Civil Engineering Design最新文献

The paper presents currently applied methods to test and monitor the preload level in mechanical fasteners and evaluates them with respect to the quality of the gained measuring results. Both, visual inspection methods and electronic state-of-the-art measurement techniques are presented. This contribution introduces recently developed and patented innovative methods to test and monitor the preload level in mechanical fasteners. The methods developed include a smart mechanical fastener with pressure indicator and a smart electronic measuring screw nut. The smart mechanical fastener has no electronic features and is able to display the loss of preload through a red dot that occurs on the upper end of the fastener. The smart measuring screw nut is an electronic fastening element, that records the current value of preload in a time-discrete or permanent manner. In order to investigate the suitability for daily use and long-term stability of the novel methods to test and monitor the preload in mechanical fasteners, laboratory experiments and in-situ tests were executed. The gained results are presented and discussed.

In building envelopes, sandwich elements with facings made of glass currently require either adhesives or mechanical connectors. The avoidance of any connectors seems to be favorable in terms of resource and energy savings both in production and in building envelopes. The present studies are part of the development of a glass-rigid foam-concrete sandwich element without additional adhesives and mechanical connectors. This paper reports on the structural bond behavior between polyurethane rigid foam and float glass with different surfaces with or without applying a bonding agent. Tensile bond and shear tests show, that a sandblasted toughened glass surface results in cohesive failure of the insulation layer. The two production-related surfaces of float glass are defined as atmosphere and tin side. Both surfaces offer an adhesive failure between the insulation layer and glass. Test specimens of glass and insulation layer without bonding agent show no significant differences between the atmosphere and the tin side. Overall, the test specimens with bonding agents achieve higher levels of adhesive tensile bond and shear strength. Light and electron microscopic studies of fractured surfaces show, that the bonding agent has a significant influence on the wetting and pore formation of the liquid polyurethane.

Around the world, building stocks are the dominant consumers of mineral resources. Mining activities for the supply of construction materials can lead to conflicts in land use. In order to minimize such sources of conflict, we need improved knowledge of material consumption in the built environment. For this, we can make use of material flow analysis (MFA), which in turn requires the determination of material composition indicators (MCIs). Usually, such indicators are defined for a building type. Currently, there is a lack of research on the impact of material substitution on these MCIs as well as studies on the potential for resource-saving that take technical issues into account. This contribution describes a preliminary study on material substitution in six different reference buildings which compare the bill of materials for structures constructed using standard clay bricks vs potential material substitutes such as hollow, lightweight, or autoclaved aerated concrete blocks. The results show that considerable reductions in material consumption can thereby be achieved for certain parts of the considered buildings. In the future, these effects should be incorporated in the MCIs as key variables for an MFA.

The narrative sustainable building is core message of European politics. Strategies discussed in this regard concern above all material minimization by using new more efficient manufacturing technologies, new form finding approaches for load-bearing structures or new high-performance materials. The goal of the research project V2.10, funded by the German Federal Ministry of Education and Research, refers to the latter by assessing the sustainability potential of building components made of innovative textile reinforced concrete. We conceptualized a life cycle sustainability assessment framework and applied it to variants of sandwich wall systems made of carbon concrete composites and steel-reinforced concrete. Results indicate hotspots in technology and material choices that could be addressed by circular strategies, for example, refuse, reduce or recycling. Overall, one design variant made of carbon concrete composites is the best performing with respect to all dimensions of sustainability.

In precast concrete sandwich construction mechanical connectors are used to transfer loads between the two concrete shells. Omitting these connectors seems economically interesting for realizing novel sandwich elements with lightweight facings made of textile-reinforced concrete or other materials. Then, the adhesion between the isolating layer and the cover layers becomes the decisive parameter. In order to evaluate the basic influence of surface texture and type of concrete on the bond strength, an experimental study including different rigid foams and ordinary performance concrete (OPC) as well as ultra-high performance concrete (UHPC) was carried out. The results of 120 tensile bond tests and 30 shear tests on concrete-rigid foam composites show that technically relevant bond strengths can be achieved by pouring the concrete onto the rigid foam. For OPC, the tensile bond strength is 50% higher than the minimum value required for external thermal insulation composite systems without mechanical connectors. For UHPC significantly higher bond strengths are obtained, which can be attributed to a better micromechanical interlock. In some cases, the strength of the composite was limited by the strength of the foam. The results are valuable for identifying promising rigid foam-concrete configurations.

