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    • YANG Xi, TIAN Chong, FANG Ruyi, LIU Zeyu, ZHANG Yinhang, LEI Kejun

      Available online:May 19, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022353

      Abstract:The classical maximum eigenvalue detection (MED) algorithm has excellent performance in detecting correlated signals. However, with the increasing signal dimensionality, the MED algorithm faces serious problems in the calculation efficiency and implementation of test statistic and decision threshold, thus greatly limiting the further application of the algorithm in modern cognitive communication systems. To this end, a low-implementation complexity MED algorithm based on a numerical analysis theoretical framework is proposed. The new algorithm uses the Rayleigh quotient accelerated power method to iteratively compute the test statistic, which has a fast convergence rate in detecting high-dimensional signals compared with the classical power method; meanwhile, different from the classical look-up table method, a threshold calculation method based on the cubic spline interpolation method is proposed, which can quickly determine the decision threshold corresponding to any given target false-alarm probability. The proposed MED algorithm effectively improves the computational efficiency and reduces the complexity of algorithm implementation while maintaining the detection performance of the original algorithm, which is particularly attractive for spectrum sensing problems in high-dimensional conditions. Finally, the simulation results demonstrate the effectiveness of the proposed algorithm.

    • Meng Fanyi, Liu Hao

      Available online:May 19, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022355

      Abstract:A terahertz fundamental up-conversion mixer with a high local oscillator (LO)/ radio frequency (RF) and local oscillator / intermediate frequency (IF) port isolation was presented, which was in the IHP 0.13μm SiGe BiCMOS process. The mixer adopted Gilbert’s double-balanced structure, local oscillator signal was transmitted through the Coplanar Waveguide (CPW) to suppress the transmission asymmetry caused by the strong parasitic coupling effect in the transmission process, which reduced the characteristic of LO/RF port isolation deterioration caused by the asymmetry. By adopting an asymmetric switch interconnection structure, the imbalance of the parasitic coupling of the local oscillator signal at the collectors of the switching transistors was reduced, and the cancellation efficiency of the local oscillator signal at the collectors of the switching transistors was improved. And the local oscillator signal was suppressed at the port of intermediate frequency by arranging the position of the transconductance transistors in a reasonable layout. The post-simulation results show that under the power supply voltage of 2.2V, the local oscillator signal is 230GHz and the intermediate frequency signal is 2-12GHz, when the up-conversion mixer works at 218-228GHz, the LO/RF port isolation is greater than 24dB, LO/IF port isolation is greater than 20dB, the conversion gain is -4dB to-3.4dB. The output 1dB compression point is -14.8dBm with an intermediate frequency signal is 10GHz. The DC power consumption is 42.4mW, the core area of the chip is 0.079mm2.

    • YUAN Yongjie, YANG Liang, CHEN Shenghai, MA Rongchang

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022296

      Abstract:Free space optical (FSO) communications offer high speed, low cost, and strong anti-interference ability. However, the atmospheric turbulence-induced fading causes deterioration in the performance of FSO communication systems. The conventional solution is to use RF links as parallel communication links to improve the system performance. On the other hand, reconfigurable intelligent surfaces (RIS) can be employed to further improve the received signal-to-noise ratio of the RF link due to its advantages of low loss, easy deployment, and no complex coding and decoding. In this paper, an RIS-assisted hybrid RF-FSO transmission system is proposed to improve the communication quality of service. Based on this hybrid model, exact expressions for the outage probability, average BER, and channel capacity are derived, and Monte-Carlo simulations are presented to verify the accuracy of the analytical results. Results show that the performance of the proposed system is significantly improved compared to the conventional hybrid RF-FSO system.

    • Wang Gang, Luo Caiming

      Available online:May 17, 2022  DOI:

      Abstract:The mechanism for asymmetric transmission is an important issue for enhanced sensing, amplification and asymmetric control of elastic waves. Parity-Time symmetric systems may provide a simple solution. The concept of Parity-Time symmetric systems comes from quantum mechanics, and one of its characteristics is unidirectional reflectionlessness. A PT symmetric beam for flexural waves is designed, which is based on piezoelectric shunting technology. Firstly, the PT symmetric condition is derived. Then, based on the effective medium method and finite element simulation, it is verified that the effective parameters of gain and loss unit meet the PT symmetric condition. The tunability of exception points is studied by changing the resonant frequency and the shunting resistance. Finally, the scattering property of the PT sym-metric beam is derived by transfer matrix method and finite element simulation, and the relationship between exceptional points and unidirectional non-reflection is illustrated. The calculated and simulated results show that the PT symmetric beam has several exceptional points including 511Hz and 520.5Hz. When the incident flexural waves of 511Hz is applied at the right side of the PT symmetric beam, the reflection coefficient is close to zero. However, when the frequency of the incident flexural waves changes to 520.5Hz, it should be applied on the left side of the PT symmetric beam in order to gain a total transmission without reflecting. The structure of the proposed PT symmetric beam is simple and the exceptional points of it are tunable, which can be used to achieve better asymmetric transmission of flexural wave.

