PSI - Issue 5

V. Epin et al. / Procedia Structural Integrity 5 (2017) 620–626

621

R. Tsvetkov/ StructuralIntegrity Procedia 00 (2017) 000 – 000

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1. Introduction

Cracking, as well as other and other damages, may occur in reinforced concrete building and engineering structures and their structural components under operational loads. The most dangerous cracks are those that run in the load-bearing elements (beams, supports, pillars, and slabs) responsible for the integrity of an entire structure. Crack propagation can significantly reduce the longevity of the structure and even can lead to its complete failure. The safety factor of the main structural elements is currently assessed by analyzing the monitoring data. There are various methods to monitor the deformation behavior of structures. One of the methods includes local deformation measurements with strain sensors of different types: strain gauge, vibrating wire sensor and fiber optic sensor. However, reliable estimates of the stress-strain state of an entire structure can be obtained only with a great number of such local strain sensors. Another approach to the assessment of the deformation state of the structure is the analysis of its response to dynamic loading, which involves the estimate of natural frequencies, mode shapes, and damping ratios (Staszewski et al. (2007)). The occurrence of defects in the structure changes its frequency and phase characteristics, which should be controlled., This approach is particularly advantageous for monitoring simple structures subjected to dynamic loads. For the structures of complex cross-sectional shape, the detection of the region and degree of probable damages based on dynamic data is a much more complicated task. Different factors might influence the structure response, and not all of these can be associated with defect accumulation. Determination of the critical threshold for changes in the dynamic characteristics necessary to assess the longevity of this structure is also a challenge. Direct measurements of the geometric parameters of structures are also important for deformation monitoring. For this purpose, different methods can be used. For instance, control of the geometry of the entire structure can be performed by photogrammetry techniques, which provides the accuracy of measurements exceeding 0.1 pixel (Maas et al. (2006)). These data can be used as boundary conditions in calculating the stress-strain state of the structure. Crack dimensions can also serve as the damage parameters of concrete structure. There are many companies, which produce crack opening sensors for monitoring systems. The usage of LVDT crack-width sensors manufactured for monitoring bridge constructions is described in the paper (Khrahmalny et al. (2016)). The non contact methods such as the image-based method for crack analysis (IMCA) can also be applied to measure crack parameters (Barazetti et al. (2009)). A monitoring object represents a reinforced concrete air bridge, which connects two parts of the building. The dimensions of the structure are as follows: length 28 m and width 56 m. The load-bearing elements of this bridge are the reinforced concrete beams of complex cross-sectional shape, resting on iron columns. One of these beams is shown schematically in Fig. 1. The scheme of the load-bearing elements (top view) is given in Fig.2. As one can see, the longitudinal beams 1..9 are rigidly attached to the elements of the main structure. In the areas of location of iron supports, these beams are bound together by transverse beams, thereby forming a lattice structure. 2. The monitoring object

Fig. 1. Schematic diagram of one of the transverse beams (side view).