Strain curves measured with different DFOS types and varying spatial resolution by an ODiSI 6108

Based on the principle of coherent optical frequency domain reflectometery (c-OFDR), cracks in concrete structures can be precisely localized and their widths determined due to the high spatial resolution in the sub-millimeter range. However, with longer distributed fiber optic sensors (DFOS) lengths, as is common in structural health monitoring, the spatial resolution is reduced. Experimental studies were carried out to investigate the influence of the spatial resolution on the measurement quality in the area of large strain gradients. Four different DFOS, two robust and two filigree DFOS types, were subsequently installed on a 4 m long reinforced concrete beam. In a displacement controlled 4-point bending test, crack widths of up to 0.5 mm were measured with four different gage pitch (gp).