    • XIE Renqiang

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022297

      Abstract:With the rapid development of Internet, virtual communities are emerging. While providing innovative resources, these communities also have problems such as low willingness of users to share and lack of good incentive mechanism. Blockchain can better solve these problems and promote community knowledge sharing. This paper constructs an online community knowledge sharing scheme based on Multi Chain, puts forward the resource access and storage mode of "metadata cloud storage" and designs the metadata information table in detail, designs the overall framework of the knowledge sharing scheme and the key processes of some businesses, puts forward the consensus mechanism of "Nominated Proof of Stake (NPOS) to design the blockchain network, Some functions of online community knowledge sharing are realized. Through analysis and experiment, the scheme of this paper has good scientific rationality, safety and execution efficiency, and has good reference value for the development of other related projects.

    • YangYan, WuXuDong, DuKang

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022299

      Abstract:Affected by suspended particles such as haze in the atmosphere,images taken outdoors often suffer from low contrast and low visibility. Existing dehazing methods fail to make full use of the local feature information of the image, and cannot fully extract the global details of the image. Therefore, there are problems such as incomplete dehazing and loss of image details. For this reason, this paper proposes a T-shaped image dehazing network based on wavelet transform and attention mechanism. Specifically, the proposed network obtains the edge detail features of the hazy image by performing multiple discrete wavelet decomposition and reconstruction on the image, and proposes a feature attention module that takes into account both the global feature and the local information extraction of the image, which strengthens the network"s learning in image visual perception and detail texture. Secondly, in the process of feature extraction, a T-shaped method is proposed to obtain multi-scale image features, which expands the network"s representation ability. Finally, perform color balance on the reconstructed clear image to obtain the final restored image. A large number of experimental results in synthetic data sets and real data sets show that the network proposed in this paper has superior performance compared with other existing network models.

    • sun hong tao

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022300

      Abstract:This paper proposes a state-sensitive event-triggered H∞ control strategy to solve the problem of unmanned ground vehicle (UGV) path tracking control under communication restriction. Firstly, the corresponding path tracking control model is established according to the dynamics of the connected vehicle. Secondly, a novel state-sensitive event-triggered communication (SS-ETC) strategy according to the state perception of path tracking in real time is proposed. Then, an event-triggered H∞ controller is designed by combining with time delay system modeling method and Lyapunov stability theory. The proposed dynamic event-triggered communication strategy based on state perception can dynamically adjust the communication threshold according to the state measurements of the control system, and effectively realize the adaptive co-design of UGV communication and control. Finally, the effectiveness of the proposed dynamic event-triggered control strategy is verified by simulation experiments.

    • Chen jian, Zhuang yao yu, Yang dan, Zhang jun jie

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022351

      Abstract:Although MIMO technology can improve the utilization rate of spectrum, multi-dimensional signal processing brings great challenges to the detection of MIMO signals. Based on the analysis of various MIMO detection algorithms, QR decomposition is selected as the research object, which is a kind of nonlinear algorithm. In order to obtain higher performance of detection, the sorted QR decomposition is further studied and propose the sorting scheme based on L1-norm. Using Matlab for performance simulation, the L1-norm sorting strategy and the L2-nrom sorting strategy have basically the same impact on MIMO system, but the L1-norm sorting strategy reduces the computational complexity. On this basis, the hardware structure of improved sorted QR decomposition by Givens rotation on FPGA is proposed. Comparing with the solution of L2-norm, the L1-norm strategy reduces at least 29.2% combinational logic resources and 32.4% register resources when calculating a single column norm in the realization of 4×4 channel matrix decomposition. Comparing with similar designs, the frequency of operating clock has been significantly improved.

    • wangzhenyu, Guo Yang, Li Shaoqing, Zeng Jianping

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022352

      Abstract:With the development and application of communication networks, the Internet of Things carries the safe transmission and storage of a large amount of sensitive information. Since devices are usually small in size and resource-constrained, complex security primitives are not suitable for authentication of lightweight IoT devices. This paper proposes a lightweight anonymous key shared authentication protocol for IoT devices, which generates a shared key by the physical unclonable function(PUF) and uses security primitives such as the MASK algorithm and the Hash function. The security analysis and verification are accomplished by Ban logic and ProVerif to prove that the protocol ensures security attributes such as anonymity, non-repudiation, and forward/backward confidentiality. Compared with other protocols, this protocol has the characteristics of low computing cost, small communication overhead and storage capacity, and high security performance, which is suitable for the secure communication transmission of resource-constrained devices.

    • LIU Guangyu, CAO Yu, ZENG Zhiyong, ZHAO Enming, XING Chuanxi

      Available online:May 17, 2022  DOI: 10.16339/j.cnki.hdxbzkb.2022354

      Abstract:Sonar image is seriously polluted by noise, which leads to the problem of low precision in underwater multi-target segmentation.Therefore, an underwater multi-object segmentation technique based on self-adjusting spectrum clustering combined with entropy weight method is proposed.The technology first by self-tuning spectral clustering of sonar image pixel clustering processing, make the image is divided into multiple independent area, and then according to the characteristics of complementarity and more sections of the redundancy of the statistical information entropy characteristics, brightness, contrast, long and narrow degree, entropy weight method is used to analyse the characteristics more empowerment and the optimal selection of a target area,Then the optimal target region is matched with all regions by multi-feature similarity. Finally, all target regions are segmented automatically by adaptive threshold iterative method according to the matching results of similarity. Experimental results show that there is not over-segmented of noise interference regions, and target regions segmented have higher accuracy, which verifies the effectiveness of the proposed method.

