The use of bundled bars in highly loaded concrete members instead of individual bars can reduce or even avoid reinforcement congestion, allowing easier placing and compaction of concrete, since bundles (with two or more side-by-side bars) are less obstructive to fresh-concrete flow. However, there is still a lack in knowledge of the fundamental phenomena related to the bond behavior of bars in bundles. Therefore, design code rules for anchorages and splices differ significantly among International Standards (Eurocode 2, fib Model Code 2010, and ACI 318–19). The present paper reports the results of more than 100 pullout tests with short embedded length with the aim of comparing the local bond behavior of bundles with that of corresponding notional individual bars. Among the three criteria usually introduced to compare bundled and individual bars, based on the concepts of “equivalent sectional area,” and “minimum or maximum sectional perimeter,” the first and the second are introduced in this paper. Experimental results show that both criteria are suitable methods for evaluating the bearing capacity of bundled bar anchorages, even if equivalent area criterion seems to be slightly more conservative. The experimental results provide also information on the bursting forces generated by the wedge action of the ribs which clearly increases with bar diameter. Finally, experimental results are compared with design rules for anchorage strength of bundled bars as prescribed by fib-Model Code 2010.

中文翻译：

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捆扎钢筋的局部粘结行为：实验研究

在高负荷混凝土构件中使用捆扎钢筋而不是单个钢筋可以减少甚至避免钢筋拥堵，从而更容易浇筑和压实混凝土，因为捆扎（具有两个或更多并排钢筋）对新鲜的阻碍较小。混凝土流。然而，仍然缺乏对与束中钢筋的粘合行为相关的基本现象的了解。因此，不同国际标准（欧洲规范 2，fib型号代码 2010 和 ACI 318-19）。本文报告了 100 多次具有较短嵌入长度的拔出试验的结果，目的是将束的局部粘合行为与相应的名义单个钢筋的局部粘合行为进行比较。在通常用于比较捆绑钢筋和单个钢筋的三个标准中，基于“等效截面面积”和“最小或最大截面周长”的概念，本文介绍了第一个和第二个。实验结果表明，这两个标准都是评估捆绑钢筋锚固承载力的合适方法，即使等效面积标准似乎稍微保守一些。实验结果还提供了由肋条的楔形作用产生的爆破力的信息，该爆破力随着钢筋直径的增加而明显增加。最后，fib -型号代码 2010。