Civil Engineering Design最新文献

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.

For an assessment of the necessity, the efficiency and the prioritization of repair and upgrading measures for bridges, object-specific knowledge of structural stresses and structural conditions is indispensable. From the identification of traffic occupancy (quantity and quality) and the analysis of the structural reactions, statements on the current load-bearing capacity of an existing bridge will derived. A necessary data basis is the traffic data of the real traffic determined for the specific bridge.

Topology optimization and additive manufacturing complement one another where the first one results in possibly complex structures, and the second one allows for manufacturing of those. For computing optimized components that also fit to the manufacturing limits, the building processes need to be accounted for already during the optimization process. A special characteristic of the additive manufacturing process is the step-by-step manufacturing. Herein, constructing large-scale structures, as for example buildings or bridges, by assembling pre-produced segments can also be considered as additive manufacturing. Especially, a design which also carries the manufacturing or assembling machine, as for example cranes or robots, on different positions during manufacturing is of interest. Therefore, we extend the established thermodynamic topology optimization for a sequential optimization process which considers changing manufacturing loads under structural self-weight.

The objective of the paper is to analyze the shrinkage and expansion strain development in thin slabs made of expansive concrete and reinforced with carbon textile reinforcement. The symmetrical textile reinforcement grid provided a biaxial restraint for the concrete shrinkage and expansion. Strains of the slabs were measured with distributed fiber optic sensors (DFOS) in both directions so that a 2D visualization of their distribution can be presented and analyzed. Parallel, standard restrained expansion tests (RET) were conducted to assess the expansive concrete mixture and large-scale beam specimens with uniaxial steel reinforcement were also equipped with DFOS and analyzed. This study aimed to compare the strains in uniaxially restrained elements with steel reinforcement and biaxially restrained textile reinforced concrete elements, in order to assess to what extent the results of the standard RET can be used for evaluation of textile reinforced concrete members.

The latest global events have shown that climate protection belongs to the biggest current issues of today. In order to initiate the change that is urgently needed, future-oriented processes are required. The excessive use of resources and the associated CO₂ emissions in the construction sector have reached levels that are harmful to the environment and will burden the future generations. Furthermore, a worrisome trend has emerged in the construction industry in recent years. Instead of preserving old and existing building structures, demolition and replacement construction is preferred. Environmental aspects or the historical value of monuments and listed buildings play no role, even though these are essential considerations of our time! How can we put an end to the waste of resources and destruction of local building history? With new and innovative materials—such as the high-performance composite material carbon reinforced concrete, especially in the field of renovation and strengthening of existing structures. A new and improved approval enables to strengthen structures more efficiently and therefore, to save material. As a result, buildings are not only protected from demolition, but also remain being used sustainably.

Against the background of global warming and the associated need to drastically reduce energy and resource consumption, action must also be taken in the building sector. Resource-efficient construction methods must be used that nevertheless allow the increasing construction tasks in areas such as infrastructure and housing to continue to be fulfilled. In order to successfully introduce a new construction method to the market, the aspects of recyclability and economic efficiency are essential, in addition to important government requirements for climate neutrality and technical performance. Above all, the economic viability, that is, the economic advantageousness, as well as its simple applicability compared to competing systems, decides on the success and widespread use of a new technology. Carbon reinforced concrete, with its outstanding technical properties and simultaneous material efficiency, is an important building block toward climate neutrality in the construction industry. It is a promising technology that still has to prove its economic advantages and robust applicability under market conditions. In addition to the infrastructure sector, there is great potential in the area of housing creation, which needs to be tapped for carbon reinforced concrete. For this challenge, it is necessary to design a competitive value chain that allows the realization of marketable products in mass production on existing plant technology. The article gives a short overview of the economic and ecological status quo in the field of prefabricated construction with carbon concrete, using the example of the C³-result building CUBE. In particular, the CUBE-BOX, which is made of prefabricated and semi-prefabricated parts, is examined in more detail and the carbon reinforced concrete components used are compared with classic reinforced concrete constructions in terms of sustainability. In this context, the conceivable global climate protection contribution of the carbon reinforced concrete construction method is forecast based on potential market segments.

The Carola Bridge (Carolabrücke), built in 1971, has a length of approximately 375 m and takes the tram and the B 170 federal road in Dresden across the river Elbe. The intensive use of the bridge and deficits in user-friendliness made building measures inevitable. One part was the widening of the upstream bridge cap. Here, the application of a new nonmetallic reinforcement within the concrete cover was planned to improve the service life of the cap, a so far unique method. Based on an installation test and an investigation of the cracking behavior, both described in the paper, two reinforcement configurations were selected for practical application. The project provides an ideal opportunity to bring carbon and basalt reinforcements closer to the public and to demonstrate their cast in during normal operation on a concrete construction site.