To understand the long-term performance degradation of asphalt, ultraviolet (UV) photo-oxidation has been used to accelerate the aging process. Three types of asphalt binders extracted from reclaimed asphalt pavements (RAPs) and one extracted from fresh hot-mix asphalt (HMA) were aged under continuous UV exposure and UV/moisture/condensation exposure. After accelerated aging tests, the weight percentage of oxygen (WPO) in all samples were measured by using energy-dispersive X-ray (EDX) spectroscopy. The testing results indicate that the aging rates of the asphalt binder under both UV and UV/moisture/condensation are fast at the beginning and stabilize after a certain period. Experimental results were also modeled by two classic asphalt aging models, namely, the fast rate–constant rate (FRCR) and nonlinear differential dynamic (NDD) models. Although the NDD model exhibits acceptable agreement with the experimental results from both the UV aging and UV/moisture/condensation aging samples, the FRCR model fits the UV/moisture/condensation aging better and thus is recommended for future UV/moisture/condensation aging performance prediction. Additionally, although exposed under UV for the same time, the WPO in samples after UV/moisture/condensation aging were lower than those in samples after continuous UV aging. This indicates that condensation and moisture reduce the UV-induced photo-oxidative aging rate.
In the case of earthquake and rockfall disasters, it is proposed to replace part of sand with geofoam material to form sand–EPS and sand–EPE composite cushions to improve the ability of structures to resist disasters. The shear performance of the sand–EPS beads mixture material with different moisture contents, the impact resistance of sand–EPS beads and sand–flocculent-EPE layered composite materials with different cushion thicknesses and different mass ratios were studied by direct shear tests and multi-impact tests. The results showed that with the increase in the moisture content, the shear strength of the sand–EPS beads decreased, the internal friction angle of sand–EPS decreased first and then increased, and the cohesion of sand–EPS increased first and then decreased. The sand–geofoam layered cushion had better buffering performance. Sand–EPE has better durability than Sand–EPS.
An improved Penzien model is proposed in this paper as a simplified model of soil–pile–structure interaction. The dynamic nonlinearity of soil under earthquake excitation is simulated by ANSYS in a free-field model and added to the original Penzien model. The improved Penzien model uses the finite element software ANSYS 2021 to simulate the dynamic nonlinearity of soil. The improved Penzien model is then used as a simplified calculation model of the numerical substructure. A substructure pseudo-dynamic test based on the improved Penzien model is carried out. The realization of the substructure pseudo-dynamic test verifies the feasibility and effectiveness of this method, which provides a convenient test method for the study of soil–pile–structure interaction in general laboratories. Soil and structure interaction reduces the acceleration of the structure, and the response exhibited a hysteresis phenomenon because of the nonlinear characteristics of the soil. The influences of soil–pile–structure interaction on velocity and displacement are very complex. The conclusions are reasonable, which proves that the substructure pseudo-dynamic test method of soil–pile–structure dynamic interaction using the improved Penzien model is feasible.
Rocking shallow foundations can be used as an effective seismic isolation means to reduce earthquake-induced damage to structures by utilizing nonlinearities arising from base uplifting and soil yielding. A number of studies have been devoted to the proposal of inelastic displacement ratios for estimating the maximum inelastic displacement demands on yielding structures on rocking shallow foundations for seismic evaluation purposes. However, there is a lack of methods for estimating structural deformations associated with damage to structures, which are usually measured using structural drift ratios. Since drift ratios of structures on rocking foundations consist of contributions due to foundation rocking, it is necessary to figure out whether these rocking rotations should be removed from structural drift ratios to obtain effective structural drift ratios related solely to structural straining. A comprehensive parametric analysis is carried out in this study to quantify the contribution of foundation rocking. Based on the results, a structural displacement ratio is proposed to estimate effective structural drift ratios excluding foundation rocking rotation, and an empirical expression is provided so that effective structural drift ratios can be directly obtained using available expressions for the inelastic displacement ratios of rocking shallow foundations.
Conventional precast structures often face the challenge of post-earthquake repair, especially at beam–column joints. A new type of precast concrete beam–column joint with a replaceable energy dissipation device consisting of cross-shaped and H-shaped steel was proposed in this paper, which was characterized by the use of replaceable energy-dissipating devices to improve the seismic capacity. Based on the previous test results of the group, this paper used ABAQUS to investigate how factors like the thickness of the H-shaped steel webs and the size and number of openings affected the seismic performance of precast concrete beam–column joints with replaceable energy dissipation devices. The results showed that (1) an increase in the H-shaped steel’s thickness in the REDDC could improve the load-carrying capacity of the node, but the energy dissipation capacity was weakened, and (2) the length and width of the H-shaped steel openings had almost no effect on the ultimate load-carrying capacity within a certain range, but increasing the size of the openings could improve the energy dissipation capacity and reduce the ultimate load-carrying capacity at the same time. Compared with the length of the openings, the width of the openings had a more significant impact on the energy dissipation capacity. (3) The peak load-carrying capacity decreased with an increase in the number of openings in the H-shaped steel.
1 January 2025 in Canadian Journal of Civil Engineering
This study proposed a new low-rise bolt–steel plate connection precast concrete sandwich wall structure (PCSWS). Shake table testing was conducted on an experimental model of the bolt–steel plate connection PCSWS with two stories. The experimental phenomenon, failure pattern, displacement response, dynamic characteristics, and global hysteresis were analyzed in detail. The test results revealed that the proposed structure demonstrated excellent seismic performance without any structural cracks when subjected to an excitation intensity level of IX for Model-1. The seismic damage was moderate with no significant structural cracks after an excitation intensity level of IX for Model-2. Cracks in Model-2 occurred in the sequence of the places at the bottoms of the columns, the door corners, window opening corners, and the filled surfaces in the bolt–steel plate connection joint zone on the first floor. The observed damage states were primarily light and moderate, indicating the structure’s ability to withstand seismic events.