PSI - Issue 64

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

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DFRP can be considered a promising candidate against impact loads. It was utilised mainly for lightweight structures like armour and helmets for military applications. It is a composite material made from ultrahigh molecular weight polyethylene (UHMWPE), combining excellent mechanical properties with low density. It is considered the most robust fibre on the market (Van Dingenen, 1989). Based on static (crush test at 5 to 500 mm/min) and dynamic (drop tower at 3.6 and 9 m/s) tests, Van Dingenen (1989) compared Dyneema ® with other composite materials like carbon, Kevlar ® , and glass and found that DFRP was the most efficient for absorbing impact energy (see Figure 3).

Figure 3. Energy absorption of composite materials against high-velocity impact.

DFRP, with its high elongation at break, can be used to reduce brittleness, thus preventing catastrophic failure and loss of structural integrity. In a study by Zhao et al. (2018), two types of DFRP, Dyneema ® woven fabric/EP and HB26, were tested against Tenax ® HTA carbon fiber and S-2 glass ® , which are considered the best types of carbon and glass with the highest strength and strain at failure. The study found that the Pure-based Dyneema ® HB26 exhibited no penetration against ballistic impact. Despite DFRP's potential, only one study has utilised this material in civil engineering structures, focusing on its performance for earthquake loading rather than impact. Wu et al. (2006) confirmed in their study that the bond strength between Dyneema ® and epoxy resin is relatively weak, necessitating further investigation to determine its suitability for structural applications. Utilising Dyneema ® to strengthen structural elements against impact loads could provide another potential solution, given its remarkable mechanical properties compared to other strengthening materials. 3. Previous Studies Most experimental studies on strengthening reinforced concrete members against impact loading in the literature focus on low-velocity impacts. Vehicle collisions with bridges typically involve low to medium-velocity effects, with actual events often occurring at speeds up to 30 m/s (Qiao et al., 2008). However, many of these studies use small scale testing specimens, which may not accurately represent the behavior of structures under impact loads. Kim et al. (2009) conducted a study to establish similitude laws for determining the ideal dimensions of test specimens to obtain reliable results for actual prototype structural elements. They found that standard similitude requirements, particularly in the inelastic range, may not be ideal and proposed a simulated law to derive the values for each variable for small specimens. Table 2 provides a summary of studies and observations regarding the use of strengthening materials against impact loads, with a predominant focus on CFRP. The table aims to highlight the anti-impact properties of CFRP, AFRP, and DFRP. Since no studies have investigated DFRP on structural members, the table includes studies of AFRP and CFRP. Many experiments in the literature are conducted on small scales due to cost and laboratory limitations. However, conducting large- or full-scale testing may provide a more accurate representation of the performance of strengthened members under impact loads. In all the studies summarized in Table 2, except for the study by Erki and Meier (1999), where the load was generated by lifting and dropping one end of the beam, the direction of the applied load was lateral to the member. This was achieved by laying down the member and dropping a specific mass to generate the impact load.