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    Vol, , No.1, 2024    

    • LIU Zhiwen1,2,3?,ZHOU Wei1,2,3,LIU Zhenbiao4,YAN Aiguo4,XIA Zhengchun4,CHEN Zhengqing1,2,3

      2024(1):1-13, DOI:

      Abstract:Based on a cable-stayed bridge with a main span of 808 m and double-level decks for highway and railway, the vortex-induced vibration (VIV) performance of the double-level decks of truss girder section under different wind attack angles and the vibration suppression effects of five aerodynamic control measures were studied by the section model wind tunnel tests. Combined with the static flow simulation via computational fluid dynamics (CFD), the VIV mechanism and control method of the double-level deck truss girder section were compared and analyzed, respectively. The research results show significant vertical and torsional VIV of the original main deck at +3° and 0° wind attack angles, and the amplitudes exceed the allowable values of the code. The torsional vortex vibration of the main girder can be effectively suppressed by enclosing the upper deck railings at intervals or adding flaps. However, the amplitude of the vertical VIV of the main girder exceeds the allowable values of the code. Furthermore, adding wind fairing at the outside of the upper chord can effectively suppress the vertical and torsional vortex vibration of the main girder. However, the main girder vortex vibration cannot be effectively suppressed by adding the wind fairing at the outside of the lower chord. Moreover, after the air flow is separated from the upper deck of the original design section of the main girder, periodic large-scale vortex shedding on its upper and lower surfaces is formed, and then attached to the rear of the upper deck, which is the main cause of the vertical VIV of the main girder. The wind fairing located at the outside of the upper chord can guide the airflow smoothly through the upper deck, eliminating periodic vortex shedding. Additionally, an along and narrow reattachment zone is formed on its upper surface. As a result, this effectively suppresses the VIV of the main deck.

    • LI Jiawu,XIE Ze’en,LI Jiayu,LI Yu?,ZHAO Xue

      2024(1):14-23, DOI:

      Abstract:In view of the limitation of the code in taking the value of the double-deck girder drag force coefficient for large-span truss bridges, a method of calculating the drag force coefficient of the girder is proposed. Based on the wind tunnel test results of the bridge’s construction phase segmental model, its aerostatic coefficients were calculated using CFD after simplifying the model of the double-deck truss girder. The effect of characteristic size on the drag force coefficient of the girder was analyzed using different windward face characteristic sizes, the number of truss bays, and the truss spacing. The influence trend of different truss spacing and number of bays on the drag force coefficient of the girder is discussed. The results show that the characteristic height and characteristic width of the windward face have different effects on the drag force coefficient of the girder. Therefore, the fitting formula of the drag force coefficient of the girder of a double-deck truss is proposed, which takes the longitudinal height ratio of the truss as the variable. When the truss spacing is small, the number of trusses has no effect on the drag force coefficient of the girder. However, when the ratio of truss spacing to truss height reaches 3, the change in the number of trusses has a considerable impact on the drag force coefficient of the girder.

    • YING Hongwei1,2,XIONG Yifan1?,Lü Wei1,CHENG Kang3,LIU Guangxin4,DU Wei5

      2024(1):24-32, DOI:

      Abstract:PLAXIS 3D software and soft soil creep model were used to establish a 3D numerical model of the excavation of a municipal road underneath an elevated bridge. The rationality of the model was verified by comparing with the measured data. The soft soil creep model was simplified into the soft soil model, and the time-dependent horizontal response of the bridge pile group was compared, taking into account the constraint condition at the pile top. The two-stage method was used to incorporate the time-dependent settlement of the soil in the free field obtained through numerical calculation as the “external load” acting on the pile foundation. The load-transfer method, which accounts for the reciprocating shear between the pile and soil, was employed to calculate the vertical mechanical response of the pile foundation under the influence of self-weight, pile top load, and excavation of the adjacent foundation pit. The results indicate that: 1) Soil creep significantly impacts the deformation and internal force of adjacent bridge pile group, and its effect can be comparable to the influence of instantaneous deformation of the wall. 2) The deformation and internal force of bridge pile exhibit a negative correlation with the distance between the pile and the foundation pit, highlighting the curtain effect of pile group. The deformation and internal force at the pile top are governed by the constraint condition at the pile top. 3) Reasonable pile diameter and length exist for bridge pile foundations in deep soft strata where both the load on the pile top and disturbance from adjacent foundation pit excavation are minimal, when the deformation of the pile top is used as the control target.

    • HE Wenyu1,ZHOU Lei1,LI Zhidong1,HE Jia2,HU Dongyang3?

      2024(1):33-42, DOI:

      Abstract:The existing studies on the influence of the environmental temperature on the natural frequency characteristics are usually carried out for a specific bridge, and their applicability is limited. As concrete beam-type bridge is the most widely used bridge type, this paper deduces the general iterative formula of the relationship between natural frequency and temperature for concrete beam-type bridges and verifies it via numerical examples and laboratory tests. The results indicate that the influence of environmental temperature on the natural frequency cannot be ignored, and the proposed general iterative formula can effectively consider the environmental temperature influence and can be used to calculate the natural frequency of concrete beam-type bridges under actual temperature.

