1. Introduction
Compared with cast-in-place concrete structures, the most prominent feature of precast concrete structures is that the main concrete elements are prefabricated in the factory, a feature that allows them to show many advantages during construction. Each prefabricated component is equivalent to further discretizing the overall concrete structure. The composition of its basic units is more adapted to standardization and parameterization compared to the overall structure, which can enable the standardized design and factory flow production upstream and downstream of the whole industry [
1]. With the main components prefabricated in the factory, the environmental pollution of the on-site construction can be effectively controlled, while the construction waste such as waste water and waste gas can be significantly reduced under the flow-through production method, and the turnover rate of auxiliary materials such as formwork can be improved to achieve energy conservation and environmental protection [
2]. The standardized design is in line with the development trend of construction informationization, and, combined with BIM technology, big data technology, and information and communication technology, it can effectively improve the degree of informationization in the construction industry and realize modernization [
3].
Precast reinforced concrete (PRC) structures have been widely used in civil engineering [
3,
4]. Beam–column joints (BCJs) in PRC structures are the core force-bearing parts, which not only affect the seismic behavior of PRC structures but also directly relate to the convenience and economy of construction. According to the presence or absence of post-cast sections at the joints, the precast concrete BCJs are divided into wet and dry connection forms [
2,
5]. At present, the investigations on the seismic behavior of PRC structures are still mainly focused on experiments [
6,
7,
8,
9], while numerical simulations for their own characteristics are still relatively lacking [
10]. The experimental investigations on precast frame joint specimens are focused on the influence of parameters such as the connection methods on the seismic performance of BCJs [
5]. However, most of the experimental studies on the seismic behavior of specimens are limited by the test conditions, time, and funding.
With the continuous development of elastic–plastic finite element theory and the rapid improvement of computer operation and processing capability, numerical simulation methods with good accuracy [
10,
11,
12] have been widely applied in civil engineering. On one hand, numerical simulation can carry out a wide range of parameterized analyses on the basis of experiments and obtain richer analysis data while reducing the test input. On the other hand, numerical simulation can be used for structural optimization analysis, which can play an important role in guiding the experimental design and actual engineering design. Combined with experiment investigations, numerical methods are important for predicting the structural response of buildings. So far, many finite element models (FEMs) [
13] have been developed to simulate the seismic behavior of reinforced concrete (RC) members. Precast BCJs are subjected to complex stresses and are prone to the formation of structural defects that lead to stress concentrations. In practical engineering, while the entire structure is often in an elastic phase, the joints may have transitioned to a plastic phase and suffered severe damage. This can eventually lead to structural failure. Therefore, it is crucial to focus on BCJs analysis for RC frame structures in numerical modeling. How to use the numerical simulation analysis to effectively reflect the seismic behavior of precast BCJs is of great significance to promote their development. Kremmyda et al. [
14] simulated the hysteretic properties of precast joints using the ABAQUS software (ABAQUS 2011). In FEMs, a reasonable contact was set at the connection interface to simulate the shear damage of splice joints under reciprocating loads. Zoubek et al. [
15] simulated the hysteresis performance of precast pin connection joints using the ABAQUS software. In Zoubek’s model, solid elements were used for the beam–column members and concealed pins, which can simulate the slip effect of concealed pin connections under seismic action more accurately. Cao et al. [
16] carried out an in-depth study on the numerical simulation method of PBCs using the OpenSees software, proposing a more refined analysis model applicable to both types of joints with wet and dry connections. In the model, the influence of energy dissipation elements such as prestressing and angles on the structure was considered. The seismic behavior of ten different types of precast joints was simulated to validate the accuracy of the FEMs. Most of the existing numerical simulation methods for precast concrete structures can be divided into two categories according to their modeling ideas: numerical simulation methods based on beam–column link elements and 3D solid elements [
17]. The two types of numerical simulation methods either pursue the convenience of use or the accuracy of the mechanism; it is difficult to achieve unity in efficiency and precision, and each has its own advantages and disadvantages. Therefore, combined with the characteristics of the assembled concrete structures, the development of fine and efficient numerical simulation methods is still worthy of in-depth study.
The existing numerical simulation methods can approximate the specific force characteristics of precast structures such as bond–slip, shear behavior at the joint, etc. The accuracy of FEMs is closely related to the selected material constitutive model [
18]. Currently, the OpenSees software has been widely adopted in various countries to conduct numerous simulations regarding practical engineering and tests. The accuracy and efficiency of the simulation results using the software have been verified [
13,
18]. In the OpenSees software, there are three main types of models used for the simulation of reinforced concrete members with link elements, namely member models based on test data, section models based on section stress–strain, and fiber models at the material level. Among them, the fiber models are computationally inexpensive, easy to model, and have better accuracy [
17]. Paulay [
19] pointed out that the deformation of BCJs consisted mainly of the shear deformation of joint shear blocks and corner deformation of the beam–column intersection through. Pantazopoulou and Bonacci [
20] pointed out that the slip of reinforcement would lead to blocked load transfer at the intersection and further lead to damage of the joint shear blocks. The beam–column joint element proposed by Lowes and Altoontash [
21] and improved by N-Mitra [
22] consisted of three components to simulate different damage behaviors at the BCJs. The shear panel component in the middle of the beam–column joint element is used to simulate the shear behavior of the stiffness and strength degradation of the joint core under shear damage. Under low-cycle reciprocating loads, bond–slip occurs between the reinforcement and the concrete, which in turn leads to hysteresis loop pinching. A reinforcement bond–slip model, Bar–Slip, is developed in the OpenSees software using the reinforcement stress–slip relationship proposed by Eligehausen and Hawkins [
23,
24]. It can take into account the effects of the material properties of concrete strength, reinforcement, and the degree of anchorage, and thus analyzes the effect of the slip on the overall joint performance.
In a previous study [
2], novel precast BCJs using mechanical connections (PBCJs-MCs) were proposed to improve the reliability and construction efficiency of PRC structures (see
Figure 1). In
Figure 1, the steel bars in the columns are bolted to the nuts [
2]. Currently, there are some investigations on the seismic behaviors of PRC BCJs. Paul and Tanapornraweekit [
25] evaluated the seismic performance improvement of composite BCJs using the LS-DYNA finite element software (Version 11 R 11.0.0). Yang et al. [
26] tested and simulated the seismic performance of precast BCJs and found that the accuracy of the simulated results obtained from the ABAQUS software was good. Bohara et al. [
27] evaluated the seismic behavior of composite wide BCJs and found that the simulated result using the LS-DYNA finite element software was in agreement with the experimental result. However, there are few numerical simulation studies on the seismic behavior of PBCJs-MCs.
Whether the existing constitutive models of concrete or reinforcement can accurately simulate the seismic behavior of PBCJs-MCs should be verified. Moreover, the parameters influencing the seismic behavior of PBCJs-MCs need to be analyzed using the numerical simulation method. In this present study, selecting appropriate element types and material constitutive models, the FEMs of PBCJs-MCs are established to analyze the seismic behavior of novel precast BCJs with mechanical connections. The simulation results are compared with the experimental results. Based on this, the factors influencing the seismic behavior of PBCJs-MCs are further investigated numerically.