PSI - Issue 64

7

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

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Figure 5. Failure modes under same impact (Liu and Xiao, 2016): (a) RC beam without stirrups; and (b) 0.04 CFRP strengthening ratio.

Other failure modes were observed to occur under impact loads, such as rupture and debonding of the composite materials and concrete cover delamination (Pham and Hao, 2017). Hence, it can be observed from existing research that the composite materials have suffered from localised damage on/around the impacted area, even though most of these studies were conducted using low-velocity impact load. However, local damage is most likely to occur in the actual case scenario where the medium or heavy truck collided with a bridge pier/girder at around 80 km/h or more. Thus, all the strengthening materials are susceptible to local failure at the impacting area. 5. Fabric types and strain rate effect of the strengthening materials Most applied composite materials to strengthen the structural members against impact loading utilise unidirectional fibre sheets (Zhou, 2021). However, the investigation of the different types of fabric orientation is quite limited. The bidirectional fabric sheets that can strengthen longitudinal and transverse directions within the same single sheet have not been explored sufficiently. Thus, shear and flexural strengthening against impact loads can be achieved by utilising the advantages of bidirectional fabrics. Further studies are required to examine the application of different composite materials against impact loading. In terms of the strain rate effect, it is commonly understood that when the strain rate of loading increases, the required time for damage is reduced, and the materials can withstand higher loads and strain to failure. The mechanical properties of composite materials, such as strength and elastic modulus, were higher under impact loads than those of static loads (Shokrieh and Omidi, 2009). In this regard, three standard rates of testing are defined by (Pham and Hao, 2016), which are: (i) quasi-static load when the strain rate is less than 10 -5 s -1 ; (ii) intermediate strain load for the load range between 10 -2 to 10 0 s -1 ; and (iii) the high-load rate when it falls within 10 2 -10 3 s -1 range. However, some studies obtained contradictory conclusions on the FRP response under high rate loading when they asserted that the composite materials show no rate-dependent behaviours for their elastic modulus, tensile strength, and failure strain (Daniel et al., 1981). Foroutan et al. (2013) confirmed the previous studies' inconsistencies regarding the strain rate effect of strengthening materials. The inconsistency might result from several factors, such as the accuracy of the testing procedure, the testing machine, and the loading rate range. Hence, a review to highlight the inconsistency is required. 6. Conclusion This study reviews and evaluates the use of composite strengthening materials to enhance bridge safety against impact loads, mainly focusing on vehicle collisions. The literature predominantly explores carbon fiber-reinforced polymer (CFRP), with relatively less attention given to other polymer alternatives. However, the mechanical properties of aramid and Dyneema ® are highlighted in the literature, suggesting that they may offer superior energy absorption capabilities, potentially outperforming CFRP when subjected to impact loads and making them promising candidates for such applications. On the other hand, most experimental works in the literature were conducted on small-scale specimens, which may not fully capture the actual inelastic response of strengthened members under real-world conditions. Furthermore, there are contradictory conclusions regarding the response of FRPs under high-rate loading. While some studies suggest no rate-dependent behaviours for composite materials' elastic modulus, tensile strength, and failure strain, others indicate inconsistencies, possibly due to testing procedures, equipment accuracy, and loading rates. A review