Abstract
Bending beams and slabs are typical examples for structural elements used for reinforced concrete structures such as bridge girders, T-beams and bridge decks. Their strength related failure modes at maximum loading can be divided into bending and shear failure. The failure of beams loaded in bending can occur with or without indication. Therefore, conventional design concepts aim on failure modes with sufficient indication (e.g. large deflections or cracks), as it occurs in the case of secondary flexural compression failure. These indicating factors can also be used for Structural Health Monitoring (SHM) of civil infrastructure systems (e.g. bridges) to identify structural changes. In this context, non-destructive testing (NDT) methods offer different techniques for measuring deflections or crack formation and opening. However, profound knowledge on the determining failure modes of bending beams and their detection by NDT methods is required for the reliable application of SHM. Different NDT methods have been used in this study for analysing the load-bearing behaviour of a reinforced concrete beam in bending. The different measuring techniques are briefly described and their applicability is discussed by means of experimental results. For this purpose, the load-bearing behaviour of a reinforced concrete beam having a span of 2.75 m was investigated in a four-point bending flexural test at laboratory scale. The focus is on the characterization of determining failure modes by optical NDT and the comparison with classical measuring techniques (e.g. deformation measurements by displacement transducers). The bending beam was equipped with two single-mode (SM) sensor fibres. One fibre served as Distributed Optical Fibre Sensor (DOFS), whereas the other fibre contained Fibre Bragg Grating (FBG) sensors. In addition, optical deformation measurements using Digital Image Correlation (DIC) and Stereophotogrammetry (SP) were conducted.
Highlights
A detailed analysis of bridges in the German trunk road network reveals that in 2016 the condition of about 55 % of the 39 000 bridges can be classified as ‘very good’, ‘good’ or ‘satisfactory’ [1]
A sub area with a side length of 10 mm was defined in the lower middle section of the Digital Image Correlation (DIC) field for calculating the beam deflection as arithmetic mean avg(d)Y of the corresponding surface component
The load-bearing behaviour of a reinforced concrete beam was investigated by optical measuring techniques and compared with results obtained by classical measuring techniques
Summary
A detailed analysis of bridges in the German trunk road network reveals that in 2016 the condition of about 55 % of the 39 000 bridges can be classified as ‘very good’, ‘good’ or ‘satisfactory’ [1]. The decision-making process in terms of repair or reconstruction of the damaged structure requires detailed information on the remaining static and dynamic load-bearing behaviour of the bridge and their condition. For this purpose, Structural Health Monitoring (SHM) is a useful tool for evaluating the condition of bridges or other structural elements exposed to bending loads. The bridge demonstrator is a two-span beam with a span of 12 m in each segment and was tested using both destructive and nondestructive measuring techniques In preparation of these field tests, the application, handling, and synchronization of various measuring systems was tested on smaller specimens on laboratory scale. The results of these preliminary tests obtained by optical measuring techniques, such as photogrammetric measurements and fibre optic sensors are discussed and compared with classical measuring techniques
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