    • LI Yu1?,FENG Pu1,LI Chen2,WANG Fei1

      2024(1):43-54, DOI:

      Abstract:Taking the Jiufengshan suspension footbridge as the observation site, the measured data of 2 236 pedestrian samples were obtained by video recording and manual screening, and then the distribution characteristics and statistical values of pedestrian walking parameters (step frequency, step length, and walking speed) on the suspension footbridge were statistically obtained. Moreover, the relations among step frequency, step length, and walking speed were also proposed. The conclusions are as follows. 1) On the suspension footbridge, the walking parameters of all pedestrians obey the normal distribution, i.e. step frequency~N(1.726, 0.258)Hz, step length~N(0.596, 0.094)m, and walking speed~N(1.013, 0.260)m/s, and their rationality is also verified in some engineering applications; 2) the mean values (standard deviations) of walking parameters on the suspension footbridge are less (greater) than the mean values (standard deviations) of walking parameters obtained from other walking environments; 3) the mean values (standard deviations) of Chinese step frequency and length are less (greater) than that of Westerners. Therefore, in the design of suspension footbridges in China, the statistical values of walking parameters of other races and walking environments cannot be directly used, while the walking parameters suitable for suspension footbridges should be used.

    • ZHOU Yun1,2,ZHOU Yi1?,LI Jian3,PAN Heng3,DU Zong3

      2024(1):55-66, DOI:

      Abstract:To investigate the factors influencing the mechanical performance of precast spliced slotted ultra-high performance concrete (UHPC) columns under eccentric compression, two fully cast UHPC columns and fourteen precast spliced slotted UHPC columns were tested under axial or eccentric compression loading with different splicing forms, different eccentric compression directions, and different eccentricities. The influence of splicing forms, eccentric compression directions, and eccentricities on the static performance of the specimens is analyzed by investigating the ultimate carrying strength, failure modes, and axial and lateral deformation capacity. The results indicate that steel fibers can prevent premature cracks of UHPC and enhance the deformation capacity of the specimens, but the precast spliced slotted UHPC columns exhibit significant brittle failure characteristics under axial and eccentric compression load. In this experiment, the failure modes mainly divide into the compression failure mode for small eccentricity and tension failure for large eccentricity. The columns with different splicing forms and eccentric compression directions have similar behavior under the same eccentricity. The ultimate carrying strength of precast spliced slotted UHPC columns decreases with the increase of eccentricity under the same section dimension and reinforcement ratio. Finally, the limitations of the current Chinese codes are pointed out qualitatively by comparing the experimental ultimate carrying strength with the theoretical values by referring to the current Chinese codes. The test date in this paper can provide a reference for precast spliced slotted UHPC column design.

    • ZHOU Dequan1,HAI Jun1,LIU Hongli1?,GAO Qi2,LIU Hailong3, GUI Haiqi1,SUN Weiyong1, XIE Ruiting1,ZHU Qing1,ZHOU Yi1

      2024(1):67-78, DOI:

      Abstract:Indoor model tests were used to compare and study the influence of the number of beaded Karst caves on the top horizontal tensile characteristics of the cast-in-places piles, so as to provide an experimental basis for the design of horizontal bearing capacity of embedded rock piles in Karst strong development areas. The results show that: 1) when the horizontal load at the top of the pile is the same, the horizontal displacement, pile bending moment (or peak value), and pile side soil resistance of the upper soil section increase with the increase of the number of Karst caves, and the horizontal bearing capacity of the single pile decreases significantly with the increase of the number of Karst caves. 2) The horizontal displacement of the pile body in the upper soil section increases with the increase of the horizontal load on the pile top. The pile top horizontal displacement is the largest, and the embedded rock section is very small or even 0. The bending moment M-depth z curve is parabolic in shape, the pile bending moment at the soil-rock interface and the interface between the upper layer Karst caves and the base plate presents two peaks, the change of bending moment only affects the upper layer Karst caves and its base plate, and the bending moment at the second layer Karst caves and below is almost 0. The bending moment at the soil-rock interface is the largest, and the section is the most dangerous. The soil resistance p-depth z curve is a “convex belly” type. 3) As the number of Karst caves increases, the higher the location, the easier the p-y curve converges. The p-y curve for the soil section can be fitted using p/pub=α(y/y50)β. The influence of the number of Karst caves has little effect on the range of α and β values. The range of α and β values reflects the sensitivity of the p-y curve with depth and the sensitivity of both increases with the number of Karst caves. 4) To improve the horizontal tensile capacity of the single pile, when engineering piles pierce Karst caves, it is recommended to use the grouting method to improve the upper geotechnical properties, increase the reinforcement rate of the pile body at the soil-rock interface, and embed the pile body into the upper Karst caves floor to a certain depth so as to prevent the foundation pile from bending damage at the soil-rock interface.

    • DENG Mingke1,LEI Heng1,ZHANG Yushun2,GUO Liying1,ZHANG Wei1?

