As previously discussed, the FOS were attached onto the concrete beam, staggered in equal clearance over its height. The measurement output of one fiber consists of one-dimensional strain data with a point distance of 0.65 mm. Assigning the strain from multiple FOS to their respective positionings and heights on the RC beam, allows for an aggregation of the one-dimensional strain data points forming two-dimensional strain fields. Figure 9
a,c depict such mapped strain data. Values in-between the support lines (FOS data with given height) were linearly interpolated. Since no extrapolation is carried out, the outer FOS (at a height of 34 and 380 mm) represent the limits of the strain field.
b,d show the
presented as a two-dimensional map (Attribute Map, cf. [31
]). The solitary results of each transducer pair were located right in the middle between them and intermediate values were linearly interpolated. Positioning the results in the middle of two transducer pairs leads to an Attribute Map with the y-limits of 75 and 325 mm. Note that the color scale (e.g., limits of
) differs for the subsequent representation of Attribute Maps due to the large variation of
with raising load.
The juxtaposition of strain field and Attribute Map anew reiterates that the tensile zone shows larger
than the compressive zone. When the test specimen at hand cracks, the height of said tensile zone approximately equals the depth of primary flexural cracks. Also, the enhanced right-sided crack occurrence is to be identified by the Attribute Map. A comparison of Figure 9
b,d reveals how
rises with increasing tensile strain and therefore likewise with growing load.
a,b represents strain and US data for a load level of 10 kN. Because of the low strain values and the, in relative terms, high measuring noise, no definite compressive zone can be identified in Figure 9
a. However, the height of the compressive zone at a load of 10 kN is estimated to range between
mm. Furthermore, in the tensile zone, at
800 mm/1000 mm/1100 mm, small strain peaks are visible, reaching approximately
strain (noted earlier as the approximate strain level at which concrete first cracks). Further scrutiny of the coordinates of said strain peaks again emphasizes that higher tensile strain is present on the beam’s right side.
b demonstrates greater
present in the lower part of the test specimen compared to the upper part. The
ranges from approximately
in the compressive to
in the tensile zone of the beam. In addition, a right-sided concentration of the largest
can be observed. Due to the missing zero crossing of the
, measured results can only be interpreted in relation to one another, i.e., as relative change over height. In order to be able to deduce the strain state from the Attribute Maps, additional information, such as the type of external force, is required. Based on a juxtaposition of strain fields and Attribute Maps, later analyses of data presented in the Attribute Maps allow for distinguishing tensile from compressive strains present in the beam. Thus, in relative terms, tensile strains overall cause a greater change in
than compressive strains. The aforementioned clustering of strains on the right side, is likewise underpinned by the US results. As discussed earlier, Figure 9
c,d exhibits the strain and Attribute Map for a load of 25 kN. Both depictions point out that, with increasing load and the associated increase in strain, measurement noise plays a lessened role compared to the lower strain levels presented earlier (cf. Figure 9
a). Thus, such relatively low measurement noise at higher strain levels renders it possible to approximate the compression zone height more precisely as lying between 150 and 175 mm. Furthermore, in addition to the points of increased strain from Figure 9
a, the higher strain level presented in Figure 9
c also features further areas of increased strain, which continue to expand vertically in a linear manner. The structure of results for the zones in which increased strain of over
strain occurs, indicates concrete cracking in these areas. It should be noted that strains exceeding
strain are only measured due to the crack edges moving relative to one another (cf. Figure 7
). In said cracked sections,
analogously also increases, as evident in the strain field. The previously identified phenomenon of tensile zones showing larger
than compressive zones, can also be deduced from Figure 9
d, so that there are values ranging from
. In accordance with previous results highlighting the right-sided clustering of higher strains,
likewise dominate in this area of the beam.