With the rise of the low-altitude economy, the application scenarios of unmanned aerial vehicle (UAV) are constantly expanding, and it play a significant role, especially in the field of emergency rescue. By virtue of its advantages such as high mobility and remote control, UAV has become key tools in various aspects of emergency rescue, including disaster monitoring, search and positioning, material delivery, and communication support. This paper comprehensively reviews the modeling methods of UAV path planning in the field of emergency rescue and the latest research progress, aiming to provide comprehensive theoretical references and technical guidance for researchers in related fields. In this paper, an overview of emergency rescue scenarios and the application requirements of UAV in different emergency rescue scenarios is first presented. Then, this paper systematically summarizes the modeling methods of UAV path planning, including dynamic models and task models, and conducts a detailed analysis of the elements such as constraint conditions, optimization objectives, and solution algorithms in path planning modeling. Finally, the challenges and opportunities faced by UAV path planning in emergency rescue are explored, and it is pointed out that technological development, collaborative operations of multiple UAV, and the integration of multiple fields are the opportunities for future development. The research of this paper provides theoretical support and practical reference for the further development and application of UAV path planning modeling.

The existing signal control methods for traffic incidents do not consider the impact of traffic flow redistribution caused by the adjustment of the current intersection control scheme on adjacent intersections, and the essence is only to transfer the traffic problem, which is not conducive to the evacuation of congestion. In view of this, based on the textability of connected traffic, the controllability of connected automated vehicles, and the inducibility of connected human-driven vehicles, aiming to solve the congestion problems caused by traffic incidents, a signal control method for adaptive traffic events - SCM-ATE (Signal control method of adaptive traffic events) is proposed. Based on identifying lanes and traffic volume blocked by traffic incidents, as well as surplus capacity at adjacent intersections, SCM-ATE employs the shortest-path algorithm to plan detour routes for obstructed traffic flows. Aiming to minimize the average vehicle delay at all intersections along these detour routes, the system adopts dynamic programming to jointly optimize traffic signal timings and the trajectories of connected vehicles. This coordinated approach mitigates the adverse impacts of traffic incidents. The simulation results show that the average delay per vehicle of SCM-ATE under low, medium, and high traffic loads decreased by 14.4%, 25.5%, and 5.6%, respectively, compared to traditional signal control method; and the average delay was reduced by 15.3%,11.6% and 1.27%, respectively, compared to a single-layer approach for joint optimization of traffic signals and cooperative vehicle trajectories at isolated intersections,(JOTS-CVT), confirming the effectiveness of SCM-ATE. Further research shows that intersection traffic load and the penetration rate of connected and automated vehicle have a significant impact on the optimization effect of SCM-ATE. SCM-ATE is demonstrated that the optimal performance in traffic environments where the penetration rate of connected and automated vehicle is more than 0.3 and the intersection volume-to-capacity ratio is less than 0.7.

This study proposes a joint optimization method for intersection signal timing and vehicle trajectory based on the Soft Actor Critic (SAC) reinforcement learning framework. The model consists of two layers: signal timing optimization and vehicle trajectory optimization. The state space for both layers includes vehicle position, speed, and traffic signal status, while the reward function is a weighted sum of traffic efficiency, safety, and fuel consumption. In the signal timing optimization layer, the action is the duration of the signal phase, and in the vehicle trajectory optimization layer, the action is vehicle acceleration. Each optimization layer has independent value networks and policy networks. The value network outputs the state-action value based on the current state and action, assessing the policy network's performance. The policy network generates the mean and standard  deviation of a Gaussian distribution based on the current state and samples actions from this parameterized Gaussian distribution. The loss function of the policy network includes entropy and temperature coefficients to automatically adjust the breadth and depth of policy exploration, reducing the model's sensitivity to hyperparameter variations. To address the inconsistency in the intervals between signal timing optimization and vehicle trajectory optimization, an asynchronous training algorithm for the signal timing layer and vehicle trajectory optimization layer is designed. Both the value network and the policy network of the same layer are trained simultaneously using backpropagation. The model is trained and evaluated using SUMO, and experimental results indicate that the proposed method reduces vehicle fuel consumption by an average of 24.24%, 5.39%, and 22.23% compared to mathematical programming methods, signal-timing-only optimization methods, and trajectory-only optimization methods, respectively.