      2024(1):79-89, DOI:

      Abstract:To study the shear performance of reinforced concrete (RC) short columns strengthened with textile-reinforced high ductile concrete (TR-HDC), six RC columns, including two control columns and four columns strengthened with TR-HDC, were designed. The effects of the shear span-to-effective depth ratio and the layers of textile on the failure mode, deformation, bearing capacity, and energy dissipation capacity of the specimens were compared and analyzed under low cyclic loading tests. The experimental results show that the use of TR-HDC can obviously improve the shear capacity of the RC short columns; TR-HDC works well with the original concrete column, and the deformation, bearing capacity, and energy dissipation capacity of the specimens are significantly improved after strengthening with TR-HDC; increasing the number of layers of textile can slightly increase the shear capacity of the member, but it can greatly enhance the energy dissipation and deformation capacity of the RC short column; when the shear span is relatively large, it is more beneficial to exert the mechanical properties of TR-HDC reinforcement materials. Based on the truss-arch model, a calculation method for the shear capacity of the RC short columns strengthened with TR-HDC is proposed. The calculation results are more accurate.

    • ZHANG Luyang1,2,YAO Jitao1,2?,HU Yukun1,2

      2024(1):90-100, DOI:

      Abstract:Based on the simplified softened strut-and-tie model (SSSTM), the calculation formula of the angle of diagonal concrete strut inclination is modified by considering the effect of the axial compression ratio. Based on the shear-lag model, a calculation formula of fiber tensile stress per unit area of the crack surface is established by considering the number of fibers and fiber orientation characteristics of the crack surface. The modified simplified softened strut-and-tie model (MSSSTM) is proposed for the calculation of the shear capacity of steel fiber concrete reinforced beam-column joints. The MSSSTM and SSSTM were used to calculate the shear capacity of 36 steel fiber reinforced concrete beam-column joints. The results show that the average experimental-to-predicted capacity ratios of MSSSTM and SSSTM are 1.01 and 1.05, respectively, and the corresponding coefficients of variation are 0.04 and 0.09, respectively. The calculated values of shear capacity of steel fiber reinforced concrete beam-column joints according to the MSSSTM model are in good agreement with the experimental values with less dispersion. Moreover, the MSSSTM can reflect the influence of axial compression ratio and concrete strength on the shear capacity of joints more reasonably.

    • YANG Chengyong1,XU Qingtao2,MA Wenhui3?,HAN Xueguo1

      2024(1):101-111, DOI:

      Abstract:For a rectangular thin plate with different support conditions of four edges, a double Fourier series with additional terms was taken as the deflection function, and linear algebraic equations for solving the undetermined coefficients were derived. A unified structural calculation formula was obtained for the plate with any combination of simply supported, clamped, and free edges. The non-convergence of a series solution of bending moment at a point where a concentrated load is applied was discussed. In addition, the aspect ratio problem that needs to be achieved when simplifying a two-way plate is also discussed. The results show that the bending moment at the point can be calculated through the finite difference method using the deflection value, where a differential step length of 10 mm was selected. A plate with two opposite edges supported and two other edges free, and a plate with one edge clamped and the other three edges free, can be taken as a one-way plate. A plate with all four edges supported can be treated as a one-way plate with two ends clamped, one end simply supported and the other end clamped, or two ends simply supported if its aspect ratio reaches 2∶1, 2.5∶1, or 4.5∶1, respectively. A plate with three edges supported and the last edge free can be seen as a one-way plate with two ends clamped (and one end simply supported and the other end clamped), or two ends simply supported if its aspect ratio gets 1∶1 or 2∶1, separately; this type of plate can also be simplified as a cantilevered one-way plate at an aspect ratio of no less than 6∶1. A plate with two adjacent edges supported and the other two edges free can be taken as a cantilevered one-way plate if its aspect ratio reaches 2∶1 when the two supported edges are all clamped, or if the aspect ratio reaches1.5∶1 when one edge is clamped and an adjacent edge is simply supported.

    • ZHANG Wangxi1,2?,YE Yuan2,ZHANG Chen2,LIN Zeyu2,CHEN Leqiu3

      2024(1):112-125, DOI:

      Abstract:The shear strength of the bonding interface between new and old concrete is a critical concern in precast concrete structures and the strengthening of concrete structures. Shear calculation formulas of the bonding interface between new and old concrete given by four codes (GB 50010―2010, ACI 318―19, Eurocode 2, and PCI7th) are compared and analyzed based on the test date of shear tests (containing 439 specimens) of bonding interface between new and old concrete (to be referred to as the interface). The results show that under the influence of each parameter, the assurance rate of ACI calculation results is the best, and the calculation results of Eurocode 2 fit shear tests best. When the size range of the interface is 300~400 mm, the performance of GB 50010―2010 is best, but both of them are not safe, and the maximum relative error is about 9. According to the parameters analysis results of the database, the shear strength τexp is affected by the size effect and is closely related to the size of the interface along the shear direction. And τexp has a good correlation with the clamping stress ρfy. Based on the analysis results, the shear strength calculation formula is modified according to the superposition calculation theory. The modification includes that the coefficient β is introduced by analyzing the size effect; the friction coefficient μ is modified; the piecewise function of dowel resistance fitted by the database is applied, and its maximum value is 6.6 MPa. It is proved by comparative calculation that the error of the modified formula is the smallest, and the fitting effect is the best when the interface is with or without rebar and has various roughness. Moreover, it can be used as a reference for applications in civil engineering.

