Search

Distributed crack width measurement in concrete structures using fibre‐optic sensor technology – New application of distributed fibre optic sensing Cracks and their changes are important indicators for concrete structures. Conventional crack sensors can only detect known cracks or determine their change in width. This paper presents a new crack measurement system that uses low‐cost fibre optic sensors subsequently bonded to the concrete surface to detect cracks over long distances without knowing their location in advance. With distributed fibre optic sensing (DFOS), new cracks can be identified using fibre length of up to 70.0 m. The position of identified cracks can be located to 3.5 cm and their change in width determined. The achieved accuracies for the width are 0.035 mm (laboratory scale) and 0.15 mm (real applications). With DFOS, individual cracks can be measured at the usual crack distances of 15 cm in reinforced concrete construction, even without a possibility of visual inspection. Furthermore, a newly developed evaluation algorithm is presented with which the historical crack development is recorded. In the case of epoch measurements, this can be used to draw conclusions about the maximum crack width that has occurred in the meantime. Laboratory tests and real measurements in the course of a pilot application of more than one year show the methodology as well as the boundary conditions for the choice of fibre and adhesive. Comparisons of different measuring systems show an achieved accuracy in a similar order of magnitude as conventional crack sensors. [ABSTRACT FROM AUTHOR]

Measurement data based load analysis of precast concrete pavements of motorways In Austria, about 40 % and in Germany about 30 % of the motorway and expressway network are concrete pavements. However, very little is known about the stress conditions and temperature loads actually acting in concrete pavements. There is little in‐situ data available, mainly because of the difficulties involved in measuring these conditions in a real paving environment. In the course of a research project, precast slabs were used for the first time to repair concrete pavements in a highway in Austria, and these were also extensively equipped with embedded fiber optic sensors. In an in‐depth analysis of the measurement data of a period of two years, temperature changes, extremes as well as gradients in connection with external weather conditions are evaluated. With regard to the formation of cracks and constraints in the slab, on the one hand measured strains without traffic load are analyzed, on the other hand a statistical analysis of the measured impacting traffic load changes is carried out. In the second section, based on a calibrated nonlinear FE model, a combined analysis of the unsteady stress profile of the slab under dynamic traffic loading with varying temperature‐mechanical loading is performed. After comparison with measured data, the dynamic stress maxima acting in the plate can be determined. [ABSTRACT FROM AUTHOR]

Test Set‐Ups on corrosion damaged cantilever walls – research project SIBS Retaining walls such as other structures are subjected to ageing or other environmental influences. Concrete structures, and especially RC‐structures, suffer from concrete spalling, cracking or corrosion. Given by slender cross sections and high degrees of reinforcement (e. g. cantilever walls) corrosion damages can influence the bearing capacity and the stability. Especially the earth‐sided regions of such structures (position of the bending reinforcement) and the connection areas between the vertical wall and the foundation slab can be subjected to such damage. In these areas, a non‐uniform and wide‐ranging corrosion pattern can be found, which is not visible during an inspection. This report gives a short overview on (corrosion related) damages and there causes, as well as a short insight in testing methods used for the safety assessment. Furthermore, a monitoring concept for corrosion damaged RC‐structures is presented. The installation and the validation of this concept is shown on a series of mock‐ups and the results are compared with numerical parameter studies. [ABSTRACT FROM AUTHOR]

Traffic vibrations during concreting work on existing road bridges – Vibration prognosis for the assessment of construction stages in course of the newly constructed highway bridge A 23 – Hochstraße Inzersdorf The construction works on existing bridges must often take place without traffic interruptions. During bridge‐widening works or closing of construction joints, the hardening concrete is exposed to traffic‐induced vibrations. This can damage the material permanently, depending on the amplitude of vibration velocity. This study investigates factors that influence amplitude of traffic‐induced vibrations of a slab bridge on the A 23 motorway in Vienna, which was rebuilt in several construction phases. Transient dynamic simulations were used to analyze the influence of the driving speed, vehicle mass and road evenness. Measured road profile data, which were collected by high‐resolution laser scanning of the road surface, were used in FEM simulations. Bridge resonance properties were verified by vibration measurements. While bridge deflections and strains are mainly influenced by vehicle mass, the vibration velocities are primarily determined by the road profile. The predicted vibration velocities were compared to a limit value taken from the literature, the observance of which should not lead to any impairment of the young concrete. The results served as a decision basis for the selection of suitable measures during the critical hardening phase of the concrete in the connection joint. [ABSTRACT FROM AUTHOR]