Abstract:To reveal the influence of prefabricated modular hollow panel reinforced earth retaining wall on panel connection stability, based on the limit equilibrium theory, the stability of modular hollow pa-nel reinforced earth retaining wall panel connection was deeply studied. Considering the hollow ratio and tilt angle of the module panel, the tensile force of the reinforcement connection and the resistance of the panel connection were calculated, and the corresponding stability analysis methods were established. The effectiveness of this method has been verified by comparing it with existing results in the literature. Further parametric analysis was conducted on different influential factors. The results show that increa-sing the module void ratio, reducing the internal friction angle of the fill, and increasing the reinforcement spacing will reduce the stability of the panel connection, with a particularly significant impact on the middle and lower parts of the retaining wall. At the same time, the stability of the inclined reinforced soil retaining wall panel connection is significantly reduced, with a more significant impact on the upper part of the retaining wall.

Abstract:In order to accurately predict the axial compression bearing capacity of steel reinforced concrete columns (SRCC) confined by carbon fiber reinforced polymer (CFRP) under multiple influencing factors. A multivariate algorithm fusion prediction model based on Random Forest (RF), categorical boosting (Catboost), eXtreme Gradient Boosting (XGBoost) and gradient boosting regression tree (GBRT) is proposed. Firstly, the synthetic minority oversampling technique (SMOTE) algorithm is used to expand the original data set, and 10 kinds of traditional machine learning and ensemble learning model tests are carried out. Four ensemble learning models of RF, Catboost, XGBoost and GBRT with determination coefficients (R²) greater than 0.92 are selected. The hyperparameters are optimized by random search, and then the RF-Catboost-XGBoost-GBRT prediction model is formed by fusion. The bearing capacity of CFRP confined steel reinforced concrete rectangular columns is predicted. The results show that the RF-Catboost-XGBoost-GBRT model shows the best prediction performance under the two datasets, and after the original dataset is processed by SMOTE, the R² of the five prediction models is increased by an average of 20.43%, among which the R² of the RF-Catboost-XGBoost-GBRT model reaches 0.942, and the prediction error is within ±10%.

Abstract:In order to study the load-carrying capacity and ductility behavior of steel square stub co-lumns with T-shaped stiffeners under combined compression and bending loads, a three-dimensional elastic-plastic finite element analysis model of steel square stub columns with rectangular stiffeners was established, taking into account initial geometric defects and welding residual stresses. The accuracy of the finite element model was verified by comparing it with existing research results. A series of parame-tric studies were carried out to investigate the effect of normalized flange width-thickness ratio, norma-lized stiffener’s slenderness ratio and axial compression ratio on the maximum flexural capacity and ultimate strain of steel square stub columns with T-shaped stiffeners. Based on the results of the parametric analysis, the calculation formulas for predicting the maximum flexural capacity and ultimate strain of these stub columns were proposed. The research results indicate that as the normalized flange width-thickness ratio, normalized stiffener’s slenderness ratio and axial compression ratio decrease, the maximum flexural capacity and ductility behavior of steel square stub columns with T-shaped stiffeners are improved.

Abstract:Traditional lap-slip mechanics models have not taken into account the important factor of steel bar spacing, leading to inaccurate predictions of steel bar overlapping performance. To address this, a tensile test considering factors such as steel bar spacing was conducted, and the influence of spacing on overlapping performance was investigated. A mechanical model considering steel bar spacing was developed and validated for accuracy and generalization. The results demonstrate that the proposed model considering steel bar spacing improves accuracy by nearly 50% compared to traditional lap-slip models. For ECC-steel overlapping members, the correlation coefficient between the model and experimental results exceeds 0.95. The model shows good generalization, effectively predicting the overla-pping performance of steel bars in high-performance concrete and ordinary concrete, and is suitable for predicting the overlapping performance of reinforced concrete overlapping members.

Abstract:Alkali-activated materials are one of the environmentally friendly materials that are expected to replace cement, but they have disadvantages such as poor resistance to carbonation and there is a lack of unified standards for carbonation research methods for alkali-activated materials. This article proposes a method for testing the carbonation of hardened concrete powder, and studies the carbonation resistance of alkali-activated slag-fly ash mortar (AAM) containing different dosages of plant ash, MgO, Sodium lactate, and C-HT. The experimental results show that when adding plant ash, the carbonation resis-tance of AAM decreases. However, as the dosage of plant ash increases, the carbonation resistance of AAM gradually improves. When the dosage is 6%, the carbonation resistance of AAM is similar to that of the control group. MgO, Sodium lactate, and C-HT can all improve the carbonation resistance of AAM. The effect is most significant when adding 6% MgO or 6% C-HT. Sodium lactate does not signi-ficantly improve the carbonation resistance of AAM. The hardened powder carbonation testing method is not only used to test the carbonation resistance of AAM, but can also be used to accurately compare the carbonation resistance of different additives by measuring the degree and rate of carbonation.

