# Performance Analysis of an Improved Gravity Anchor Bold Expanded Foundation
## 1 Introduction  
With the continuous development of wind resources, the number of wind farms is increasing. Onshore wind power is a mature technology, and its development costs are much lower than that of offshore wind power. Figure 1 shows the installed capacity of global onshore and offshore wind farms from 2018 to 2022, according to statistics released by the Global Wind Energy Council (GWEC). Although the proportion of onshore wind farms has declined in the past two years, onshore wind farms still account for a large proportion of the entire wind power market [1]. Figure 2 shows the net new capacity of onshore wind power by country and region (2022-2024) [2]. Onshore wind power has continued to develop in the past five years, maximizing the power generation per megawatt installed capacity. In this process, as the fan becomes larger, the hub height becomes higher, the rotor diameter becomes larger, and the probability of the tower bending, the foundation overturning, the untimely replacement of anchor bolts, the deterioration of foundation cracks, and many other problems that will cause great harm to the fan increases. The market has put forward higher requirements for the safety performance of wind turbines. Therefore, the stress analysis and design of an onshore wind turbine's foundation structure are very important [3, 4]. The working environment of wind turbines is very wet and harsh, which is because they are usually built in mountainous and open areas. The foundation is subjected to a combination of torque-vertical load-horizontal load-bending moment load (T-V-H-M) under operating conditions. The crack monitoring, fatigue damage, and vibration response of the wind turbine foundation have become the focus of research. [PERSON] et al. [5] proposed a method to determine and characterize the crack deterioration in the foundation of onshore wind turbines. [PERSON], [PERSON] et al. [6] used the double K crack propagation criterion to evaluate the stability of horizontal crack propagation in the foundation of an onshore wind turbine. [PERSON], [PERSON] et al. [7] studied the fatigue behavior of an onshore wind turbine foundation and the influence of cyclic load on stress distribution. [PERSON] et al. [8] carried out structural health monitoring of an offshore wind turbine jacket foundation with only vibration response through a convolutional neural network. In addition, the study of structural vibration theory plays an important role in many fields of structure and foundation engineering [9; 10; 11; 12; 13; 14; 15]. The soil-structure interaction will cause a vibration response in the wind turbine foundation, which may cause damage to the foundation [16; 17; 18]. With the advent of the big data era, artificial intelligence [19; 20; 21; 22; 23] is gradually becoming an important tool in structural engineering and other fields. [PERSON] et al. [24] proposed an optimization method for wind turbine towers and provided important design parameters for them. Figure 1: Installed capacities of onshore and offshore wind power plants worldwide from 2018 to 2022 (unit: GW). Figure 2: Net onshore wind electricity capacity additions by country or region, 2022–2024. The common tower types of wind turbines are steel towers, concrete towers, steel lattice towers, hybrid towers, and guyed rods [25]. Most onshore wind turbines are built on extended foundations, which are divided into gravity foundations and anchor pile foundations. As shown in Figure 3, there are two ways to connect the tower and the foundation in the extended foundation: one is to embed the tower directly into the concrete foundation slab ('foundation ring'); the other is to fix the bottom flange of the tower on the concrete by using prestressed bolts ('anchor cage ring') [26]. The foundation ring is widely used because of its simple structure, large production, convenient quality control, and convenient installation [28; 29].