中交第二航务工程局有限公司

Temperature-induced imaging drift is a major factor affecting the long-term stability of vision-based displacement measurement systems.This study aims to develop an online correction method that can identify and compensate thermally induced camera projection errors during measurement,without relying on external temperature sensors,repeated multi-temperature calibration,or pre-established temperature-parameter mapping databases.The objective is to improve the robustness and accuracy of long-term vision-based displacement monitoring under dynamic thermal conditions,especially for applications in outdoor engineering structures and other temperature-sensitive measurement scenarios. A compact dual-channel co-viewing imaging system was developed to provide a shared optical and imaging basis for online thermal error correction.The system optically couples a calibration plane and a measurement plane onto the same camera sensor through an optical coupling module.The calibration channel provides stable feature points for sensing thermally induced image drift,while the measurement channel records the targets used for displacement calculation.Because the two channels share the same camera sensor,imaging lens,and main optical path,the thermal perturbations observed from the calibration plane can be used to estimate the thermal disturbance affecting the measurement points.Based on the pinhole projection model,small perturbations were introduced into the camera intrinsic and extrinsic parameters to describe temperature-induced changes in the imaging geometry.Through first-order linearization and parameter coupling analysis,the original high-dimensional disturbance model was simplified into a seven-parameter linear image-point drift model.The model combines strongly coupled terms such as principal-point drift,equivalent focal-length variation,translational effects,and small rotational disturbances,thereby improving numerical stability and engineering applicability.During online measurement,the pixel drift of multiple calibration feature points is extracted relative to the initial reference frame.These observations are then used to construct an overdetermined linear system,and the thermal disturbance parameters are estimated by least squares.The estimated parameter vector is substituted into the image-point drift model to calculate the thermally induced drift of each measurement point.The distorted image coordinates are corrected in the pixel plane,and the corrected coordinates are then used to recover the in-plane physical displacement of the measurement points through the scale factor determined during initial calibration.The whole procedure requires only initial system calibration and can be performed continuously during measurement. The proposed method was validated through both indoor temperature-controlled experiments and outdoor long-term monitoring tests.In the indoor experiment,the measurement system was placed inside a temperature-controlled chamber,and the ambient temperature near the camera was varied cyclically from approximately 15℃to 50℃,with a temperature difference of about 35℃.The experimental results showed that the camera projection parameters exhibited clear and repeatable temperature-dependent drift.The principal point and equivalent focal length changed periodically with the heating-cooling process,confirming that thermal effects introduce systematic and time-varying imaging errors.After applying the proposed online correction method,the image-point drift of the selected measurement point was significantly suppressed in both horizontal and vertical directions,and the residual fluctuation was controlled within 0.3 pixels.Full-field evaluation further showed that the original image-point drift had clear spatial correlation and systematic distribution,while the corrected residual drift was greatly reduced over the entire image plane.The average residual RMSE decreased from 0.704 pixels before correction to 0.085 pixels after correction,corresponding to a reduction of approximately 87.9%.Statistical indicators including RMSE,MAE,peak error,and directional RMSE values all demonstrated substantial improvement,with the global image-point drift reduced by more than 87%.These results indicate that the proposed model can effectively suppress both average thermal drift and extreme thermal errors under non-steady cyclic temperature conditions.In the outdoor experiment,five infrared active targets were arranged at a distance of approximately 27～28.5 m from the camera system,and the dual-channel imaging system was installed in an optical enclosure for long-duration monitoring.The system was tested from 07∶00 to 09∶30 the next day under natural ambient temperature variations.For static measurement points,temperature-induced displacement drift was significantly reduced,and the corrected displacement errors in both X and Y directions were controlled within 2 mm.A controlled displacement test was further conducted using a two-dimensional precision translation stage with a positioning accuracy of 0.1 mm and a step size of 1 mm.Compared with the uncorrected results,the corrected displacement curves agreed more closely with the known displacement inputs.In the X direction,the maximum displacement error was reduced from 1.01 mm to 0.42 mm;in the Y direction,the maximum displacement error was reduced from 5.42 mm to 0.78 mm.The maximum improvement reached 90.2%,demonstrating that the proposed method remains effective under outdoor non-steady thermal conditions and known displacement inputs. The proposed dual-channel co-viewing online correction method can effectively estimate and compensate thermally induced projection-parameter drift in vision-based measurement systems.By using calibration-plane feature drift as an online sensing source,the method eliminates the need for external temperature measurement,repeated offline recalibration,or pre-trained temperature-parameter models.The experimental results demonstrate that the method improves image-coordinate stability,reduces systematic thermal drift,and enhances displacement measurement accuracy under both controlled and outdoor thermal conditions.The method provides a practical and adaptable solution for long-term,unattended vision-based displacement monitoring of engineering structures and other temperature-sensitive measurement applications.

