Retrofit of Rocking Structures

许多结构在动态加载时表现出摇摆行为，包括未加固的砖石结构、纪念碑、塔楼、桥墩、雕塑等。这些结构因动态加载而倒塌，造成了全球破坏，最近世界各地的地震都表明了这一点。在英国，在繁忙的交通负荷下，砖石桥梁的坍塌也是一个很大的问题。因此，国内和国际上都需要防止这些结构倒塌造成的破坏。尽管在这一领域进行了大量的研究，但工程师们仍然误解了摇摆结构的动力响应与典型弹性结构之间的根本区别，因此从有缺陷的角度对摇摆结构进行评估。典型的解决方案是防止摇摆行为，而不是控制摇摆行为。预防通常是通过捆绑或加固结构来实现的。对于砖石结构，这是通过钻穿结构和添加钢筋，或通过用纤维增强聚合物(FRP)包裹结构来完成的。虽然这些方法可能是有效的，但它们可能会使结构过度僵硬，并具有破坏性。增加刚度会极大地改变基本的动态行为，并可能导致高应力，从而导致局部损坏。这种损害可以通过替代的改装方案来防止。本研究的主要目标是开发使用优化的减震方案(例如减震器)控制摇摆运动的新方法。不是增加结构的刚度，而是提出了阻尼，因为它允许一些运动，同时耗散不需要的能量。因此，既可以防止没有加固的结构的破坏性倒塌，也可以防止由于过度加固而造成的不必要的局部破坏。在这种情况下，本研究的目的是通过分析模型来表征减振摇摆运动的基本行为。一个单一的摇块分析模型将作为工具来确定最能控制摇摆运动的阻尼类型，然后优化减振机构的具体特性。随后，将建立更复杂的分析模型来描述砖石拱门的摇摆行为。拱门是砖石结构建筑和桥梁的典型构件，因此了解它们的动态行为对于制定适当的加固解决方案至关重要。分析ARCH模型将用于测试各种包含优化减振机制的改型方案。虽然分析模型对于描述行为和设计改型解决方案至关重要，但实验测试对于评估其准确性是必不可少的。分析模型的结果将首先用于优化弹簧-阻尼器元件的设计和构造。这些元素将使积木和拱形的改造成为可能，这将使用小型振动台在水平地面运动下进行测试。实验结果将被用来评估解析建模结果和确定改进方案的有效性。最后，解析建模对于简单的结构是有效的，但对于较复杂的结构通常是不可行的。因此，这项工作的最终目标是使用商业离散元建模(DEM)软件来预测实验结果。DEM是一个合适的工具，因为它是为模拟多个不同区块的相互作用而量身定做的。如果确定DEM是准确的，它可能是设计和测试更复杂结构的改造方案的必要工具。总之，需要新的改造方案。这项研究旨在为开发一类新型的利用智能减振系统的改装解决方案奠定基础。在这一过程中，将在非光滑动态系统的总体控制方面取得科学进展。

Numerous structures exhibit rocking behaviour when loaded dynamically, including unreinforced masonry structures, monuments, towers, bridge piers, sculptures, etc. The collapse of these structures due to dynamic loading has caused global destruction, as recently exhibited by earthquakes throughout the world. In the UK, collapse of masonry bridges during intense traffic loading is also a large concern. Thus, there is a national and international need to prevent the devastation caused by the collapse of these structures.Despite a significant amount of research in this area, engineers still misunderstand the fundamental difference between the dynamic response of rocking structures and typical elastic structures, and therefore assess rocking structures from a flawed perspective. The typical solution is to prevent rocking behaviour instead of controlling it. Prevention is usually achieved by tying structures down or reinforcing them. In the case of masonry structures, this is accomplished by drilling through structures and adding steel reinforcing, or by wrapping structures in Fibre-Reinforce Polymers (FRP). While these methods can be effective, they can over-stiffen structures and be destructive. Adding stiffness drastically changes fundamental dynamic behaviour, and can cause high stresses which lead to local damage. Such damage could be prevented with alternate retrofit solutions.The primary goal of this research is to develop new methods of controlling rocking motion using optimized damping solutions (e.g. shock absorbers). Instead of adding stiffness to the structure, damping is proposed because it allows some motion while dissipating unwanted energy. Thus, both devastating collapse of structures which have not been reinforced, and unnecessary local damage due to over-stiffening, could be prevented.In this context, this research will aim to characterize the fundamental behaviour of damped rocking motion through analytical modelling. A single rocking block analytical model will serve as tool to determine the type of damping which best controls rocking motion, and then to optimize the specific characteristics of damping mechanisms. Subsequently, more complex analytical models which describe the rocking behaviour of masonry arches will be created. Arches are typical components of masonry buildings and bridges, so understanding their dynamic behaviour is critical in developing appropriate retrofitting solutions. Analytical arch models will be used to test a variety of retrofit schemes which incorporate optimized damping mechanisms.While analytical models are critical for characterizing behaviour and designing retrofit solutions, experimental testing is essential to evaluate their accuracy. Results of analytical modelling will first be used to inform the design and construction of optimized spring-damper elements. These elements will enable the retrofit of blocks and arches which will be tested under horizontal ground motion using a small scale shake table. Experimental results will be used to evaluate analytical modelling results and to determine the effectiveness of retrofit solutions.Finally, analytical modelling is effective for simple structures, but it is typically not feasible for more complicated ones. Thus, the final aim of this work is to use commercial Discrete Element Modelling (DEM) software to predict experimental results. DEM is an appropriate tool for this purpose because it is tailored to model the interaction of multiple distinct blocks. If DEM is determined to be accurate, it could be an essential tool for designing and testing retrofit solutions for more complicated structures.In summary, new retrofit solutions are needed. This research aims to lay the foundation for the development of a new class of retrofit solutions which exploit clever damping systems. In the process, scientific progress will be made regarding the control of non-smooth dynamic systems in general.