Urban rail transit passenger flow corridor areas connect the urban core area with the main functional areas of different urban circles, and are regions where urban spatial resources and economic activities are concentrated. Their transportation efficiency has a significant impact on the capacity of the rail transit network and socio-economic activities. In view of this, for the urban rail transit passenger flow corridor areas, based on the "one main line with multiple branches" topological structure of passenger flow corridors, a multi-objective nonlinear optimization model is proposed with the objectives of enterprise operation cost, passenger travel cost, and load factor imbalance coefficient. The model takes the departure frequency and marshalling scheme as decision variables, and designs a NSGA-II algorithm for solving. Taking the passenger flow corridor from Huilongguan/Tiantongyuan to Zhongguancun in Beijing as an example, the effectiveness of the model is verified. The results show that the model can effectively match the multi-directional travel demands between job-housing clusters. To verify the optimization effect of the model, an improved distance-based optimal solution solving method is proposed. The obtained optimal solution shows that the passenger travel time, enterprise operation cost, and load factor imbalance coefficient are 2639.170, 103716.24, and 0.086 respectively. Compared with the independent operation scheme of this line, the passenger travel time is reduced by 14.09%, the load factor imbalance coefficient is reduced by 43.01%, and the enterprise operation cost is increased by 17.22%. At the same time, in complex line networks, the restrictions of the maximum carrying capacity of the main line section and the minimum service level of the branch section have a great impact on the effect of the optimization scheme. By increasing the upper limit of the main line capacity, the study investigates the impact of capacity restrictions on the optimization of train operation schemes in passenger flow corridors. The results show that under the condition of improving the line carrying capacity, the diversity of Pareto solutions increases, passenger travel time is significantly reduced, and the balance of service is improved. The research results provide corresponding experience and guidance for further optimizing the cross-line operation scheme and actual operation.

To enhance the traffic efficiency of the upstream area of signalized intersections and reduce fuel consumption and emissions, this paper proposes a secondary speed guidance strategy considering the acceptance degree of drivers, aiming to address the issue of insufficient execution of guidance strategies by drivers in manual driving environments. The study focuses on manual driving connected vehicles, introduces the parameter of driver acceptance degree, and improves three primary guidance strategy models: acceleration guidance through, deceleration guidance through, and deceleration guidance to stop. Considering the impact of low driver acceptance, secondary acceleration guidance through and secondary deceleration guidance through models are constructed. A simulation environment is established using the MATLAB simulation platform, taking into account vehicle trajectory, speed, acceleration, and fuel consumption and emission factors. The effects of no speed guidance, primary guidance under different driver acceptance degrees, and secondary guidance are compared and analyzed. The simulation results show that strictly following the primary guidance strategy can enable more vehicles to pass through the intersection without stopping, improving traffic efficiency by approximately 14.3%, and reducing fuel consumption and emissions by 10% to 15%. Low driver acceptance has a significant negative impact on primary speed guidance, rendering the primary guidance strategy ineffective and causing additional fuel consumption and emissions. The secondary guidance strategy can effectively alleviate the impact of low driver acceptance, restoring traffic efficiency to over 95% of that of primary guidance and reducing fuel consumption and emissions by approximately 8% to 12%.

There are four types of failure modes of reinforced concrete (RC) beam-column joints under lateral load: shear failure in the core zone of the joint, shear failure in the core zone of the joint after the column end yielding, shear failure in the core zone of the joint after the beam end yielding and beam end failure. The beam-column joints with different failure modes have different influences on the structural performance. Therefore, in performance-based seismic design of structures, accurately classifying the failure mode of the component is the key to determine the deformation performance limit of a component. According to recent research, there is no sharp line separating failure mode of beam-column joints from each other, and the variation law with single influence parameter is not obvious, so it is difficult to distinguish the corresponding interval of different failure modes through a single influence parameter. Based on Fisher transform and Bayes classification principle, this paper proposes a more accurate and convenient method to distinguish the failure pattern of beam-column joints considering multiple parameters. The algorithm first uses Fisher discriminance to find the maximum separation projection space between classes, and then projects the original sample to the maximum separation space to obtain new samples. On this basis, the new samples for better classification are deduced according to Bayes classification principle. In the classification of beam-column joints failure mode, a multi-parameter discriminant equation is established based on this classification method considering four parameters, axial compression ratio, shear compression ratio, concrete compressive strength and stirrup characteristic value, which achieves the purpose of dividing the failure modes of beam-column joints and clarifying the corresponding intervals of different failure modes better.

