PSI - Issue 64

Haider Mraih et al. / Procedia Structural Integrity 64 (2024) 1402–1410 Haider Mraih/ Structural Integrity Procedia 00 (2019) 000–000

1407

6

32

5.5

-

2L

72.7

-

F+LR+D

3.5 2.3 2.4

20

- -

2L

92.8 85.6 58.5

-

F+R S+F

U-AFRP (t= 0.57mm ) U-CFRP (t= 0.33 mm) U-AFRP (t= 0.19 mm)

- -

- -

1542 1527

(Kishi et al., 2020, Sinh et al., 2022)

200 × 250 × 3000

1L-AFRP

D

300

L

2.3

-

1L-CFRP

-

58.5

1457

D

0.3 0.6 0.6

- - -

-

- - -

15 17

- - -

S

20 20 20

100 × 25 × 500

(Kurihashi et al., 2021)

1L 2L

L

R

-

-

1 load direction:- L: Lateral to the member, DOE: drop one end of the beam 2 Failure mode:- S: Shear, F: Flexural, SF: shear-flexural, CC: Concrete crushing, D: strengthening de-bounding, R: Rupture, LR: Local Rupture, PY: Plate yielding, and SY: Steel yielding. 3 U:- Unidirectional fibre

4. Failure modes and energy dissipation This section discusses the failure modes observed in un-strengthened and strengthened specimens under static and impact loads, as summarized in Table 2, for both shear and flexural strengthened structural members. In most of the tested plain reinforced concrete structural elements, shear failure was observed to govern the failure mechanism (Micallef et al., 2014). The interesting phenomenon studied in both experiments and numerical analyses discussed in published works is that when a projectile hits a beam and makes it move faster, it stays balanced due to the interaction between impact, reaction, and inertial forces. Based on an experimental study, Saatci and Vecchio (2009) found no reaction force when the impact force is at its maximum peak value, indicating that inertia forces entirely counter the impact force at the beginning of an impact event. Hence, it was observed that the strengthening materials as external reinforcement transform the failure mechanism of the structural member from brittle shear failure to shear-flexural or flexural dominant ductile failure. However, various failure modes, such as localised and overall failures, may arise when subjected to impact loading. Different studies have been undertaken concerning local failures (Gurbuz, 2018), revealing the loss of structural integrity due to the sudden rupture of the strengthening materials that can occur within impact zones. An example of the local failure mode is presented in Figure 4- a and b, which provide a clear view of reducing the effectiveness of the strengthening materials under impact load. The intended purpose of these materials might be entirely lost, leading to a possible overall failure of the structural member.

a

b

Figure 4. Local failures in impacting areas: (a) AFRP damage (Ağcakoca and Bıyıklıoğlu, 2020) ; and (b) Local rupture (Gurbuz, 2018)

The efficiency of the strengthening materials in changing the failure mode from shear to flexural was also observed for structural members lacking shear reinforcement (Liu and Xiao, 2016). These studies confirm the significant influence of these strengthening materials on enhancing the shear strength of reinforced concrete beams when subjected to impact loads, as depicted in Figure 5. It can be observed from this figure that the composite materials effectively transform failure mode from a shear-dominant brittle pattern (Figure 5-a) to a combined shear-flexural mode (Figure 5-b), signifying their transformative impact on structural performance.