Abstract:In order to verify the influence of different damages on the lateral distribution law of load in prefabricated multi-girder bridges and explore a bridge damage identification method based on the lateral distribution law, the influences of joint damage degree, local damage degree of girder, damage location, and damage area length are considered. The rigid joint plate beam method is used to study the lateral distribution law of load in prefabricated multi girder bridges under joint and girder damage conditions. The results indicate that the transverse distribution influence line of the girder on both sides after joint damage intersects with the influence line before damage. The impact line of a damaged girder decreases overall. The smaller the residual stiffness coefficient, the closer the damage location is to the mid span, and the larger the damage range, the greater the degree of decrease. When the girder and joint damage occur simultaneously, the analysis can be conducted by comparing the impact line with the sensitive beam when damaged separately. Based on the variation law of the lateral distribution influence line of the sensitive girder before and after damage, the damage category of the bridge can be identified, while the specific damage location cannot be identified.

Abstract:To investigate the vertical compressive load bearing characteristics of rock-socketed piles in medium-weathered granite, this paper carried out in-situ tests and ABAQUS finite element numerical simulations on 12 rock-socketed piles to evaluate the ultimate bearing capacity of rock-socketed piles by various methods and to clarify the vertical compressive load bearing characteristics of rock-socketed piles in medium-weathered granite. The study shows that the 12 rock-socketed piles in medium-weathered granite do not exhibit fully end-bearing piles, but are friction piles or friction end-bearing piles; the vertical compressive ultimate bearing capacity of rock-socketed piles in medium-weathered granite foundation is high, and the settlement at the top of the piles is small, which meets the bearing requirements of the foundation. The finite element simulation load-settlement curve matches well with the measured load-settlement curve, and the pile top settlement error is small; under this test condition, the pile end resistance accounts for 56.9% of the pile top load, and the pile side friction resistance accounts for 43.1%, and the pile side friction resistance plays a sufficient role in the load transfer process. The ultimate pile load capacity obtained from finite element simulation is in good agreement with the prediction result of exponential function model, which can be used for the prediction of vertical compressive ultimate load capacity of rock-socketed pile and the analysis of bearing characteristics and load transfer law of rock-socketed pile.

Abstract:The thixotropic recovery characteristics of marine clay in different regions of the South China Sea after remolding at different times were studied using a falling cone test. The recovery law of soil strength under the influence of water content, plasticity index, sensitivity and other factors is analyzed. The results show that the clays in different areas of the South China Sea exhibit obvious thixotropic recovery characteristics, which are significantly affected by various physical factors. Pay special attention to soil with high sensitivity to avoid damage caused by excessive loading during the initial installation period. In the range of water content w=30.2%-43.8%, plasticity index I_p=10.2%-19.7%, liquid index I_L=0.56-1.17, and sensitivity S_t=4-7.9, the soil recovery characteristics increase, increase, and decrease with the increase of water content, plasticity index, liquid index, and sensitivity, respectively. When the soil mass is disturbed for 3 hours, 1 day, 3 days, 10 days, 30 days, and 60 days, it recovers to 20.0%, 22.4%, 25.1%, 28.6%, 32.6%, and 35.9% of the original soil strength on ave-rage.

Abstract:A improved YOLOv5 asphalt pavement crack detection method is proposed to address the i-ssues of complex crack image backgrounds, small detection targets, poor detection performance, and missed detections in YOLOv5 crack detection. Firstly, the lightweight Mobilenet v3 network, as the feature extraction network of YOLOv5, is used to reduce the complexity of the model and speed up reaso-ning. Secondly, an efficient channel attention mechanism (CBAM) is employed to enhance the network’s ability to capture and fuse local features. Finally, an embedded Panet module is used to enhance the multi-scale feature expression ability of crack images and improve the detection performance of small targets. The experimental results show that compared to the original YOLOv5 algorithm, the improved YOLOv5 algorithm improves the mAP of asphalt pavement crack detection by 5.5%, reduces the number of model parameters by 86.3%, and reduces image detection time by 75.8%.

Abstract:Machine vision displacement measurement technology provides a new solution for linear control of large-span bridges, and ensuring high-precision two-dimensional to three-dimensional coordinate conversion is crucial. A method based on improved genetic algorithm BP neural network is proposed to improve the calibration accuracy of binocular cameras. By improving the crossover and mutation probability functions in traditional neural networks, the calibration efficiency and accuracy are improved. Through corresponding experimental examples, it has been verified that the mean square error of mea-suring coordinates using the traditional Zhang calibration method is 4.67 mm. After applying this method for calibration, the mean square error of measuring coordinates is 0.82 mm, which improves the calibration accuracy and can meet the monitoring requirements of bridge construction linearity.