This study investigates the effect of prestressing tensioning in the negative moment zone on the force performance of wet joints in the flange slabs against the background of an under-construction simply-supported and then continuous T-girder bridge.The stress distribution law of wet joints is analysed through construction process monitoring and parametric numerical simulation. In order to facilitate the construction, the prestressing bundles were firstly tensioned and the longitudinal wet joints were poured afterwards in the background project. In addition to the original construction sequence (first type), the parametric analysis considered two additional conditions: the joints were poured first and then prestressed (second type), and the negative moment zone was partially poured with joints, then prestressed and finally poured with the remaining joints (third type). Monitoring showed that: the difference in prestressing tensioning level during construction exceeded 10%, but the wet joints were not significantly affected due to post-casting; the transverse direction of the joints was basically compressed after casting, and the longitudinal direction was only tensed at a low level in the beams (15 με); the monitoring showed that the prestressing tensioning did not directly increase the risk of cracking of the joints. Parametric analyses show that there is a certain degree of stress redundancy in the joints under all three construction sequences. The maximum main tensile stresses under constant load were 0.2 MPa, 1.9 MPa and 0.8 MPa in order; and the first two tensile stresses continue to be significant after the second period of constant load; while the third one, casting wet joints in stages still has lower tensile stress after the second stage of constant load, but the construction process is more complicated. The above results can provide support for the force analysis and process optimisation of the construction process of similar structures.

In order to investigate the changing rule of shear force transfer mechanism in reinforced concrete beams without stirrups, 9 rectangular shaped and 27 T-shaped reinforced concrete beams without stirrups were designed and fabricated, and shear damage tests were carried out on them. Digital Image Correlation (DIC), displacement meters and strain gauges were used to record the data on displacement, strains and crack kinematic diagrams of critical shear cracks were plotted. Ultimately, the shear resistance contributions of the four shear force transfer mechanisms (aggregate interlock, dowel action, residual tensile stress across cracks, and uncracked compression zone) in the whole process of loading were calculated, and the changes of various shear force transfer mechanisms during the loading process were analyzed. Results show that the number, development level and height of shear cracks have complex coupled effects on the four shear mechanisms; the aggregate interlock basically reaches its maximum at 0.9P_u (P_u is the peak load), and its shear resistance value changes little with the shear span-to-depth ratio, but its contribution proportion gradually decreases as the shear span-to-depth ratio decreases; the dowel action is more stable during the whole loading process, but its proportion also shows a certain decrease with the increase in overall shear capacity; the contribution of the residual tensile stress across cracks is mainly observed in the early loading period, and at the maximum load, this mechanism no longer provides shear resistance due to the full development of cracks; the shear resistance of the uncracked compression zone is influenced by many factors, among which the shear span-to-depth ratio has the most significant effect; the shear resistance of the compression zone in beams with small shear-span-to-depth ratios can exceed twice that of beams with large shear span-to-depth ratios. At the peak load, the aggregate interlock is the most important mechanism in beams with larger shear span ratios, but with the decrease of shear span ratio, the shear capacity of the uncracked compression zone increases rapidly and becomes the most important mechanism.

This study investigates the lateral resistance of multi-storey steel frames with sparse Chevron bracing. The mechanical behaviour of structures with insufficiently strengthened horizontal beams was numerically and theoretically investigated. The series-parallel theoretical model for dual lateral force-resisting systems was first validated through nonlinear pushover analysis. The variation patterns of bracing internal forces with inter-story drift angles were presented. After the buckling of compressed braces, the stiffness and strength of horizontal beams were shown to have a significant effect on the development of axial forces in tensile braces. As a secondary lateral force-resisting system, the steel frame helps compensate for the loss of load-bearing capacity after buckling of compressed bracing. The composite effect of concrete slabs and steel beams enhances the flexural stiffness of horizontal beams, thereby facilitating the development of axial forces in the tensile braces and reducing the degradation of load-bearing capacity. In rigidly connected frames with Chevron bracing and insufficiently strengthened horizontal beams, plastic hinges first form at the beam end near the compressed brace side, then at the mid-span of the horizontal beam. Based on this failure mechanism, accurate formulas for calculating axial tensile forces in braces and unbalanced forces in horizontal beams are derived. The study shows that even if horizontal beams do not meet strengthening requirements in the Code for Seismic Design of Buildings, the overall structural capacity remains intact if the frame’s lateral resistance is sufficiently strong. This ensures compliance with seismic performance requirements in regions with a seismic intensity of 7 degrees (0.1g). The proposed calculation method for unbalanced forces offers a new approach to optimizing Chevron-braced frame designs, addressing the issue of excessive beam height in traditional designs, and providing valuable theoretical and practical insights for structural engineering.

