PSI - Issue 64

Szymon Grzesiak et al. / Procedia Structural Integrity 64 (2024) 269–276 S. Grzesiak, C. de Sousa, M. Pahn / Structural Integrity Procedia 00 (2019) 000 – 000

272

4

Table 2. Concrete mix design and properties of used materials.

Material

Raw density (kg/m 3 )

Weight (kg/m 3 )

Reinforcement

E-Modulus (MPa)

Mechanical properties (MPa)

Cement (CEM II 32,5) Aggregate 0 to 2 mm Aggregate 2 to 8 mm

3100 2600 2600 1000

280 740 900 195

BFR strip

54,463 202,000

f f = 1,366.0 f y = 506.0 f u = 597.0 f cm = 24.8

Steel reinforcement

Water

Concrete

21,289

2.3. CT measurements As the use of CT in structural engineering is still a relatively new research approach, there is still a lack of well founded results in the literature regarding the evaluation of concrete samples strengthened with FRP materials using CT images (Rettinger and Guhathakurta et al. (2022)). In this study, specimens previously subjected to bending test are exposed to CT scans in order to develop methods for detecting defects through CT image data. Figure 2 shows the CT device, consisting of an X-ray source ① , a detector ② and a rotating table containing the concrete samples ③ . For the CT examinations in this study, the flat-panel detector of the tomography portal “Gulliver” from RPTU Kaiserslautern was used. The X-ray source used had a high voltage of 8.0 MeV and electric current of 500 mA. Samples were scanned in 1300 projections with a rotation range of 200 °. Each scan took about 20 minutes.

2

1

3

(a)

(b)

(c)

Fig. 2. (a) BFRP strip on sample, (b) test sample for CT scan; (c) CT-test setup with: ① x-ray source, ② detector, ③ sample on rotating table. 3. Results and discussion 3.1. Behavior of beam in experimental test The first step for the analysis of results is to understand and define the general component behavior of the strengthened beam. In each of the beams, separation of the concrete cover at the end of the FRP strip due to the vertical offset between the longitudinal reinforcement bar and the FRP strip took place. This failure mode is called concrete cover separation failure. The force F exp was determined using the load cells detailed in Section 2.2. The maximal force F exp is presented in Table 3. The next step consisted on the analysis of the load bearing and deformation behavior of the reinforced concrete components with FRP strips. With regard to the three-point bending tests that were carried out, the maximum deflection at mid-span is of particular interest. For the analytical calculation of deflections, loads F exp were used. The bending line along the y - coordinate for loaded single-span beams was determined according to equation (1) (see in Timoshenko (1955)). In stage I with uncracked concrete, the full height h of the section had to be considered to determine the second moment of area I (EI I ). The test beams analyzed in this study later reached crack stage II (EI II ).