To accurately analyze the shrinkage and creep effects in external prestressed reinforced concrete beams,a method was proposed for analyzing the shrinkage and creep of such beams based on refined finite element analysis.First,considering the force characteristics of the external prestressed tendons as constant-strain components,a differential treatment was performed on the geometric and nodal displacement relationships between the external prestressed tendons at the anchorage and deviation points and the concrete beam.Using the principle of virtual work,the element stiffness matrix that needed to be iteratively solved was derived for the external prestressed tendons.Second,based on the assumption that there was good bond between the reinforcement and the surrounding concrete under the action of shrinkage and creep,and that both materials exhibited coordinated strains,a finite element model was established for analyzing the shrinkage and creep of reinforced concrete beams that incorporated the effects of the reinforcements,utilizing the initial strain method in shrinkage and creep analysis.Finally,based on the aforementioned results,a method for analyzing shrinkage and creep in external prestressed reinforced concrete beams was established,along with the development of the corresponding programs.An analysis of the shrinkage and creep of two external prestressed reinforced concrete beams was conducted,and the results were compared with relevant literature.The findings indicate that the method established in this paper for analyzing the shrinkage and creep of external prestressed concrete beams is accurate.It was observed that in the computational model,treating the external prestressed tendons as if they were bonded internal tendons,or neglecting the influence of ordinary steel reinforcement in the concrete beam,can lead to significant errors in the calculated results.

Objective High-entropy alloys have become ideal candidates for wear-and corrosion-resistant coatings materials because of their unique structure and excellent physical properties.Owing to their outstanding corrosion resistance and formability,FeCoCrNi high-entropy alloys are used extensively in corrosion-resistant coatings.However,their comparatively low mechanical strength does not satisfy the requirements for wear-and corrosion-resistant coatings.Adding high-melting-point Mo can promote the formation of Mo-rich phases in the alloy,thereby improving its mechanical strength and crevice corrosion resistance.This study aims to investigate the microstructure,forming process,and corrosion resistance of FeCoCrNiMo by fabricating FeCoCrNiMo high-entropy alloy coatings on 45 steel round bars or 316L stainless steel primer using extremely high-speed laser cladding(EHLC)technology.This study is expected to provide some essential technicalities for high-entropy FeCoCrNiMo alloy coatings that can be applied under different and complex wear and corrosion conditions. Methods In this study,scanning electron microscopy(SEM)in conjunction with backscatter imaging and energy dispersive X-ray spectroscopy(EDS)was employed to characterize the microstructure and composition of the coatings.X-ray diffraction(XRD)was adopted to ascertain the physical phase composition of the coatings,where Co was utilized as the target material.Transmission electron microscopy(TEM)samples of the coatings were prepared using a focused ion beam.The microstructure of the coating was characterized using high-resolution scanning TEM,and microhardness measurements were performed on the polished coating surfaces using a Vickers hardness tester.Electrochemical and neutral salt spray experiments were conducted to evaluate the corrosion resistance of the coatings. Results and Discussions A reduction in the linear velocity from 15 to 5 m/min results in a decrease in the number of cracks in the cladding coated on the 45 steel substrate.Additionally,a transition from reticulated to striated cracks is observed,as shown in Fig.5.By using 316L stainless steel as a primer and reducing the linear speed to 5 m/min,cold cracks are effectively mitigated,as illustrated in Fig.7.Therefore,one can reasonably conclude that the heat-affected zone of the 45 steel substrate undergoes a martensitic transformation,which increases the tensile stress within the coating and resultes in reticulated or striped peritectic cracking.Nevertheless,the induction of the 316L primer reveals no alteration in the microstructure of the coatings,which is dominated by the typical lamellar eutectic microstructure,as shown in Fig.7.In contrast to the microstructure of the coatings created under higher linear velocities,the basic microstructural characteristics remain unaltered.However,a reduction of 15 percentage points is detected in the face-centered cubic(FCC)phase(Fig.9),which is assumed to have contributed to the modest decrease in the Vickers hardness,although the latter remained at a prominently high level. Conclusions This study employed extremely high-speed laser cladding technology to fabricate a FeCoCrNiMo high-entropy alloy coating.Subsequently,a detailed analysis of its microstructure,phase composition,forming process,and corrosion resistance was performed.The findings indicate that the coatings comprise primarily an FCC matrix phase enriched in Fe,Co,and Ni,with a body-centered cubic(BCC)precipitated phase enriched in Mo and Cr.The lower and middle regions of the coating feature columnar crystals of the FCC phase,intersperse with alternating submicron BCC/FCC lamellar eutectic structures among the dendrites.Additionally,the heat-affected zone of the 45 steel substrate undergoes a martensitic transformation,thus increasing the tensile stress within the coating and resulting in reticulated or striped peritectic cracking.Using 316L stainless steel as a primer as well as reducing the line speed effectively mitigates these cracks and maintains high hardness levels.By contrast,the upper region is dominated by equiaxed crystals with similar alternating lamellar eutectic microstructures.Compared with a standard 304 stainless steel coating,the high-entropy alloy coating exhibits a higher self-corrosion potential by 0.130 V,a significantly lower self-corrosion current density by one-sixth,and a 235-fold increase in the coating film resistance,thus suggesting substantially enhanced corrosion resistance.In conclusion,the fine and uniform FCC/BCC lamellar eutectic microstructure at the top of the coating is believed to have contributed significantly in improving the corrosion resistance.