The stress conditions and force transmission mechanisms of the steel-arch box and concrete arch foot junction in a flat arch bridge were studied in-depth， Using a 196m span flat arch bridge in Guangdong as the engineering background， a detailed finite element model of the steel-concrete combined structure was established on the Abaqus platform. The stress levels and distribution patterns of the model were analyzed under six adverse working conditions. Additionally， a scaled-down model with a ratio of 1：8 was used to study the stress conditions of the segment-scale model under various working conditions. The research results indicate that under the six loading conditions， the maximum stress occurs at the bottom plate of the steel arch box， which is the primary load-bearing component， and the maximum stress does not exceed 120 MPa. The stress level of the concrete bearing platform is relatively small， with the maximum stress not exceeding 0.73 MPa. From the self-loading end of the steel arch box to the concrete bearing platform， the axial compressive stress shows a decreasing trend. During loading， the steel arch box primarily transfers the applied load to the concrete bearing platform through the bottom plate of the steel box and the web plates near the bottom plate. Under all test conditions， the stress level at the steel-concrete junction is relatively low， and most of the stress from the steel arch box bottom plate is distributed to the concrete bearing platform through components such as PBL shear keys， bearing plates， intensified stiffeners， and through reinforcement.

If the recycled components which are obtained from the old concrete members generated by precise demolition and appropriate treatment can be directly used in the structural members, it undoubtedly has significant material and energy-saving, and carbon-reduction effects. The relevant performance of the new members still needs to be quantitatively revealed and ascertained through systematic research. As a preliminary exploration, this paper investigated the flexural performance of precast concrete floor slabs containing recycled components. Bending experiments under sagging and hogging moment of this type of prefabricated floor slabs were carried out respectively. The influences of factors such as the surface treatment methods of recycled components and the strength difference between new and old concrete on the flexural performance under sagging and hogging moment of this type of prefabricated floor slab were investigated, as well as the influence of the construction methods of locally added connecting reinforcing bars on the flexural performance under hogging moment. The calculation methods for the flexural bearing capacities of this type of prefabricated floor slabs were proposed. The study shows that: (1) The flexural bearing capacity under sagging moment of this type of prefabricated floor slabs is significantly higher than that of the cast-in-place floor slabs; (2) The different surface treatment methods of the recycled components have a limited overall impact on the flexural bearing capacity under sagging moment. (3) Adding local connecting reinforcing bars at the ends of the recycled components can significantly enhance the flexural bearing capacity under hogging moment of this type of prefabricated floor slabs. (4) The results of the proposed methods for calculating flexural bearing capacities are generally conservative.

A multi-source large-sample model for chloride diffusion coefficient of concrete was proposed by introducing cement type factor, considering the influence of cement category and strength grade. Firstly, the database with 179 sets of rapid chloride migration (RCM) test data from 70 laboratories was employed for determination of function of chloride diffusion coefficient on water-binder ratio, the type and strength grade of cement through regression analysis. Furthermore, the cement type factor was determined while the computational model was developed for chloride diffusion coefficient of concrete by means of the two-phase regression method. Then, comparison was implemented with different computational models and experimental data, the results show that the multi-source large-sample model has a 15.7~19.6% higher fitting degree to the experimental data than the traditional mono-source small-sample model. Moreover, the cement type factor can reasonably reflect the influence of cement category and strength. By comparing with traditional models and test data, the proposed model is validated with higher predicting accuracy and wider adaptability, reducing the weighted average error by 32.0% and the coefficient of variation by 25.0%.

