1. Introduction
In recent years, the risks caused by impacts to nuclear power plants, such as nuclear leakage, have attracted considerable worldwide attention, and the impact resistance requirements of nuclear power plant containment structures have become increasingly stricter. Dynamic loads, including impact, must be considered in the design of major national defense projects, such as nuclear power plants. Previous studies [
1,
2,
3,
4,
5,
6,
7,
8,
9] showed that the strain rate of stressed rebars in reinforced concrete structures under impact may exceed 1.0/s; however, the connection performance and mechanical behavior of reinforcement joints under impact conditions are not clear yet. Therefore, more research on this specific problem is necessary.
The impact resistance of the third-generation nuclear power reactors, including China′s Hualong One, is regarded as the main performance characteristic. At the same time, a large number of studies have been conducted by various countries to evaluate the ability of the third-generation nuclear power reactors to resist the deliberate impact. The Nuclear Regulatory Commission (NRC) of America amended federal regulation 10 CFR 50 in 2009 to require applications for new nuclear power plants to assess the impact of a large commercial aircraft strike on the plant [
10]. In 2016, the National Nuclear Safety Administration of China issued a new version of Nuclear Power Plant Design Safety Regulations (HAF 102—2016) [
11], which also put forward requirements to combat the impact of large commercial aircraft. As the main force material of the concrete structure of nuclear power containment, the reinforcement and its joints are inevitably affected by the dynamic load. Numerous studies on the strain rate effect in rebars have been carried out. Malvar [
12] et al. conducted experimental dynamic studies on the rebars with a yield strength of 290–710 MPa and proposed dynamic increase factor formulas for the rebar yield strength and ultimate tensile strength (UTS) based on the test results. Yang [
13] et al. conducted a quasi-static tensile test and a dynamic tensile test on Q550 rebars under different strain rates. They found that the yield strength of Q550 rebars increased with the strain rate, but the strain-rate sensitivity of Q550 rebars was lower than that of ordinary low-carbon steel rebars. Zeng [
14] et al. carried out dynamic tensile tests on HRB500E rebars, modified the Cowper–Symonds and the Malvar formulas for predicting dynamic yield stress based on the test results, and verified the Johnson–Cook formula and its modification. Lin [
15] et al. studied the mechanical properties of HRB500E rebars under a strain rate of 4.9~59.0/s and established dynamic constitutive models for two types of HRB500E rebars based on the test results. Qiao [
16] et al. studied HRB600 rebars under a strain rate of 0.0000395~0.0827/s and found that the strain-rate sensitivity of HRB600 rebars was lower than that of low-strength rebars. Wang [
17] et al. studied the dynamic mechanical properties of HRB400E and HRB500E rebars and proposed a dynamic constitutive model suitable for the specimens used in the test. As can be seen from this literature survey, a broad consensus on the strain rate effect in rebars has been reached in the academic community.
However, only limited studies on the strain rate effect on rebar joints have been conducted in recent decades. Given that the strain rate effect on rebars will improve their strength, the design of rebar joints based on the original design criteria may cause rebar joints to fail before the failure of the rebars themselves. Preliminary studies on the connection performance of rebar joints under dynamic impact were conducted by some researchers. To highlight the dynamic characteristics of the fully grouted sleeve connection at loading rates of 0.6 mm/s, 6 mm/s, and 60 mm/s, Yin [
18] et al. conducted static and low-speed dynamic tensile impact tests on 29 specimens and proposed that the connection failure of fully grouted sleeves was fundamentally determined by bond strength. To study the effect of impact load on rebar joints, Hu [
19] et al. elaborated the principle of the impact-resistant tensile test and carried out process evaluation and improvement on the aircraft impact-resistant mechanical rebar splice of the Hualong One reactor in China. Feng [
20] et al. conducted a sensitivity analysis on APC shells to determine the sensitive area of wall impact, thus narrowing the application scope of special mechanical splices in the design of anti-plane crash (APC) shells. Rowell [
21] et al. compared the performance of different types of mechanical splices tested under the same strain rate and compared them to the requirements of UFC3-340-02. However, due to the lack of equipment to perform the impact test, most of the existing equipment cannot complete the rapid tensile of large tonnage specimens, resulting in a lack of domestic and foreign research on the dynamic mechanical properties of large diameter high-strength steel bars and the connection properties of connectors under impact load and a lack of relevant research results.
Therefore, in order to obtain the dynamic mechanical properties of high-strength rebar and the connection properties of steel bar extrusion sleeves for anti-plane crash nuclear containment under impact conditions, the impact test of anti-impact joints adapted to high-strength steel HRB500E at five strain rates of 1.395/s, 1.348/s, 1.298/s, 1.184/s and 1.079/s was carried out.