    • ZENG Ling2,GUO Yu2,ZHA Huanyi2,GAO Qianfeng3?,LI Fan2,BIAN Hanbing1

      2024(1):126-136, DOI:

      Abstract:To investigate the fracture characteristics of silty mudstone under moisture-thermo-mechanical conditions, fracture evolution tests were carried out, and the fracture development of silty mudstone under single-factor cycles and multi-factor coupling cycles was obtained. Meanwhile, X-ray diffraction and scanning electron microscope were employed to examine the microstructural change of silty mudstone. By combining the correlation of macro and micro test results, the crack propagation mechanism of silty mudstone under moisture-thermo-mechanical conditions was revealed. The results show that the fracture development of silty mudstone under moisture-thermo-mechanical conditions generally exhibits a growth-gentle trend. Under single-factor cycles, humidity cycles (soaking-drying) are most likely to cause fracturing of silty mudstone, followed by temperature cycles (5~60 °C) and mechanical cycles (0~50 kPa). Under multi-factor coupling cycles, their order to cause fracturing is moisture-thermo-mechanical cycles, moisture-thermo cycles, moisture-mechanical cycles, and thermo-mechanical cycles, which verifies the finding that humidity cycles are the dominant factor in causing fractures. After 15 moisture-thermo-mechanical cycles, the fracture rate can reach 0.92%, the number of fractures increases up to 30, the average fracture length extends to 60.58 mm, and the average fracture width is stable at about 0.47 mm. The gray correlation between the porosity and fracture rate is the largest, which is 0.813, indicating that the correlation between pore development and fracture expansion is the greatest in microstructure changes. Under moisture-thermo-mechanical conditions, humidity cycles cause the interlayer spacing changes of clay minerals, resulting in particle breakages and pores expansion to form microcracks. The temperature cycle produces differential thermal stress and water distribution in silty mudstone, which promotes the development of microcracks. The mechanical cycle increases the fracture tip stress and finally leads to a fracture network.

    • QIAO Hongxia1,2,3,SHU Xiuyuan1,2?,CAO Feng1,2,3,CUI Lijun1,2

      2024(1):137-146, DOI:

      Abstract:To study the feasibility of using magnesium oxychloride cement mortar (MOCM) modified by highland barley straw ash (HBSA) as an outer protective layer of ordinary concrete in the western salt lake area to resist brine erosion in the salt lake area and prolong the service life of the concrete, experimental research on the bonding strength of MOCM mixed with HBSA under water immersion environment was carried out. Ordinary concrete was used as the bonding base, and the influence factors such as the application of interface agent on the concrete base, the mixing of HBSA in MOCM, and the thickness of the mortar layer were used as variables. The bond pull-out tests were carried out to analyze the effect of each factor on MOCM bonding strength and to determine the optimal design parameters. Through numerical simulation methods such as polynomial simulation and grid processing in MATLAB, a time-varying model of magnesium oxychloride cement bond strength was established, and the damage degradation law of the bond strength of modified MOCM under water immersion environment was further analyzed. The phase composition, functional group structure, microscopic morphology, element mapping, and other characteristics of MOCM were analyzed by microscopic testing technology, and the mechanism of the influence of HBSA on the bonding performance of MOCM was revealed. The results show that there is more active SiO2 in HBSA, which can undergo a secondary hydration reaction with the hydration products in MOCM to form hydrated magnesium silicate (M―S―H) gel, which can fill the internal pores of MOCM, enhance the compactness, and improve the adhesive properties. The MOCM with a thickness of 18 mm, mixed with HBSA, and coated with interface agent has the highest bond strength, the bond strength degradation rate is the slowest in water immersion environment, and the numerical model based on the cubic polynomial can better reflect its bond strength. The degradation law of the optimal group YY-18 has a correlation coefficient R2 of 0.98.

    • HAO Jianbin?,LI Gengchun,LIU Zhiyun,CUI Fuqing,JIANG Zhenwei

      2024(1):147-158, DOI:

      Abstract:To study the anti-cracking effect of fiber-reinforced expansive soil under the dry-wet cycles, the dry-wet cycle tests of plain soil and sisal fiber-reinforced expansive soil were carried out, respectively. The surface crack parameters of the sample were extracted by image processing technology, and the effects of sisal fiber content and length, dry-wet cycle times, and sample moisture content on the crack development were analyzed. The results show that: 1) The sisal fiber-reinforced expansive soil has good crack resistance, and the addition of sisal fiber has a great impact on the crack ratio and average crack width of the expansive soil. Compared with the plain soil sample, the crack ratio and average crack width of the optimal reinforced soil sample are about 1/2 less than that of the plain soil sample. 2) When the fiber length is the same, with the increase of the fiber content, the fracture ratio, the total length of the crack, the average width of the crack, and the fractal dimension all decrease first and then increase, and when the fiber content is 0.4%, each parameter value is the smallest. When the fiber content is the same, the fiber length has little influence on the fracture parameters. 3) With the increase of dry-wet cycles, the fracture parameters of both reinforced soil and plain soil samples gradually increase, but the increase of fracture ratio and average width of fiber-reinforced soil is smaller than that of plain soil. From the fifth dry-wet cycle, the growth of fracture parameters slows down. 4) During the single dehumidification process, when the water content of the sample decreases from 20% to 10%, the fracture develops rapidly, and the development of the plain soil fracture is more sensitive to the change in the water content. When the water content is lower than 10%, the fracture ratio of the sample decreases and tends to be stable. Under the same moisture content, sisal fiber-reinforced soil has better crack resistance. 5) The anti-cracking mechanism of sisal fiber-reinforced expansive soil is mainly manifested in two aspects. On the one hand, the addition of sisal fiber increases the permeability coefficient of expansive soil, promotes the uniform distribution of water in the sample, and reduces the difference between expansion and contraction across the sample. On the other hand, the crisscross sisal fibers restrict the shrinkage of macropores between aggregates.