The traditional R & D process of new materials, which is based on a large number of experiments and experiences, is inefficient, time - consuming, and costly. The Materials Genome Initiative is of great guiding significance for engineering design. By coordinately integrating efficient experimental techniques with rapid computational simulation and prediction, it can significantly shorten the R & D cycle of new materials and their engineering application process and reduce costs. The short - cut basalt fiber - reinforced polylactic acid (BF/PLA) composite material is naturally green, environmentally friendly, and degradable. As one of the ideal alternative materials for some interior and exterior parts of automobiles, it has broad development prospects. To study the influence mechanism of different fiber parameter ratios on the thermal properties of BF/PLA composite materials and rapidly develop suitable materials for automotive parts, this paper first conducts experiments on the thermal properties of BF/PLA composite materials with various fiber parameter ratios. Through data correlation analysis, the influence of different fiber parameter ratios on the thermal properties of the composite materials is explored. Using the F - value from the three - factor analysis of variance method, a method for quasi - centralizing fiber parameters is proposed. Fitting regression functions between the glass transition temperature, crystallinity, and the centralized variables are established to predict the thermal properties. The determination coefficients R² are 0.8870 and 0.8551 respectively, and the prediction accuracy is within the acceptable range of practical engineering. A finite element analysis of the thermal properties of the inner door panel of an actual vehicle model of an automobile enterprise is carried out. The simulation results of the predicted data are compared with those of the original vehicle. The results show that the thermal properties of the composite material with the optimal ratio selected by the method proposed in this paper are slightly better, and the R & D efficiency is significantly improved, which verifies the effectiveness of the method proposed in this paper. It provides important theoretical guidance and method reference for the rapid development, cost reduction, material substitution, and green design of automotive composite materials in the future.

In order to reveal the influence mechanism of coarse aggregate profile characteristics on the mesoscopic mechanical properties of asphalt mixtures, this study employed digital image processing technique to obtain the profile characteristics of coarse aggregates, constructed discrete element models of coarse aggregates with multiple morphological features, and studied the impact of aggregate geometric morphology on the mesoscopic mechanical response of asphalt mixtures in conjunction with a uniaxial penetration virtual testing system. The results indicate that a mixed tensile-compressive stress mode exists at aggregate contact points in the DEM-based uniaxial penetration model. Compressive stress accounts for 40%–50% of the total stress，tensile stress for 10%–20%，and combined tensile-compressive stress for 30%–40%. The effect of uniaxial penetration load leads to a rapid increase in the number of microcracks. In mixtures with a high content of needle-like aggregates, the microcracks at the aggregate-asphalt interface quickly connect to form through cracks. Microcracks are mainly induced by shear stress, accounting for about 90% of the total number of microcracks; the number of microcracks caused by tensile stress is relatively small, accounting for about 10% of the total. The longest microcrack can reach 10mm, while the shortest crack length is 0.2mm. The mixture with a higher amount of cubic aggregates can effectively resist load effects due to the skeleton interlocking effect, resulting in a smaller distribution area of micro-cracks and lower stress levels. The research findings provide a theoretical basis for the selection of coarse aggregates during asphalt pavement construction and for improving the processing quality of coarse aggregates.

To investigate the bonding mechanical properties between polypropylene fiber and concrete interface, the debonding process of the interface was studied through single fiber pull-out microscopic mechanical experiments and numerical simulations. An in-situ scanning observation system was established using micro CT and a self-developed single fiber drawing device to observe the process of pulling out a single polypropylene fiber with indentation from the mortar matrix. By employing mechanically regularized global digital volume correlation, the deformation fields of the interface between fiber and matrix was obtained, and the interface debonding was quantified by calculating the relative displacement of the shared nodes between the fiber and the matrix. A 3D microscopic numerical model reflecting the true shape of fibers and matrix was established based on CT images, and the single fiber drawing process was simulated and analyzed. The results show that the force-displacement curves displayed multi-peak fluctuations corresponding to the fiber geometry after the peak. The strain fields at interfaces measured by digital volume correlation and numerical simulation showed a strain concentration phenomenon related to the geometric shape of the indentation fiber, indicating that the periodic indentation of the fiber increases mechanical interlocking and friction forces between the fiber and the matrix during pullout. The relative displacement at the interface was maximum at the embedded initiation and decreases along the fiber toward the embedded end. In the plane perpendicular to the fiber direction, the variation of relative displacement was correlated with the geometric shape of the fiber. The relative displacement along the fiber direction reflected that the fiber and matrix have completely debonded before the pullout force reaches the peak load.