Current Issue : January-March Volume : 2024 Issue Number : 1 Articles : 5 Articles
To make the bearing capacity tests safer and more affordable for prestressed high-strength concrete (PHC) piles, this paper proposes a reaction device for anchor piles filled with core grout based on the geometric and mechanical characteristics of PHC piles. The proposed reaction device has the advantages of convenient construction, strong controllability of the connection quality and low cost. In addition, the pile will not experience prestress unloading or tensile stress under the effect of the upward pulling load. To promote the application of the reaction device developed for PHC pile bearing capacity tests, experimental studies are conducted on the bonding performance between the core grout and the inner wall of the PHC pile. The influence of various factors such as the strength of the core grout, the grouting length, the curing time, and the inner diameter of the PHC pile on the bond strength between the core grout and the inner wall of the PHC pile are investigated. Results show that as the inner diameter of the PHC pile increases, the bond strength between the core grout and the inner wall of the PHC pile decreases with a maximum difference of 5%. The bond strength decreases as the grouting length increases, and gradually stabilizes, with a difference of no more than 10% between the maximum and minimum bond strength values. The higher the strength of the grout is, the greater the bond strength between the core grout and the inner wall of the PHC pile is. The bond strength between the core grout and the inner wall of the PHC pile increases with the increase of the curing time within 28 days of curing, and the bond strength at 3 days meets the requirements of the PHC pile bearing capacity test....
Steel fiber-reinforced reactive powder concrete (SFRPC) has good mechanical properties and is thus useful for engineering applications. Generally, the fibers in SFRPC are randomly distributed. To study the effects of the amount, length, and orientation of steel fibers on the shear strength of SFRPC beams, nonreinforced aligned steel fiber-reinforced reactive powder concrete (ASFRPC) beams were prepared using a large-scale electromagnetic field orientation device. Shear tests of specimens with a shear span ratio of 1.5 were performed under two fiber contents (1.0% and 2.0%) and three fiber lengths (20, 30, and 40 mm). The fullfield strain during the loading process was obtained via the digital image correlation method, and the effects of fiber quantity and orientation on the shear strength of the beams were analyzed. The ASFRPC beams exhibited higher ductility but lower shear capacity than the SFRPC beams under the same conditions. The shear capacity increased with the quantity of steel fibers. According to the test results, the calculation formulas of the shear-bearing capacities of ASFRPC and SFRPC beams were established....
Viscoelastic dampers (VEDs) have been implemented successfully to reduce structural vibrations due to earthquakes and wind events. Conventional VEDs consist of two viscoelastic (VE) layers chemically bounded at their entire contact surface to three steel plates. This configuration has proven to be efficient in controlling the structure vibration. It has also been reported that VEDs can dissipate energy at any level of vibration, producing damping forces. However, when very large damping forces are required, the shear area of the VE layers and the steel plates should be increased to reach the target damping force since the energy is dissipated by hysteretic shear deformation developed in the VE material. Two main issues are associated with this large area. First, the steel plates are more susceptible to experiencing buckling due to out-of-plane deformations. Second, the overall size of the damper becomes larger which is not desirable from the architectural perspective and sometimes from the space usage perspective. As a solution, this study proposes an innovative VED so-called multiple-layers viscoelastic damper (MLVED) able to produce larger damping forces. The proposed MLVED consists of four VE layers bounded between five steel plates. The dynamic mechanical properties of MLVED are initially investigated through a full-scale test. With the test results, the finite element model is developed and calibrated using the commercial software ABAQUS. At a later stage, the calibrated model was used to investigate numerically the mechanical performance of MLVED if different VE layers areas and thicknesses are considered. Results indicated that the proposed MLVED possesses good energy dissipation capacity and its mechanical properties are strongly influenced by strain amplitude rather than loading frequency. Numerical results also showed that the damper is effective in dissipating energy even if different VE layers areas and thicknesses are considered. However, an optimal combination between the area and thickness of the VE layers needs to be found to maximize the damper performance....
To investigate the possibility of quantitative monitoring of the fracture process zone (FPZ) at the shotcrete-rock interface, the acoustic emission (AE) and digital image correlation (DIC) are used to monitor the three-point bending test of shotcrete-rock specimens. Firstly, the AE intensity signal characteristics during damage to the shotcrete-rock interface are analyzed. Then, the spatial b-value of AE is used to visually characterize the shotcrete-rock interface damage, and the interface damage characteristics of two specimens, shotcrete-granite and shotcrete-sandstone, are analyzed using this analysis method. The analysis reveals that not only the AE spatial b-value can determine the location of microdamage within the interface but it can also characterize the degree of damage. Finally, a new parameter, Tb-value, is constructed based on the AE spatial b-value to quantitatively characterize the FPZ, and the newly established characterization method is validated with the FPZ monitored by DIC. The results show that the Tb-value not only locates and visually characterizes the location of the FPZ within the specimen but also enables the quantitative determination of the FPZ. This provides a new idea for localizing and quantitatively monitoring cracks and FPZs inside structures using AE techniques....
Three groups of filling materials with different mix proportions were prepared. PO42.5 grade cement was selected as the binding material, mechanized granular coal gangue and fine sand were used as the filling aggregate, and then the specimens were curing at room temperature and 95% moisture. Through the uniaxial compression test, the influence of gangue–sand ratio, the mass fraction, and curing age on the mechanical properties of filling materials was analyzed. The microstructure analysis of SEM was conducted to explore the internal mechanism of the strength difference of filling materials. The results show that the gangue–sand ratio dramatically influences the uniaxial compressive strength. The strength increases first and then decreases with the gangue–sand ratio increase. The mass fraction of filling paste is positively correlated with specimen strength. When the sand–cement ratio, gangue–sand ratio, and the mass fraction remain unchanged, the longer the curing age, the greater the uniaxial compressive strength of specimens. The specimens with a sand–cement ratio of 3.5 : 1, a gangue–sand ratio of 5 : 5, and a mass fraction of 86% reach the maximum value of 11.03 MPa at a curing age of 10 days. It can be seen that when the gangue–sand ratio is 5 : 5, the filling material has the best mechanical properties, so it can be recommended as the optimal mix proportion for goaf filling. Thus, it provides a solid technical guarantee for the treatment of mine surface collapse disasters and the utilization of bulk coal gangue resources....
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