This study continues a series of theoretical and experimental investigation of two‐layer beams (TLBs), performed by the authors. Such beams consist of normal strength concrete (NSC) layer in the tensile zone and steel fibered high strength concrete (SFHSC) in the compressed one. The present research is focused on comparison of prestressed single layer beam and three repaired prestressed two‐layer beams. The research includes experimental investigation of full‐scale simple supported beams under four‐point bending. A TLB represents possibility of strengthening by addition of high strength steel fibered concrete layer. Therefore, nonrepaired beam section height is equal to that of the NSC layer in repaired ones. All prestressed specimens with equal section height were produced at real industrial conditions. After that, a SFHSC layer was added in laboratory conditions to obtain three identical TLBs (one single‐layer beam was used as a control specimen). The main aim of the research is to study the effect of repairing, using a SFHSC layer on load‐bearing capacity. All specimens were tested from initial loading up to failure. The study was focused on cracking and deflections in TLBs, compared to single‐layer one. It was found that initial cracks' development in the investigated beams starts at same mid span deflection, but the corresponding load in the repaired beams is about 50% higher, compared to the control specimen. Additionally, proper interaction between the layers without de‐bonding was verified. The load bearing capacity in the control specimen is about 77% lower, compared to the repaired ones. Results, obtained in the present study, enable to recommend using SFHSC layer for strengthening prestressed beams. This method is a promising way for repairing existing elements and creating attractive structural systems.

中文翻译：

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预应力单层和修复后的两层钢筋混凝土梁的试验研究与比较

这项研究继续了作者对两层光束（TLB）进行的一系列理论和实验研究。这种梁由拉伸区中的普通强度混凝土（NSC）层和压缩区中的钢纤维高强度混凝土（SFHSC）组成。目前的研究集中在比较预应力单层梁和三个修复的预应力两层梁。该研究包括在四点弯曲下对全尺寸简支梁的实验研究。TLB表示通过添加高强度钢纤维混凝土层来增强的可能性。因此，未修复的梁截面高度等于修复后的NSC层的截面高度。所有具有相同截面高度的预应力试样都是在实际工业条件下生产的。之后，在实验室条件下添加SFHSC层以获得三个相同的TLB（一个单层光束用作对照样品）。该研究的主要目的是研究使用SFHSC层对承载力进行修复的效果。从初始加载到破坏，对所有样本进行了测试。与单层相比，该研究的重点是TLB的裂纹和挠曲。已发现，在研究的梁中，最初的裂纹扩展是在相同的跨距挠度下开始的，但与对照试样相比，修复后的梁中相应的载荷高出约50％。此外，还验证了层之间正确的交互作用而没有脱粘。与修复后的试样相比，对照试样的承载能力降低了约77％。在本研究中获得的结果 建议使用SFHSC层来加强预应力梁。这种方法是修复现有元素并创建有吸引力的结构系统的有前途的方法。