    • KANG Xin1,2,3,ZHAO Shicheng1,2,3 ?,LIU Peng1,2,3

      2024(1):159-169, DOI:

      Abstract:Due to the intergranular cementation of free iron oxides (FIOs), granite residual soils (GRS) are highly structural and water-sensitive. Therefore GRS exhibits structural disintegration and reorganization and complex shear deformation properties when subjected to dissolution of the intergranular cemented oxides under repeated drying and wetting (D-W) cycles. In order to further investigate the structural changes caused by the dissolution of the cement FIOs under D-W cycles and its effect on the weakness in mechanical properties of GRS, a series of macroscopic tests were carried out to reveal the complex mechanical behaviors of GRS under different numbers of D-W cycles (0, 1, 2, 4). The experimental results show that the stress-strain relationship of GRS gradually transforms from a weak strain-hardening type into a strain-softened state with the increase in the number of D-W cycles. The microscopic analysis indicates that the FIOs lead to the cementation of soil particles into soil aggregates. However, the content of FIOs shows a decreasing trend but finally tends to be a stable value after the D-W cycles. In addition, the particle size distribution (PSD) curve exhibits an evident bimodal peak, then changes to a single peak curve after the D-W cycles or the removal of FIOs. The repeated D-W cycles weaken the cementation structural properties of the GRS, resulting in the obvious softening characteristics of the soil. During the shear process, GRS first displays shear shrinkage properties, followed by the trend of dilatancy. With an increasing number of D-W cycles, the effective cohesion of the GRS gradually decreases, but the effective internal friction angle shows a trend of increase. The complicated mechanical properties of GRS are characterized by coupling effects among the irreversible volume shrinkage, the variation of collodion content, and the development of microcracks.

    • BAO Xuming1?,LOU Wenjuan1,LIAO Sunce1,LIN Chenqi1,CHEN Keji2,BIAN Rong2

      2024(1):170-179, DOI:

      Abstract:To study the wind speed-up effect of real terrain, the geometric features of real terrain were extracted to establish an ideal simplified terrain. Then, the π-shaped mountain range was proposed in this paper. The CFD numerical simulation was used to study the influence of the distance, length, and slope of subsidiary mountain ranges on the wind speed-up effect at the main ridge line in the wind direction along subsidiary mountain ranges. The difference in the speed-up ratio of the main ridge line between the π-shaped mountain range and the three-dimensional cosine-shaped mountain range was compared by combining with the terrain characteristics. Based on the latter, a simplified calculation formula of the wind speed-up ratio at the feature points of the main ridge line of the π-shaped mountain range was obtained and verified by a true π-shaped mountain range. The results showed that the speed-up ratio at the midpoint of the main ridge line of the π-shaped mountain range was greatly affected by the distance and the length of the subsidiary mountain ranges, and the speed-up ratio at the intersection point of the ridge line was greatly affected by the length and slope of the subsidiary mountain ranges. Compared with the three-dimensional cosine-shaped mountain range, the speed-up ratio of the main ridge line of the π-shaped mountain range was the same at the end of the ridge line, but it was smaller as a whole, especially the part shielded by the subsidiary mountain ranges was significantly smaller. The difference disappeared after exceeding the height of 70m above the ground. Compared with the wind field of the real π-shaped mountain, it was found that the simplified terrain and simplified calculation formula can reflect the speed-up effect of the feature points at the main ridge line of the real terrain.

    • ZHANG Zihang,HAN Yan?,SHENG Guogang,LI Kai

      2024(1):180-189, DOI:

      Abstract:Based on the strain-displacement relationship of the spatial curved beam theory, a hybrid model for galloping analysis of iced bundle conductors with three translational degrees of freedom and one rotational degree of freedom is established. Considering the aerodynamic force nonlinearity and the geometric nonlinearity of the large amplitude motion for the iced conductor, the nonlinear dynamic equation of the iced bundle conductors is established with the virtual work principle. The equation is transformed into the sub-space according to the mode superposition method and solved by the time integration algorithm. Then, the element independence is verified by numerical calculation, and the influence of the number of elements on the first six frequencies of iced conductors is analyzed. Furthermore, the modal convergence is studied, and the effect of modal truncation on galloping response is analyzed. Finally, the influence of aerodynamic force on structural frequency is analyzed. The results show that the aerodynamic force has a significant effect on the torsional frequency of the bundle conductor, which accurately reflects the dynamic characteristics of the transmission line. On the other hand, the hybrid model of iced bundle conductors has reliable accuracy in calculating the galloping analysis of transmission lines, indicating that the hybrid model can predict the actual galloping response of transmission lines and facilitate the implementation of subsequent control design.

    • QIU Weixing1,ZHAO Lianheng1,WU Bo2,3,SHAN Lingzhi4,XU Shixiang3?

