Abstract:

To study the variation law of the response of silo-shaped parking garages under the seismic action, vibration table tests and numerical simulation methods were employed. The effect of seismic waves with different incident directions, peak accelerations, and loading frequencies on the seismic response of the structure was analyzed by monitoring the stress distribution, displacement, deformation response, and acceleration of the structure. The results show that the stress concentration areas remain unchanged under different incident directions. When the horizontal seismic wave acts, the response of the structure in the horizontal direction (the direction parallel to the ground) is greater than that in the vertical direction (gravity direction), while when the vertical seismic wave acts, the opposite is true, and the vertical response of the floor slab is obvious. The horizontal-vertical coupled seismic wave intensifies the vibration of the soil and increases the structural stress. The change of peak acceleration does not cause a change in stress distribution, but will make the stress concentration phenomenon more significant. When the frequency is too high or too low, the change of radial stress is not significant. Overall, the stress mainly concentrates at the joints between the cylinder wall and the bottom plate, as well as those between the columns and the floor slabs, which are the key areas for aseismic design.

Abstract:

To investigate liquefaction behavior in deep liquefied soil layers, this paper performed shaking table tests using three seismic waves, i.e., the Ming Shan wave, Beijing Hotel wave and Beijing artificial wave, as the dynamic loads. By comparing free-field and structural conditions, the liquefaction characteristics of deep liquefied soil layers were analyzed. For the soil layer, no water spraying and sand bubbling occurred on the surface, but cracking developed near the structure. The pore-pressure ratio in the free-field condition was much smaller than that in the structural condition. The pore-pressure ratio induced by the Beijing Hotel wave was the largest, followed by that induced by the Beijing artificial wave and then the Ming Shan wave. For the structure, the Beijing Hotel wave produced the largest structural acceleration and the greatest increase in tensile strain, followed by the Beijing artificial wave and then the Ming Shan wave. These results indicate that liquefaction of deep liquefied soil layers is mainly controlled by overburden stress and the frequency content of the seismic wave: larger overburden load and higher dominant seismic frequency both reduce the degree of liquefaction. The seismic response of the station structure correlates closely with the dominant seismic frequency.

Abstract:

To address sectional damage occurring in either the steel girder or the concrete slab, this paper derived the Deflection Influence Line (DIL) for an arbitrary cross-section. Damage identification was performed based on the difference of DIL (DDIL) before and after damage and its second-order difference, and the method was then validated through finite element analysis and model tests. Finally, a damage identification method using the symmetric DDIL and its second-order difference under service conditions was proposed. The results show that damage localization can be achieved by identifying the inflection point of the DDIL curve or the peak on its second-order difference curve. Both the DDIL and its second-order difference increase approximately linearly with increasing damage severity and damage length. Model tests indicate that the DDIL yields better damage identification performance than its second-order difference. The proposed method based solely on the symmetric DDIL and its second-order difference under service conditions does not require pre-damage deflection data.

Abstract:

To explore a green and low-carbon scheme for self-compacting concrete, a comparative study on the chloride ion erosion resistance of self-compacting alkali-activated concrete and self-compacting cement concrete was conducted using the dry-wet cycle accelerated test method. The free chloride ion content, total chloride ion content, chloride ion binding capacity, and apparent chloride diffusion coefficient of concrete were analyzed. The results indicate that when the chloride ion erosion duration and depth are constant, the free chloride ion and total chloride ion contents are the highest in self-compacting cement concrete, followed by self-compacting alkali-activated concrete, and the lowest in self-compacting alkali-activated concrete modified with 2% nano-SiO₂. The chloride ion binding capacity of self-compacting alkali-activated concrete is 29.90% higher than that of self-compacting cement concrete, and its apparent chloride diffusion coefficient is lower, demonstrating superior resistance to chloride ion erosion. Although the incorporation of nano-SiO₂ reduces the chloride ion binding capacity of self-compacting alkali-activated concrete, it also contributes to a decrease in the apparent chloride diffusion coefficient.

Abstract:

To explore the deterioration mechanism of the bonding performance of Embedded Through-Section (ETS) Glass Fiber Reinforced Plastic (GFRP) bar-concrete interface in high-temperature environments, and based on the Fiber Reinforced Polymer (FRP) bar technology, 108 pull-out specimens were designed and prepared in this study. The test variables included three key parameters: temperature (20,40,60,80,120 and 160 ℃), concrete strength grade (C30, C40 and C50) and GFRP bar diameter (8, 12 and 16 mm). The test showed that when the temperature reached the glass transition temperature (T_g) of the adhesive, the failure mode of the specimens changed significantly, and the splitting failure of the concrete matrix evolved into interfacial debonding failure. Under the interfacial debonding failure mode, the typical bond-slip curve could be divided into three characteristic stages: linear rising stage, softening stage and residual strength stage. Based on the theory of fracture mechanics and the regression analysis of experimental data, a calculation model of the correlations of bond strength, residual bond strength and fracture energy with temperature parameters was established. The results showed that the increase of temperature had a significant deteriorating effect on the interfacial bonding performance, especially when it was close to the adhesive's T_g, the bond strength showed an exponential decay trend. Compared with the experimental data, the prediction error of this model was within 10%, and the model has high engineering applicability.

