Beton- und Stahlbetonbau最新文献

Long-time bond behaviour of fibre-reinforced polymer

Due to their high resistance to environments that promote steel corrosion, fiber-reinforced polymers (FRP) offer significant potential for producing durable and low-maintenance concrete structures. However, FRP materials are subject to chemical and physical degradation over time, which can lead to a reduction in mechanical performance. This degradation is influenced by the properties of the fibers and polymer matrix, the fiber-matrix interface, and exposure to environmental factors. As a result, the time-dependent material behavior has a direct impact on the structural performance and deformation characteristics of FRP-reinforced concrete elements. While current research on the long-term behavior of FRP has primarily focused on its tensile properties, studies addressing the time-dependent bond behavior between FRP and concrete remain limited. This paper investigates the time-dependent bond behavior of FRP reinforcement in concrete. It begins with an analysis of the underlying damage mechanisms, followed by the presentation of a testing methodology specifically developed to capture time-related bond degradation. Experimental results are provided for sand-coated FRP bars subjected to temperature, moisture, and concrete alkalinity. The objective of the study is to derive a time-dependent bond strength suitable for structural design over a service life of up to 100 years under relevant in-service temperature conditions.

Preparation of reused concrete members into detachable, modular precast elements: Capacity under compressive stress

The reuse of reinforced concrete members from demolished buildings has great potential for reducing grey emissions in new construction projects. The concept envisaged in this article provides for the conversion of dismantled components into modular precast members and their further reuse in standardised modular construction kits. Automated and robot-based processing and detachable post-tensioning techniques for joining are to be adapted in order to establish a circular reuse process chain. In this article, the capacity under compressive stress is analysed as a function of the contact surface properties of dismantled and segmented components in order to derive the necessary automated reprocessing methods. Targeted reworking of the cut surfaces can achieve an equally high compressive capacity compared to new parts. The feasibility of the concept is demonstrated by the initial application of the derived preparation techniques for a real, dismantled beam and by subsequent post-tensioning.

A framework for the reuse of reinforced concrete elements

The reuse of reinforced concrete components from existing buildings offers significant potential for conserving resources and reducing emissions. The aim of this article is to develop a structured framework for the assessment, classification and reuse of load-bearing components. The presented research project focuses on in-situ concrete components that are not designed for demolition and systematically analyses their reusability depending on construction period, damage condition, durability and load-bearing capacity. Based on extensive preliminary investigations, a multi-stage investigation and classification system is presented. Critical boundary conditions such as insufficient concrete cover, the use of plain rebar, detailing of reinforcement and contamination with harmful substances are considered. The article concludes with a process model for reuse and initial evaluation criteria for structural suitability. The results provide a basis for technical regulations and integration into the planning processes of future construction projects.

Monitoring at the gear rack tunnel of the kiel lock

As part of the replacement construction project for the Kleine Schleuse Kiel, a monitoring system was designed and installed in the gear rack tunnels at Gate 1 of the Große Schleuse. A comprehensive hydrostatic leveling system (hose balance) was used to monitor possible impermissible shifts, such as those caused by lifting or settlement, during construction. Additionally, temperature measurement points and provisions for geodetic control measurements were implemented. An uninterruptible power supply (UPS) ensures continuous operation of the monitoring system. As part of the project, a quasi-real-time data stream based on MQTT (Message Queuing Telemetry Transport) was implemented. This system transfers pre-processed measurement data to the MKP online platform iris, where it is visualized. An alarm function has already been configured to monitor this data, and corresponding threshold values will be defined as the project progresses. Additionally, infrastructure has been designed and implemented for the automated generation and dispatch of monthly reports.

Profile laser scanning for static load tests using the example of the Unkelstein Viaduct

In view of the increasing need for precise structural monitoring, profile laser scanning (PLS) was used for high-resolution recording of vertical displacements as part of a load test on the Unkelstein Viaduct. The method is based on the continuous recording of vertical profiles using terrestrial laser scanners, without the need to attach sensors directly to the structure. During defined load cycles using a truck as a reference vehicle, several thousand profiles are recorded per position and averaged over the load holding phase. This results in the derivation of sub-millimetre-accurate displacements and complete bending lines. The influence of the load position on the load-bearing behaviour can thus be reliably verified. In addition to the technical implementation, the report also describes the evaluation steps, identified challenges and the results achieved. The high accuracy, coupled with the corresponding spatial resolution, makes PLS a promising addition to existing monitoring concepts, especially regarding digital twins.