Abstract:In order to objectively evaluate the safety risks of the processing of the new modular steel trestle and ensure smooth production, an improved AHP grey cloud model was used to evaluate the safety risks of the manufacturing process of a certain modular wharf. A systematic study was conducted from five aspects: human, machinery, materials, environment, and management, and a safety risk assessment index system was established, including 9 secondary indicators and 28 tertiary indicators. Using an improved Analytic Hierarchy Process to determine the weight values of indicators, the on-site safety risk assessment values are input into the Grey Cloud model to determine the risk level. The research results indicate that this method is suitable for the safety risk assessment of module trestle processing and manufacturing. After analyzing the intersection between cranes and ground operations, inspection and maintenance of mechanical equipment, and the impact of noise, the risk values of three indicators are relatively high, and the corresponding risk prevention measures are proposed.

Abstract:Taking a three-span continuous box girder bridge as the research object, a bridge model and a vehicle model are established to form a vehicle-bridge coupled dynamic model, and the impact coefficient of the bridge structure under the action of vehicle load is studied and analysed. The study shows that: the number of transverse lanes increases the impact coefficient of the bridge, the greater the longitudinal distance the smaller the impact coefficient of the bridge; the impact coefficient of the bridge in the braking state of the vehicle is significantly greater than the impact coefficient of the vehicle at constant speed, and when the vehicle brakes in the first half of the bridge mid-span, the power impact coe-fficient is greater than the second half of the span; the vehicle in the jump impact effect, the impact coefficient of the bridge mid-span increases significantly, and in the mid-span jump when the vehicle The bridge power impact coefficient is the largest.

Abstract:In order to improve the performance of air source heat pump and better meet the special technical requirements of wellhead antifreeze, an air source split heat pipe heat pump heating system experimental platform was built by coupling air source heat pumps with heat pipe technology and using a small pressure ratio heat pump unit. In this coupled system, phase change heat transfer is adopted at both ends of the evaporator and condenser, and their performance characteristics under different opera-ting conditions are studied. The results show that even under outdoor conditions around 0 ℃, the Coe-fficient of Performance (COP) can still reach 4.5 or above, far superior to traditional air source heat pump units.

Abstract:A set of sand and gravel reservoirs with quasi in-situ sedimentary genesis are commonly developed on the surface of ancient buried mountain oil and gas reservoirs, which have good physical pro-perties and high productivity but complex distribution patterns. It is urgent to carry out reservoir distribution prediction to support the development of buried mountain oil and gas reservoirs. This article takes the Archean buried hill in Bohai A oilfield as an example and adopts the approach of "discussing the present and the past" to establish a prototype model of sand and gravel sedimentation in the source area. Based on the restoration of micro ancient landforms and fully utilizing the low-frequency response cha-racteristics of 3D seismic data, the distribution prediction of sand and gravel reservoirs in the ancient buried hill erosion source area has been achieved. The following understanding has been obtained: (1) The sedimentation of sand and gravel in the erosion source area is controlled by local terrain and landforms, forming different sedimentary combination patterns in mountain areas, inter mountain depre-ssions, and inter mountain valleys; (2) On the basis of the impression method, the fine characterization of micro paleogeomorphology is achieved using the technique of amplifying the difference in layer slope attributes. Based on the low-frequency seismic data, seismic attribute analysis is carried out, and the corresponding relationship between attribute distribution and micro geomorphic units is used to further judge the rationality of reservoir distribution prediction results. The research results of Oilfield A show that the distribution of sand and gravel in its erosion source area conforms to the "mountain eroded river front alluvial fan" combination model developed in mountainous areas. The sand and gravel in the mountain valleys are in a continuous strip shape, while the sand and gravel in the peak and ridge areas are poorly developed and distributed in discontinuous patches. The sand and gravel in the geomorphic units of the mountain slope are distributed in continuous patches.

Abstract:In order to explore the main influencing factors of femtosecond laser cutting of carbon fiber reinforced resin matrix composites (CFRP), the influence of different energy densities and spot overlap rates on the width of the heat affected zone, surface roughness, and slit taper was investigated using the controlled variable method. Based on the dual temperature equation, the temperature field evolution process of the electron lattice during the interaction between femtosecond laser and carbon fiber was si-mulated using the time difference method. The experimental results show that under the condition of constant pulse frequency, increasing laser power can increase the width of the heat affected zone of the cutting seam, increase the roughness and taper of the cutting seam, and decrease the cutting quality; Under the condition of fixed laser power and a single increase in pulse frequency, the cutting quality decreases but tends to saturate as the pulse frequency increases. The simulation results show that the higher the energy density, the higher the equilibrium temperature of electrons and lattice, the longer it takes to reach thermal equilibrium, and the more obvious the thermal effect. The analysis points out that the overlap rate of light spots and the pulse energy density are two important factors affecting the processing quality. Variations in laser power and pulse frequency can change the pulse energy density and overlap rate of light spots, indirectly affecting the processing quality.