Abstract:

To study the mechanical behavior of fractured sandstone after freeze-thaw cycles under displacement constraints, a customized constraint device was used to apply displacement constraints to the sandstone specimens. Through the freeze-thaw cycle tests and uniaxial compression tests, the variation law of resistivity during the freeze-thaw cycles was investigated, and based on the results of uniaxial compression tests, the effects of fracture inclination, the number of freeze-thaw cycles and displacement constraints on the mechanical properties of the rock mass were analyzed. Real-time monitoring of the fracture propagation process during compression reveals the fracture propagation law and failure modes of the specimens. The results show that during the freeze-thaw cycles, the resistivity changes periodically: it increases when cooling down and decreases when warming up Under the displacement constraints, the peak displacement of the specimen increases first and then decreases with the increase of the fracture inclination angle. When loading from both directions, the peak displacement decreases first and then increases with the increase of the number of freeze-thaw cycles. The uniaxial compressive strength and elastic modulus of the fractured sandstone decrease first and then increase with the increase of the inclination angle, and reach the minimum at 45°. Displacement constraints inhibit fracture freeze-thaw damage when the number of freeze-thaw cycles is less than 30 times. and exacerbate the specimen damage when it is greater than 30 times. The larger the fracture inclination angle is, the faster the crack extension speed is, and the more the crack tends to propagate horizontally. According to the crack fracture morphology of specimens, the failure modes can be divided into X-type and Y-type.

Abstract:

The influence laws of different fly ash dosage and curing regimes on the macroscopic mechanical properties, ion erosion resistance and microscopic pore structure of concrete are explored. The internal correlations among fly ash dosage, steam curing regime, macro-microscopic properties and ion erosion resistance of concrete are revealed. Through mechanical property tests, potentiometric titration and pore structure tests, the macroscopic and microscopic properties of concrete with different fly ash dosages and curing regimes are systematically investigated. The results show that the compressive strength of concrete decreases with the increase of fly ash dosage. At the same fly ash dosage, the 1 day compressive strength of steam-cured concrete is 36.2% higher than that of standard-cured concrete. With the increase of fly ash dosage, the chloride ion binding capacity of steam-cured concrete is gradually enhanced and the sulfate ion reaction coefficient decreases slightly. When the fly ash dosage reaches 45%, the steam-cured concrete exhibits the optimal macroscopic and microscopic properties. The pore size peak of steam-cured specimens is higher than that of standard-cured specimens and the steam curing increases the proportion of transition pores and capillary pores in the total porosity, while reducing the proportion of gel pores.

Abstract:

Stress relaxation is one of the typical manifestations of soil rheology. For further investigation, drained triaxial stress relaxation tests were carried out on deep low liquid limit clay from an overburden layer, and the stress relaxation characteristics of the clay under different confining pressures were studied. It was found that the initial volume change was rapid under different confining pressures, but the overall volume change was small. The stress relaxation property of the clay decreased significantly with the increase of the confining pressures. In the coordinate system with time on the logarithmic axis, the initial section of the stress relaxation curves under different confining pressures did not follow a linear relationship, but did after a certain period of time. The empirical formulae for the stress relaxation proposed by Lacerda and Houston was further extended based on the test results. A new parameter Q was introduced and defined as the stress relaxation rate, and it was found that the stress relaxation rate Q under different confining pressures decreased rapidly with time and then gradually tended to be stable. Based on this, an empirical equation associated with the stress relaxation rate, confining pressure and time is established, which reveals the law of stress relaxation with time. Based on the volume change results, the relationship of volume change with confining pressure and time under stress relaxation conditions is established, which provides a basis for the generalization and establishment of relevant rheological models.

Abstract:

In order to establish an efficient calibration method for the microscopic parameters of soil-rock mixtures with different rock contents and improve the accuracy of the discrete element simulation of direct shear tests, numerical model samples of soil-rock mixtures were constructed based on the particle flow code in 2 dimensions (PFC2D) and Python programming to realize Monte Carlo random generation of rock blocks. A cluster particle aggregate was used to simulate irregular rock blocks, and a systematic study was conducted on the calibration of microscopic parameters between rock blocks and soil particles. A microscopic parameter grading calibration process based on uniaxial tension, uniaxial compression, biaxial compression, and direct shear tests was proposed. The influence of rock content on the shear strength characteristics of soil-rock mixtures was investigated. The results show that with increasing rock content, the cohesion of the soil-rock mixture initially rises and subsequently declines, peaking at 60% rock content, while the internal friction angle increases monotonically. The study has clarified the influence of key microscopic parameters in the contact model on macroscopic mechanical behavior, and the simulated internal friction angles and cohesion values are very close to the results of in-situ tests.