To investigate the effects of the spraying process and different fibers on the mechanical properties and failure patterns of ultrahigh performance concrete(UHPC),three types of fibers were used.These fibers were formed using both spraying and molding methods.Uniaxial compression tests were conducted,and two nondestructive monitoring techniques,acoustic emission(AE)and digital image cor-relation,were employed to monitor the uniaxial compres-sion tests.The results indicated that the compressive strength of UHPC with single steel fibers and hybrid fibers increased by about 19%and 14%compared with those of UHPC with polyoxymethylene fibers.In comparison with molded UHPC,sprayed UHPC showed a slight improve-ment in compressive strength.Specimens containing steel fibers exhibited better post-cracking ductility,whereas those with only polyoxymethylene fibers displayed a certain degree of brittle failure.In sprayed UHPC,the onset of sig-nificant internal damage was delayed,which was related to the redistribution of internal fibers.The failure of UHPC was characterized by primary tensile cracks,supplemented by shear cracks.The spraying process can better restrict the development of tensile cracks in UHPC.Sprayed UHPC typically exhibited multiple crack developments leading to failure,whereas molded UHPC generally failed in the form of a single main crack penetrating the specimen.The addi-tion of steel fibers delayed the occurrence of local stress concentration zones,aligning well with AE monitoring data.

As the planning and deployment of cross-sea and river-crossing passages continue,prominent issues such as high labor demand and poor working conditions have become evident during the construction of large-span and ultra-high cable towers.To address these issues,this paper explored efficient construction methods for ultra-high cable towers based on the concepts of intelligent,industrialized,standardized,and assembled construction technology for cable towers.The research method combined qualitative analysis of reasonable construction organization,and integrated intelligent tower construction equipment for ultra-high cable towers,as well as industrialized forming and assembled construction technologies for tower column reinforcement was proposed.Through the application in the Lingdingyang Bridge along the Shenzhen‒Zhongshan Bridge project,the research results indicate that this key technology significantly enhances the level of intelligent construction technology for cable towers,effectively ensures operational safety,and further improves the quality of bridge tower construction.The paper verifies the feasibility and effectiveness of the proposed technology,providing important theoretical and practical guidance for the construction of ultra-high concrete cable towers.This has significant reference value for similar future projects and contributes to the innovative development of cable tower construction technology.