PSI - Issue 64

Yunus Harmanci et al. / Procedia Structural Integrity 64 (2024) 2067–2074 Author name / Structural Integrity Procedia 00 (2019) 000–000

2069

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The FeSMA strips comprised of a Fe–17Mn5Si–10Cr–4Ni-1(V, C) alloy, developed at the Swiss Federal Laboratories for Materials Science and Technology (Empa) in Switzerland (Shahverdi et al. 2018), featuring 2.6 m in length, 20 mm in width, and a nominal thickness of 1.7 mm. The beams comprised concrete with a mix of Type I Portland cement (350 kg/m 3 ), coarse aggregate (maximum size: 16 mm), and a water–cement ratio of 0.50. The compressive strength, splitting tensile strength, and elastic modulus of the concrete at 28 days was measured at 53.4 MPa, 3.4 MPa, and 35.4 GPa, respectively. Internal reinforcement of four Ø8 mm longitudinal bars and Ø8 mm stirrups every 150 mm with an elastic modulus of 200 GPa and yielding strength of 508 MPa was used. The flowable and expansive cement-based grout SikaGrout-311 was employed for bonding the Fe-SMA strips into the grooves. First, Fe-SMA strips were pre-strained to 2% elongation and allowed to relax to a stress-free state. Grooves were cut at the bottom side of both beams and strips were placed into the grooves and filled with cement-based grout. After curing, resistive heating was used to activate the strips of Beam 7 while the strips of Beam 8 remained non-activated. Thermocouples installed within the grooves were used to monitor and control the activation process. Mid-span displacements were monitored using two LVDTs, and strain gauges recorded strain on both sides of the beam Both beams were then taken outside the Structural Engineering Research Laboratory of Empa in Switzerland and loaded with 1535 kg concrete blocks suspended at two points 400 mm apart in the middle, which amounts to roughly 45% of the ultimate capacity. Long-term testing began on May 7, 2015 and ended on March 16, 2023. During this period, mid-span deflection and crack propagation were monitored on both beams, with measurements taken using a dial-gage LVDT and mechanical strain gages on the upper and lower sides of the concrete, accompanied by temperature readings. The two beams were then taken inside and subjected to four-point bending until failure. After failure, one beam was used to obtain concrete drilling cores to assess compressive strength according to SN EN 13791:2019. The technical drawings, long-term loading and 4-point bending setups are provided in Figure 1, more detailed information can be obtained from (Harmanci, Czaderski, and Shahverdi 2024).

Figure 1: Technical drawing of the beams (top), long-term loading (bottom left) and four-point bending (bottom right) setup