PSI - Issue 64

Bertram Richter et al. / Procedia Structural Integrity 64 (2024) 1208–1215 Richter et al. / Structural Integrity Procedia 00 (2019) 000–000

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Second, two kinds of data processing approaches for damage detection are developed: (1) machine learning based approaches for fault detection, isolation, identification and correction (Al-Zuriqat et al., 2023; Al-Zuriqat et al., 2023) and (2) analytic evaluation algorithms for distributed strain data (Richter et al., 2023). Third, a large-scale bridge, called openLAB, is built and equipped with an extensive monitoring system solely for research purposes. The openLAB is a newly built, three-span, 45 m long research bridge on the premises of Hentschke Bau GmbH near Bautzen, Saxony (Herbers et al., 2024). Each span has a different focus: the first span models the typical shortcomings of last century's concrete bridges, the second span is built with state-of-the-art technology, and the third span is built with a special type of hollow core girder, a rapid construction system. The first two spans are realized with 1.5 m wide and 15 m long precast and pretensioned T-beams with an in-situ concrete layer. The extensive monitoring system installed in the openLAB covers environmental conditions, global structural behavior (via accelerometers and inclinometers), and local behavior (via strain gauges, displacement transducers, and temperature sensors). DFOS take a special role, measuring both global and local behavior at once. DFOS are installed in a variety of ways in the openLAB: directly embedded in the concrete, glued to the reinforcement, integrated in tendons, or applied subsequently. In addition to measuring longitudinal concrete and reinforcement strain at the lower reinforcement level of each girder, DFOS are used to measure strains in areas of particular interest, such as column connections or the in-situ concrete layer. Mechanically decoupled DFOS are employed for distributed temperature sensing. In total, approximately 1 km of DFOS are installed in the openLAB. To create a solid data basis of the structure under real world environmental conditions, various experiments will be performed on the openLAB in three phases: (1) preliminary tests on the precast girders before assembly, (2) a one year reference phase after the completion of the bridge in April 2024 with moderate traffic load (no damage should be introduced), and (3) destructive tests causing serious damage to the bridge. This data basis will be used to validate various data evaluation methods with the goal of reliably distinguishing between sensor failures and structural damage. A digital twin combines all relevant information about the openLAB(Collin et al., 2024). 2. Experimental investigations 2.1. Test specimen and experimental setup

A 15m long prestressed concrete girder was tested in a 4 point bending test. Fig. 1 shows the girder in the test stand and, the experimental setup and the geometry of the specimen is depicted in Fig. 2. The girder was placed on elastomer bearings, approximately 30cm from the girder’s end. Load was applied by hydraulic jacks located 1.5 m from the center. The investigated girder is the result of the synergic collaboration between the research projects “IDA-KI” and “smart_tendon”, as it combines prestressing with two bonded strands (one of them a smart_strand) with a nominal cross section of each 93mm² and apost-tensioned smart_tendon – a type 6-4 tendon according to the “SUSPA-Litze DW” strand anchor system (Deutsches Institut für Bautechnik, 2023) – equipped with four strands of a nominal cross-section of 150mm² each. The post-tensioned tendon follows the bending moment from permanent actions in the final state and is therefore asymmetrical with the lowest point approximately

Fig. 1. Test setup with counterweights for load application

1m from the girder’s middle toward axis30. The prestressing press was located at axis20. The longitudinal reinforcement and the stirrups are both made of steel B500 with a diameter of 10 mm. The girder was cast in C50/60 concrete with a Young’s modulus E = 37 000 N/m².