      2024(1):190-200, DOI:

      Abstract:Tunnel collapse risk assessment is a multi-attribute decision problem due to many influencing factors. It is difficult for the assessment method of a single information source to fully consider all risk factors, leading to bias in the prediction results. To assess the tunneling collapse risk and provide a more accurate risk-controlling strategy, this research proposes a new multi-source information fusion approach that combines cloud model (CM), support vector machine (SVM), and evidence-based reasoning (ER). Multiple sources of information were analyzed to obtain different collapse risk assessment models (where classification probability values for visual inspection data are obtained from SVM, and probability values for monitoring data are obtained from the cloud model). The quality of each model is evaluated by reliability and importance weights. The ER theory is then applied to fuse the results of each assessment model to give an overall collapse probability risk assessment. Compared with the D-S theory, the ER rule has more advantages in dealing with high-conflict information. When the risk assessment results of different single information sources are inconsistent, the fusion by the ER rules considers the importance weight and credibility of the assessment results, which is more suitable for the high-conflict information fusion. The novel approach has been successfully applied in the case of Yutangxi tunnel of Pu-Yan Highway (Fujian, China). The results indicate that the proposed multi-source information fusion method has an evaluation accuracy of 87.5%, while the single-source information method has an accuracy of less than 70%. Furthermore, the fusion model has excellent performance even if the risk result of different models has high conflict.

    • CAO Jingyu1,2,ZHENG Ling1,PENG Jinqing1,2?,SONG Jiaming1,LI Nianping1,2,PEI Gang3

      2024(1):201-216, DOI:

      Abstract:The development and promotion of photovoltaic power generation technology is one of the key solutions to achieve carbon neutrality, but the efficiency of conventional photovoltaic cells decreases with rising temperature. Thus, taking measures to reduce its temperature becomes a hot issue in the photovoltaic field, among which heat pipe with a simple structure, high heat transfer efficiency, strong plasticity, and passive operation has received attention in recent years. However, the research status of heat pipes in photovoltaic cooling has yet to be analyzed and summarized. Therefore, the field is discussed in depth from the perspective of different heat pipe types, covering heat pipes and various cooling modes coupled with sky radiant cooling, phase change energy storage, thermoelectric cooling, and nanotechnology in this review paper. Combined with the development status of photovoltaic cooling technology based on heat pipes, the system performance, economic, and environmental benefits are discussed to prospect the research direction in this field. Based on the existing research, it is found that heat pipe cooling is an environmentally friendly and economically feasible method of photovoltaic cooling, which can effectively reduce the temperature of photovoltaic, improve its temperature uniformity, and realize the scientific collaborative utilization of solar energy and other clean energy under the technical coupling to improve its power generation performance or realize refrigeration, storage, and other additional functions. Its development and application will contribute to the cause of energy saving and emission reduction.

    • CHEN Youming1,3?,GUO Ying1,3,NING Baisong2,FANG Zhengcheng1,3,LIU Jiaming1,3

      2024(1):217-224, DOI:

      Abstract:A method for generating coincident design days by the heat balance method (HBM) was proposed. The hourly dynamic cooling load of a city over the years was calculated, the theoretical design load was determined based on no guarantee of 50 hours for an average year, and the coincident design day was selected by the comprehensive clustering method. The peak loads of the coincident design day and the traditional design day were calculated by the HBM and identified as the coincident design load and the traditional design load. The difference rates among the coincident design load, traditional design load, and theoretical design load of the sample rooms in Harbin, Beijing, Changsha, and Guangzhou were compared, respectively. The result shows that the deviation range of the difference rate between the coincident design load and the theoretical design load in each city is much smaller than the deviation range of the difference rate between the traditional design load and the theoretical design load. It indicates that it is more reasonable and accurate to calculate the design load of the air conditioning system based on the meteorological parameters of the coincident design day, and the coincident design day suitable for engineering application can be accurately generated by the HBM.

    • GONG Guangcai?,WANG Hongshun,LIU Yongchao,SHI Xing

      2024(1):225-236, DOI:

      Abstract:Based on the energy conservation of building envelope, this paper takes an internal plastering WSE (Wood fibre、Sepiolite and Expanded perlite) composite moisture control and thermal insulation mortar exterior wall as a research subject and compares it with an ordinary mortar exterior wall for the analysis of moisture absorption and desorption as well as its impact on energy load. Using a thermal and moisture coupling model of building materials from the COMSOL Multiphysics finite element software, this paper analyzes humidity transferring change between ambiance humidity change and exterior walls, as well as the heat transferring mechanism of exterior walls. For the WSE wall, total heat loads and the rate of latent heat loads to total heat loads are investigated in Changsha represented as a typical area with hot summer and cold winter. Besides, the annual energy consumption of the WSE wall is compared and analyzed in Beijing for cold areas and Guangzhou for hot summer and warm winter areas . It was found that velocities of moisture absorption and desorption of the WSE wall outperformed those of the ordinary mortar exterior wall for a long time. Moreover, the WSE wall can conserve annual energy consumption by 22.31% to 23.85% compared with the ordinary mortar exterior. Temperature rise is consistent with the moisture absorption velocity in the process of moisture absorption of walls, which reflects that moisture transfer has a great impact on temperature on the inner surface of walls. The impact is enhanced with the augment of moisture transfer. For the process of moisture desorption of the wall, cooling velocity is faster for the higher moisture desorption velocity. In conclusion, the WSE wall possesses a superior performance on moisture transfer and energy conservation, and it is conducive to the development of the building envelope in energy conservation.

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