RWTH Aachen University. These are to be based on profound insights into the mechanical behavior of novel mineral structures. Innovative lightweight construction strategies and material composites reduce resource and energy consumption while maintaining high levels of usability, structural safety, and durability, while the aspirational esthetics make a valuable contribution to the culture of building. The long-term research alliance of TUD and RWTH pools the excellent competencies, inspiring research into material-minimized construction with mineral composites. The article highlights the research activities planned for the first period from July 2020 to June 2024.

Building in heavy rain is seldom beneficial, but common practice on site. It promotes inaccuracies and impairs the use of modern but sensible high-performance materials and costs time, since disruption in construction frequently causes complicated returns to the planning process. Nevertheless, a handcrafted production process is still considered the one and only alternative since all buildings are unique and thus must be manually constructed on site. Indeed? The priority program entitled “Adaptive modularized constructions made in a flux” funded by the German Research Foundation follows a completely new approach. Buildings are divided into similar modular precast concrete elements, prefabricated in flow production, quality-assured, and just-in-time assembled on site. Comparable to puzzles with many pieces, the uniqueness of the structure is maintained. The motto is: “Individuality on a large scale-similarity on a small scale”. The contribution presents approaches of modularization, production concepts, and linking digital models. Serial, stationary prefabrication enables short production times and resource-efficient modules that are assembled to load-bearing structures with low geometrical deviations. Stringent digitalization ensures high quality of all intermediate steps. These comprise fabrication, assembly, and the whole service life of the structure. The result is a lean production process.

Wind flow transfers forces to the wind turbine's rotor blades. These then set the rotor in motion. The hub and the gearbox, where present, transfer this rotational energy to the generator for conversion into electrical power. All the rotating components have significant mass and are located at the head of a slender, elastic load-bearing tower in which they induce dynamic effects. The resulting vibrations, generated at the upper end of the tower, are modified by the dynamic properties of the tower structure and pass through the foundations into the ground. Broadband seismometers record these ground vibrations not only directly adjacent to the wind turbine but also at greater distances of (up to) several kilometers from the turbine. We are aware that local residents and opponents of wind power consider that these vibration phenomena bear potential negative health effects. In the context of this paper, seismic vibrations were measured at the foundation of a 2 MW reference turbine. These seismic signals were compared to numerical simulations. Based on this, we explain the physical background. In the past, any ground vibrations measured have usually been attributed exclusively to the excitation frequencies from the rotor. However, the investigations presented here show that the structural properties of the tower structure significantly influence the type and intensity of the vibrations induced in the ground and dominate the ground motion amplitudes. Finally, we show that the targeted use of absorbers can significantly reduce the vibrations induced in the ground.

Cracks are an essential characteristic of reinforced concrete (RC) construction. Serviceability and durability, however, require a reasonable limitation of the maximum crack width. The prediction of the maximum crack width of RC, however, is not trivial and has been much debated over the past decades. This article starts with a fundamental comparison of basic procedures for determining the crack width, namely using a mechanical or calibrated model. Following, the behavior of reinforced concrete during crack formation is thoroughly discussed with a focus on the bond stress-slip relation at the reinforcement-concrete interface and with regard to the particular crack stage. Based on these fundamentals, a mechanical calculation model is then proposed for practical calculation of maximum crack width in RC members. The suitability of the proposed model is demonstrated by the comparison of predicted and experimentally obtained maximum crack widths for a database including 460 crack width measurements. It is shown that the current state of knowledge enables a mechanically plausible calculation of the maximum crack width. Although the formulation based on the bond law is not trivial, the calculation model can be prepared with appropriate simplifications in a practical way.

The use of fire protection materials is a common approach to ensure the fire resistance of steel elements exposed to fire. In this article, experimental investigations regarding the thermal behavior of gypsum plasterboards for steel elements exposed to natural fires are presented. Material properties, such as the specific heat, the thermal conductivity, and the density of gypsum plasterboards, have been investigated yet, but not especially for natural fire scenarios with different heating rates and cooling phases. For this purpose, experimental investigations of gypsum plasterboards under natural fire exposure are presented. Based on our own experimental investigations, the thermal properties of the investigated gypsum plasterboard for both the heating and cooling phases are demonstrated. Additionally, results from a large-scale fire test on loaded steel beams as well as unloaded steel columns protected with gypsum plasterboards are presented. The test results show a clear dependency on the heating and cooling rate. Furthermore, the thermal material properties change within the heating and cooling phase. So, the main objective of this article is to provide the thermal properties of selected gypsum plasterboard exposed to natural fires in the heating and cooling phases.

Thin glass is typically applied for displays on devices. In addition, it enables new applications in architecture, for example, in glass façades. Due to its high strength and small thickness (0.1-2 mm) thin glass is very flexible, lightweight and easily bendable. However, thin glass cannot simply replace conventional façade glazing. To avoid too high deformations of the glazing as a result of the high flexibility, it must be stiffened. An appropriate solution is the use of sandwich panels consisting of two thin glass panes with an inner polymer core. To achieve lightweight façade elements, 3D printed polymer structures are used instead of a solid core. The present study is dedicated to find a suitable adhesive to bond the polymer core to the thin glass. The mechanical and thermomechanical performances of different combinations of typical 3D printed polymers and transparent adhesives are evaluated. In addition, the influences of temperature and UV aging that occur in the area of the façades are investigated.