During long-duration dynamic loads, such as wind loads or seismic effects, the internal temperature and pressure of a damping cylinder escalate rapidly, which induce shifts in the mechanical attributes of viscous fluid dampers (VFDs). This study investigated the mechanical performance of VFD considering the coupling effects of temperature and pressure under long-duration loads. First, we analyzed the mechanical and energy-dissipation performances of the dampers based on the dynamic mechanical tests considering different loading frequencies, displacement amplitude, and loading cycles. The experimental results indicated that both temperature and pressure influenced the output of the dampers, and in the sealed environment of the damper pip, temperature and pressure exerted mutual influence. Furthermore, the relationship between the damping coefficient and temperature–pressure coupling effects was obtained. Subsequently, an improved mathematical model for the mechanical performance of a gap-type VFD was proposed by considering the macroscopic energy balance of the entire fluid within the damper. Finally, the accuracy of the mathematical model for VFD under long-duration dynamic loads was validated by comparing the computational results with the experimental data.

At present, the engineering designers generally design and analyze the precast structural models according to the equivalent cast-in-situ principle, and have a vague understanding of non-identical problems. However, these issues cannot be ignored, especially for high-intensity areas. This paper considers the differences of the hysteretic relationship between two typical precast joints and cast-in-situ (RC) joints, and researches the influence of these differences on the seismic response of frame structures. For the monolithic precast joint, the force mechanism was analyzed based on its assembly form, and the differences with the RC joint in the testing phenomena were explained accordingly. The dimensionless hysteresis models of two types of joints were proposed, and the rationality of the monolithic precast joint model was verified according to the existing experimental results. Different performances of joints were realized by assigning the constitutive models calculated from sectional reinforcement to the spring elements of analysis models. Considering two possible performance deficiencies of each type of precast joint separately, a total of seven structural analysis models were formed. Nonlinear static analysis and dynamic time-history analysis methods were adopted to reveal the differences between precast frames and the RC frame in terms of structural capacity curve, displacement response, ductility demands of components and structural residual deformation. The results showed that under strong seismic excitation, the response differences between precast frames and the RC frame were significant, so it is worthwhile to establish nonlinear models suitable for precast frames in seismic analysis. This study is valuable for understanding and distinguishing the nonlinear response of precast frames and traditional RC frames.

In the present study, three modification methods, including water washing, sodium hydroxide (NaOH), and styrene–acrylic emulsion, were used to modify waste rubber powders. The influence of rubber powders on the mechanical properties and frost resistance of magnesium oxychloride cement was examined, and the different modification mechanisms were also analyzed. Based on the analysis of hydrophilic properties after modification, styrene–acrylic emulsion achieved the best modification effect, while water washing produced the least modification effect; regarding mechanical properties, magnesium oxychloride cement mixed with NaOH modified rubber powders achieved the best modification effect, in which the 28 d flexural strength and compressive strength increased by 41.2% and 59.6%, respectively. During the freeze-thaw cycles, the mass loss of specimens was reduced with an increase in the content of rubber powders. In addition, after 300 cycles, the relative dynamic modulus of elasticity of the blank sample was about 28.12%, while that of the magnesium oxychloride cement mixed with NaOH modified rubber powders was approximately 42.38%. In general, the properties of the modified rubber powder–magnesium oxychloride cement composite material can meet the requirements for engineering materials, which provides a theoretical basis and technical support for the application of rubberized magnesium oxychloride cement.

The intensity non-stationarity is one of the basic characteristics of ground motions, the influences of which on the dynamic responses of structures is a pressing issue in the field of earthquake engineering. The BP neural network modified by the genetic algorithm was adopted in this research to investigate the influence of intensity nonstationary inputs on the structural dynamic responses from a new perspective. Firstly, many training data were generated from the prediction formula of dynamic response. The BP neural network was then pre-trained by sparsely selected data to optimize the initial weights and biases. Finally, the BP neural network was trained by all data, and the mean square error of predicted responses compared with the target response were less than 10⁻⁵. The calculation formula of sensitivity was also derived here to quantify the influence of the input change on the output. The presented method combines the advantages of neural networks in nonlinear multi-variable fitting and provides a new perspective for the study of earthquake nonstationary characteristics and their influence on the structural dynamic responses.