Abstract:

This study aims to investigate the soil stability at the end of working well during rectangular pipe jacking construction and its impacts on engineering safety, as well as the ground settlement issues induced by insufficient soil reinforcement at the end. Based on the Longgang Road utility tunnel project in Hefei, a scaled model of rectangular pipe jacking with a geometric similarity ratio of 1∶20 was fabricated, and model tests together with simulation verification were carried out to explore the influence of different reinforcement lengths on soil stability. The test results indicate that the soil reinforcement at the end can effectively reduce the ground settlement. The ground settlement at the front of the working well presents a V-shaped distribution during pipe jacking. When the reinforcement length increases from 0.30 m to 0.34 m, the maximum ground settlement is only reduced by 7.14%, and the improvement effect tends to be insignificant with further increase of the reinforcement length. The lateral earth pressure of the working well is concentrated in the upper area of the tunnel opening and increases with the increase of the jacking distance, reaching a maximum value of 647.435 kPa at the jacking distance of 400 mm. This study reveals the nonlinear relationship between reinforcement length and settlement control, and proposes 6 m as the economical reinforcement length for practical engineering applications.

Abstract:

To investigate the deformation control and support optimization methods of surrounding rock in a large longitudinal slope tunnel with a fault zone, by considering the maximum design inclination angle of the arc section of the flood spillway tunnel, geological parameters of the fault, and support parameters such as anchor rods and steel mesh, and with reference to the Saint-Venant’s principle to control the model boundary, the finite element method was used to establish an analysis and calculation model for the construction support of the tunnel. The deformation of the surrounding rock and the stress on the support structure were calculated and dynamically analyzed. The results show that the stability of the surrounding rock of the large longitudinal slope tunnel in the fault zone is poor. The vertical displacement of the surrounding rock at the fault increases by 0.8 to 1.5 times compared with the complete stratum, and the horizontal displacement increases by 1.0 to 1.2 times. It is necessary to strengthen the initial support strength of the large longitudinal slope tunnel in combination with the engineering practice. The control effect of surrounding rock pressure of steel arch erected in vertical direction is better than that in perpendicular direction. Increasing the density of steel arch can effectively reduce its stress. The maximum displacement values of the vault, arch bottom and side wall under the optimal steel arch erection method are reduced by 17.8%, 36.31% and 18.54% respectively compared with the results of numerical simulation. The on-site monitoring results show that the steel arch support has a significant effect.

Abstract:

To reveal the erosion mechanism of debris flow bends, this study conducted flume experiments, focusing on analyzing the movement characteristics of debris flow in bends, the erosion patterns of concave banks, and shear stress. The results indicate that: the apex of the bend experiences the most intense erosion, and the erosion intensity in the upstream is significantly greater than that in the downstream. The erosion depth and super-elevation are important factors affecting the instability of soil on concave banks. The dynamic coupling relationship between hydraulic erosion and gravitational erosion influences debris flow erosion. The concave banks in the upper and middle reaches of the bend are high shear stress areas, while the lower reaches are low shear stress areas, and the maximum shear stress occurs near the apex of the debris flow. The flow velocity of the debris flow in the bend varies synchronously with its shear force, with the highest velocity decay rate and the strongest debris flow erosion both occurring at the apex. The circulation within the bend exacerbates the erosion effect of the debris flow.

Abstract:

To address the issues encountered in robotic visual acquisition of bolt connection box images in prefabricated building units (such as overall low brightness, uneven illumination on bolt rods, and unclear texture details), this paper proposes an image enhancement algorithm based on logarithmic transformation and multi-scale feature fusion. For the problem of overall dim lighting in bolt connection box images, a logarithmic transformation is adopted and combined with Gamma correction to optimize dynamic range expansion. By adaptively adjusting parameters, the proposed method improves image performance under varying illumination conditions and effectively recovers latent detail information. Furthermore, a multi-scale feature fusion strategy is introduced, in which image information at different scales is integrated through dynamic weight allocation, thereby significantly enhancing texture clarity. Targeted enhancement is applied to the bolt rod region using the Contrast Limited Adaptive Histogram Equalization (CLAHE) to improve local contrast. In addition, edge sharpening and noise suppression techniques are employed to ensure that the enhanced images remain smooth while preserving fine details. Comparative experiments with mainstream image enhancement algorithms demonstrate that the proposed method achieves superior performance in terms of brightness, clarity, and texture detail. Specifically, the average Structural Similarity Index Measure (SSIM) and Peak Signal-to-Noise Ratio (PSNR) are improved by 5.89% and 4.73%, respectively, while the Mean Squared Error (MSE) is reduced by 12.55%.