提高纤维增强聚合物穗锚质量控制的安装方法
Summary
本文介绍了一种控制钢钉锚杆安装质量的方法, 旨在延缓外部粘结纤维增强聚合物的脱层。该协议包括钻孔的准备和插入过程。讨论了影响锚杆效率的最重要参数。
Abstract
纤维增强聚合物 (FRP) 锚杆是提高外部粘结 FRPs 在现有结构中的性能的一种有希望的方法, 因为它们可以延缓甚至防止脱粘失效。然而, 设计者所面临的一个主要问题是由于应力集中导致锚杆过早失效。安装质量差和间隙孔的准备会导致应力集中, 从而引发过早的故障。本文论述了一种安装方法, 旨在减少应力集中的影响, 为钻孔的制备提供适当的质量控制。该方法涉及三部分: 钻孔和清洗的孔, 平滑的孔边缘与定制钻头, 并安装锚本身, 包括浸渍的锚钉和其插入。锚杆风扇 (峰值的自由长度) 然后粘结到外部 FRP 加固。对于末端锚固, 并且在多层层增援的情况下, 建议将锚杆风扇插入两层之间以协助应力传递机制。
根据广泛的数据库, 所提出的程序辅以一种用于钉锚的设计方法。提出了设计中应遵循的几个步骤, 即: 选择锚径和后续抗拉强度的连接器 (即在扇出自由端前的锚杆), 评价降低抗拉强度的原因弯曲, 提供足够的嵌入, 以防止滑移失败, 并考虑到锚的数量和间距的一个给定的加固。在这个意义上, 应该指出, 需要进一步的研究, 以获得一个普遍的表达, 为钉锚的贡献, 整体粘结强度的 FRP 加固。
Introduction
FRP 锚提供了一种有希望的方式来增强外部粘合 FRPs 应用于现有结构的性能, 因为它们可以延迟甚至防止剥离失败1,2。然而, 对于设计者来说, 一个主要的问题是由于弯曲区域的应力集中导致了在剪切中锚杆的过早失效。安装质量和间隙孔的准备对于限制这种过早失效的应力集中至关重要。
本文论述了一种安装方法, 旨在减少应力集中的影响, 为钻孔的制备和锚杆的安装提供适当的质量控制。该方法涉及四部分: 钻孔和清洗孔, 平滑的孔边缘与定制钻头, 以避免不规则的应力分布在弯曲区域内, 安装锚本身, 包括浸渍锚栓和它的插入, 并且锚的黏附力到加强。
从以前发布的研究3,4,5,6,7, 它可以得出结论, 钉锚与弯曲的区域 (也就是说, 在自由端之间的某一角度和嵌入区域), 受应力集中, 容易引发过早失败。由于原始成员的几何形状, 因此不能始终避免这种情况。在许多情况下, 90°的销角是广泛使用的, 虽然它普遍认为, 135°的桩角允许减少应力集中, 并导致更好的性能的钉锚。使用90°定位角的主要原因是, 它们在任何方向上的执行和控制都更简单, 并降低了满足内部增援的可能性。
图 1显示了一个典型的钉锚, 其中最常见的定位角。与90°定位角安装的钉锚, 不过, 可以显示一个相对良好的性能, 如果适当控制的应力集中。极限应力集中通常涉及设计具有较大内弯曲半径的锚杆, 因为内部弯曲半径已被发现在光纤扭结8,9中发挥主要作用。在这个意义上, 作者如奥登等人3建议使用锚直径四倍的弯曲半径。这项建议导致不实际的弯曲半径, 即使对小的锚直径, 因为增加弯曲半径涉及减少实际嵌入长度的给定孔深度。
作者认为, 大弯曲半径的建议与控制实际内弯曲半径的难度有关, 从几何角度看, 当用手进行平滑处理时。因此设计了自定义钻头, 使安装易于质量控制, 并确保在设计中考虑弯曲半径。
本文考虑了两个不同的过程。第一个是与连接器 (锚, 特别是在扇出自由端之前) 的安装程序有关, 而第二个则包括建议的钉锚设计方法和验证需求。
Protocol
Representative Results
Discussion
提出了一种用于 FRP 钉锚杆安装与设计的分步协议。据作者所知, 在安装参数和工艺对锚固能力的影响方面, 没有制定关于钉锚的详细协议。
所提出的平滑钻头对钉锚杆的性能有很有利的作用, 通过降低应力集中度, 证明了其在减小孤立锚杆试验散射方面的有效性。这与安装质量控制的提高有关。此外, 在建议的安装协议之后执行的锚点的低分散允许降低标准偏差, 从而有助于可…
Disclosures
The authors have nothing to disclose.
Acknowledgements
作者希望对西卡的支持表示感谢, 特别是他们为锚杆和增援部队提供的材料。Betazul 是特别承认他们的帮助与定制钻头和视频的准备。
Materials
| Concrete | The concrete for support has a dosage made by the authors, and a strength class no lower than C40 | ||
| SikaWrap anchor C | SIKA | This material has been used for the FRP spike anchors. SikaWrap Anchor C is a unidirectional, carbon fiber rope, sheathed in an elastic gauze. The gauze can be cut onsite to create a fan end that anchors CFRP fabrics and plates used in the structural strengthening of masonry and concrete. | |
| Sikadur 330 | SIKA | Impregnating resin, apt for manual saturation methods. The product was used for impregnating the anchor dowel before insertion | |
| Sikadur 30 | SIKA | Thixotropic, two part epoxy resin applied by spatula and therefore suitable for virtually any application, including overhead | |
| Drill bit | Betazul | Drill bit employed to smooth the holes that was designed by the authors and developed by Betazul SA | |
| Hammer drill | Hilti | Tool for the execution of anchor holes on masonry and concrete, for different drilling ranges | |
| Wire brush | Hilti | Hit series | For the proper brushing of drilled holes of varying diameters and embedment depths |
| Blow-out pump | Hilti | Hit series | Manual blow-out pump |
| SikaWrap-230 C | SIKA | Unidirectional woven carbon fiber fabric for dry application process | |
| Aluminium Bubble Roller | Fibre glast | For laminations where increased pressure is necessary to release air bubbles. They are straight across the width of the head and provide excellent air relief for nearly all applications. | |
| Brush | For impregnation of FRP bundle and sheet | ||
| 600 kN testing machine | Proeti | DI-CP/S | This is used for the shear test of anchors, in order to evaluate the efficacy of the proposed insertion method |
| Cable ties | Cable ties are needed to fasten the end of the anchor dowel in order to prevent fanning out of the fibers during insertion | ||
| Measuring tape | The measuring tape is necessary to control the embedment length as well as the diameter of the drill bit and hole clearance | ||
| Steel wire | Required to assist insertion | ||
| Rigid (steel) bar | A rigid bar of any material (in this case, it was made with a steel bar) is needed to control the embedment length |
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