Wdowiak-Postulak Agnieszka, Bahleda František, Prokop Jozef
Faculty of Civil Engineering and Architecture, Kielce University of Technology, 25-314 Kielce, Poland.
Faculty of Civil Engineering, University of Zilina, Univerzitná 8215/1, 010 26 Zilina, Slovakia.
Materials (Basel). 2023 Mar 30;16(7):2776. doi: 10.3390/ma16072776.
Damage often develops in glued laminated timber members under high bending loads due to natural defects in the timber, which results in their low load-bearing capacity and stiffness. In order to improve the bending mechanical properties of glulam beams, a new type of longitudinal glulam reinforcement with pre-stressed basalt fibre-reinforced polymer composites (BFRP) was developed using the Near Surface Mounted (NSM) technique. The strengthening method consisted of two pre-stressed BFRP bars glued into the grooves at the bottom side of the beam; meanwhile, for the second strengthening alternative, the third BFRP bar was embedded into the groove at the top side of the beam. Therefore, an experimental study was carried out to verify this strengthening technique, in which fifteen full-size timber beams were tested with and without bonded BFRP bar reinforcement in three series. According to the results of this experimental study, it can be seen that the effective load-bearing capacity of the reinforced beams increased up to 36% and that the stiffness of the beams increased by 23% compared to the unreinforced beams. The tensile stresses in the wooden fibres were reduced by 11.32% and 25.42% on average for the beams reinforced with two and three BFRP bars, respectively. On the other hand, the compressive stresses were reduced by 16.53% and 32.10% compared to the unreinforced beams. The usual failure mode saw the cracking of the wood fibres at the defects, while for some specimens, there were also signs of cracks in the epoxy adhesive bond; however, the crack propagation was, overall, significantly reduced. The numerical calculations also show a good correlation with the experimental results. The difference in the results between the experimental and numerical analysis of the reinforced and unreinforced full-sized beams ranged between 3.63% and 11.45%.
由于木材存在天然缺陷，胶合木构件在高弯曲荷载作用下常常会出现损伤，这导致其承载能力和刚度较低。为了提高胶合木梁的弯曲力学性能，采用近表面粘贴（NSM）技术开发了一种新型的预应力玄武岩纤维增强聚合物复合材料（BFRP）纵向胶合木增强材料。加固方法包括将两根预应力BFRP筋粘贴到梁底侧的凹槽中；同时，对于第二种加固方案，将第三根BFRP筋嵌入梁顶侧的凹槽中。因此，进行了一项实验研究来验证这种加固技术，其中对15根全尺寸木梁进行了测试，分三个系列，有粘贴BFRP筋加固和未加固的情况。根据该实验研究结果可以看出，与未加固梁相比，加固梁的有效承载能力提高了36%，梁的刚度提高了23%。对于粘贴两根和三根BFRP筋加固的梁，木纤维中的拉应力平均分别降低了11.32%和25.42%。另一方面，与未加固梁相比，压应力分别降低了16.53%和32.10%。常见的破坏模式是缺陷处木纤维开裂，而对于一些试件，环氧胶粘剂粘结处也有裂纹迹象；然而，总体上裂纹扩展明显减少。数值计算结果也与实验结果具有良好的相关性。加固和未加固全尺寸梁的实验结果与数值分析结果之间的差异在3.63%至11.45%之间。