Concrete is a building material that is widely used worldwide. The main ingredient in concrete is cement, which causes high CO₂ emissions into the atmosphere. An alternative to conventional cement-based concrete is geopolymer concrete. This material is inadequately researched to be used as a building material. In this work, mechanical properties of geopolymer-based concrete are investigated to estimate its potential in construction industry.

Mineral waste, including non-hazardous construction waste, is the largest waste stream once a country has reached a certain degree of urbanization. This waste stream has a significant potential to replace primary raw materials. Although a large part of the construction waste is reused, other mineral materials such as ashes or slags have only been used for backfilling or are deposited in landfills. The aim of the investigations is to determine the usability of substitute building materials (SBM) in higher-quality applications, particularly in urban green infrastructure, for example, Reinforced Soil Structures (RSS) or Green Roofs (GR). In addition to technical and environmental requirements, the greening of the material is relevant. The study concept includes soil mechanical laboratory tests as well as greening tests on SBM, namely slags, ashes, residue sands, and crushed/milled brick. The lab results illustrate the feasibility and applicability conditions for the investigated SBM. Upscaling the lab test results, in the next step the construction of a RSS with complete substitution of the primary building materials is started as large scale pilot test.

Due to the construction of more and more bridges out of textile respectively carbon reinforced concrete (CRC) or strengthening with it, the fatigue behavior of the material becomes more important and has to be investigated. However, next to the tensile load-bearing behavior, the bond behavior is crucial as well. As for the carbon textiles used nowadays, concrete splitting gaines in importance as failure mode, a suitable test setup has to be found which allows representing realistic conditions. Therefore, in this paper, two different test setups—the double-sided textile pull-out (DPO) and the overlap test—are compared regarding their results in quasi-static reference and residual strength tests as well as in fatigue tests with different bond lengths. In the end, it will be clear that one of the test setups clearly creates the more realistic results.

The ingenious bridge, roof, and shell structures of the last century were designed from the understanding of the congenial interaction of the two materials concrete and steel. Nowadays, reinforced concrete is the most widely used material in construction. The use of system formwork and easy-to-install reinforcement support structures that are optimized in terms of labor costs, but often have inefficient use of material. In this context, Stefan Polónyi has repeatedly criticized the engineers' lost understanding of the interaction of concrete and reinforcement. With Additive Manufacturing, an innovative digital manufacturing technology is now available that allows new freedom in concrete design with a resource-efficient use of materials at the same time. With regard to practical application, the integration of reinforcement represents a central challenge in 3D-concrete-printing. The authors see here the future chance of a force-flow controlled reinforcement layout. The paper shows new strategies for the combined Additive Manufacturing of concrete and reinforcement and presents first 3D-printed reinforced concrete elements.

In Concentrated Solar Power (CSP) plants the incident solar radiation is focused onto a receiver by means of collectors. A fluid is heated up and in a downstream power block electricity is generated. In point-focusing solar towers, the solar concentration is achieved by so-called heliostats that are arranged to a solar field. In this contribution, the development of concrete heliostats with circular shapes and an aperture area of 30 m² is presented. A high-performance concrete with high tensile and compressive strength values is used. The circular structure is dissolved into identical but symmetrically reduced modules derived from system reduction methods. For designing, the tensile strength of the concrete is restrictive to ensure linear-elastic material behavior and to avoid softening by cracking. After dimensioning, the derived equivalent plate is converted into strut-like structures possessing equal stiffnesses with respect to the partial module size. These modules are circularly post-tensioned to form a heliostat. Numerical investigations of the modules prove their accuracy. A full solar concentration, that is, the reflected solar radiation is completely focused on the receiver, is achieved. Due to the multitude of modules within a solar field, serial production with integrated quality control is recommended.