Many historical masonry towers belong to architectural heritage. Their preservation is still a critical issue in several countries. In fact, the experience of past earthquakes has shown that even earthquakes of moderate intensity can cause the collapse of these historical structures due to their slenderness together with irregularities, openings, leaning phenomena and adjacent lower buildings. The damage and changes suffered over the centuries, and the complex behaviour of the materials makes the performance of this type of structures more uncertain, and the seismic analysis and the remedial measures to achieve their protection a very complex task. This paper presents a complete study (from the on-site diagnostic investigations to the seismic assessment and non-invasive strengthening) of an ancient masonry tower in Torre Orsaia (Southern Italy). The paper, through the discussion of the case study, shows effective procedures to assess the seismic safety of masonry towers and plan interventions without too time- and cost-consuming processes. The results have established that the deep and wide cracks on the belfry are due to the loss of tension of the ancient tie-rods. The seismic safety of the tower has been carried out using three levels of analysis: LV1 (evaluation with simplified models), LV2 (analysis of local collapse mechanisms) and LV3 (global analysis). The analyses have shown that the critical mechanism is the simple overturning of the masonry piers of the belfry due to the ineffective tie-rods. The corresponding safety index in terms of peak ground acceleration is 0.305. To avoid this undesired mechanism and, at the same time, fully close the cracks, a strengthening intervention based on stainless steel reinforcing rings has been developed. This chaining system avoids the local mechanisms of the piers of the belfry and allows developing global mechanisms. After retrofit intervention, the seismic analysis has shown that the safety index increases to 0.716 for the LV2 analysis and 0.793 for the LV3 analysis.

中文翻译：

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意大利南部一座中世纪砖石塔的抗震评估、修复和加固

许多历史悠久的砖石塔楼属于建筑遗产。在一些国家，它们的保存仍然是一个关键问题。事实上，过去地震的经验表明，即使是中等强度的地震，由于这些历史建筑的细长，加上不规则、开口、倾斜现象和相邻的较低建筑物，即使是中等强度的地震也会导致倒塌。几个世纪以来所遭受的破坏和变化，以及材料的复杂行为，使得这类结构的性能更加不确定，实现其保护的抗震分析和补救措施是一项非常复杂的任务。本文介绍了 Torre Orsaia（意大利南部）一座古老砖石塔的完整研究（从现场诊断调查到地震评估和非侵入性加固）。该论文通过案例研究的讨论，展示了评估砌体塔抗震安全性的有效程序，并在没有太多时间和成本的过程中规划干预措施。结果表明，钟楼上的深而宽的裂缝是由于古代拉杆失去张力造成的。塔的抗震安全性已使用三个分析级别进行：LV1（使用简化模型进行评估）、LV2（局部倒塌机制分析）和 LV3（全局分析）。分析表明，关键机制是由于拉杆无效而导致钟楼砌体桥墩的简单倾覆。就峰值地面加速度而言，相应的安全指数为0.305。为了避免这种不受欢迎的机制，同时完全封闭裂缝，已经开发出一种基于不锈钢加强环的加强干预措施。这种链接系统避免了钟楼码头的局部机制，并允许开发全局机制。改造干预后，地震分析表明，LV2 分析的安全指数增加到 0.716，LV3 分析的安全指数增加到 0.793。