PSI - Issue 68

Pascal Franck et al. / Procedia Structural Integrity 68 (2025) 119–125 P. Franck et al./ Structural Integrity Procedia 00 (2025) 000–000

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unprecedented demand for sustainable solutions and substitutes in all technical and social fields. When taking a look at civil engineering, bamboo is a suitable substitute for environmentally harmful building materials, such as concrete. In the recent past, the industry has already seen a shifted focus on wood in particular, and several new buildings are already been built out of the natural material wood. In recent research, bamboo has shown material properties that are equal to or even superior to wood (Kelkar et al., 2023; Verma et al., 2014). Further, bamboo has a very positive impact on the environment, since it possesses a high potential for eco-restoration as well as binding of carbon (Isukuru et al., 2023; Mishra et al., 2014). The widespread planting of bamboo therefore has a positive influence on the surrounding ecosystem and because of the significantly shorter growing time of 3-6 years, when compared to wood, the European forests could be preserved. In addition to the good material properties of bamboo (Al-Rukaibawi et al., 2024; Dauletbek et al., 2022), the material has some characteristics, that need to be taken into consideration when planning to build with it. Bamboo is a fibrous material with a multitude of fibers running through the culm wall. All fibers are aligned in the same direction, leading to an anisotropy of the material (Qiu et al., 2020), meaning that the mechanical properties of the material are highly dependent on the direction the load is applied. Further, bamboo is a hygroscopic material, that strives for the equilibrium state and thus adjusts its moisture content in accordance with the surrounding environmental conditions. The moisture content itself has a high impact on the mechanical performance of the material (Wakchaure and Kute, 2012). Often, the bamboo material is further fabricated into engineered bamboo, such as the laminated bamboo lumber (LBL) investigated in this work. The bamboo is therefore split into lamellas and these are pressed into a rectangular beam shape, that can be then used in a manner comparable to wood. The fabrication of bamboo helps with eliminating naturally grown flaws and brings the material closer to possible applications. The research activity on the tensile fatigue behavior of the material should lead to a further dissemination and awareness for the sustainable and fast-growing material bamboo. It is intended to lay the foundation for further investigations and qualifications for the material and a broad distribution among technical fields in Europe. 2. Experimental setup Different material tests were conducted to determine the fatigue properties of laminated bamboo lumber (LBL) in tensile direction. In preparation, the specimens were cut from the pre-fabricated LBL material made out of Moso bamboo. As it can be seen in Fig. 1a, the specimens were designed in a bone shape, to have the clamping areas as large as possible. The testing area was intended to have a smaller cross-section, to lower the expectable tensile forces during the tests, since bamboo in general has shown outstanding tensile properties in previous investigations (Verma et al., 2014; Dauletbek et al., 2014; Zhang et al., 2021). In addition, the clamping areas were strengthened using multiple metal screws to avoid the soft material being squashed by the clamping devices of the testing machine. Because of the aforementioned hygroscopicity of the bamboo and the significant influence of the material’s moisture content, all specimens were stored in a climate room with a temperature of 20°C and 65% relative humidity for a minimum of 14 days. This led to an average moisture content of 7-8 % for all specimens tested. To determine the fatigue behavior of the material as effectively as possible, different types of tests were conducted building up on each other. First, tensile tests were performed to get information about the general tensile behavior of the available engineered bamboo. Based on the results of the tensile tests, the multiple amplitude tests (MAT) were planned and conducted. By recording the occurring material reactions, the results of the investigations are in turn incorporated into the following constant amplitude tests (CAT). The tests were conducted on a servo-hydraulic testing machine (Fig. 1b) with a maximum force of F max = 630 kN. Since only the tensile fatigue performance should be investigated, the load ratio was chosen to be R = 0.1 with a testing frequency f = 3 Hz. All tests were performed under laboratory climate around 23°C and 50-65% relative humidity. To record the material reactions during the fatigue tests, different types of measurement technologies were used. For the long-term fatigue tests in the high cycle fatigue (HCF) regime, displacement sensors were glued to the LBL specimens and thus occurring strains in the testing area could be recorded. In order to image the material behavior in the low cycle fatigue (LCF) regime, two high-resolution camera systems with subsequent digital image correlation