PSI - Issue 64

Zhikang Deng et al. / Procedia Structural Integrity 64 (2024) 400–408 Zhikang Deng / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Glass has experienced a rising trend in its utilization for structural components over the past two decades. Among the prevalent forms are glass beams or fins, as depicted in Fig. 1(a). The inherent brittleness of glass and its limited capacity to redistribute stress concentrations present obstacles to its effective application for structural elements. Post-tensioned glass beams have been developed to overcome these constraints, as illustrated in Fig. 1(b). These post-tensioned glass beams have higher load-carrying capacity and retain the capacity to support substantial loads even after glass crack initiation, thereby enabling a ductile failure mode, as shown in Fig. 1(c). Materials such as stainless steel, as investigated by Cupać et al. (2021) and Firmo et al. (2020), or fibre-reinforced plastic (FRP), as studied by Achintha and Balan (2019) and Cagnacci et al. (2021), have been employed as post-tensioning components for glass beams. Nonetheless, the post-tensioning process of stainless steel and FRP often involves significant labour inputs and specialised facilities such as hydraulic jacks. Shape memory alloys (SMAs) have been used in pre-stressing applications due to their efficient application procedure. After being prestrained, they are capable of recovering their original shape through activation at a specific temperature due to phase transformation from martensite back to austenite. This is called the shape memory effect (SME). The SME enables SMAs to provide the pre-stress when they are fixed to a parent structure. The structural performance of the parent structures can therefore be improved through the generated pre-stress. Iron-based shape memory alloys (Fe-SMAs), with the advantages of low manufacturing costs and outstanding mechanical properties, are promising for applications in civil engineering. The structural behaviour of steel beams strengthed with adhesively bonded memory-steel strips was investigated experimentally by Wang et al. (2023). The findings indicated the adhesively bonded Fe-SMA strips as promising pre-stressing components. The debonding behaviour of Fe-SMA-to-steel joints was investigated by Li et al. (2023c), and a debonding model for Fe-SMA strips bonded with nonlinear adhesives was given by Li et al. (2023b). Previous investigations by Silvestru et al. (2022b) and Rocha et al. (2023) have proved the feasibility of post-tensioning glass beams with adhesively bonded Fe-SMA strips. Silvestru et al. (2022a) investigated the mechanical behaviour of glass to Fe-SMA adhesively bonded shear joints. Two different types of adhesives were considered and the corresponding maximum effective bond length was defined experimentally. The effect of adhesive thickness, Fe-SMA strip thickness and bond length on the structural behaviour of glass-to-Fe-SMA lap shear joints was investigated by Deng et al. (2022). Deng et al. (2023) investigated the effect of elevated service temperature on the structural performance of glass-to-Fe-SMA adhesively bonded joints. The results indicated the feasibility of reinforcing glass elements with adhesively bonded Fe-SMA strips at elevated service temperatures. The application of pre-stressing glass elements using adhesively bonded Fe-SMA tendons involves three main steps: • (c) Activating the Fe-SMA tendons at a target temperature followed by cooling naturally to ambient temperature. The activation is a crucial step for the application of adhesively bonded Fe-SMA tendons on glass elements. A higher activation temperature has proven to be more effective in strengthening with pre-stressed Fe-SMAs by Li et al. (2024). From the application and economic points of view, a relatively high pre-stress level should be targeted; however, a high activation temperature is required to achieve a high pre-stress level, which may cause glass failure or debonding. Hence, the activation of the glass-to-Fe-SMA adhesively bonded joints was further investigated in this study with three primary objectives: • (a) Evaluation of temperature development during the activation process: This objective aimed to assess the effect of the activation temperature on the specimens, especially on the anchorage zone; • (b) Understanding the pre-stress generation with activation temperatures of 160 °C and 200 °C; • (c) Investigation of pre-stress loss due to elevated service temperatures. The obtained results are crucial for pre-stressing applications of glass elements with adhesively bonded Fe-SMA tendons at both room temperature and elevated temperature. • (a) Pre-straining of Fe-SMA tendons to a target strain level under tension force; • (b) Adhesively bonding pre-strained Fe-SMA tendons to the target structures;